Anterior Cortical Nucleus Research Articles

Distribution of cholecystokinin-immunoreactive cell bodies in the male and female rat: II. Bed nucleus of the stria terminalis and amygdala.

The distribution of cholecystokinin-immunoreactive (CCK-I) cell bodies was studied in the bed nucleus of the stria terminalis (BST) and amygdaloid complex of colchicine-treated male and female rats. Immunoreactive cells were visualized in the BST medial amygdaloid (MeA), central lateral, basolateral, basolateral ventral, medial, intercalated, anterior cortical, and posterior cortical nuclei and the amygdalohippocampal zone. Several significant sex differences were observed. In the male, a dense aggregation of CCK-I cell bodies was visualized in the MeA, especially in the dorsocaudal part and in the encapsulated part of the BST. In comparison, female rats had relatively fewer immunoreactive cells in both of these regions. In the lateral and basolateral amygdaloid nuclei, however, more CCK-I cells were visualized in the female than in the male, but the difference was not statistically significant. These data provide characterization of a sexually differentiated CCK system. In addition, we observed that the number of CCK-I cells in the BST and posterodorsal part of the MeA was substantially reduced after castration. The number of CCK-I cells in female rats, however, was not significantly reduced after ovariectomy in any of the regions studied. These findings imply that the steroid regulation of CCK is sexually differentiated. The sexually dimorphic distribution of CCK-I cells in areas that are targets of steroid hormones and regulate reproductive processes is consistent with the possibility that CCK participates in central integration of sensory and steroidal input that modulates reproductive behavior.

Convergence of main and accessory olfactory pathways onto single neurons in the hamster amygdala.

Chemoreceptor pathways from the vomeronasal organ (VNO), and main olfactory system are known to be separate as they pass into the brain, at least until the level of the amygdala. In the amygdala, vomeronasal pathways project to the posteromedial cortical nucleus (PMCN), and medial nucleus (MN). The main olfactory pathways have terminations in the posterolateral cortical nucleus (PLCN), and anterior cortical nucleus (ACN), both of which project to the PMCN and MN. The anatomy thus suggests that the PMCN and MN are sites for convergence of input from the main and accessory olfactory pathways. We have recorded single units in the amygdala and found that electrical stimulation of either the main olfactory bulbs or the VNO could drive some of the same units in the PMCN. Units were also found that were driven by one system but not the other, and units in which activity driven by one system was suppressed by stimulation of the other system.

Angiotensin converting enzyme in rat brain visualized by quantitative in vitro autoradiography

Angiotensin converting enzyme was localized in rat brain by quantitative in vitro autoradiography using an [ 125I]labelled converting enzyme inhibitor called “351A”. This radioligand was found to bind with high affinity and specificity to angiotensin converting enzyme. Very high levels of converting enzyme were observed in the ventricular choroid plexus, ependyma of all ventricles and large and medium blood vessels, subfornical organ and organum vasculosum of the lamina terminalis. High levels of converting enzyme were found in the basal ganglia including caudate putamen, nucleus accumbens, globus pallidus, entopenduncular nucleus and substantia nigra pars reticulata. The neurosecretory nuclei, paraventricular nucleus and supraoptic nucleus, as well as the median eminence and posterior pituitary displayed high levels of the enzyme. In the amygdala, basolateral, lateral, basomedial, medial and anterior cortical nuclei showed moderate converting enzyme activity. The medial habenula and molecular layer of the dentate gyrus showed high levels of activity. In the cerebellum, dense labelling was observed in the Purkinje cell layer. Moderate levels of convering enzyme occurred in the gelatinosus subnucleus of the caudal part of the nucleus of the spinal tract of the trigeminal. There was a close correspondence between the distribution of angiotensin converting enzyme and angiotensin II in the neurosecretory nuclei (paraventricular and supraoptic nuclei) and median eminence and this suggests a role of angiotensin converting enzyme in the production of angiotensin II in this system. There was also a good correspondence between the distribution of angiotensin converting enzyme and angiotensin II in the subfornical organ, median preoptic nucleus and organum vasculosum of the lamina terminalis, structures abutting the anterior wall of the third ventricle which are implicated in fluid and electrolyte homeostasis. A striking discrepancy occurs in the basal ganglia which is reported to contain very little angiotensin II or angiotensin II receptors but is very rich in angiotensin converting enzyme. It is concluded that the enzyme may act to (a) convert circulating angiotensin I to angiotensin II in circumventricular organs; (b) generate intraneuronal angiotensin II in pathways such as the hypothalamichypophyseal tract; and (c) process neuropeptides other than angiotensin II in regions such as basal ganglia.

