Neurotransmission in the rat amygdala related to fear and anxiety

Neurotransmission in the rat amygdala related to fear and anxiety

Acknowledgements D C andFA arePhD students We thank D Pareandan anonymousreferee for commentson an earherversionof the manuscnpt Supportedby the Medtc...

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Acknowledgements D C andFA arePhD students We thank D Pareandan anonymousreferee for commentson an earherversionof the manuscnpt Supportedby the MedtcalResearch Counalof Canada (grantM T-3689)

21 Stenade, M, Amzlca, F and Nufiez, A (1993) J Neurophyslol 70, 1385-1400 22 McCormick, D A (1990) m Brain Chohnerglc Systems (Stenade, M and Bmsold, D, eds), pp 236-264, Oxford Un)verslty Press 23 Nicoll, R A and Madison, D V (1982) Science 217, 1055-1057 24 Stenade, M and McCarley, R W (1990) Bramstem Control of Wakefulness and Sleep, Plenum 25 Stenade,M, Datta, S, Pare, D, Oakson, G and Curro DossL R (1990)J Neuroso 10, 2541-2559 26 Stenade,M, Curro Doss~,R, Pare, D and Oakson, G (1991) Proc Natl Acad 5ct USA 88, 4396-4400 27 Lhnas. R and Pare, D (1991) Neurosoence 44. 521-535 28 Lhnas, R and Rlbary, U (1993) Proc NatlAcad Sct USA 90, 2078-2081 29 Stenade, M , Curro Doss), R and Contreras, D (1993) Neurosoence 56. 1-9 30 Pape, H C (1992) J Physlol 447, 729-753 31 Haas, H L and Greene, R W (1988) Arch Pharmacol 337, 561-565 32 Mitchell. J B, Luplca, C R and Dunwlddle, T V (1993) J Neuroso 13, 3439-3447 33 McCormick, D A and Wdhamson, A (1989) Proc NatlAcad Sc~ USA 86, 8098-8128 34 Ramme. D G, Grunze, H C R. McCarley. R W and Greene, R W (1994) 5oence 263, 689-692 35 Stenade, M and Contreras, D (1993)5oc Neurosc~ Abstr 19, 1446 36 Contreras, D, Curro DossL R and Stenade. M (1993) J Phys~ol 470, 273-294 37 Mulle, C, Madanaga-Dom)ch, A and Deschenes,M (1986) J Neuroscl 6. 2134-2145 38 AvanzmL G, DeCurtls, M . Panz~ca, F and Spreafico, R (1988) J Phys~ol 416, 111-122 39 Bal, T and McCormick, D A (1993) J Phys~ol 468, 669-691 40 Hirsch, J C, Fourment, A and Marc, M E (1983) Brain Res 259, 308-312 41 Monson, R S and Dempsey, E W (1943) Am J Phys~ol fill

138, 297-308 42 Stenade, M, Wyzmskl, P and Apostol, V (1972))n Cortlcothalamlc Prolectlons and Sensonmotor Actlwbes (FngyesL T L, R)nwk, E and Yahr, M D, eds), pp 221-272, Raven 43 Stenade, M (1984) m Dynamic Aspects of Neocorbcal Funcbon (Edelman, G M , Gall, W E and Cowan, W M, eds), pp 107-157, Wdey 44 Nufiez. A, Curro DossL R, Contreras, D and Stenade, M (1992) Neurosoence 48, 75-85 45 Stenade, M (1964) Electroencephalogr CIm Neurophystol 16, 221-236 46 Ster)ade, M and Yossff, G (1974) Electroencephalogr Chn Neurophyslol 37, 633-638 47 Stenade, M, Oakson, G and Dlallo, A (1976) Electroencephalogr Chn Neurophystol 41,641-644 48 Gloor, P, Avoh, M and Kostopoulos, G (1990))n General1zeal Epilepsy (Avoh, M, Gloor, P, Kostopoulos, G and Naquet, R, eds), pp 190-212.81rkhauser 49 Avoh, M, Gloor, P, Kostopoulos, G and Gotman, J (1983) J Neurophyslol 50, 819-837 50 Von Kros)gk, M, 8al, T and McCormick, D A (1993) 5oence 261,361-364 51 Huguenard, J R and Prince, D A J Neuroso On press) 52 Stenade, M (1974)Electroencephalogr Chn Neurophyslol 37, 247-263 53 Kellaway, P (1985) Epflepsla 26 (Suppl 1). 15-30 54 Marescaux, C, Vergnes, M and Depauhs,A (1992)J Neural Transm 35 (Suppl), 37-69 55 Noebels, J L (1984) Nature 310, 409-411 56 Kostopoulos, G K (1992) J Neural Transm 35 (Suppl), 21-36 57 Churchland. P S and Se]nowskl, T J (1992) The Computabonal Brain, MIT Press 58 Stenade, M , Desch(~nes, M, Domlch, L and Mulle. C (1985) J Neurophystol 54, 1473-1494 59 Wang, X J and Rmzel, J (1993) Neurosoence 53,899-904 60 Destexhe, A, Contreras, D, SejnowskL T J and Stenade,M J Neurophyslol (in press) 61 Lancel, M, van Rmzen, H and Glatt, A (1992) Brain Res 596, 286-295

