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.     

Efferents of the medial preoptic area in the guinea pig: An autoradiographic study

Medial preoptic axons were traced into the diagonal band of Broca and septum, particularly lateral septum. Other labeled fibers could be followed dorsally from medial preoptic area injections adjacent to the stria medullaris, and in the periventricular fiber system and the stria terminalis and its bed nucleus. The anterior and medial amygdaloid nuclei were labeled by fibers via the stria terminalis and others arching over the optic tract and through the substantia innominata. The lateral habenula was labeled. Labeled periventricular fibers reached the periventricular nucleus of the thalamus. Descending efferents were traced principally below the fornix and in the adjacent lateral hypothalamus to label the anterior hypothalamus, the tuberal nuclei, and median eminence. Axons of the medial preoptic area joined the medial part of the medial forebrain bundle and distributed to the reticular formation and the central gray of the midbrain and pons. A small amount of contralateral connections were described.     

Projections of the nucleus and tracts of the stria terminalis following lesions at the level of the anterior commissure.

The projections of the stria terminalis were traced with the Fink-Heimer stain following lesions at the level of the anterior commissure. The pre-commissural stria terminalis is amygdalofugal only, and projects to the nucleus of the anterior commissure, the medial preoptic area, the ventral portion of the capsule surrounding the ventromedial nucleus, and to the area closely adjacent to the periventricular nucleus by way of the medial corticohypothalamic tract. The postcommissural stria terminalis is both amygdalofugal and amygdalopetal. Its hypothalamic projection is to the lateral preoptic area and the bed nucleus of the stria terminalis, and to the lateral hypothalamus by way of the lateral preoptic area. The amygdaloid projection is mainly to the basolateral nucleus, with fewer terminations to the basomedial nucleus and the area surrounding the central nucleus. The projections of the bed nucleus of the stria terminalis are quite similar to the postcommissural stria, except for an additional projection to the magnocellular paraventricular and dorsal periventricular nuclei by way of the lateral filiform tract. The commissural stria terminalis projects contralaterally to cells within its fiber bundle and the posterior limb of the anterior commissure.     

Efferents from the medial anterior hypothalamic area in the guinea pig

Medial anterior hypothalamic connections were studied with H³-proline and autoradiography. Most of the axons projected to other hypothalamic nuclei. The major pathways were found ventral medial to the fornix and in the periventricular tract. Substantial projections were apparent in the ventromedial and dorsomedial nuclei with less label in the arcuate nucleus. The dorsal premammillary nuclei were labeled bilaterally, particularly with more caudal injections of anterior hypothalamus. Efferents were evident in the posterior hypothalamus and continued into the central gray of the midbrain. Labeled fibers reached the ventral tegmental area and in the reticular formation were traced only through pons. Rostral projections were to the medial and lateral preoptic areas and ventral lateral septum. The bed nucleus of stria terminalis was labeled and a very few fibers reached the medial amygdaloid nucleus. The periventricular nucleus of thalamus was labeled.     

Prodynorphin- and substance P-containing neurons project to the medial preoptic area in the male Syrian hamster brain.

To determine if substance P- or prodynorphin-containing neurons of the medial nucleus of the amygdala and medial bed nucleus of the stria terminalis send projections to the medial preoptic area in the male Syrian hamster, we placed a fluorescent retrograde tract tracer (either Fluoro-gold, or rhodamine- or fluorescein-impregnated latex microspheres) into the medial preoptic area. Five to seven days later, the animals were treated with colchicine, allowed to survive for 48 h and the brains were processed for immunofluorescence histochemistry. Tissue sections were incubated in either rat anti-substance P or rabbit anti-C-peptide (the C-terminal sequence of dynorphin B) antiserum followed by incubation in either fluorescein- or rhodamine-conjugated anti-rabbit or anti-rat antiserum. When the injection site of retrograde tracer was centered within the caudal one-third of the medial preoptic area, labeled cell bodies were observed caudally in the medial part of the bed nucleus of the stria terminalis. Retrogradely labeled cell bodies were also observed in the posterodorsal subdivision of the medial nucleus of the amygdala. Both prodynorphin and substance P immunolabeling were observed in retrogradely labeled neurons in these two areas but fewer of these projection neurons were immunolabeled with substance P antiserum than with C-peptide antiserum. These projections may play a role in the peptidergic modulation of reproductive behavior in this species.     

