New perspectives on the functional anatomical organization of the basolateral amygdala

Brain stem afferent connections of the amygdala in the rat with special references to a projection from the parabigeminal nucleus: a fluorescent retrograde tracing study

A recently revealed important function of the amygdala (Am) is that it acts as the brain's "lighthouse", which constantly monitors the environment for stimuli which signal a threat to the organism. The data from patients with extensive lesions of the striate cortex indicate that "unseen" fearful and fear-conditioned faces elicit increased Am responses. Thus, also extrageniculostriate pathways are involved. A multisynaptic pathway from the retina to the Am via the superior colliculus (SC) and the pulvinar was recently suggested. We here present data based on retrograde neuronal labeling following injection of the fluorescent tracer Fluoro-Gold in the rat Am that the parabigeminal nucleus (Pbg) emits a substantial, bilateral projection to the Am. This small cholinergic nucleus (Ch8 group) in the midbrain tegmentum is a subcortical relay visual center that is reciprocally connected with the SC. We suggest the existence of a second extrageniculostriate multisynaptic connection to Am: retina-SC-Pbg-Am, that might be very effective since all tracts listed above are bilateral. In addition, we present hodological details on other brainstem afferent connections of the Am, some of which are only recently described, and some others that still remain equivocal. Following selective injections of Fluoro-Gold in the Am, retrogradely labeled neurons were observed in parasubthalamic nucleus, peripeduncular nucleus, periaqueductal gray, dopaminergic nuclear complex (substantia nigra pars lateralis and pars compacta, paranigral, parabrachial pigmented and interfascicular nuclei, rostral and caudal linear nuclei, retrorubral area), deep mesencephalic nucleus, serotoninergic structures (dorsal, median and pontine raphe nuclei), laterodorsal and pedunculopontine tegmental nuclei (Ch6 and Ch5 groups), parabrachial nuclear complex, locus coeruleus, nucleus incertus, ventrolateral pontine tegmentum (A5 group), dorsomedial medulla (nucleus of the solitary tract, A2 group), ventrolateral medulla (A1/C1 group), and pars caudalis of the spinal trigeminal nucleus. A bilateral labeling of the upper cervical spinal cord was also observed.

Synaptic connections of distinct interneuronal subpopulations in the rat basolateral amygdalar nucleus

Although it is well established that the activity of pyramidal projection neurons in the basolateral amygdala (ABL) is controlled by gamma-aminobutyric acid (GABA)ergic inhibitory interneurons, very little is known about the connections of specific interneuronal subpopulations in this region. In the present study, immunohistochemical techniques were used at the light and electron microscopic levels to identify specific populations of interneurons and to analyze their connections with each other and with unlabeled presumptive pyramidal neurons. Double-labeling immunofluorescence experiments revealed that antibodies to vasoactive intestinal peptide (VIP) and calbindin-D28K (CB) labeled two separate interneuronal subpopulations in the ABL. Light microscopic double-labeling immunoperoxidase experiments demonstrated that many VIP-positive (VIP+) axon terminals formed intimate synaptic-like contacts with the CB-positive (CB+) neurons and that both CB+ and VIP+ terminals often contributed to the formation of pericellular baskets that surrounded unlabeled perikarya of pyramidal neurons. By using a dual immunoperoxidase/immunogold-silver procedure at the ultrastructural level, it was found that 30% of VIP+ terminals in the anterior subdivision of the basolateral nucleus innervated interneurons that were either CB+ (25%) or VIP+ (5%). A smaller percentage (15%) of CB+ terminals formed synapses with labeled interneurons. Both VIP+ and CB+ terminals also innervated unlabeled perikarya, dendrites, and spines, most of which probably belonged to pyramidal neurons. The interconnections between interneurons may be important for disinhibitory mechanisms and the mediation of rhythmic oscillations in the ABL.