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Neurotransmissionin the rat amygdalarelated to fear and anxiety M ) c h a e l D a w s , D o n R m n n ) e a n d M a r t ) n Cassell

MmhaelDavls~sat An zmpresswe amount of ewdence from many dzfferent theDeptof laboratories using a vane& of expertmental techmques Psychiatry, m&cates that the amygdala plays a cruczal role m the YaleUnlverslty, acquzs#zon, consohdatwn and retentwn or expresswn of ConnectlcutMental con&twned fear Electrophyswloglcal data are beginHealthCenter, ning to detazl the transm#ters and mter-amygdala 34 ParkStreet,New connectwns that transm# mformatwn to, wzthm, and Haven,CT06508, out of the amygdala In general, treatments that USA,DonRammeis at theDeptof increase the exc#ab~h& of amygdala ou~Out neurons m Psychiatry.Harvard the basolateral nucleus (for example, by decreasing Unwers~ty, opzate and GABA transm~sswn, and increasing norBrocktonVeterans adrenerg~c transm~sswn) zmprove averswe cond#wnmg, Admm~strabon whereas treatments that decrease exc#abth& of these /vled~calCenter, neurons (by increasing opzate and GABA transmzsswn, Brockton,MA 02401, and decreasing NMDA and noradrenergw transUSA,andMarbn m~sswn) retard averswe cond#wnmg as well as proCassdl~sat the Dept oiAnatomy, ducmg anxwlyhc effects m approprtate ammal tests A Unwemtyof lowa, better understanding of brain systems that mhzb# the IowaQty. IA52242, amygdala, as well as the role of #s very hzgh levels of USA peptzdes, mzght eventually lead to the development of

more effectwe pharmacologwal strategies for treating chmcal anxzety and memory dzsorders Despite its name, the rat amygdala bears only a passing resemblance to the 'almond' that Karl Burdach saw on dlssechons of the human brain nearly 200 208

© 1994 Efsev,erSoenceLtd

years ago Nonetheless, it contains almost all the nuclear groups present m the primate amygdala, its extnns~c and mtnns~c connectaons and neurochemastry are also remarkably stmflar, and the evidence for its role m complex behawor, learning and memory is generally consistent with the functions attributed to the human and non-human primate amygdala In the past decade, the development of the m v#ro shce preparation and the availability of a wide range of neurotransrrntter agomsts and antagomsts, as well as the availability of detailed anatormcal studies on the intrinsic macroclrcultry of individual amygdalold nuclei, have led to a considerable increase in the understandnag of the synaptlc events underlying some of the behaviors me&ated by the rat amygdala This review will integrate the current knowledge of synaptlc transmission within the rat amygdala w~th the effects of local infusion of drugs into the amygdala on a spectfic form of averslve learumg fear condlUonLng Emphasis will be placed on the role of GABA and glutamate, because the actaons of these neurotransmatters m the amygdala have been strongly maphcated m fear condltaonmg A large and consistent hterature indicates that the amygdala is critically involved m the acquisition and expression of conditioned fear (for revaew see Ref 1) TINS. Vol 17. No 5. 1994

Electrical stimulation of the amygdala produces a pattern of behavioral changes that closely resembles that produced by stressful or fearful stnnuh, and les~ons of the amygdala block innate or con&tloned reactions to stress Averswe st~muh readily actwate the amygdala, and results obtained after local infusion of compounds into the amygdala mchcate that it is especially important m the formation, consohdatlon and expression of memories of events paired with these averslve stimuli A better understanding of the chemical neuroanatomy of synaptlc transmission within the amygdala will eventually lead to novel and superior strategnes for treating chnlcal anxiety chsorders such as post-traumatic stress syndrome and panic, as well as hawng general relevance to the study of learning and memory However, it should be emphasized that restnctlng this rewew to fear condltlonmg does not mean that this is the only function of the amygdala On the contrary, tins complex structure is also involved critically m attention, secondary reinforcement, reward magnitude and social behavior (for review see Ref 2) Intrinsic and extrinsic c o n n e c t i o n s of the amygdala Intormatlon from all sensory modahtles reaches the amygdala via projections from the cortex and a variety of subcortlcal structures (most notably the thalamus and parabracinal complex) that converge on the basolateral amygdalold complex, in particular the lateral nucleus~ The cortical projections, which arise from secondary and polymodal association cortices 4, probably relay cogmtlve, but otherwise affectlvely neutral, information pertaining to sensory stimuli Information concerning the averslve properties of stimuli are probably relayed separately via projections from the external lateral part of the parabracinal complex~, the dysgranular insular cortex °, and mldhne and lntralamlnar thalamlc nuclei7, each of which receives noclceptlve inputs and projects to the basolateral complex Direct proJections from the parabrachlal nucleus and insular cortex to the central nucleus might also be especially Lrnportant for relaying averslve information to the amygdala5 The basolateral complex (consisting of the lateral, basolateral and basomedlal nuclei) contains two basic types of neurons 8 large, spine-dense pyranudal neurons containing glutamate, and providing the major extrinsic projections of the complex, and spine-sparse non-pyramidal cells that contain GABA, choline acetyltransferase (CAT) and neuropeptldes9, and most of wtuch are presumed to be local circuit neurons, although some also project to the thalamus Intracellular electrophyslologncal recordings from morphologically identified neurons of the basolateral complex suggest that the spine-dense and spreesparse neurons (Fig 1) have charactenstac firing properties and membrane input resistance (Table I) Importantly, the Ingh spree density of projection neurons In the basolateral complex suggests that they are capable of integrating a vast array of synaptlc contacts from extnnslc afferent Inputs There are four main output projections from the basolateral complex that arise from the pyramidal neurons of the basolateral nucleus reciprocal projectlons back to the cortex including the frontal cortex, and umdlrectlonal projections to ventral TIN& Vol 17, No 5, 1994