Topography of projections from the medial prefrontal cortex to the amygdala in the rat

The projections from the rat medial prefrontal cortex to the amygdaloid complex were investigated using retrograde transport of fluorescent dyes and anterograde transport of horseradish peroxidase-WGA. The ventral anterior cingulate, prelimbic, infralimbic and medial orbital areas and the taenia tecta were found to project to the amygdaloid complex. The projections from the prelimbic area arose bilaterally. The medial orbital, prelimbic and anterior cingulate areas send convergent projections to the basolateral nucleus. The prelimbic area has additional projections to the posterolateral cortical nucleus and amygdalo-hippocampal area. The infralimbic area does not project to the basolateral nucleus and cortico-amygdaloid projections from this area are focussed on the anterior cortical nucleus and the anterior amygdaloid area. Both prelimbic and infralimbic areas project to an area situated between the central, medial and basomedial nuclei. Based on similar projections, this area appears to be a caudal continuation of the anterior amygdaloid area. The results indicate that the medial prefrontal component of the “basolateral limbic circuit” is restricted to the anterior cingulate and prelimbic areas. No evidence was obtained to support the existence of a medial prefronto-amygdaloid component of the “visceral fbrebrain”.

Quantitative autoradiographic analysis of the distribution of binding sites for [ 125I]Bolton Hunter derivatives of eledoisin and substance P in the rat brain

[ 125I]Bolton and Hunter eledoisin binds to a single class of non-interacting sites in rat cerebral cortex tissue sections with an apparent K d of 9.9 nM and a B max of 244 fmol/mg protein. When concentrations of up to 23 nM [ 125I]Bolton and Hunter eledoisin were used, [ 125I]Bolton and Hunter eledoisin binding was specific, saturable and reversible. Kassinin, eledoisin and neurokinin B were more potent than substance P and neurokinin A in inhibiting the specific binding of [ 125I]Bolton and Hunter eledoisin to cerebral cortex tissue sections. These kinetic and pharmacological characteristics are consistent with results obtained from binding studies on cortical synaptosomes. When the localization of [ 125I]Bolton and Hunter substance P and [ 125I]Bolton and Hunter eledoisin binding sites were compared, differences in many areas of the brain were noted. Large differences were seen in the paraventricular and supraoptic hypothalamic nuclei, and in layers IV and V of the cerebral cortex, which were densely labeled by [ 125I]Bolton and Hunter eledoisin, but not by [ 125I]Bolton and Hunter substance P. In contrast, nuclei of the septum (diagonal band of Broca, septohippocampal nucleus, dorsal part of the lateral septal nucleus), the rostrodorsal part of the hippocampus and other discrete nuclei [endopyriform nucleus, anterior cortical amygdaloid nucleus, the vermis columns (9–10), the dorsal tegmental nucleus, the hypoglossal and ambiguus nucleus] had high levels of [ 125I]Bolton and Hunter substance P binding but were only labeled weakly by [ 125I]Bolton and Hunter eledoisin. Thus, the two ligands seem to label different sites, since these binding sites have different biochemical and pharmacological properties, and are localized in different anatomical structures.