GABAergic innervation of alpha type II calcium/calmodulin-dependent protein kinase immunoreactive pyramidal neurons in the rat basolateral amygdala

Although calcium/calmodulin-dependent protein kinase II (CaMK) has been shown to play a critical role in long-term potentiation (LTP) and emotional learning mediated by the basolateral amygdala, little is known about its cellular localization in this region. We have utilized immunohistochemical methods to study the neuronal localization of CaMK, and its relationship to gamma-aminobutyric acid (GABA)-ergic structures, in the rat basolateral amygdala (ABL). Light microscopic observations revealed dense CaMK staining in the ABL. Although the cell bodies and proximal dendrites of virtually every pyramidal cell appeared to be CaMK(+), the cell bodies of small nonpyramidal neurons were always unstained. Dual localization of CaMK and GABA immunoreactivity with confocal immunofluorescence microscopy revealed that CaMK and GABA were found in different neuronal populations in the ABL. CaMK was contained only in pyramidal neurons; GABA was contained only in nonpyramidal cells. At the ultrastructural level, it was found that CaMK was localized to pyramidal cell bodies, thick proximal dendrites, thin distal dendrites, most dendritic spines, axon initial segments, and axon terminals forming asymmetrical synapses. These findings suggest that all portions of labeled pyramidal cells, with the exception of some dendritic spines, can exhibit CaMK immunoreactivity. By using a dual immunoperoxidase/immunogold-silver procedure at the ultrastructural level, GABA(+) axon terminals were seen to innervate all CaMK(+) postsynaptic domains, including cell bodies (22%), thick (>1 microm) dendrites (34%), thin (<1 microm) dendrites (22%), dendritic spines (17%), and axon initial segments (5%). These findings indicate that CaMK is a useful marker for pyramidal neurons in ultrastructural studies of ABL synaptology and that the activity of pyramidal neurons in the ABL is tightly controlled by a high density of GABAergic terminals that target all postsynaptic domains of pyramidal neurons.

Expression of calbindin-D28k and parvalbumin during development of rat's basolateral amygdaloid complex

Parvalbumin and calbindin-D28k are calcium-binding proteins, which are considered to be markers for certain populations of GABAergic neurons. Their correct development in the basolateral amygdaloid complex is critical for the proper emotional functioning in adult live of human and animals. Therefore, in this paper we describe the pattern of the morphological differentiation and distribution of immunoreactive elements of the parvalbumin and calbindin-D28k in this complex on the basis of immunohistochemically stained material obtained from embryonic (E20) and postnatal (P0-P90) rat brains. Calbindin-D28k appeared early in the development, already in the prenatal life. At this time immunopositive reaction was visible only in cell bodies. However, during development the population of immunopositive neurons was divided into four types: (1) polygonal; (2) piriform-like; (3) bipolar; and (4) pyramidal-like. Two weeks after birth calbindin-D28k immunoreactivity also appeared in neuropil. First, there were visible calbindin-D28k positive fibers and granules that encircled unstained cell bodies and formed basket-like structures. Subsequently, these granules appeared along proximal parts of unstained dendrites forming, so called 'cartridges'. The distribution of calbindin-D28k positive cells during postnatal life was rather homogenous throughout whole basolateral complex. Intensity of calbindin-D28k immunoreactivity reached mature level on the 21st day after birth.The maturation pattern of parvalbumin immunopositive elements followed the same sequence as calbindin-D28k, but it started much later - since the 17th day after birth and reached mature appearance on the 30th day of life. Contrary to calbindin-D28k, parvalbumin was not homogeneously distributed in the basolateral complex. Originally, parvalbumin was restricted to the magnocellular part of basolateral nucleus but it was finally expressed also in the parvicellular part of basolateral nucleus and the dorsolateral part of lateral nucleus. The differences in development of these two calcium-binding proteins indicate that parvalbumin and calbindin-D28k play diverse roles during development and maturation of the basolateral amygdala.

