Intrinsic connections of the rat amygdaloid complex: Projections originating in the central nucleus

Inputs from the amygdaloid and extraamygdaloid areas terminate in various divisions of the central nucleus. To elucidate the interconnections between the different regions of the central nucleus and its connectivity with the other amygdaloid areas, we injected the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L) into the capsular, lateral, intermediate, and medial divisions of the central nucleus in rat. There were a number of labeled terminals near the injection site within each division. The intrinsic connections between the various divisions of the central nucleus were organized topographically and originated primarily in the lateral division, which projected to the capsular and medial divisions. Most of the connections were unidirectional, except in the capsular division, which received a light reciprocal projection from its efferent target, the medial division. The intermediate division did not project to any of the other divisions of the central nucleus. Extrinsic projections from the central nucleus to the other amygdaloid nuclei were meager. Light projections were observed in the parvicellular division of the basal nucleus, the anterior cortical nucleus, the amygdalohippocampal area, and the anterior amygdaloid area. No projections to the contralateral amygdala were found. These data show that the central nucleus has a dense network of topographically organized intradivisional and interdivisional connections that may integrate the intraamygdaloid and extraamygdaloid information entering the different regions of the central nucleus. The sparse reciprocal connections to the other amygdaloid nuclei suggest that the central nucleus does not regulate the other amygdaloid regions but, rather, executes the responses evoked by the other amygdaloid nuclei that innervate the central nucleus. J. Comp. Neurol. 395:53–72, 1998. © 1998 Wiley-Liss, Inc.     

Projections from the amygdaloid complex to the piriform cortex: A PHA-L study in the rat

Projections from the amygdala to the piriform cortex are proposed to provide a pathway via which the emotional system can modulate the processing of olfactory information as well as mediate the spread of seizure activity in epilepsy. To understand the details of the distribution and topography of these projections, we injected the anterograde tracer Phaseolus vulgaris-leucoagglutinin into different nuclear divisions of the amygdaloid complex in 101 rats and analyzed the distribution and density of projections in immunohistochemically processed preparations. The heaviest projections from the amygdala to the piriform cortex originated in the medial division of the lateral nucleus, the periamygdaloid and sulcal subfields of the periamygdaloid cortex, and the posterior cortical nucleus. The heaviest terminal labeling was observed in layers Ib and III of the medial aspect of the posterior piriform cortex. 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. The results indicate that only selective amygdaloid nuclei or their subdivisions project to the piriform cortex. In addition, substantial projections from several amygdaloid nuclei converge in the medial aspect of the posterior piriform cortex. Via these projections, the amygdaloid complex can modulate the processing of olfactory information in the piriform cortex. In pathologic conditions such as epilepsy, these connections might provide pathways for the spread of seizure activity from the amygdala to extra-amygdaloid regions.     

Intrinsic connections of the rat amygdaloid complex: Projections originating in the lateral nucleus

The amygdaloid complex receives sensory information from a variety of sources. A widely held view is that the amygdaloid complex utilizes this information to orchestrate appropriate species-specific behaviors to ongoing experiences. Relatively little is known, however, about the circuitry through which information is processed within the amygdaloid complex. The lateral nucleus is the major recipient of extrinsic sensory information and is the origin of many intra-amygdaloid projections. In this study, we reinvestigated the organization of intraamygdaloid projections originating from the lateral nucleus using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). The lateral nucleus has highly organized intranuclear connections. Dense projections interconnect rostral and caudal levels of the lateral and the medial divisions of the nucleus, and the lateral and medial divisions of the lateral nucleus are also interconnected. The major extranuclear projections of the lateral nucleus are (in descending order of magnitude) to the accessory basal nucleus, the basal nucleus, the periamygdaloid cortex, the dorsal portion of the central division of the medial nucleus, the posterior cortical nucleus, the capsular division of the central nucleus, and the lateral division of the amygdalohippocampal area. The pattern of extranuclear projections varied depending on the rostrocaudal or mediolateral location of the injection site within the lateral nucleus. These findings indicate that intra-amygdaloid projections originating in the lateral nucleus are both more widespread and more topographically organized than was previously appreciated. © 1995 Wiley-Liss, Inc.     