Fig 1 (A) Photomicrograph of a class I pyramidal neuron of the basolateral nucleus of the amygdala (BLA) Class I neurons compnse >75% of the neurons of the BLA, and are charactenzed by the spree-laden appearance of the dendntes This class I neuron has a prominent apical dendrite and pynform cell soma, and was fdled wffh 2% blocytm dunng electrophyslologlcal recording, and subsequently wsuahzed wffh a peroxldase-antlperoxldase complex using dlammobenzedme as the chromogen (B) Photomicrograph of a non-spray neuron Scale bars, 100 t~m

caudate-putamen, the nucleus accumbens, and the central amygdalold nucleus 1° The reciprocal cortical projections maght be revolved in the conscious perception of fear or anxiety, but tins awaits verification m humans ProJections to the two stnatal areas might relay motlvatlonally slgntficant reformation to motor areas necessary for the avoidance of harmful stLmuh or approach to stlmuh associated with primary reinforcers Projections to the central nucleus of the amygdala, the major lntra-amygdalold target of the basolateral complex, are critical for autonormc and somatic responses produced by stLmuh that were previously parred with averslve events The central nucleus is orgaruzed m a manner similar to both the dorsal and ventral stnatopalhdal systems H The lateral central nucleus contains mostly medium sized, spree-dense neurons, many of which have GABA as thetr neurotransnutterlz and contain a variety of neuropeptldes 13 Further slmdantles w~th the caudate-putamen and nucleus accumbens include the heavy dopammerglc mnervataon of the lateral central nucleus 14, direct corhcal input to GABA neurons 15, and the projections of these GABA neurons onto the large, spine-sparse output neurons 209

TABLE I Mean membrane input resistance for several subtypes of amygdalold neurons Spree-dense

Spree-sparse

Cortex-hke Basolateral Lateral

40-60 M~ 80 M ~

58 M ~ 90 M ~

Noncortex-hke Central

113 M ~

111 M ~

Cortex-hke neurons have the lowest resistanceand can be further subdw~ded into spree-laden putative projection neurons and spine-sparse putatwe mterneurons Neurons of the lateral nucleus generally have a h~gher input resistance than the neighboring basolateral nucleus md~cahngthe possibility of greater spatial and temporal summation of synapbc rnputs onto these neurons Neurons of the non-cortex-hke central nucleus have the highest input resistance, suggesting an electromcally more compact neuron These neurons are both sptne-laden and spree-sparse However, they have been tentatively subdivided according to the presence (Type A) or absence (Type B) of an afterhyperpolar~zahon following repehtwe burst fmng

of the medial central nucleus 15 These medial central nucleus neurons contain a vanety of neuropeptldes ~ and, m some cases, glutamate ~7, and project to a variety of bramstem regaons capable of influencing or initiating autonomic and somatic components of the fear reaction (Fig 2) Electrophys]ological studies suggest that the pnnc~pal neurons of the two central nucleus subdivisions have high input resistances (Table 1) and can be further differentiated according to the presence (type A, medial neurons) or absence (type B, lateral neurons) of a slow after hyperpolanzmg potential following repetitive finng ~s The basic mtnns]c amygdalold clrcuKry potenhally revolved in conditioned associations between neutral and averswe shmuh, based on both anatomical and electrophys~ological recording studies, ~s shown in Fig 3 For slmphficatlon, a number of other mtnns~c and other extnns~c connections, pnnc~pally subcortlcal ones, are not included Anatomical target

Lateral hypothalamus Conditioned fear shmulus

Effect of amygdala stlrnulatlon

Behavioral test or sign of fear or anxiety

Sympathetic actwatlon

Tachycardia, galvanic skin response, paleness, pupil dflahon, blood pressure elevation

/ .