Efferents and centrifugal afferents of the main and accessory olfactory bulbs in the hamster

The efferents and centrifugal afferents of the hamster olfactory bulbs were studied using orthograde and retrograde tracing techniques. Following injections of tritiated amino acids which were restricted to the main olfactory bulb (MOB), autoradiographic grains were observed ipsilaterally over layer IA of the entire anterior olfactory nucleus (AON), the ventral portion of the hippocampal rudiment (HR), the entire prepyriform cortex and olfactory tubercle, the anterior and posterolateral cortical amygdaloid nuclei and the lateral entorhinal cortex. An ipsilateral projection to the nucleus of the lateral olfactory tract (nLOT) was also indicated. No subcortical or contralateral projections were observed. Amino acid injections into the accessory olfactory bulb (AOB) revealed ipsilateral projections to the superficial plexiform layer of the medial and posteromedial cortical amygdaloid nuclei and to the bed nucleus of the accessory olfactory tract (nAOT) and the bed nucleus of the stria terminalis (nST). Following injections of HRP which were restricted to the MOB, contralateral HRP-positive neurons were found predominantly in pars externa and to a lesser extent in the other subdivisions of the AON. Centrifugal projections to the MOB were identified ipsilaterally from the entire AON, the ventral portion of the HR, the anterior portion of the prepyriform cortex, and the nLOT. No labelled neurons were found in the olfactory tubercle, the anterior and posterolateral cortical amygdaloid nuclei or the entorhinal cortex. Centrifugal projections to the MOB were also identified from subcortical structures of the ipsilateral basal forebrain and from midline structures of the midbrain. Labelling occurred in the fusiform neurons of the diagonal band near the medial base of the forebrain at the level of caudal olfactory tubercle. Heavy labelling was seen in a distinct group of large, predominantly multipolar neurons (magnocellular preoptic area) that continued from the level of caudal olfactory tubercle to the level of the nLOT. This band of HRP-positive neurons could be followed more caudally to a position dorsal and medial to the nLOT near the lateral margin of the lateral anterior hypothalamic area. The midbrain projections to the MOB originated in the dorsal and median raphe nuclei. After injections of HRP into the AOB, centrifugal projections were identified from the nAOT and the posteromedial cortical amygdaloid nucleus. In addition, isolated neurons were labelled in the medial cortical amygdaloid nucleus but no labelled neurons were found in the nST. These results support the notion of two anatomically distinct olfactory systems and demonstrate two previously unreported pathways through which the limbic system may modulate sensory processing in the olfactory bulb.     

Efferents from medial basal forebrain and hypothalamus in the rat. I. An autoradiographic study of the medial preoptic area.

Efferent projections from the medial and periventricular preoptic area, bed nucleus of the stria terminalis and nuclei of the diagonal band were traced using tritiated amino acid autoradiography in albino rats. Medial and periventricular preoptic area efferents were not restricted to short-axon projections. Ascending projections from the medial preoptic area (mPOA) were traced through the diagonal band into the septum. Descending mPOA axons coursed in the medial parts of the medial forebrain bundle. Projections to most hypothalamic nuclei, including the arcuate nucleus and median eminence, were observed. In the midbrain, mPOA efferents were distributed in the central grey, raphe nuclei, ventral tegmental area and reticular formation. Projections from the mPOA were also observed to the amygdala through the stria terminalis, to the lateral habenula through the stria medullaris, and to the periventricular thalamus. Axons of the most medial and periventricular preoptic area (pvPOA) neurons had a distribution similar to more lateral mPOA neurons but their longest-axoned projections were weaker. The pvPOA did not send axons through the stria medullaris but did project more heavily than the more lateral mPOA to the arcuate nucleus and median eminence. Projections from the bed nucleus of the stria terminalis (nST) were in most respects similar to those from the medial preoptic area, with the major addition of a projection to the accessory olfactory bulb. The nuclei of the diagonal band of Broca (nDBB) gave a different pattern of projections than mPOA or nST, projecting, for instance, to the medial septum and hippocampus. Descending nDBB efferents ran in the ventral portion of the medial forebrain bundle. Among hypothalamic cell groups, only the medial mammillary nuclei received nDBB projections. nDBB efferents also distributed in the medial and lateral habenular nuclei and the mediodorsal thalamic nucleus.     