Intrinsic connections of the rat amygdaloid complex: Projections originating in the basal nucleus

The amygdaloid complex is involved in associational processes, such as the formation of emotional memories about sensory stimuli. However, the anatomical connections through which the different amygdaloid nuclei process incoming information and communicate with the other amygdaloid nuclei, is poorly understood. As part of an ongoing project aimed at elucidating the intrinsic connections of the rat amygdaloid complex, we injected the antero grade tracer PHA-L (Phaseolus vulgaris-leucoagglutinin) into different rostrocaudal levels of the basal nucleus of the amygdala in 21 rats and analyzed the distribution of labeled fibers and terminals throughout the amygdaloid complex. The connectional analysis, together with cytoarchitectonic observations, suggested that contrary to previous notions the basal nucleus in the rat has three divisions: magnocellular, intermediate, and parvicellular. The magnocellular division has heavy reciprocal connections with the lateral portion of the parvicellular division and the intermediate division projects weakly to the parvicellular division, whereas the projection from the medial: portion of the parvicellular division to the intermediate division is heavy and the lateral and medial portions of the parvicellular division are only weakly interconnected, as are the magnocellular and intermediate divisions. The main intraamygdaloid targets of the basal nucleus projections are the nucleus of the lateral olfactory tract, the anterior amygdaloid area, the medial and capsular divisions of the central nucleus, the anterior cortical nucleus, and the amygdalohippocampal area. Our findings provide the most detailed understanding of the intra-amygdala connections of the basal nucleus to date and show that the connections within the basal nucleus and between the basal nucleus and other amygdaloid areas are more widespread and topographically organized than previously recognized. © 1995 Wiley-Liss, Inc.     

Intrinsic connections of the rat amygdaloid complex: Projections originating in the accessory basal nucleus

The amygdaloid complex plays an important role in the detection of emotional stimuli, the generation of emotional responses, the formation of emotional memories, and perhaps other complex associational processes. These functions depend upon the flow of information through intricate and poorly understood circuitries within the amygdala. As part of an ongoing project aimed at further elucidating these circuits, we examined the intra-amygdaloid connections of the acessory basal nucleus in the rat. In addition, we examined connections of the anterior cortical nucleus and amygdalahippocampal area to determine whether portions of these nuclei should be included in the accessory basal nucleus (as some earlier studies suggest). Phaseolus vulgaris leucoagglutinin was injected into different rostrocaudal levels of the accessory basal nucleus (n = 12) or into the anterior cortical nucleus (n = 3) or amygdalahippocampal area (n = 2). The major intra-amygdaloid projections from the accessory basal nucleus were directed to the medial and capsular divisions of the central nucleus, the medial division of the amygdalohippocampal area, the medial division of the lateral nucleus, the central division of the medial nucleus, and the posterior cortical nucleus. The projections originating in the anterior cortical nucleus and the lateral division of the amygdalohippocampal area differed from those originating in the accessory basal nucleus, which suggests that these areas are not part of the deep amygdaloid nuclei have different intra-amygdaloid connections. The pattern of these various connections suggests that information entering the amygdala from different sources can be integrated only in certain amygdaloid regions. © 1996 Wiley-Liss, Inc.     

Organization of the intrinsic connections of the monkey amygdaloid complex: Projections originating in the lateral nucleus

We have used the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L) to study the intrinsic projections of the lateral nucleus of the Macaca fascicularis monkey amygdaloid complex. A reanalysis of the monkey lateral nucleus indicated that there are at least four distinct cytoarchitectonic divisions: dorsal, dorsal intermediate, ventral intermediate, and ventral. The major projections within the lateral nucleus originate in the dorsal, dorsal intermediate, and ventral intermediate divisions and terminate in the ventral division. The ventral division also projects to itself but does not project significantly to the other divisions of the lateral nucleus. Thus, the ventral division appears to be a site of convergence for information entering all other portions of the lateral nucleus. There are substantial regional and topographic differences in the projections from each of the lateral nucleus divisions to other amygdaloid nuclei. 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. The dorsal intermediate division projects to the intermediate and parvicellular divisions of the basal nucleus, to the parvicellular division of the accessory basal nucleus, and to the periamygdaloid cortex. The ventral intermediate division projects to the magnocellular division of the accessory basal nucleus and to the parvicellular division of the basal nucleus. The major projections from the ventral division are directed to the parvicellular division of the basal nucleus, the parvicellular division of the accessory basal nucleus, the medial nucleus, and the periamygdaloid cortex. Projections from all portions of the lateral nucleus to the central nucleus are generally very light. It appears, therefore, that each division of the lateral nucleus originates topographically organized projections to the other amygdaloid areas that terminate in distinct portions of the target regions. The topographic organization of intrinsic amygdaloid projections raises the possibility that serial and parallel sensory processing may take place within the amygdaloid complex. J. Comp. Neurol. 398:431–458, 1998. © 1998 Wiley-Liss, Inc.     