~

S

Dorsal motor n of vagus Nucleus amb~guus Parabrachlal nucleus

u

E x c i t a t o r y a m i n o acid t r a n s m i s s i o n Electraphyswlogy Intra- and extracellular recordings from anesthetized rats have demonstrated both EPSPs and IPSPs in the amygdala 1~, and have confirmed that lnd]wdual amygdalold neurons can receive and rotegrate synaptlc inputs from diverse sources-'" Intracellular recordings from brain slice preparations have shown that stimulation of afferent pathways to the lateral and basolateral amygdala elicit EPSPs Stimulation of the stna termlnahs, the lateral amygdala, the external capsule, or the ventral endopynform nucleus evokes a glutamate-mediated EPSP in the basolateral amygdala "~--~ These EPSPs cons]st of a fast component mediated by b, L-o~-ammo-3-hydroxy-5-methyl-4lsoxazole proplonlc acid (AMPA)/kalnate receptors (that is, the fast component is blocked by the antagomst 6-cyano-2, 3-dlhydroxy-7-nltroqumoxahne, CNQX), and a slower component mediated by NMDA receptors (that is, blocked by the antagonist 2-ammophosphonopentanolc acid 21, APV) Similarly, focal stimulation of the basolateral amygdala evokes a glutamate-mediated EPSP m the lateral nucleus za z~ Thus, most afferents from the projection neurons ot the lateral and basolateral nuclei to the central nucleus are glutamaterg]c, and stimulation of the basolateral amygdala evokes an EPSP m the central nucleus which has both AMPA/kamate and NMDA receptormediated components '~ Behavtor It has been suggested that fear conditionmg mLght be mediated by associative long-term potenhatlon z7 ~'~~(LTP) In pavlowan fear conditioning, a neutral st]mulus, which has little behaworal effect by itself, is consistently paired with a strong avers~ve stimulus Following a small number of pairings, the neutral stimulus produces effects formerly only produced by the strong, a~erswe stimulus This change is not seen when the stlmuh are presented m an unpaired/ash]on In associative LTP, activation of a weak input to a given postsynapt[c cell ~s paired wzth act]vat]on ot a second, strong input

J. Parasympathetic activation Increased respirahon

~

Ulcers, unnation, defecation, bradycard~a

~

Pantlng, respiratory distress Behavioral and EEG arousal, increased vlgdance

Ventral tegmental area Locus coeruleus Dorsal lateral tegmental n

Achvat~on of dopamme, ~- noradrenahne and ACh neurons

~

Pontme reticular formation

}. Increased reflexes

~- Increased startle

Central grey

Cessation of •- behavior, analgesia

Freezing, confhct test, CER, )- social interaction condJtaoned analgesia

Trigemmal, facial motor n Paraventnoular n (hypothal)

Mouth open, jaw movements }. ACTH release

)- Facial expressions of fear CortJcosteroid release ('stress response')

Fig 2 Schemattc diagram of selected outputs of the central nucleus of the amygdala to hypothalamlc and bramstem

targets, and possfbte relationship of these connections to specfftc signs of fear and anxiety Abbrewatlon CER, conditioned emotion response Adapted, w~th permission, from Ref 1 210

TINS, Vol 17, No 5, 1994

Insular cortex

Central nucleus I

Secondary sensory cortex, penrhmal and entorh~nal cortex

I I I

Basolaterall nucleus

Secondary sensory cortex, penrhmal cortex

Lateral nucleus

ZX

Fig 3 Schematic &agram of pnnclpal connecbons within the central, basolateral and lateral amygdalold nuclei based on m vitro electrophyslologlcal recording and anatomical data For stmphctty, many other connecbons, notably subcortlcal projections, are not included

projecting to the same cell Following a small number of pairings, the lnltlatb weak synaptm Input is potentiated This potentiation is not seen when an equal number of the weak and strong inputs are presented in an unpaired fashmn In the CA1 region of the hlppocampus, activation of the weak input releases excitatory amino acids, such as glutamate, which bind to both NMDA and AMPA/ kalnate receptors on the postsynaptlc neuron (for rewew see Ref 30) Binding to the NMDA receptor has little effect because the highly Ca'+-permeable NMDA channel is normally blocked by Mg e+ However. if the postsynaptlc neuron is depolarized by a strong synaptlc input activating a sufficient number of AMPA/kamate receptors, the Mg e+ block ts removed and glutamate binding to the NMDA receptor allows Ca e+ to enter the cell. tnggenng a series of events that leads to a lasting potentiation of synaptlc efficacy in the tonnerly weak input If glutamate is prevented from binding to the NMDA receptor by administration of a competitive NMDA-receptor antagonist, such as APV, shortl~ before pmnng the weak and strong stimuli, assoclam e LTP does not occur In classical fear conditioning, a neutral shmulus (condmoned stimulus) could ehclt release of glutamate onto neurons in the amygdala, and this glutamate could bmd to both NMDA and AMPA/kalnate receptors However. this mtght not produce much of a behavioral response because at resting membrane potentials only weak activation of AMPA/kalnate receptors, and pamal blockade of NMDA-channel permeablhty by Mg "+ occur However, presentation of a strong averslve stimulus at about the same t~me could further depolarize the neuron, reheve the remaining Mg -'+ blockade, and enable Ca -,+ to enter the cell This could trigger events that would Increase TIN& Vol 17, No 5, 1994