Afferent connections of the sexually dimorphic area of the hypothalamus of male and female gerbils

We studied neural inputs to the sexually dimorphic area (SDA) of the gerbil hypothalamus by injecting wheat-germ agglutinin-horseradish peroxidase into its medial or lateral components in males and females. To confirm the topography of SDA afferents, we injected Phaseolus vulgaris-leucoagglutinin into areas where retrograde labeling from the medial and lateral SDA differed. Both methods indicated that the medial SDA received stronger inputs from the medial part of the bed nucleus of the stria terminalis, the ventral part of the lateral septal nucleus, the medial amygdaloid nucleus, and the amygdalohippocampal area, than the lateral SDA does. In contrast, the rostrodorsal part of the lateral septum, the lateral part of the bed nucleus of the stria terminalis, the anterior and posterior hypothalamic areas, and the dorsomedial hypothalamic nucleus project more heavily to the lateral than to the medial SDA. In addition, retrograde labeling suggested that the ventral part of the premammillary nucleus projects more strongly to the medial than to the lateral SDA, whereas the infralimbic area of the cortex and the lateral preoptic area project more strongly to the lateral than to the medial SDA. The densities of cells in the bed nucleus of the stria terminalis and medial amygdaloid nucleus that could be retrogradely labeled from the medial SDA were greater in males than in females. This was not true of labeling in the arcuate nucleus or in the ventral part of the lateral septal nucleus. Since the medial SDA receives strong inputs from areas with many steroid-accumulating cells, it could respond to steroids directly and via these afferents. In contrast, hormonal effects on the lateral SDA are more likely to occur locally.     

Amygdaloid and pontine projections to the ventromedial nucleus of the hypothalamus

Amygdaloid and pontine projections to the feline ventromedial nucleus of the hypothalamus (HVM) were studied with retrograde transport of horseradish peroxidase (HRP) and anterograde transport of tritiated amino acids. Following injections of HRP into HVM, amygdaloid neurons were labeled in the ipsilateral cortical and medial nuclei and the ventral portion of the parvocellular part of the basal nucleus. In experiments in which HRP was injected into the tuberal hypothalamus following stria terminalis lesions, it was determined that amygdaloid neurons projecting to HVM by way of the stria terminalis were located in the cortical and medial nuclei while those projecting through another route, presumably the ventral amygdalofugal pathway, were found in the rostral part of the medial nucleus and the parvocellular basal nucleus. Following HRP injection into lateral hypothalamus at the level of HVM, labeled neurons were seen in the magnocellular basal nucleus. After preoptic injections, neurons containing the HRP reaction product were in cortical and medial nuclei and magnocellular and parvocellular parts of the basal nucleus. In addition to cells in the amygdala, rostral pontine neurons were labeled after HRP injections into HVM. The cells were located ipsilateral to the injection, mostly in the dorsal nucleus of the lateral lemniscus, lateral and dorsolateral to the brachium conjunctivum. The pontine cells labeled following HVM injections of HRP were different from those labeled following lateral hypothalamic and preoptic region injections. The pontine projection to HVM was confirmed using axoplasmic transport autoradiography. A mixture of tritiated leucine and tritiated proline was injected into the lateral pontine region labeled after HRP injections into HVM. Labeled axons ascending in the medial forebrain bundle terminated throughout the rostro-caudal extent of HVM.     

