We demarcated the amygdaloid complex and the three nuclei constituting its basolateral division, the lateral, basal, and accessory basal nuclei, in 12 histological series representing all six hominoid species. While the gorilla had a smaller than predicted lateral nucleus, its basal and accessory basal nuclei were larger than predicted. 
The basolateral amygdala, including the lateral, basal, and accessory basal nuclei, produced a stronger response for threatening than appeasing expressions.
In controls, the basal nucleus contained the highest choline acetyltransferase activity; the activity in the lateral and central nuclei and those in the cortical, medial and accessory basal nuclei were comparable.
Lighter projections to the posterior piriform cortex originated in the dorsolateral division of the lateral nucleus, the magnocellular and parvicellular divisions of the basal and accessory basal nuclei, and the anterior cortical nucleus. The projections to the anterior piriform cortex were light and originated in the dorsolateral and medial divisions of the lateral nucleus, the magnocellular division of the basal and accessory basal nuclei, the anterior and posterior cortical nuclei, and the periamygdaloid subfield of the periamygdaloid cortex.
In contrast, orbitofrontal, medial prefrontal, and anterior cingulate regions project primarily to the basal and accessory basal nuclei and provide little innervation to the lateral nucleus. The agranular and dysgranular insula, the parainsula, and rostral portions of the superior temporal gyrus project both to the lateral, basal, and accessory basal nuclei and to the medially situated nuclei.
The basal nucleus was the major source of these amygdala efferents, and there was a crude topography as parts of the basal and accessory basal nuclei terminated in different parts of nucleus accumbens.
In addition PSA-NCAM immunoreactive neuronal somata and processes exist in the lateral, basal and accessory basal nuclei, anterior amygdaloid area and amygdalo-striatal area.
We used the anterograde tracers Phaseolus vulgaris-leucoagglutinin (PHA-L) and biotinylated dextran amine (BDA) to examine the projections from the lateral, basal, and accessory basal nuclei of the amygdaloid complex to the entorhinal cortex in Macaca fascicularis monkeys.
The basal and accessory basal nuclei are the major source of input to the ventromedial striatum, innervating both the shell and ventromedial striatum outside the shell.
Areas TAi and TAr received projections from the lateral, lateral basal and accessory basal nuclei.
The present study investigated the organization of amygdaloid projections to the perirhinal and postrhinal cortices by injecting the anterograde tracer Phaseolus vulgaris leucoagglutinin into the different subdivisions of the lateral, basal or accessory basal nuclei of the amygdala in rat (n = 53).
To determine which of these regions is necessary, and thus whether conditioning requires the direct or one of the indirect intra-amygdala pathways, we made lesions in rats of the lateral, central, basal, accessory basal, and medial nuclei, as well as combined lesions of the basal and accessory basal nuclei and of the entire amygdala.
The lateral (the medial division and the caudal portion of the dorsolateral division) and the accessory basal nuclei (the parvicellular division) provide moderate-to-heavy projections to the amygdalostriatal transition area. These data suggest that the amygdalostriatal transition area is one of the major targets for projections originating in the lateral and accessory basal nuclei of the amygdala.
IL and PL projected densely to the ventromedial caudate nucleus, the core and shell of the nucleus accumbens (Acb), parvicellular lateral basal and magnocellular accessory basal nuclei of the amygdala, lateral preoptic area, ventromedial hypothalamic nucleus, tubero-mammillary nucleus (TM), medial part of the magnocellular and dorsal part of the parvicellular (MDpc) dorsomedial thalamic nuclei, reunience and medial part of the medial pulvinar nucleus, and dorso-lateral part of the periaqueductal gray (PAGdl) in the mesencephalon.
The present study investigated the intrinsic connections of the basal and accessory basal nuclei of the Macaca fascicularis monkey by means of the anterograde tracers Phaseolus vulgaris-leucoagglutinin (PHA-L) and biotinylated dextran amine (BDA). Projections to other amygdaloid areas originate in select divisions of the basal and accessory basal nuclei, and are topographically distributed.
Using unbiased stereology, we estimated total neuronal numbers in the lateral, basal and accessory basal nuclei of the amygdala and in the hilus of the dentate gyrus 6 months after the induction of amygdala kindling.