the ablllt~ of the conditioned stimulus to actlx ate that neuron, enabling it then to produce effects similar to those previously produced only by the strong averslve stimulus That Mg e+ appears to only partially block NMDA currents in the amygdala might explain why fear conditioning occurs so readily Like the hlppocampus, both NMDA-dependent ~1 and NMDA-lndependent Je forms of LTP have been observed in neurons of the basolateral complex, depending on the amygdalold afferent stimulated (Fig 4) Therefore, would local infusion of antagonists of NMDA receptors into the amygdala block the acquisition of averslve conditioning > Using the fearpotentiated startle paradigm, Mlserendlno and colleagues e~ found that infusion of APV into the basolateral nucleus caused a dose-dependent blockade of the acqmsltlon, but not the expression, of condltloned fear Tins effect did not seem to result from a decrease m sensitivity to footshock, a local anesthetic effect, blockade of visual transmission or permanent damage to the amygdala Using similar doses, Fanselow and colleagues ~ found that local lntuslon of APV into the basolateral nucleus before training blocked conditioned Ireezlng measured 24h later Infusion of APV Into the Immediately adjacent central nucleus had no effect, implying that the effect was highly localized Using a multiple-trial step through avoidance paradigm, Klm and McGaugh /ound that lntra-amygdala infusion of t)L-APV, I>APV or (_+)-2(carboxyplperazlne-4-yl)propyl-1-phosphonlc acid (CPP) before training, caused a dose-dependent impairment of retention measured 48h later ~ The potency of the drugs was consistent with their relative affinities to the NMDA receptor This effect was not seen when APV was Infused Into the stnatum, immediately above the amygdala Intra-amygdala 211

lntuslon of DL-APV did not affect footshock sensitivity or locomotor acUvlty, and the blockade of memory formation could not be attributed to state-dependent effects Using step-down inhibitory avoidance, lzqulerdo and colleagues ~5 found that immediate posttraining infusion of APV into either the amygdala. medial septum, or hlp[~ocampus, blocked memory measured 18h after training t~-2-Ammo-5-phosphonovalerate caused amnesia when infused into either the hlppocampus or amygdala immediately after trainlng, but not thereatter ~(' However, the AMPA/ kalnate antagonist CNQX caused amnesia if infused into the hlppocampus or amygdala either immediately, 90 or 180 rain after training By contrast, APV infused into the entorhlnal cortex caused amnesia when given either 90 or 180. but not immediately or 360, mln alter training ~'~ ~7 These data suggest that a process sensitive first to APV and CNQX and then only to CNQX in the amvgdala and hlppocampus, is cntlcal for post-training memory processing of this step-down inhibitor:> task Later, an APV-sensmve process in the entorhlnal cortex might come into play As mentioned earlier, once learning has occurred, local infusion ot APV into the amygdala does not block the expression ot either tear-potentiated startle or lnhlbltot~ avoidance In contrast, local infusion of CNQX into the amygdala dose-dependently blocks the expression of fear-potentiated startle ~a or retention m a step-down inhibitory avoidance test ~ Once again, this pattern is similar to LTP where APV does not reverse LTP once it is established, whereas CNQX blocks last synaptlc transmission either before or atter LTP Thus, excitatory amino acids mediate svnaptlc transmission in the amygdala originating trom both cortical inputs and intrinsic amygdalold connections In the amygdala. NMDA receptors seem to be lnvol~ed in the tormatlon of conditioned tear, whereas AMPA kamate receptors appear to be involved m the expression ol conditioned tear As such, these data are consistent ~ t h , but b} no means pro~e, the Idea that an NMDA-bensltlVe fornl ol LTP m the amygdala might mediate lear conditioning Inhibitory a m i n o acids Electrophyswlo~o' In the basolateral nucleus, stimulation-induced EPSPs are followed by both tast and slou IPSPs The tast, GABA-medlated IPSP results trom acre atlon ot GABAa receptors, and the slouer IPSP is mediated by activation of GABAB receptors ~() (Fig 4) The last IPSP is associated with a large decrease In resistance, and its possible somatic or dendritic origin ensures that neurons of the basolateral complex will be effectively inhibited lrom firing action potentials, e~en m the face of strong excitatory stimuli The fast onset and short duration of the IPSP also enables precise moment-to-moment adjustment ot the cellular response to excitatory input In contrast, the bmall conductance increase and long duration associated with the slow IPSP might only tegulate lo~-trequency excitatory input during times of normal neuronal tunctlon Blockade of the fast IPSP wlth the GABAa-receptor antagonist bmuculhne rebults in eplleptlform burst firing of normally quiescent basolateral neurons, suggesting that the last IPSP probably dictates the primary state of excltablhb in the nucleus It IS possible that both GABA 212