Projections from the periamygdaloid cortex to the amygdaloid complex, the hippocampal formation, and the parahippocampal region: a PHA-L study in the rat

The periamygdaloid cortex, an amygdaloid region that processes olfactory information, projects to the hippocampal formation and parahippocampal region. To elucidate the topographic details of these projections, pathways were anterogradely traced using Phaseolus vulgaris leukoagglutinin (PHA-L) in 14 rats. First, we investigated the intradivisional, interdivisional, and intra-amygdaloid connections of various subfields [periamygdaloid subfield (PAC), medial subfield (PACm), sulcal subfield (PACs)] of the periamygdaloid cortex. Thereafter, we focused on projections to the hippocampal formation (dentate gyrus, hippocampus proper, subiculum) and to the parahippocampal region (presubiculum, parasubiculum, entorhinal, and perirhinal and postrhinal cortices). The PACm had the heaviest intradivisional projections and it also originated light interdivisional projections to other periamygdaloid subfields. Projections from the other subfields converged in the PACs. All subfields provided substantial intra-amygdaloid projections to the medial and posterior cortical nuclei. In addition, the PAC subfield projected to the ventrolateral and medial divisions of the lateral nucleus. The heaviest periamygdalohippocampal projections originated in the PACm and PACs, which projected moderately to the temporal end of the stratum lacunosum moleculare of the CA1 subfield and to the molecular layer of the ventral subiculum. The PACm also projected moderately to the temporal CA3 subfield. The heaviest projections to the entorhinal cortex originated in the PACs and terminated in the amygdalo-entorhinal, ventral intermediate, and medial subfields. Area 35 of the perirhinal cortex was lightly innervated by the PAC subfield. Thus, these connections might allow for olfactory information entering the amygdala to become associated with signals from other sensory modalities that enter the amygdala via other nuclei. Further, the periamygdalohippocampal pathways might form one route by which the amygdala modulates memory formation and retrieval in the medial temporal lobe memory system. These pathways can also facilitate the spread of seizure activity from the amygdala to the hippocampal and parahippocampal regions in temporal lobe epilepsy.     

Projections from the amygdalo-piriform transition area to the amygdaloid complex: a PHA-l study in rat

The amygdalo-piriform transition area is a poorly defined region in the temporal lobe that is heavily connected with the olfactory system. As part of an ongoing project aimed at understanding the neuronal pathways that provide sensory information to the amygdala, we investigated the cytoarchitectonic and chemoarchitectonic features of the amygdalo-piriform transition area and its connections to the amygdaloid complex in 13 rats by using the anterograde tracer, Phaseolus vulgaris-leucoagglutinin. Our analysis indicates that the amygdalo-piriform transition area has medial (rostral and caudal portions) and lateral parts. The rostromedial part projects heavily to the intermediate and lateral divisions of the central nucleus, whereas the caudomedial part projects mainly to the medial division. The lateral part of the amygdalo-piriform transition area projects heavily to the capsular and lateral divisions of the central nucleus. Electron microscopic analysis revealed that the projection to the lateral division of the central nucleus forms asymmetric contacts with the spines and shafts of postsynaptic neurons and, therefore, is assumed to be excitatory. The amygdalo-piriform transition area also projects moderately to other amygdaloid nuclei, including the parvicellular division of the basal nucleus, the anterior cortical nucleus, and the nucleus of the lateral olfactory tract. The lateral and medial parts of the amygdalo-piriform transition area also project to the distal temporal CA1 and distal temporal subiculum, respectively. Unlike the adjacent entorhinal cortex, the amygdalo-piriform transition area does not project to the dentate gyrus. These data suggest that the amygdalo-piriform transition area is a region that influences both emotional and memory processing in parallel by means of pathways to the amygdala and the hippocampus, respectively.     