The amygdala of the box turtle, Terrapene c. carolina

The amygdala of the box turtle lies beneath the posterior hypopallial ridge. Three nuclear groups may be distinguished in it: (1) the anterior amygdaloid area, (2) the basolateral group and (3) the corticomedial group. The anterior amygdaloid area shows no subdivisions; its location ventral and ventromedial to the caudal part of the small-celled portion of the piriform area is evident. The basolateral group is subdivided into lateral and basal amygdaloid nuclei. The interconnections of this group through the anterior commissure with the comparable area in the opposite amygdala and with the corticomedial group indicate that it is functionally a vicarious cortex. The corticomedial group is divisible into medial and cortical amygdaloid nuclei. The medial nucleus is poorly defined. The cortical nucleus is bounded by the medial amygdaloid nucleus on the medial side and the ventral border of the piriform cortex laterally, and is comparable to the cortical amygdaloid nucleus of higher vertebrates. The lateral olfactory tract arises from mitral cells of the olfactory bulb and accessory olfactory bulb and neurons of the anterior olfactory nucleus. The lateral part of the anterior olfactory nucleus, the lateral and the intermediate parts of the tuberculum olfactorium and the small-celled part of the piriform cortex contribute to and receive fibers from the lateral olfactory tract. The lateral olfactory tract sends fibers to the anterior amygdaloid area and the corticomedial group. The lateral corticohabenular tract has an anterior and a posterior division. The anterior division arises from cells of the nucleus of the lateral olfactory tract and the lateroventral portion of the piriform cortex. It is joined by those fascicles arising in the corticomedial group and designated as the amygdalohabenular tract. This tract crosses in the habenular commissure and retraces its course to enter the corticomedial amygdaloid nuclear group on the side opposite its origin. The basolateral group is interconnected through the anterior commissure. The stria terminalis contains three components which interconnect the corticomedial amygdaloid nuclear group with the septum, the preoptic area and the hypothalamus. The supracommissural and the intracommissural components relate the cortical and the medial nuclei to the septum, the preoptic area and the hypothalamus of the same side. The infracommissural component interconnects the cortical and the medial amygdaloid nuclei with the septum, the preoptic area and the hypothalamus of the same and the opposite side. The dorsal and the ventral olfactory projection tracts arise from the corticomedial amygdaloid nuclear group. They terminate in the preoptic area and anterior hypothalamus.     

Distribution and efferent projections of corticotropin-releasing factor-like immunoreactivity in the rat amygdaloid complex

Using cobalt-enhanced immunohistochemistry, the tracing of retrograde transport of horseradish peroxidase (HRP) and experimental manipulations, a widespread localization of corticotropin-releasing factor-like immunoreactive (CRFI) structures in the rat amygdaloid complex, and CRFI-containing pathways from the amygdala to the lower brainstem, bed nucleus of the stria terminalis (bst) and ventromedial nucleus of the hypothalamus (VMH) have been demonstrated. By means of cobalt-enhanced immunohistochemistry, CRFI cells were detected in almost all the regions of the amygdala, including the central amygdaloid nucleus (Ce), basolateral amygdaloid nucleus (B1), intra-amygdaloid bed nucleus of the stria terminalis (Abst), medial amygdaloid nucleus (Me), amygdalohippocampal area (Ahi), posterior cortical amygdaloid nucleus (Aco), lateral amygdaloid nucleus (La), anterior amygdaloid area (AAA) and basomedial amygdaloid nucleus (Bm). Neural processes with CRFI were found in all of the above areas. The greatest density of CRFI fibres was observed in the Ce, the Me and Ahi. Unilateral lesions located in the Ce and adjacent areas caused an ipsilateral decrease in CRFI fibre number in the lateral hypothalamic area (LH), mesencephalic reticular formation (RF), dorsal (Dpb) and ventral (Vpb) parabrachial nuclei, mesencephalic nucleus of the trigeminal nerve (MeV) and in the lateral division of the bst (bstl). In addition, ipsilateral CRFI fibres decreased in number in the core and shell of the VMH after unilateral lesions of the corticomedial amygdala (CoM) and ventral subiculum (S). These findings suggest that the CRFI cells in the Ce and adjacent areas innervate the Dpb, Vpb and MeV through the LH and RF; the CRFI fibres in the bstl are supplied by the Ce and adjacent areas; and the CoM and S give rise to the CRFI fibres to the VMH. The distribution of retrogradely transported HRP has confirmed these projections. Furthermore, combined HRP and immunohistochemical staining has demonstrated double labeled cells in the Ce following HRP injection into the Dpb, Vpb, MeV and bstl. This provides direct evidence for the amygdalofugal CRF-containing projections to the lower brainstem and bstl. Double-labeled cells were not seen in the CoM and S after HRP injection into the VMH.     