and GABA~ responses might be mediated by activation of a heterogeneous population of GABA lnterneurons w l l In addition, both baclofen, a GABA~-receptor agonlst, and trans-l-amlnocyclopentane-l,3-dlcarboxyhc acid (trans-ACPD), a metabotroplc glutamate-receptor agonlst, reduce glutamatergm transmission via stimulation of the striatermlnahs by an action at presynaptlc receptors~2 ~ A reduction in presynaptlc GABAt~- or metabotroplc glutamate-receptor activation might contribute to the induction of LTP in the basolateral complex Indeed, klndhng results in a decreased sensitivity ot presynaptlc GABA~ receptors on terminals of the stria termmallS that are presumed to be glutamatergnc 12 In the central nucleus, focal, low-intensity stimulation of the lateral central nucleus ehclts a GABA xmediated inhibition (blocked by blcuculhne methiodide) of medial central nucleus neurons, whereas higher intensity stimulation elicits a GABAB-medlated lnhlbmon (blocked by phaclofen) "(~ Repetitive stimulation also reveals a slow GAgAB-medlated IPSP In addition, glutamatergnc transmission was blocked b) presynaptlc activation ot GABA~ receptors and A~ adenosine receptors Anatomical studies l~' indicate some terminals ot GABA neurons appear to be presynaptlc to cortical terminals m the lateral part ol the central nucleus The presence ot presynaptlc A1 adenosine receptors further suggests that, during periods ot high metabolic actlvlt) in the adjacent basolateral nucleus, glutamaterglc transmission in the central nucleus will be restricted In addition, output neurons In the central nucleus are heavily innervated by GABA terminals of intrinsic origin 1~ Nose and coworkers "(' also demonstrated a strychnine-sensitive long-lasting IPSP following repetitive stimulation of the dorsal lateral subdivision of the central nucleus This presumed glyclne-medlated IPSP probably results lrom an input arising in the bralnstem In a nucleus that has such a strong output to the bralnstem cardiovascular regulatory centers, this tight control ot excitability is probably essential In fact, local infusion ot GABA or chlordlazepoxlde into the central nucleus reduces the severity ot stress-reduced ulcers, whereas antagonists of GABA receptors increase severity (tot review see Rel 44) Bdmwor The amygdala has a high density ot benzodlazeplne receptors 1~', which are known to facilitate GABA transmission Local Infusion of benzodlazeplnes into the amygdala (for review see Ref 1) has anxlolytlc effects in the operant conflict test, social interaction test, measures of conditioned freezing and hypoalgesla, the light-dark box test in mice, and antagonizes the discriminative stimulus properties ot pentylenetetrazol The antlconfllct effect can be reversed by systemic administration of the benzodlazeplne antagonist flumazenll or co-administration into the amygdala of the GABAa antagonist blcuculhne, and mimicked by local mtuslon, into the amygdala, of GABA or the GABAA agorust musclmol In general, antlconfllCt ettects ot benzodlazeplnes occur alter local Infusion Into the lateral and basolateral nuclei, which ha~e the highest densities of benzodlazeplne receptors in the amygdala, and not alter local infusion into the central nucleus More recently, it has been shown that the antenor part ot the basolateral and central nucleus is especially important for conflict performance based on both lesion and local TINS, Vol 17, No 5, 1994

A

~

a Control

20 V -85 mV

/

EPSP

b APV 50 p.M

1 ,/flPSP

f

-%

C CNQX 10 gM d APV 50 ~M slPSP

+

I

5 mV

CNQX 10 ~tM

50 ms e CNQX 10 gM

+

BMI 30 ~IM B

post tetanus

/

0 gM A P V •

300 3 "~ 250~

0 IxM APV _

50 pM APV O 100 pM APV •

~.

is01

__" . . . . . . . . . . . .

50 ~IMAPV II)

100 gM APV _

~

~

-

n

-

C

>

a+b

g

c+d

O "O

Q_ q) Q_

20 mV

Lu

20 ms

-5

35 30 25 20 15 10 5 0

0

5

10 Tffne (mm)

15

20

d o

a

t

HFS APV -5 17

b

c

t

HFS 1'0 1.5 2'0 2'5 30 35"4'0 4'5 5'0 Time (mm)

Fig. 4 5ynaptlc transmission tn the basolateral amygdalold nucleus (BLA) (A, left) Sbmutabon of the stna termlnahs evokes a mulbphaslc postsynapbc potential (PSP) in neurons of the BLA Typically, sbmulabon (arrow head) ehots an EPSP followed by a fast IPSP (flPSP), and subsequent slow IPSP (slPSP) (A, r)ght) The PSP results from a dual component glutamate-mediated EPSPand acbvabon of a feedforward inhibitory input a A typical response to stria sbmulabon b 2-Amtno-5-phosphonovalerate (APV) (50 #M) apphcabon caused a reducbon m the amphtude of both the fast and slow IPSP c CNQX (101xM) abohshed both the EPSPand the flPSPand slPSP to reveal a slow EPSP d The slow EPSPrevealed by CNQX is blocked by subsequent addfflon of APV e Antagomsm of GABAA receptors with blcuculhne (BMI) enhanced the expression of the slow EPSP (B) Long-term potenbabon (L TP) reduced m BLA neurons following sbmulabon of the external capsule (EC) is resistant to APV (50 #M) (B, left) High-frequency sbmulabon of the EC resulted m an ~ncrease m the EPSPamphtude (upper trace), the increase was unaffected by 50#/~ APV (mMdle trace), and blocked by IO0 #M APV (lower trace) (B, right) The 50 #M APV-reslstant LTPperslsted for several minutes following high-frequency sttmulabon, suggesbng that in this pathway NMDA-receptor acbvabon is not needed for synapbc plasboty (C) LTP reduced in BLA neurons following sbmula bon of the endopynform nucleus Is senslbve to APV (50 #M) (C, right) In the presence of APV (50 #M), EPSPsevoked before (a), and after (b) high-frequency sbmulabon of the endopynform nucleus are of slmdar amphtude Followmg washout of APV, a similar sbmulabon paradigm resulted Jn an enhanced EPSP (C, left) The APV-sensfftve LTP persisted for several minutes following high-frequency sbmulabon, suggestmg that NMDA-receptor acbvabon is required for synapbc plasbcffy m this pathway