Projections of the medial preoptic nucleus: a Phaseolus vulgaris leucoagglutinin anterograde tract-tracing study in the rat

The projections of the medial preoptic nucleus (MPN) were examined by making injections of the anterogradely transported lectin Phaseolus vulgaris leucoagglutinin (PHA-L) into the MPN and charting the distribution of labeled fibers. The evidence indicates that the MPN projects extensively to widely distributed regions in both the forebrain and brainstem, most of which also supply inputs to the nucleus. An important neuroendocrine role for the MPN is underscored by its extensive projections to almost all parts of the periventricular zone of the hypothalamus, including the anteroventral periventricular, anterior part of the periventricular, paraventricular (PVH), and arcuate nuclei, and a role in autonomic mechanisms is indicated by projections to such regions as the dorsal and lateral parvicellular parts of the PVH, the lateral parabrachial nucleus, and the nucleus of the solitary tract. Other projections of the MPN suggest participation in the initiation of specific motivated behaviors. For example, inputs to two nuclei of the medial zone of the hypothalamus, the ventromedial and dorsomedial nuclei, may be related to the control of reproductive and ingestive behaviors, respectively, although the possible functional significance of a strong projection to the ventral premammillary nucleus is presently unclear. The execution of these behaviors may involve activation of somatomotor regions via projections to the substantia innominata, zona incerta, ventral tegmental area, and pedunculopontine nucleus. Similarly, inputs to other regions that project directly to the spinal cord, such as the periaqueductal gray, the laterodorsal tegmental nucleus, certain medullary raphe nuclei, and the magnocellular reticular nucleus may also be involved in modulating somatic and/or autonomic reflexes. Finally, the MPN may influence a wide variety of physiological mechanisms and behaviors through its massive projections to areas like the ventral part of the lateral septal nucleus, the bed nucleus of the stria terminalis, the lateral hypothalamic area, the supramammillary nucleus, and the ventral tegmental area, all of which have extensive connections with regions along the medial forebrain bundle. Although the PHA-L method does not allow a clear demonstration of possible differential projections from each subdivision of the MPN, our results suggest that each of them does give rise to a unique pattern of outputs.(ABSTRACT TRUNCATED AT 400 WORDS)     

The central amygdaloid nucleus innervation of the dorsal vagal complex in rat: a Phaseolus vulgaris leucoagglutinin lectin anterograde tracing study

The central nucleus of amygdala (Ce) participates in expression of autonomic responses associated with fear or stress-related behaviors. The Ce can alter autonomic activity through its direct projection to the dorsal vagal complex [i.e., nucleus of the solitary tract (nTS) and the dorsal vagal nucleus]. In order to more precisely define the anatomical organization of the neurons within the Ce and their terminal fields within the dorsal vagal complex, the Phaseolus vulgaris leucoagglutinin lectin (PHA-L) anterograde tracing method was employed in rats. In cases where injections of PHA-L were centered within the medial Ce, dense axon terminal labeling was observed within the medial nTS at rostral levels. Terminal boutons were also observed within the ventral part of the lateral nTS, the dorsal vagal nucleus and contralateral medial nTS. At and just rostral to the obex, numerous axonal boutons were seen within the medial and commissural parts of the nTS and adjacent parts of the dorsal vagal nucleus. Contralateral axon terminal labeling was present within the medial and commissural parts of the nTS. Caudal to the obex, PHA-L immunoreactive boutons were concentrated bilaterally within the medial and commissural nTS and dorsal vagal nucleus. In cases where injections of PHA-L were centered within the lateral Ce moderate axon terminal labeling was observed throughout the rostrocaudal extent of the medial and commissural part of the nTS. Very few PHA-L immunoreactive terminals were observed within the ventral part of the lateral nTS, dorsal vagal nucleus and contralateral medial nTS. The results demonstrate that the medial Ce projects bilaterally to the medial and commissural subnuclei of the nTS and the dorsal vagal nucleus. The lateral Ce projects mainly to the ipsilateral medial and commissural nTS. Thus, both the medial and lateral Ce can directly influence regions of the nTS where peripheral cardiovascular, cardiopulmonary and gastric afferents terminate. The medial Ce can also directly affect vagal nerve outflow through its projection to neurons within the dorsal motor nucleus.     