Benzodiazepine receptors: localization in rat amygdala

Behavioral, electroencephalographic, and evoked potential studies, as well as experiments utilizing the direct intracerebral injection of benzodiazepines (BZs), have implicated the amygdala, particularly its basolateral nuclear division, as an important locus of the therapeutic actions of these drugs. BZ receptor localization within the amygdala could further define which amygdaloid nuclei are important for BZ action and suggest neuroanatomical pathways especially sensitive to these drugs. Using a quantitative light microscopic autoradiographic technique, this study has localized type 1 and type 2 BZ receptors within the amygdaloid nuclear complex of the rat. BZ receptors were labeled with [3H]flunitrazepam, and type 1 BZ receptor binding was preferentially displaced by CL218,872 in 8-micron coronal sections of rat brain. Autoradiograms were generated by the apposition of emulsion-coated coverslips and quantified by standardized procedures. Ten amygdaloid nuclei were examined at nine levels over the rostrocaudal extent of the amygdala. Total BZ receptor density was highest in the basolateral nuclear complex, and the majority of these receptors were of the type 2 subclass. Type 1 receptors were concentrated in the anterior aspects of the amygdala, particularly the anterior cortical nucleus. These results are consistent with an important role for the basolateral amygdala in anxiogenesis and seizure induction. Furthermore, a larger circuit which includes the amygdala, ventromedial hypothalamus, mammillary body, anterior thalamus, and frontal cortex could be involved in the anxiolytic actions of the BZ drugs.

The laminar distribution of intracortical fibers originating in the olfactory cortex of the rat.

In this study, the autoradiographic method for tracing axonal connections was used to identify the laminar distribution of intracortical fibers originating in the olfactory cortical areas of the rat. Most of the projections can be divided into two major fiber systems with different laminar patterns of termination. The first of these, termed the layer Ib fiber system, arises in the anterior olfactory nucleus, the anterior and posterior piriform cortex, and the lateral entorhinal cortex, and terminates predominantly in layer Ib and, in many cases, layer III of the entire olfactory cortex. The second system, termed the layer II-deep Ib fiber system, originates in three relatively small olfactory cortical areas--the dorsal peduncular cortex, the ventral tenia tecta, and the periamygdaloid cortex--and terminates in and around the cells of layer II in most parts of the olfactory cortex. There is significant overlap in the laminar distribution of the two systems, although the distinction between them is readily apparent. Within the layer Ib fiber system there are relatively slight but consistent differences in the lamination of fibers from different areas. The fibers from the anterior olfactory nucleus are concentrated in the deep part of layer Ib while those from the anterior piriform cortex are concentrated in the superficial part of this layer. The fibers from the posterior piriform cortex tend to be densest in the middle of layer Ib. These differences are maintained in all areas of termination of each set of fibers, both ipsilaterally and contralaterally. In addition, intracortical fibers from the anterior cortical nucleus of the amygdala are distributed throughout layer I, including layer Ia and Ib. Fibers from the nucleus of the lateral olfactory tract terminate bilaterally around the cells of the islands of Calleja and the medial edge of the anterior piriform cortex.

The topographic organization of associational fibers of the olfactory system in the rat, including centrifugal fibers to the olfactory bulb.

This study analyzed the topographic organization of the associational fibers within the olfactory cortex of the rat, by using the autoradiographic method. Small injections of 3H-leucine were placed in all of the subdivisions of the olfactory cortex, to label selectively the fibers arising in each area. Intracortical fibers were identified from all of the olfactory cortical areas except the olfactory tubercle and were classified into two major systems (the layer Ib system and the layer II-deep Ib system) on the basis of their laminar pattern of termination (see Luskin and Price, '83). The layer Ib fiber system arises in the anterior olfactory nucleus, piriform cortex, and lateral entorhinal area, and is broadly organized in relation to the lateral olfactory tract. Cortical areas deep to or near the lateral olfactory tract are preferentially interconnected with areas near the tract, while parts of the cortex lateral and caudal to the lateral olfactory tract are most heavily interconnected with areas lateral, caudal, and medial to the tract. Commissural projections from the anterior olfactory nucleus and the anterior piriform cortex match some (but not all) components of the ipsilateral layer Ib fiber system. The layer II-deep Ib fiber system arises in three small areas--the ventral tenia tecta, the dorsal peduncular cortex, and the periamygdaloid cortex. The fibers from the ventral tenia tecta terminate in layer II of the anterior olfactory nucleus and are topographically organized. The fibers from the dorsal peduncular cortex and the periamygdaloid cortex are more widely distributed, especially in the lateral and caudal parts of the cortex. Two other intracortical projections do not fit into either of these fiber systems. The nucleus of the lateral olfactory tract projects bilaterally to the islands of Calleja and the medial edge of the anterior piriform cortex. The anterior cortical nucleus projects to many parts of the olfactory cortex, but the fibers end in both superficial and deep parts of layer I (layer Ia and Ib). There are projections from several of the olfactory cortical areas to the cortical areas surrounding the olfactory cortex. Virtually all of the olfactory areas also project to the ventral and dorsal endopiriform nuclei deep to the piriform cortex and/or to the polymorph zone deep to the olfactory tubercle. In addition, projections have been demonstrated to the deep amygdaloid nuclei, especially from the more ventromedial and caudal parts of the olfactory cortex.