An HRP study of the afferent connections to rat medial hypothalamic region

Afferent connections to the medial hypothalamic region in the rat were studied using horseradish peroxidase (HRP). HRP was injected iontophoretically by a parapharyngeal approach. After HRP injections into the ventromedial hypothalamic nucleus, labeled cells were found mainly in the medial and basolateral amygdaloid nuclei, subiculum, peripeduncular nucleus and the parabrachial area. Labeled cells following HRP injections into the dorsomedial hypothalamic nucleus were found mainly in the lateral septal nucleus, nucleus accumbens, bed nucleus of the stria terminalis, pontine central gray and the parabrachial area. HRP-labeled cells following the medial preoptic area injections were found mainly in the infralimbic cortex, lateral and medial septal nuclei, nucleus accumbens, diagonal band, bed nucleus of the stria terminalis, medial amygdaloid nucleus, subiculum, peripedunclar nucleus and the parabrachial area. The intrahypothalamic connections were also discussed.     

The efferent connections of the ventromedial nucleus of the hypothalamus of the rat.

The efferent connections of the ventromedial nucleus of the hypothalamus (VMH) of the rat have been examined using the autoradiographic method. Following injections of small amounts (0.4-2.0 muCi) of tritium labeled amino acids, fibers from the VMH can be traced forward through the periventricular region, the medial hypothalamus and the medial forebrain bundle to the preoptic and thalamic periventricular nuclei, to the medial and lateral preoptic areas, to the bed nucleus of the stria terminalis and to the ventral part of the lateral septum. Some labeled axons continue through the bed nucleus of the stria terminalis into the stria itself, and hence to the amygdala, where they join other fibers which follow a ventral amygdalopetal route from the lateral hypothalamic area and ventral supraoptic commissure. These fibers terminate in the dorsal part of the medial amygdaloid nucleus and in the capsule of the central nucleus. A lesser number of rostrally directed fibers from the VMH crosses the midline in the ventral supraoptic commissure and contributes a sparse projection to the contralateral amygdala. Descending fibers from the VMH take three routes: (i) through the medial hypothalamus and medial forebrain bundle; (ii) through the periventricular region; and (iii) bilaterally through the ventral supraoptic commissure. These three pathways are interconnected by labeled fibers so that it is not possible to precisely identify their respective terminations. However, the periventricular fibers seem to project primarily to the posterior hypothalamic area and central gray, as far caudally as the anterior pole of the locus coeruleus, while the medial hypothalamic and medial forebrain bundle fibers apparently terminate mainly in the capsule of the mammillary complex, in the supramammillary nucleus and in the ventral tegmental area. The ventral supraoptic commissure fibers leave the hypothalamus closely applied to the medial edges of the two optic tracts. After giving off their contributions to the amygdala, they continue caudally until they cross the dorsal edge of the cerebral peduncle to enter the zona incerta. Some fibers probably terminate here, but others continue caudally to end in the dentral tegmental fields, and particularly in the peripeduncular nucleus. Within the hypothalamus, the VMH appears to project extensively to the surrounding nuclei. However, we have not been able to find evidence for a projection from the VMH to the median eminence. Isotope injections which differentially label the dorsomedial or the ventrolateral parts of the VMH have shown that most of the long connections (to the septum, amygdala, central tegmental fields and locus coeruleus) originate in the ventrolateral VMH, and there is also some evidence for a topographic organization within the projections of this subdivision of the nucleus.     