Projections of the vestibular nuclei to the thalamus in the rat: a Phaseolus vulgaris leucoagglutinin study.

Injections of the anterograde axonal tracer Phaseolus vulgaris leucoagglutinin were made into individual nuclei of the vestibular nuclear complex of the rat to identify specific projections to the thalamus. The results showed that the superior vestibular nucleus and the medial vestibular nucleus, especially its rostral-to-middle parts, project to the lateral part of the parafascicular thalamic nucleus (corresponding to the centromedian nucleus in primates), the transitional zone between the ventrolateral thalamic nucleus (VL) and the ventral posterolateral thalamic nucleus (VPL) (the region considered to be the nucleus ventralis intermedius of Vogt [Vogt C. 1909. La myeloarchitecture du thalamus du cercopitheque. J Psychol Neurol 12:285-324.]), the lateral part of the centrolateral thalamic nucleus and the dorsal part of the caudal VL; the spinal vestibular nucleus projects to the lateral part of the parafascicular thalamic nucleus, the transitional zone between the VL and the VPL, the caudal part of the ventrobasal complex, and the suprageniculate thalamic nucleus. These results suggest that vestibular information is transmitted not only to the cerebral cortex (mainly area 2V and area 3a) but also to the striatum. They also suggest that vestibular activity may affect gaze control by means of vestibulothalamocortical pathway in addition to vestibulo-ocular and vestibulopremotoneuronal routes.     

Organization of projections from the basomedial nucleus of the amygdala: A PHAL study in the rat

The organization of axonal projections from the basomedial nucleus of the amygdala (BMA) was examined with the Phaseolus vulgaris leucoagglutinin (PHAL) method in adult male rats. The anterior and posterior parts of the BMA, recognized on cytoarchitectonic grounds, display very different projection patterns. Within the amygdala, the anterior basomedial nucleus (BMAa) heavily innervates the central, medial, and anterior cortical nuclei. In contrast, the posterior basomedial nucleus (BMAp) sends a dense projection to the lateral nucleus, and to restricted parts of the central and medial nuclei. Extra-amygdalar projections from the BMA are divided into ascending and descending components. The former end in the cerebral cortex, striatum, and septum. The BMAa mainly innervates olfactory (piriform, transitional) and insular areas, whereas the BMAp also innervates inferior temporal (perirhinal, ectorhinal) and medial prefrontal (infralimbic, prelimbic) areas and the hippocampal formation. Within the striatum, the BMAa densely innervates the striatal fundus, whereas the nucleus accumbens receives a heavy input from the BMAp. Both parts of the BMA send massive projections to distinct regions of the bed nuclei of the stria terminalis. Descending projections from the BMA end primarily in the hypothalamus. The BMAa sends a major input to the lateral hypothalamic area, whereas the BMAp innervates the ventromedial nucleus particularly heavily. Injections were also placed in the anterior cortical nucleus (COAa), a cell group superficially adjacent to the BMAa. PHAL-labeled axons from this cell group mainly ascend into the amygdala and olfactory areas, and descend into the thalamus and lateral hypothalamic area. Based on connections, the COAa and BMAa are part of the same functional system. The results suggest that cytoarchitectonically distinct anterior and posterior parts of the BMA are also hodologically distinct and form parts of distinct anatomical circuits probably involved in mediating different behaviors (for example, feeding and social behaviors vs. emotion-related learning, respectively). © 1996 Wiley-Liss, Inc.     