Long-term depression of excitatory synaptic transmission in the rat amygdala

In view of the fact that both kindling and fear-potentiated startle are expressed by long-term enhancement of synaptic transmission in the amygdala, synaptic plasticity in this area of the brain is of particular importance. Here, we show for the first time that low-frequency stimulation of the lateral nucleus at 1 Hz for 15 min elicited a long-term depression (LTD) in the basolateral amygdala (BLA) neurons. LTD is expressed specifically at the lateral-BLA synapses but not at ventral endopyriform nucleus-BLA synapses. The induction of LTD requires activation of both NMDA and metabotropic glutamate receptors. Loading cells with a Ca(2+) chelator BAPTA or extracellular superfusion with protein phosphatase inhibitors prevents LTD, suggesting that LTD may result from dephosphorylation of AMPA receptors. The same stimulating protocol could not elicit LTD in neurons from kindled animals, whereas neurons from sham-operated or age-matched control rats were able to exhibit LTD. Together, this study characterizes the properties of LTD in the naïve amygdala slices for the first time and demonstrates that epileptogenesis in vivo induces disruption of LTD in the in vitro preparation.

Microinfusions of flumazenil into the basolateral but not the central nucleus of the amygdala enhance memory consolidation in rats

Extensive evidence indicates that benzodiazepine receptors in the amygdala are involved in regulating memory consolidation. Recent findings indicate that many other drugs and hormones influence memory through selective activation of the basolateral amygdala nucleus (BLA). This experiment examined whether the memory-modulatory effect of flumazenil, a benzodiazepine receptor antagonist, selectively involves the BLA. Bilateral microinfusions of flumazenil (12 nmol in 0.2 microl) into the BLA of rats administered immediately after training in an inhibitory avoidance task significantly enhanced 48-h retention performance whereas infusions into the central nucleus were ineffective. These findings indicate that the BLA is selectively involved in mediating flumazenil's influence on memory storage and are thus consistent with extensive evidence indicating that the BLA is involved in regulating memory consolidation.

Ethanol induces taurine release in the amygdala: an in vivo microdialysis study

The effect of acute IP ethanol injections on the extracellular aspartate, glutamate, taurine and GABA content of the basolateral amygdala microdialysate was investigated in relationship with total brain ethanol. Each acute intraperitoneal injection of ethanol, 0.5, 1.0, 2.0 and 3.0 g/kg body weight, induced an immediate increase in microdialysate taurine; both 0.5 and 1.0 g/kg ethanol evoked an increase during the first 20 minutes following injection which returned to baseline value by 40 minutes, despite the fact that ethanol was detectable in the brain until 60 or 120 minutes, respectively. After either 2.0 or 3.0 g/kg ethanol there was an increase in taurine of gradual intensity which gradually declined to reach baseline values by 100 minutes. In contrast, the ethanol concentration for 2.0 g/kg remained elevated at the end of the 120 minutes; approximately 25 mg ethanol/mg protein. The stimulated release of taurine within the amygdala could participate in the regulation of ethanoli-nduced changes in osmolarity, since taurine is postulated to act as an osmoregulator in the brain. Taurine could also mediate or interact with ethanol-induced central nervous system effects, as it exerts a modulatory action on cell excitability and neurotransmitter processes.

Neuronal changes in the basolateral complex during development of the amygdala of the rat

Neuronal changes in the amygdala basolateral complex were studied during development and maturation in fetal and postnatal rat brains using morphometrical methods. Forty brains of animals of various ages were fixed in formalin, frozen and cut into 25 microm thick sections and stained with cresyl violet or haematoxylin and eosin (H&E). In cresyl violet preparations, the complex appeared for the first time on embryonic day (E)17 and was composed of two homogeneous nuclei lateral and basolateral. On about the seventh postnatal day, each of these nuclei was divided into two parts the first one into the dorsolateral and ventromedial and the second one into the anterior and posterior. Morphometric investigations showed a different increase of the neuronal and nuclear size in various parts of the basolateral complex up to postnatal day (P)14; after that time these parameters did not change significantly. The neuronal density and the total number of neurons stabilized at P7 in all parts of this complex, except for the dorsolateral part of the lateral nucleus in which a 30% decrease of the total number of cells was observed. From P14, in all nuclei under study, the total number of neurons did not change significantly.