Efferent Projections from the Ovarian Steroid Receptor-Containing Area of the Ventrolateral Hypothalamus in Female Guinea Pigs

The ventrolateral hypothalamus (VLH) in female guinea pigs includes a subset of neurons which contain estrogen and progestin receptors, and which are implicated in the regulation of female sexual behavior by steroid hormones. However, little is known about where these neurons project, and consequently which other brain areas are involved in sexual behavior in female guinea pigs. The anterograde tracer Phaseolus vulgaris -Leucoagglutinin was used to label efferents from the ovarian steroid receptor-containing part of the VLH. To identify the correct placement of the tracer specifically within the group of neurons containing estrogen receptors, medial hypothalamic sections were also immunostained for estrogen receptors. Forebrain areas receiving dense projections from the ventrolateral hypothalamus included the bed nucleus of the stria terminalis, medial preoptic area, anterior hypothalamic area, anterior ventromedial hypothalamus, and caudal ventrolateral hypothalamus. The midbrain central gray was also heavily labeled. Moderate innervation was observed in the forebrain in the basolateral amygdala, medial preoptic nucleus, lateroanterior hypothalamic nucleus, dorsal hypothalamic areas, posterior hypothalamus, zona incerta, and in the midbrain interspersed among the central and lateral tegmental tracts. The major efferent pathways from the VLH appeared to travel rostrally through the mediobasal hypothalamus and preoptic area, and caudally via the medial thalamic nuclei and periventricular fiber system. These findings are similar to those of previous studies tracing the efferents from the ventromedial nucleus in rats and from the lateral hypothalamus in guinea pigs. Many of these areas that receive input from the steroid receptor rich area within the VLH are likely to be involved in the regulation of female sexual behavior.     

Amygdaloid efferents through the stria terminalis in the rat give origin to zinc-containing boutons

Many regions of the basal forebrain are innervated by zinc-containing axonal boutons. In the present work, the lesion/degeneration method, coupled with histochemical staining for zinc-containing boutons, was used to determine the origins and efferent pathways of these zinc-containing projections to the basal forebrain. Knife cuts of the stria terminalis or extensive electrolytic lesions of the amygdala resulted in the bleaching of the staining for zinc (Timm stain) and terminal degeneration (Fink-Heimer method) ipsilaterally in the following areas: granule cell layer of the accessory olfactory bulb, shell of nucleus accumbens, bed nucleus of the stria terminalis, striohypothalamic nucleus, retrochiasmatic area, ventromedial hypothalamic nucleus (in the cell-sparse shell), medial tuberal nucleus, terete hypothalamic nucleus, and ventral premammillary nucleus. Small lesions made with ibotenic acid in the posteromedial part of the amygdalohippocampal area caused bleaching of the stain for zinc in the accessory olfactory bulb, in the medial zone of the bed nucleus of the stria terminalis, and in the ventral premammillary nucleus. Lesions in either the ventral subiculum or the anterolateral part of the amygdalohippocampal area caused bleaching in the ventromedial hypothalamic nucleus. Lesions in the hippocampus or in the neocortex did not produce bleaching of the stain for zinc in the above-mentioned terminal fields. The present results agree with previous studies on amygdaloid efferents and suggest that neurons in the amygdalohippocampal area and, possibly, in the ventral subiculum give origin to zinc-containing boutons.     