infusion of benzo&azepmes. Therefore, taken together, these results might be sufficient to explain both fearreducing and anxiety-reducing effects of various drugs gwen systemically Local infusion of the benzodlazeplne antagomst flumazeml into the amygdala s~gnlficantly attenuates the antlconfllct effect of the benzodlazeplne agonlst chlordlazepoxlde gwen systemically 4~ This strongly nnpllcates the amygdala in mediating the anxlolyhc effects of benzodlazeplnes in normal animals However, benzodlazepmes can still TIN& Vol 17, No 5, 1994

have anxiolytlc effects in aramals with lesions of the amygdala47 45 In these stuches, the lesions produced anxlolytlc effects by themselves Nonetheless, some fearful behavior could still be obtained, presumably because other brain areas can mediate conditioned fear following damage to the amygdala, and these areas also seem to be affected by benzodlazeplnes Using inhibitory avoidance, lntra-amygdala infusion of the GABA antagonists blcuculhne methlodlde 49, picrotoxm or Ro54864 (4'-purodlazepine) (Ref 50) 213

J Neurophyslol 65 1227-1241 27 Clugnet, M C and LeDoux, J E (1990) J Neuroso 10, 2818-2824 28 Kim, J J, DeCola, J P, Landelra-Fernandez, J and Fanseiow, M S (1991)Behav Neuroso 105, 126-133 29 Miserendino M J D, Sananes C B, Meha, K R and Daws, M (1990) Nature 345 716-718 30 Bhss, T V P and Cothngndge, G L (1993) Nature 361, 31-39 31 Gean, P W Chang, F C Huang, C C Lin, J H and Way, L J (1993) Brain Res Bull 31, 7-11 32 Chapman, P F and Bellavance, L L (1992) Synapse 11 310-318 33 Fanselow M S,Kim, J J andLandepra-Fernandez, J (1991) Sac Neuroscl Abstr 17, 659 34 Kfm M and McGaugh, J L (1992) Brain Res 585, 35-48 35 Izqumrdo, I eta/ (1992)Behav Neural BIol 58, 16-26 36 Jerusarinsky, D etal (1992)Behav Neural BIol 58, 76-80 37 Ferreira, M B C, Da Silva R C, Median, J H and Izqumrdo, I (1992) Pharmacol Biochem Behav 41, 767-771 38 Kpm, M , Campeau S, Falls W A and Daws, M (1993) Behav Neural Bio/ 59, 5 - 8 39 Izqulerdo, I etal (1993)Behav Neural BIol 59, 1 - 4 40 Ramn~e, D G Asprodml E K and Shmmck-Gallagher P (1991) J Neurophyssol 66, 999-1009 41 Sugita S,Johnson, S W and North, R A (1992) Neuroso Lett 134,207-211 42 Asprodim E K, Ralnme, D G and Shtnnick-Gallagher, P (1992) J Pharmacol Exp Ther 262, 1011-1021 43 Ramme D G and Shmnick-Gallagher P (1992)Neuroso Selected references Lett 139 87-91 1 Daws M (1992)in The Amygda/a Neuroblologlea/Aspects 44 Henke, P G (1992) In The Amygdala Neuroblologlcal of Emohon, Memory and Mental Dysfuncbon (Aggleton Aspects of Emohon Memory, and Mental Dysfuncbon (Aggfeton J P, ed ), pp 323-338 John Wlley-Liss and Sons J P ed), pp 255-306, John Wfley-Lissand Sons 2 Aggleton, J P, ed (1992) The Amygdala Neuroblologlca/ 45 Nlehoff D L and Kuhar M J (1983) J Neuroso 3 Aspects of Emohon, Memory, and Mental Dysfunction, John 2091-2097 46 Hodges H, Green, S and Glenn, B (1987) PsychopharmaWfley-Dss and Sons 3 LeDoux, J E Occheth, P Xagorans, A and Romanskl, cology 92,491-504 L M (1990)J Neuroscl 10, 1062-1069 47 Kopcha K L Airman H J and Commtssans, R L (1992) 4 Turner B and Zimmer, J (1984) J Camp Neural 227, Pharmacol Biochem Behav 43 453-461 320-334 48 Yadm E Thomas, E, Stnckland, C E and Gnshkat, H L 5 Bernard, J F, Alden, M and Besson, J M (1993) J Camp (1991 ) Psychopharmacology 103,473-479 Neural 329, 201-229 49 Brlom J D, Nagahara, A H and McGaugh J L (1989)Brain 6 Yasu~, Y Breder C D, Saper, C B and Cechelto, D F Res 487 105-111 (1991) ] Camp Neural 303 355-374 50 Da Cunha C eta/ (1991) Brain Res 544, 133-136 7 Turner B and Herkenham, M (1991)J Camp Neural 313 51 McGaugh J L (1992) in The Amygdala NeurobJologJcat 295-325 Aspects of Emohon, Memory and Mental Dysfunction 8 McDonald A J (1984)J Camp Neural 222, 589-606 (Aggleton, J P ed ) pp 431-451 John Wiley L~ssand Sons 9 McDonald, A J and Pearson J C (1989)Neuroscl Lett 100, 53-58 10 McDonald, A J (1991) Neurosc/ Lett 44, 15-33 11 Alheld, G and Helmer, L (1988) Neurosoence27, 1-39 12 Sun, N and Cassell, M D (1993) J Camp Neural 330, 381-404 At a meeting of The Royal Society, hetd on 10 March 13 Cas~ell,M D and Gray, T S (1989)J Camp Neural 281, 1994, the following new Fellows were elected 320-334 Dr Raymond Baker 14 Freedman, L J and Cassell M D (1994) Brain Res 633, Execuhve Director of Medicinal Chemrstry, Merck Sharp 243-252 and Dohme Research Laboratones, Harlow, Essex, UK 15 Sun, N, Y~ H and Cassell, M D (1994)J Camp Neural 370, 43-64 Dr Timothy Vivian Pelham Bliss 16 Gray, T S (1989) Jn Autonomic Neuropepbde Connechons Head of the Dwlslon of Neurophysiology and of the Amygda/a (Tache, Y, Morley, J E and Brown, M R, Neuropharmacology at the National Institute of Medmal eds), pp 92-106, Springer Verlag Research, London, UK 17 Takayama, K and Mrura, M (1991) Neuroso Lett 134, 62 -66 Prof Jeremy Patrick Brockes 18 Schess M C,Asprodmi, E K Ramme,D G andShmnlckProfessor of Cell Biology at the Ludwig Inshtute for Gallagher, P S (1993)Brain Res 604 283-297 Cancer Research, Umversity College London, London, 19 Brothers L A and Finch, D M (1985) Brain Res 359 UK 10-20 Dr Henry Marshall Charlton 20 Meflo L E A M Tan, A M andFmch, D M (1992) Brain Reader in Endocnnology, U ntverslty of Oxford, Oxford, Res 587 24-40 UK 21 Rainnm, D G, Asprodmh E K and Shmmck-Gallagher, P (1991) J Neurophys/ol 66, 986-998 Prof Andrew Gmo Sita Lumsden 22 Washburn, M S and Molses H C (1992)J Neuroscl 12 Professor of Developmental Neuroblology, United 4066-4079 Medical and Dental Schools Guy's and St Thomas', 23 Gean, P W and Chang, F C (1992) Synapse 11 1 - 9 Universfty of London, UK 24 Suglta, S, Shen, K Z and North, R A (1992) Neuron 8, Trends m Neurosoences offers its congratulations to the 199-203 above for their election to The Royal Society 25 Suglta, S Tanaka, E and North R A (1993) J Physlol 460, 705-718 26 Nose I HigashJ H, Inokuchh H and Nishl S (1991)