Connections of the corticomedial amygdala in the golden hamster. II. Efferents of the "olfactory amygdala".

The anterior cortical (C1) and posterolateral cortical (C2) nuclei of the amygdala are designated the "olfactory amygdala" because they each receive direct projections from the main olfactory bulb. The efferents of these nuclei were traced after stereotaxic placement of 1-5 muCi tritiated proline in the corticomedial amygdala of the male golden hamsters. Following survival times of 12, 24, or 48 hours, 20 micron frozen sections of the brains were processed for light microscopic autoradiography. Efferents from C2 terminate in layers II and III of the olfactory tubercle and in layer Ib of pars ventralis and pars medialis of the anterior olfactory nucleus. Fibers from this nucleus also project to layers I and II of the infralimbic cortex and to the molecular layer of the agranular insular cortex. More posteriorly, fibers from C2 terminate in layer I of the dorsolateral entorhinal cortex, and in the endopiriform nucleus. From C1, efferent fibers travel in the stria terminalis and terminate in the precommissural bed nucleus of the stria terminalis and in the mediobasal hypothalamus. Efferents from C1 also innervate the molecular layer of C2, the amygdalo-hippocampal area, and the adjacent piriform cortex. Neurons in both C1 and C2 project to the molecular layer of the medial amygdaloid nucleus and the posteromedial cortical nucleus of the amygdala, the plexiform layer of the ventral subiculum, and the molecular layer of the lateral entorhinal cortex.

Quantitative 3H-thymidine radiographic analyses of neurogenesis in the rat amygdala.

AbstractNeurogenesis in the rat amygdala was examined with 3H‐thymidine radiography. The animals were the offspring of pregnant females given two injections of 3H‐thymidine on consecutive days in an overlapping series: Embryonic day (E) 12 + E13, + E14. E21 + E22. On 60 days of age, the percentage of labelled cells and the proportion of cells added during each day of formation were determined at several anatomical levels within the following components of the amygdala: anterior amygdaloid area, bed nuclei of the lateral and accessory olfactory tracts, central, medial, anterior cortical, posterolateral cortical, posteromedial cortical, basomedial, basolateral, and lateral nuclei, the amygdalo‐hippocampal area, and the intercalated masses.All large and many small neurons originate in most nuclei between E13 and E17, those in the intercalated masses between E15 and E19, those in the amygdalo‐hippocampal area between E16 and E19. The anterior amygdaloid area, intercalated masses, central, medial, posterolateral cortical, posteromedial cortical, basomedial, basolateral, and lateral nuclei have strong rostral‐to‐caudal intranuclear gradients. There are five additional intranuclear gradients: 1) medial to lateral in the central nucleus, anterior amygdaloid area, and anterior intercalated masses; 2) lateral to medial in the bed nucleus of the lateral olfactory tract and basolateral nucleus; 3) superficial to deep in the amygdalo‐hippocampal area, posterolateral, and posteromedial cortical nuclei; 4) ventral to dorsal in the medial nucleus; and 5) dorsal to ventral between the small and large‐celled parts of the lateral nucleus. Only the bed nucleus of the accessory olfactory tract and the anterior cortical nucleus do not have intranuclear gradients. Between 10 and 15% of the total cell population in most nuclei are very small neurons and/or glia which originate simultaneously between E18 and E20. This population is absent in the ventral part of the medial, anterior cortical, and anterior basomedial nuclei; these contiguous areas may form a distinct subunit in the amygdala.In contrast to the pronounced intranuclear gradient, internuclear gradients are weak. Neurogenesis in the central nucleus and corticomedial and basolateral complexes appears to take place both concurrently and independently. There are groups of early‐originating neurons in the central, medial, and basolateral nuclei located near the periphery of the amygdala. Each of these groups is surrounded by younger neurons farther within the interior. The youngest calls are in the centrally placed intercalated masses. These settling patterns suggest that cells in the amygdala arise simultaneously from more than one neuroepithelial source during morphogenesis.The chronology of neurogenesis in the amygdala can be related to some of its anatomical connections. Rostral‐to‐caudal gradients in the corticomedial complex may be timed to coincide with early vs. late arrival of olfactory fibers. The subdivisions bases on intranuclear gradients in the central, medial, and basolateral nuclei match the subdivisions based on patterns of anatomical connections.