The organization of the efferent projections from the pontine parabrachial area to the amygdaloid complex: A phaseolus vulgaris leucoagglutinin (PHA-L) study in the rat

The organization of the efferent projections from the pontine parabrachial (pPB) area to the amygdala has been studied in the rat by using microinjections of Phaseolus vulgaris leucoagglutinin (PHA-L), a sensitive and selective anterograde axonal marker, into restricted subregions of the pPB area. The results confirmed that the pPB area primarily projected onto the ipsilateral nucleus centralis of the amygdala (Ce), and to a lesser extent onto the ipsilateral posterior basolateral (BLP), anterior basomedial (BMA), and amygdaloid cortical (ACo) nuclei of the amygdala. Substantial projections were also found in the substantia innominata dorsal/ventral portion of the globus pallidus (SId/GPv), substriatal (SStr), and fondus striatal (FStr) regions which continue the amygdala rostrally. The results demonstrated that the projections of the pPB area onto the Ce were topically organized: (1) The region of the pPB area mainly including the medial subnucleus (pPBm), the waist area (pPBwa), and a thin rostral lamina of the ventral lateral subnucleus (pPBvl) projects primarily to the medial portion of the Ce (CeM). Dense projections were also found in the BLP, BMA, and ACo nuclei of the amygdala, and in the SId/GPv, SStr, and FStr rostral areas. (2) The region of the pPB mainly including the rostral portion of the central lateral subnucleus (pPBcl) and the outer-rostral protion of the external lateral subnucleus (pPBel) projects primarily to the lateral portion of the Ce (CeL). (3) The region of the pPB mainly including the dorsolateral subnucleus (pPBdl), the remaining pPBel, and the external medial (pPBem) subnuclei projects primarily to the lateral capsular protion of the Ce (CeLC) and bilaterally to its rostral portion. Dense projections were also found in the regions which extend the CeLC rostrally and in the SId/GPv, SStr, and FStr rostral areas. The possible role of each of the three parabrachio-amygdaloid pathways described is discussed. It was suggested that the pPB-CeM pathway is mainly implicated in gustatory processes; the pPB-CeL pathway is mainly implicated in visceral and chemosensitive processes; and the pPB-CeLC pathway is mainly implicated in respiratory, cardiovascular, and nociceptive processes. © 1993 Wiley-Liss, Inc.     

Amygdalonigral pathway: an anterograde study in the rat with Phaseolus vulgaris leucoagglutinin (PHA-L)

The projection from the central nucleus of the amygdala to the substantia nigra was labeled by injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin into different subregions of the nucleus. A sparse projection of labeled bouton-like swellings was observed in the rostral, medial substantia nigra pars compacta and ventral tegmental area from all subregions of the central nucleus of the amygdala that were injected. A dense projection of labeled axons and bouton-like swellings was observed in the lateral part of the substantia nigra pars compacta and pars lateralis when the injection site included the dorsal and rostral central nucleus. Heavy labeling was also seen in the lateral retrorubral field in these cases. In no instances were labeled terminals observed in the substantia nigra pars reticulata. The same pattern of labeling in the lateral substantia nigra and retrorubral field was seen after injections rostral to the central nucleus or dorsal and medial to it in the sublenticular region. The results suggest that the amygdalonigral pathway contributes to the innervation of extensive areas of the substantia nigra pars compacta. The major component of the pathway, however, projects only to a subregion of the substantia nigra. The origin of this pathway is confined to a discrete region of the dorsal central nucleus of the amygdala but extends rostrally into an area that is part of the "extended amygdala."     

Zinc-containing afferent projections to the rat corticomedial amygdaloid complex: A retrograde tracing study