Projections of the medial and lateral prefrontal cortices to the amygdala: a Phaseolus vulgaris leucoagglutinin study in the rat

The projections of different subfields of the medial and lateral prefrontal cortices to the amygdala were studied in the rat using the sensitive Phaseolus vulgaris leucoagglutinin anterograde tract tracing technique. Injections into the infralimbic cortex produced anterograde labeling in the lateral capsular subdivision of the central nucleus, superficial (corticomedial) amygdaloid nuclei, lateral and accessory basal nuclei, and the anterior amygdaloid area. Injections into the caudal portion of the infralimbic cortex produced additional labeling in the intermediate subdivision of the central nucleus. The prelimbic cortex had projections to the medial portion of the magnocellular basal nucleus and adjacent portions of the lateral nucleus and lateral capsular subdivision of the central nucleus. The medial precentral cortex had projections to the rostromedial part of the magnocellular basal nucleus and adjacent portions of the lateral capsular subdivision of the central nucleus. Injections into the lateral orbital and ventral agranular insular cortices produced labeled fibers in the rostral part of the superficial amygdala, lateral capsular subdivision of the central nucleus, and the lateral and accessory basal nuclei. The dorsal agranular insular area had projections to several different subdivisions of the central nucleus as well as to the rostrolateral magnocellular basal nucleus; the latter projections were complementary to those originating in the prelimbic area. The present study indicates that each portion of the prefrontal cortex has a distinctive projection to the amygdala. The ventral areas of the lateral and medial prefrontal cortices, which receive olfactory projections, are the only prefrontal cortical areas with projections to the olfactory-related superficial amygdaloid nuclei. The more dorsally situated prefrontal areas, the dorsal agranular insular area and prelimbic cortex, have complementary projections to the basal nucleus, suggesting that they modulate separate prefrontal cortico-striatal-pallid circuits. The specificity of prefrontal cortico-amygdaloid projections is indicative of their involvement in discrete functions.

Synaptology of prefrontal cortical projections to the basolateral amygdala: an electron microscopic study in the rat

Prefrontal projections to the magnocellular basal amygdaloid nucleus (Bmg) of the rat were investigated using Phaseolus vulgaris leucoagglutinin (PHA-L) as an anterograde tracer. Electron microscopic examination revealed that most axon terminals in Bmg labeled by PHA-L injections into the prelimbic area contained round synaptic vesicles and made asymmetric synapses. The great majority of labeled terminals (93%) made synaptic contact with dendritic spines; a few contacts (7%) were seen with thin dendrites. These findings indicate that the main postsynaptic targets of PFC afferents to Bmg are spiny pyramidal neurons, the projection neurons of the basolateral amygdala. The morphology of the synapses suggests that they are excitatory.

Activation of dopaminergic neurons modulates ventral pallidal responses evoked by amygdala stimulation

The ventral pallidum is a basal forebrain region that is thought to integrate cognitive processes with motoric behaviors. These functions are influenced by ventral pallidal inputs, which include projections from the amygdala and the ventral tegmental area/substantia nigra zona compacta. By examining the consequences of this convergence at the neuronal level, the present study indicates that electrical activation of ventral tegmental regions releases dopamine in the ventral pallidum which subsequently modulates pallidal electrophysiological responses evoked by stimulating the amygdala. Stimulation-evoked responses were characterized for extracellular single unit recordings of spontaneously active ventral pallidal neurons from chloral hydrate anesthetized rats. Stimulation of the amygdala evoked short latency (< or = 12 ms; possibly monosynaptic) and/or long latency (> 12 ms; polysynaptic) responses in all ventral pallidal neurons tested. Fifty-nine per cent of the tested neurons responded to ventral tegmental stimulation with short latency inhibition, and these neurons were often sensitive to microiontophoretically applied dopamine. Iontophoresis of dopamine antagonists SCH23390 (a D1 antagonist) or sulpiride (a D2 antagonist) attenuated the ventral tegmental-induced inhibitions. These observations indicate that the evoked responding was the result of endogenously released dopamine, and that D1 and D2 receptors were involved in this effect. Ninety-two per cent of the ventral pallidal neurons that demonstrated short latency responses to amygdala stimulation also exhibited short latency responses to activation of the ventral tegmentum. This suggests that these inputs often converge onto the same pallidal neurons. Amygdala-evoked responses were consistently attenuated by prior stimulation of the ventral tegmentum. Similarly, microiontophoretic ejection of dopamine attenuated amygdala-evoked effects. These results indicate that dopamine modulates amygdala-evoked pallidal responses. Such modulation may contribute to the integrative functions of the ventral pallidum.