Afferent connections to the amygdaloid complex of the rat and cat: II. Afferents from the hypothalamus and the basal telencephalon.

The projections from the basal telencephalon and hypothalamus to each nucleus of the amygdaloid complex of the rat, and to the central amygdala of the cat, were investigated by the use of retrograde transport of horseradish peroxidase (HRP). The enzyme was injected stereotaxically by microiontophoresis, using three different approaches. The ventral pallidum (Heimer, '78) and ventral part of the globus pallidus were found to project to the lateral and basolateral nuclei of the amygdala. The substantia innominata projects diffusely to the entire amygdaloid complex, except to the lateral nucleus and the caudal part of the medial nucleus. The anterior amygdaloid area shows a similar projection field, the only difference being that this structure does not project to any parts of the medial nucleus. The dorsal subdivision of the nucleus of the lateral olfactory tract sends fibers to the ipsilateral as well as the contralateral basolateral nucleus, and possibly to the ipsilateral basomedial and cortical amygdala. The ventral subdivision of the nucleus of the lateral olfactory tract was massively labeled after an injection in the ipsilateral central nucleus, but this injection affected the commissural component of the stria terminalis. The nucleus of the horizontal limb of the diagonal band of Broca connects with the medial, central, and anterior cortical nuclei, whereas the bed nucleus of stria terminalis and medial preoptic area are related to the medial nucleus predominantly. the lateral preoptic area is only weakly labeled after intra-amygdaloid HRP injections. The hypothalamo-amygdaloid projections terminate preponderantly in the medial part of the amygdaloid complex. Thus, axons from neurons in the area dorsal and medial to the paraventricular nucleus of the hypothalamus distribute to the medial nucleus and intra-amygdaloid part of the bed nucleus of stria terminalis. Most of the amygdalopetal fibers from the ventromedial, ventral premammillary, and arcuate nuclei of the hypothalamus end in the medial nucleus, but some extend into the central nucleus. A few fibers from the ventromedial nucleus of the hypothalamus reach the basolateral nucleus. The lateral hypothalamic area projects heavily to the central nucleus, and more sparsely to the medial and basolateral nuclei. The dorsal hypothalamic area and supramammillary nucleus show restricted projections to the central and basolateral nuclei, respectively. There are only a modest number of crossed hypothalamo-amygdaloid fibers. Most of these originate in the ventromedial nucleus of the hypothalamus and terminate in the contralateral medial nucleus. The projections from the basal telencephalon and hypothalamus to the central nucleus of the amygdala of the cat are similar to the corresponding projections in the rat.

An experimental study of the ventral striatum of the golden hamster. II. Neuronal connections of the olfactory tubercle.

As part of an experimental study of the ventral striatum, the horseradish peroxidase (HRP) method was used to examine the afferent and efferent neuronal connections of the olfactory tubercle. Following iontophoretic applications or hydraulic injections of HRP in the tubercle, neurons labeled by retrograde transport of HRP were observed ipsilaterally in the telencephalon in the main olfactory bulb, the medial, lateral, ventral, and posterior divisions of the anterior olfactory nucleus, and in the orbital, ventral, and posterior agranular insular, primary olfactory, perirhinal, and entorhinal cortices. Labeled cells were also present in the basolateral, basomedial, anterior cortical, and posterolateral cortical amygdaloid nuclei, and bilaterally in the nucleus of the lateral olfactory tract. In the diencephalon, ipsilateral HRP-containing neurons were observed in the midline nuclei paraventricularis, parataenialis, and reuniens, and in the parafascicular intralaminar nucleus. Retrograde labeling was present in the ipsilateral brainstem in cells of the ventral tegmental area, substantia nigra, and dorsal raphe. Many of the above projections to the tubercle were found to be topographically organized. Anterograde axonal transport of HRP from the olfactory tubercle labeled terminal fields ipsilaterally in all parts of the anterior olfactory nucleus, in the ventral pallidum, and in the substantia nigra, pars reticulata. Contralaterally, terminal fields were present in the dorsal and lateral divisions of the anterior olfactory nucleus. The projections to the tubercle from the orbital, ventral, and posterior agranular insular, and perirhinal neocortices, intralaminar thalamus, and dopamine-containing areas of the ventral mesencephalon are analogous to the connections of the caudatoputamen, as are the efferents from the tubercle to the ventral globus pallidus and substantia nigra. These connections substantiate the recent suggestion that the olfactory tubercle is a striatal structure, and provide support for the ventral striatal concept. In the present study of the olfactory tubercle, and in the first study in this series on the nucleus accumbens, the ventral striatum was found to receive projections from a number of limbic system structures, including the main olfactory bulb, anterior olfactory nucleus, amygdala, hippocampus, and subiculum, and the entorhinal and primary olfactory cortices. These findings suggest that the ventral striatum is concerned with integrating limbic information into the striatal system.