To investigate the connections that regulate the interactions between these regions, we injected the anterograde tracer Phaseolus vulgaris-leucoagglutinin into various divisions of the lateral, basal, and accessory basal nuclei of the rat amygdala.
The dorsal division projects to all divisions of the basal and accessory basal nuclei, to the periamygdaloid cortex, the nucleus of the lateral olfactory tract, the dorsal division of the amygdalohippocampal area, and the lateral capsular nuclei.
In the adult monkey, neurons in ventromedial, dorsomedial, and arcuate nuclei of the hypothalamus; cortical, medial, and accessory basal nuclei of the amygdala; and regions of the hippocampus and the anterior pituitary gland contained immunoreactive AR.
In the present study we extend our earlier findings which indicated that the lateral nucleus of the rat amygdala is reciprocally connected with the basal and accessory basal nuclei. An anterograde tracer, Phaseolus vulgaris leucoagglutinin, was injected into the basal (n=22) or accessory basal nuclei (n=12) of the rat amygdala.
In the present study, we investigated the interamygdaloid projections originating in the different divisions of the basal and accessory basal nuclei of the rat amygdala by using the Phaseolus vulgaris leucoagglutinin anterograde tract-tracing technique.
The basal and accessory basal nuclei are the source of a less significant amygdalofugal projections to both cortical areas.
The highest density of calbindin-D28k-positive neurons were found in the anterior cortical, medial, posterior cortical and accessory basal nuclei, in the parvicellular division of the basal nucleus and in the amygdalohippocampal area. The deep nuclei (lateral, basal and accessory basal nuclei) contained a high density of calbindin-D28k-immunoreactive fibres and terminals.
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 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 predilection sites include the entorhinal region, the CA2-sector of the hippocampal formation, the limbic nuclei of the thalamus, anterior cingulate areas, agranular insular cortex (layer VI), and - within the amygdala - the accessory cortical nucleus, the ventromedial divisions both of the basal and accessory basal nuclei, and the central nucleus.
The basal, lateral, and accessory basal nuclei display the most intense immunostaining with local heterogeneities.
Type 4 cells were observed primarily in the lateral, basal, and accessory basal nuclei and in the periamygdaloid cortex. The neuropil labeling was substantially lighter in the lateral, basal, and accessory basal nuclei.
The most intense staining occurred in the basolateral subdivision, consisting of the lateral, basolateral and accessory basal nuclei.
We found no major changes in the putamen or in the basal or accessory basal nuclei of the amygdala.
Based on the intensity of the reaction product, three different types of NADPH-d-positive cells were described: type 1 cells, the most intensely stained, varied in morphology and were most commonly found in the accessory basal, basal, and lateral nuclei and in the nucleus of the lateral olfactory tract; type 2 cells, the most common NADPH-d-positive cells, were more lightly stained, were generally stellate in shape, and were found in the lateral, basal, and accessory basal nuclei; type 3 cells were very lightly stained, oval or round in shape, and mostly found in the medial, anterior cortical, and paralaminar nuclei.
They were most numerous in middle and upper cortical layers, especially lamina II of the entorhinal cortex and the cortical and accessory basal nuclei of the amygdala.
Thus, the lateral and accessory basal nuclei of the amygdala project to layer 3 of areas Pr1, 28I, 28L, and 28S, and the accessory basal nucleus projects strongly to layer 1 of these same areas. Similarly, in 28I there is a major projection from the presubiculum and a lighter projection from the subiculum and CA1 to layer 3, where the lateral and accessory basal nuclei also project.
Area 25 also received afferents from cingulate areas 24b, 24c, and 23b, from rostral auditory association areas TS2 and TS3, from the subiculum and CA1 sector of the hippocampus, and from the lateral and accessory basal nuclei of the amygdala (LB and AB, respectively).
Relatively few fibers to the substantia innominata arise in the rostrodorsal part of the magnocellular basal nucleus, or in the lateral or parvicellular accessory basal nuclei.
The heaviest intrinsic projections arose from the lateral and basal nuclei while the central, medial, cortical, and accessory basal nuclei received the greatest number of these afferents.
These projections probably terminate predominantly in either the lateral or accessory basal nuclei.
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