lmmedmtel} alter training, produced a dose-dependent enhancement ot retenhon measured 2 4 - 4 8 h later Conversel}, infusion of the GABA~ against musomol or the (,ABAh agonlst bac]olen produced retent]on deficits Inluslons into the cattdate nucleus, dorsal to the am~ gdala, had no elfect Thu~, it is clear that GABA can potently regulate cellulm excltabdltv in the lateral and basolateral am\ gdalold nuclei b,, decreasing the release ol glutamate at bv d~rect mh~b~toD acUons These d~rect decreases m exc~tabdltv might explain the depressant eltects at GABA on a~erswe cond~Uonmg Ho~e~er, the} might also result tram an alteraUon m the release at noradtenahne which ts known to modulate learning x~thm the amxgdala (for rex~e~ see Ret 51) Fo~ example, the Iacd~tatoD effect at b~cuculhne can be p~evented b} the [a,-adrenerg~c antagonist propranolol at a dose which has no s~gmflcant effect b) ~tself In addmon, output neurons of the central nucleus, ~h~ch pzoject to bramstem targets areas known t() be m~ohed m the autonomm and somahc aspects at cond~tumed tear, are tightly regulated by GABA and othez inhibitor} transmltter~, d]sruphon oI which m~ght greath amphly fear and stress

The Royal Society

Acknowledgements Thiswork wa~ supportedby NIMH GrantMH 47840, ResearchSczenflst Deve/opmentAward MH-O0004,anda grant from theA~r ForceOffice of 5c~enflfmResearchto M D, Alzhe~mer's Assoc/Harold W and Georg~anaSpaght MemonalPdot ResearchGrantNo PRG-92-119toDR and NIH Grant N525139to M C 214

TINS, Vol 17, No 5, 1994