Cortical afferents of the amygdaloid complex in the rat: An HRP study

The retrograde axonal transport of horseradish peroxidase has been used to determine the cortical afferent connections of the amygdaloid complex of the albino rat. It appears that a number of corticoamygdaloid projections exist, namely from prepiriform, periamygdaloid, insular, perirhinal, entorhinal and ventral subicular areas. Besides, the relationship between periamygdaloid cortex and the lateral, basal and anterior cortical amygdaloid nuclei shows a topical organization.

Association and commissural fiber systems of the olfactory cortex of the rat.

The association and commissural fiber systems arising in the olfactory cortical areas caudal to the olfactory peduncle (the piriform cortex, nucleus of the lateral olfactory tract, anterior cortical nucleus of the amygdala, periamygdaloid cortex and entorhinal cortex) have been studied utilizing horseradish peroxidase as both an anterograde and a retrograde axonal tracer. In the piriform cortex two sublaminae within layer II (IIa and IIb) layer III have been found to give rise to distinctly different projections. Retrograde cell labeling experiments indicate that the association fiber projection from layer IIb is predominatnly caudally directed, while the projection from layer III is predominantly rostrally directed. Cells in layer IIa project heavily to areas both caudal and rostral to the piriform cortex. The commissural fibers from the piriform cortex are largely restricted in their origin to layer IIb of the anterior part of the piriform cortex and in their termination on the contralteral side to the posterior part of the piriform cortex and adjacent olfactory cortical areas. A projection to the olfactory bulb has also been found to arise from cells in layers IIb and III of the ipsilateral piriform cortex, but not in layer IIa. In addition to those from the piriform cortex, association projections have also been found from other olfactory cortical areas. The nucleus of the lateral olfactory tract has a heavy bilateral projection to the medial part of the anterior piriform cortex and the lateral part of the olfactory tubercle (as well as a lighter projection to the olfactory bulb); both the anterior cortical nucleus of the amygdala and the periamygdaloid cortex project ipsilaterally to several olfactory cortical areas. The entorhinal cortex has been found to project to the medial parts of the olfactory tubercle and the olfactory peduncle. The olfactory tubercle is the only olfactory cortical area from which no association fiber systems (instrinsic or extrinsic) have been found to originate. A broad topographic organization exists in the distribution of the fibers from several of the olfactory areas. This is most obvious in the anterior part of the olfactory cortex, in which fibers from the more rostral areas (the anterior olfactory nucleus and the anterior piriform cortex) terminate in regions near the lateral olfactory tract, while those from more caudal areas (the posterior piriform cortex and the entorhinal cortex) terminate in areas further removed, both laterally and medially, from the tract. Projection to olfactory areas from the hypothalamus, thalamus, diagonal band, and biogenic amine cell groups have been briefly described.

Amygdaloid projections to subcortical structures within the basal forebrain and brainstem in the rat and cat.