The mammalian amygdaloid complex is densely innervated by zinc-containing neurons. The distribution of the terminals throughout the region has been described, but the origins of these zinc-containing fibers have not. The present work describes the origins of one major component of the zinc-containing innervation of the amygdaloid complex, namely, the component that innervates the corticomedial complex. Selective labeling of zinc-containing axons was accomplished by intracerebral microinfusion of selenium anions (SeO₃²⁻), a procedure that produces a ZnSe precipitate in zinc-containing axonal boutons with subsequent retrograde transport to the neurons of origin. After infusions of SeO₃²⁻ into combinations of cortical, medial, or amygdalohippocampal regions, retrogradely labeled zinc-containing somata were found in all amygdaloid nuclei except for the medial and central nuclei, the bed nucleus of the accessory olfactory tract, the nucleus of the lateral olfactory tract, and the anterior amygdaloid area. Extrinsic zinc-containing projections to the same amygdaloid terminal fields were found to originate from the infralimbic, cingulate, piriform, perirhinal and entorhinal cortices, and from the prosubiculum and CA1. Commissural zinc-containing projections were found to originate from the posterolateral and posteromedial cortical nuclei and from the posterior part of the basomedial nucleus. Zinc-containing neurons have been implicated in the pathophysiology of epilepsy, in cell death after seizure or stroke, and in Alzheimer's disease, all clinical conditions that involve the amygdaloid complex. Identification of the zinc-containing pathways is a prerequisite to the elucidation of zinc's role in these disorders. J. Comp. Neurol. 400:375–390, 1998. © 1998 Wiley-Liss, Inc.     

Descending projections of the posterior nucleus of the hypothalamus: Phaseolus vulgaris leucoagglutinin analysis in the rat

No previous report in any species has systematically examined the descending projections of the posterior nucleus of the hypothalamus (PH). The present report describes the descending projections of the PH in the rat by using the anterograde anatomical tracer, Phaseolus vulgaris leucoagglutinin. PH fibers mainly descend to the brainstem through two routes: dorsally, within the central tegmental tract; and ventromedially, within the mammillo-tegmental tract and its caudal extension, ventral reticulo-tegmental tracts. PH fibers were found to distribute densely to several nuclei of the brainstem. They are (from rostral to caudal) 1) lateral/ventrolateral regions of the diencephalo-mesopontine periaqueductal gray (PAG); 2) the peripeduncular nucleus; 3) discrete nuclei of pontomesencephalic central gray (dorsal raphe nucleus, laterodorsal tegmental nucleus, and Barrington's nucleus); 4) the longitudinal extent of the central core of the mesencephalic through medullary reticular formation (RF); 5) the ventromedial medulla (nucleus gigantocellularis pars alpha, nucleus raphe magnus, and nucleus raphe pallidus); 6) the ventrolateral medulla (nucleus reticularis parvocellularis and the rostral ventrolateral medullary region); and 7) the inferior olivary nucleus. PH fibers originating from the caudal PH distribute much more heavily than those from the rostral PH to the lower brainstem. The PH has been linked to the control of several important functions, including respiration, cardiovascular activity, locomotion, antinociception, and arousal/wakefulness. It is likely that descending PH projections, particularly those to the PAG, the pontomesencephalic RF, Barrington's nucleus, and parts of the ventromedial and ventrolateral medulla, serve a role in a PH modulation of complex behaviors involving an integration of respiratory, visceromotor, and somatomotor activity. © 1996 Wiley-Liss, Inc.     

Plasticity of intra-amygdaloid connections following the denervation of fibers from accessory olfactory bulb to medial amygdaloid nucleus in adult rat: immunohistochemical study of anterogradely transported lectin (Phaseolus vulgaris leucoagglutinin)

The rearrangement of the terminations of intra-amygdaloid fibers was examined in the medial amygdaloid nucleus (MAN) following denervation of the fibers from the accessory olfactory bulb (AOB) of adult rat using immunohistochemistry of anterogradely transported lectin (Phaseolus vulgaris leucoagglutinin, PHA-L). The AOB was removed unilaterally by suction at two months before the PHA-L injection. The PHA-L was injected bilaterally into the posteromedial region of the amygdala (posteromedial amygdaloid nucleus and amygdala-hippocampal transitional area). After the tissue was processed by the routine immunohistochemical method, the immunologically labeled axons and axon terminals in the MAN were observed with the light microscope. On the control side, labeled axons were observed in the cellular part of the MAN, but they were not found in the molecular layer in which the fibers from the accessory olfactory bulb terminate. On the side of the AOB removal, the labeled axons were found not only in the cellular part but also in the molecular layer. Electron microscopic observations showed that the labeled axon terminals made synaptic contacts in the molecular layer. These results indicate that terminals of intra-amygdaloid fibers expand from the cellular part to the molecular layer in the MAN and make synaptic contacts in this layer following the denervation of the AOB fibers.