Localization in the amygdala of the amnestic action of diazepam on emotional memory

It is well known that systemically administered benzodiazepines (BZDs) induce anterograde amnesia in a variety of learning tasks. BZs effects are mediated through the GABAA complex by enhancing GABA-induced synaptic inhibition. As the GABAergic system in the amygdaloid complex (AC) is a site of action for the anxiolytic effects of BZs, such findings suggest that BZs may also influence memory through the amygdala. The present report summarizes a recent series of experiments designed to examine this implication. In a first experiment rats received either sham or bilateral AC lesion using N-methyl-D-aspartic acid (NMDA). One week later, animals were trained on an inhibitory avoidance task and tested 48 h later. Diazepam (DZP; 1.0 and 2.0 mg/kg, i.p.) or vehicle was injected 30 min prior to acquisition. The results demonstrate that DZP-induced retention deficits was blocked in rats with AC lesions. In a second experiment, in an attempt to localize the site of BZDs amnestic action in the AC, we tested the effects of DZP in rats with bilateral ibotenic acid-induced lesions of central (CE), lateral (LAT) or basolateral (BL) amygdala nuclei. The results shown that retention was impaired in animals with CE and LAT lesions but not in animals with BL lesions. In a third experiment we tested the effects of DZP microinjections in different nuclei of the AC on retention performance of rats trained in an avoidance task. The results demonstrate that DZP microinjection prior training in the BL/LAT, but not CE nuclei produce anterograde amnesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Noradrenergic and cholinergic interactions in the amygdala and the modulation of memory storage

Numerous studies have reported that, in rats, memory can be affected by manipulations of the amygdala noradrenergic system. Typically, low doses of norepinephrine facilitate while higher doses impair memory storage. Muscarinic cholinergic agonists facilitate, while antagonists impair memory storage. Recent evidence from studies using systemic injection of drugs, indicates that these two systems interact in modulating memory storage. The experiments reported here examined interactions between the amygdala noradrenergic and muscarinic cholinergic systems. The results indicate that activation of muscarinic cholinergic mechanisms in the amygdala enhances retention, and that such activation mediates the facilitatory effects of systemically administered oxotremorine. beta-Noradrenergic agonists appear to exert their effects in the amygdala by activating the release of acetylcholine.

Membrane properties and synaptic potentials of three types of neurone in rat lateral amygdala

1. Intracellular recordings were made from the lateral nucleus of the amygdala in tissue slices cut from rat brain and maintained in vitro. 2. Three types of neurones were distinguished according to the after-potential that followed an action potential. Type 1 cells (44%, n = 225) had depolarizing after-potentials, resulting from a calcium-dependent chloride conductance. Type 2 cells (48%) had long-lasting (> 250 ms) hyperpolarizing after-potentials and type 3 cells (8%) had shorter hyperpolarizing after-potentials. The average resting potentials of the three cell types were -78, -69 and -62 mV respectively. Intracellular labelling with biocytin showed that type 1 cells were pyramidal neurones; type 2 and type 3 cells were non-pyramidal. 3. Experiments with receptor antagonists identified synaptic potentials mediated by excitatory amino acids and by GABA (acting at GABAA receptors) in all three cell types. A longer duration inhibitory synaptic potential resulting from activation of GABAB receptors was present in type 1 (pyramidal) and type 2 cells. 4. Cholecystokinin (100 nM to 1 microM) depolarized type 2 and type 3 cells but had no effect on type 1 (pyramidal) cells. Baclofen (1-3 microM) hyperpolarized type 1 and type 2, but not type 3 cells. [Met5]enkephalin (1-10 microM) hyperpolarized only type 2 cells. 5. It is concluded that the lateral nucleus of the amygdala contains pyramidal neurones and two types of non-pyramidal neurone; these can be differentiated by membrane properties, synaptic inputs and sensitivities to transmitters.