AbstractThe efferent fiber connections of the nuclei of the amygdaloid complex with subcortical structures in the basal telencephalon, hypothalamus, midbrain, and pons have been studied in the rat and cat, using the autoradiographic method for tracing axonal connections. The cortical and thalamic projections of these nuclei have been described in previous papers (Krettek and Price, ′77b,c). Although the subcortical connections of the amygdaloid nuclei are widespread within the basal forebrain and brain stem, the projections of each nucleus have been found to be well defined, and distinct from those of the other amygdaloid nuclei.The basolateral amygdaloid nucleus projects heavily to the lateral division of the bed nucleus of the stria terminalis (BNST), to the caudal part of the substantia innominata, and to the ventral part of the corpus striatum (nucleus accumbens and ventral putamen) and the olfactory tubercle; it projects more lightly to the lateral hypothalamus. The central nucleus also projects to the lateral division of the BNST and the lateral hypothalamus, but in addition it sends fibers to the lateral part of the substantia nigra and the marginal nucleus of the brachium conjunctivum. The basomedial nucleus has projections to the ventral striatum and olfactory tubercle which are similar to those of the basolateral nucleus, but it also projects to the core of the ventromedial hypothalamic nucleus and the premammillary nucleus, and to a central zone of the BNST which overlaps the medial and lateral divisions. The medial nucleus also projects to the core of the ventromedial nucleus and the premammillary nucleus, but sends fibers to the medial division of the BNST and does not project to the ventral striatum. The posterior cortical nucleus projects to the premammillary nucleus and to the medial division of the BNST, but a projection from this nucleus to the ventromedial nucleus has not been demonstrated. Projections to the “shell” of the ventromedial nucleus have been found only from the ventral part of the subiculum and from a structure at the junction of the amygdala and the hippocampal formation, which has been termed the amygdalo‐hippocampal area (AHA). The AHA also sends fibers to the medial part of the BNST and the premammillary nucleus.Virtually no subcortical projections outside the amygdala itself have been demonstrated from the lateral nucleus, or from the olfactory cortical areas around the amygdala (the anterior cortical nucleus, the periamygdaloid cortex, and the posterior prepiriform cortex). However, portions of the endopiriform nucleus deep to the prepiriform cortex project to the ventral putamen, and to the lateral hypothalamus.

Projections from the amygdaloid complex to the cerebral cortex and thalamus in the rat and cat.

Projections are described from the basolateral, lateral and anterior cortical nuclei of the amygdaloid complex, and from the prepiriform cortex, to several discrete areas of the cerebral cortex in the rat and cat and to the mediodorsal thalamic nucleus in the rat. These projections are very well-defined in their origin, and in their area of laminar pattern of termination. The basolateral amygdaloid nucleus can be divided into anterior and posterior divisions, based on cytoarchitectonic and connectional distinctions. In both the rat and cat the posterior division projects to the prelimbic area (area 32) and the infralimbic area (area 25) on the medical surface of the hemisphere. The anterior division projects more lightly to these areas, but also sends fibers to the dorsal and posterior agranular insular areas and the perirhinal area on the lateral surface. Furthermore, in the cat the perirhinal area is divided into two areas (areas 35 and 36) and the anterior division projects to both of these and also to a ventral part of the granular insular area; this last area is adjacent to, but separate from the auditory insular area and the second cortical taste area. In most of these areas, the fibers from the basolateral nucleus terminate predominantly in two bands: one in the deep part of layer I and layer II, and a heavier band in layer V (in the rat) or layers V and VI (in the cat). The lateral amygdaloid nucleus projects heavily to the perirhinal area, and also to the posterior agranular insular area. These fibers terminate predominantly in the middle layers of the cortex, although the cellular lamination in these two areas is relatively indistinct. The anterior cortical amygdaloid nucleus and the prepiriform cortex both project to the infralimbic area and the ventral agranular insular area, and the anterior cortical nucleus also projects to the posterior agranular area and the perirhinal area. In all of these areas, the fibers from these olfactory-related structures terminate in the middle of layer I. In the rat, the two divisions of the basolateral nucleus also project to the medial segment of the mediodorsal thalamic nucleus, with the anterior division projecting mainly to the posterior part of this segment and the posterior division to the anterior part. The endopiriform nucleus, deep to the prepiriform cortex, projects to the central segment of the mediodorsal nucleus; this may constitute the major olfactory input into the mediodorsal nucleus, since little or no projection could be demonstrated from the prepiriform cortex itself. Projections to the mediodorsal nucleus have not been found in the cat.