The role of the amygdaloid complex in Gilles de la Tourette's syndrome

Gilles de la Tourette's syndrome (GTS) is a relatively rare neuropsychiatric disorder characterised by multiple motor tics accompanied by vocalisations. It usually starts in early childhood and is more common in males than females. Obsessional compulsive disorder (OCD) is an integral part of GTS (Robertson, 1989). GTS is also associated with coprolalia, copropraxia, and other echophenomena, as well as attention-deficit disorder, self-injury, and other behaviour problems (Robertson et al, 1988; Robertson, 1989). Family pedigree studies have demonstrated that most GTS cases in the community are mild and do not receive medical attention (Kurlan et al, 1987; Robertson & Gourdie, 1990).

Topographic nonoverlapping distribution of D1 and D2 dopamine receptors in the amygdaloid nuclear complex of the rat brain

The distribution of D1 and D2 dopamine (DA) receptors in the nuclei and subnuclear zones of the rat amygdaloid complex was mapped using quantitative light microscopic autoradiography. [125I]iodosulpiride and [125I]SCH 23982 (in the presence of 50 nM ketanserin) were used to label D2 and D1 DA receptors, respectively. The DA receptor subtypes exhibited a topographic, nonoverlapping distribution which generally conformed to the cytoarchitectonic boundaries of the component nuclei and subnuclear zones of the amygdaloid complex. The highest density of [125I]iodosulpiride binding sites was observed in the main intercalated cell group and the central amygdaloid nucleus where a medial to lateral gradient of binding sites was localized to its subnuclear zones. [125I]SCH 23982 binding sites were localized in the main intercalated cell group and the basolateral amygdaloid nucleus with a uniform low density in the central nucleus. The functional topography of mesoamygdaloid DA neurons may therefore be mediated, in part, at the level of DA receptor subtypes. The pattern of distribution of [125I]iodosulpiride binding sites in subdivisions of the central amygdaloid nucleus and bed nucleus of the stria terminalis suggests that the functions of the "extended amygdala," a major system of the functional organization of the basal forebrain, may be regulated by DA afferents at multiple key sites of D2 receptor action.

Muscarinic responses of rat basolateral amygdaloid neurons recorded in vitro

1. Intracellular recordings were obtained from pyramidal-type neurons in the basolateral amygdaloid nucleus (BLA) in slices of rat ventral forebrain and used to compare the actions of exogenously applied cholinomimetics to the effects produced by electrical stimulation of amygdalopetal cholinergic afferents from basal forebrain. 2. Bath application of carbachol depolarized pyramidal cells with an associated increase in input resistance (Ri), reduced the slow after-hyperpolarization (AHP) that followed a series of current-evoked action potentials and blocked spike frequency accommodation. All of these effects were reversed by the muscarinic antagonist atropine but not by the nicotinic antagonist hexamethonium. 3. Electrical stimulation of amygdaloid afferents within the external capsule evoked a series of synaptic potentials consisting of a non-cholinergic fast excitatory postsynaptic potential (EPSP), followed by early and late inhibitory postsynaptic potentials (IPSPs). Each of these synaptic potentials was reduced by carbachol in an atropine-sensitive manner. 4. Local application of carbachol to pyramidal cells produced a short-latency hyperpolarization followed by a prolonged depolarization. The hyperpolarization and depolarization to carbachol were blocked by atropine but not hexamethonium. 5. The carbachol-induced hyperpolarization was associated with a decrease in Ri and had a reversal potential nearly identical to that of the early IPSP. The inhibitory response was blocked by perfusion of medium containing tetrodotoxin (TTX), bicuculline or picrotoxin, while the subsequent depolarization was unaffected. On the basis of these data, it is concluded that the muscarinic hyperpolarization is mediated through the rapid excitation of presynaptic GABAergic interneurons in the slice. 6. The findings that the carbachol-induced depolarization was associated with an increase in Ri, often had a reversal potential below -80 mV, was sensitive to changes in extracellular potassium concentration and was blocked by intracellular ionophoresis of the potassium channel blocker caesium suggest that it resulted from a muscarinic blockade of one or more potassium conductances. 7. Repetitive stimulation of sites within the slice containing cholinergic afferents evoked a series of fast EPSPs followed by IPSPs. These non-cholinergic potentials were followed by a slow EPSP that lasted from 10 s-4 min. The slow EPSP was enhanced by eserine and blocked by atropine. It was also blocked by TTX or cadmium, indicating that it was dependent on spike propagation and calcium-dependent release of acetylcholine (ACh). 8. Stimulation of cholinergic afferents in the slice mimicked other effects produced by carbachol including blockade of the slow AHP and accommodation of action potential discharge and these actions were potentiated by eserine and blocked by atropine.(ABSTRACT TRUNCATED AT 400 WORDS)

Attenuation of Fos-like immunoreactivity induced by a single electroconvulsive shock in brains of aging mice

c-fos is a proto-oncogene that encodes for a nuclear phosphoprotein with DNA binding properties and is presumed to have an important role in the long-term regulation of neuronal function. It is thought to act as a 'third messenger' molecule in signal transduction systems and its expression has been shown to be induced by a variety of exogenous and endogenous stimuli. This study examines the differential expression of the Fos protein in various brain regions after a single electroconvulsive shock (ECS) in 6-, 13-, and 28-month-old B6C3 mice. The animals received an acute electroconvulsive shock (90 V for 0.3 s), without prior anesthesia, through earclip electrodes and exhibited generalized tonic-clonic seizures lasting 20-36 s. Animals were anesthetized and perfused intracardially with 2.5% acrolein, 4% paraformaldehyde at 0.5, 1.0, 2.0 and 4.0 h postshock. The brains were Vibratome-sectioned (30 microns) and examined using a Fos antibody, directed against a conserved region of both mouse and human Fos by standard immunocytochemical methods. Systematic sampling of the total number of Fos immunostained neurons in amygdala, hippocampus and the cerebral cortex showed peak values at the 1-h time point followed by a steady decline thereafter in all age groups. In a second experiment, Fos-like immunoreactivity was compared 1 h after ECS in the hippocampus, amygdala and the cortex in all 3 age groups. There was increased expression of Fos-like immunoreactivity after ECS- compared to non-ECS-treated controls in all age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Hippocampal input to a "visceral motor" corticobulbar pathway: an anatomical and electrophysiological study in the rat

The hippocampus has previously been shown to influence cardiovascular function, and this effect appears to be mediated by the connection the hippocampus has with the infralimbic area of the medial frontal cortex (MFC), a region which projects directly to the nucleus of the solitary tract (NTS) in the dorsal medulla. In the present study, anatomical and electrophysiological techniques were utilized to determine the degree of convergence of hippocampal input to the MFC on neurons in the MFC which project to the NTS. Injections of the anterograde and retrograde neuroanatomical tracer wheat-germ agglutinin-horseradish peroxidase (WGA-HRP) into the NTS retrogradely labelled cells in the infralimbic and prelimbic regions of the MFC. Injections of WGA-HRP into the ventral hippocampus anterogradely labelled terminals in the MFC which, at the light microscopic level, closely overlapped the origin of the descending projection from the MFC to the brainstem. Electron microscopic analysis revealed that anterogradely labelled terminals make synaptic contact primarily on dendritic processes in the neuropil adjacent to retrogradely labelled cells. In addition, anterogradely labelled terminals did, in some cases, make synaptic contact on the somas of retrogradely labelled cells. Electrical stimulation of the NTS antidromically activated cells in the infralimbic and prelimbic areas of the MFC. The average latency of antidromic activation was 30 msec, corresponding to a conduction velocity of approximately 0.7 m/s. Electrical stimulation of the ventral hippocampus orthodromically activated cells in the MFC. With an appropriate delay between the hippocampal and NTS stimuli, the orthodromic and antidromic potentials could be made to collide. The results of this study establish a structural as well as functional link between the hippocampus and NTS-projection neurons in the MFC.