Direct reciprocal connections between the bed nucleus of the stria terminalis and dorsomedial medulla oblongata: Evidence from immunohistochemical detection of tracer proteins

Connections between the bed nucleus of the stria terminalis and the dorsomedial medulla oblongata have been examined by immunohistochemical detection of the tracer proteins horseradish peroxidase (HRP) or wheatgerm agglutinin (WGA). Two sets of four rats received 0.2 or 0.4 μl of eithertracer injected into the dorsomedial medulla oblongata, were fixed by perfusion 48 hours later, and were processed for immunohistochemical detection of the tracers. Rats receiving HRP showed only a few single neurons retrogradely labelled in the ipsilateral bed nucleus, and some anterogradely labelled fibers. Rats receiving WGA showed a large number of retrogradely labelled neurons in the ipsilateral bed nucleus. Labelled neurons were most concentrated in a group in the central, dorsal, and lateral aspects of the nucleus at the level of the anterior commissure and just caudal to this. Just ventral to this group was a dense cluster of anterogradely labelled fibers. The retrogradely labelled neurons ranged from 12 to 20 μm in size and were multipolar. These findings indicate that there are direct reciprocal connections between the bed nucleus of the stria terminalis and the autonomic centers of the dorsomedial medulla oblongata and strengthen the concept that this nucleus is involved in forebrain integration of autonomic functions.     

An HRP study of the afferent connections to rat lateral hypothalamic region

Afferent connections to the lateral hypothalamic region in the rat were studied using horseradish peroxidase (HRP). HRP was injected iontophoretically by a parapharyngeal approach. After HRP injections into the lateral hypothalamic area, labeled cells were found mainly in the medial prefrontal and infralimbic cortices, lateral and dorsal septal nuclei, nucleus accumbens, bed nucleus of the stria terminalis, medial and lateral amygdaloid nuclei, lateral habenular nucleus, peripeduncular nucleus, ventral tegmental area, mesencephalic and pontine central gray, ventral nucleus of the lateral lemniscus, lateral parabrachial area, raphe nuclei and the nucleus locus coeruleus. Labeled cells following HRP injections into the lateral preoptic area were found mainly in the lateral and dorsal septal nuclei, nucleus accumbens, diagonal band, ventral part of the globus pallidus, bed nucleus of the stria terminalis, central amygdaloid nucleus, mesencephalic and pontine central gray, dorsal raphe nucleus, parabrachial area and the nucleus locus coeruleus. The intrahypothalamic connections were also discussed.     

Efferents from medial basal forebrain and hypothalamus in the rat. II. An autoradiographic study of the anterior hypothalamus.

Using tritiated amino acid autoradiography, the efferent projections of the anterior hypothalamic area (AHA) were studied in albino rats. Axons from AHA neurons were not confined to local projections in the hypothalamus. Ascending AHA axons ran through the preoptic region, joined the diagonal band and distributed in the lateral septum. Descending AHA efferents within the hypothalamus coursed in a bundle ventromedial to the fornix. Projections were observed to the dorsomedial, ventromedial, arcuate and dorsal premammillary nuclei, and to the median eminence. Sweeping dorsomedially in the posterior hypothalamus, some AHA axons distributed in the central grey. AHA axons staying ventral projected to the supramammillary region, ventral tegmental area, raphe nuclei and midbrain reticular formation. Other AHA efferents distributed to the periventricular thalamus, to the medial amygdala via the stria terminalis or supraoptic commissure, and to the lateral habenula through the stria medullaris. For comparison with the AHA, efferent projections from the paraventricular nucleus (PVN) and from the ventromedial nucleus and adjacent basal hypothalamus (VMR) were studied. Projections from PVN neurons were not restricted to the median eminence and neurohypophysis. PVN efferents also distributed to many of the same regions as did those of the AHA but had somewhat different fiber trajectories and longer descending projections. VMR efferents were more widespread than those of the AHA, with projections extending into the lateral zona incerta and pontine reticular formation. Projections from the AHA were distinct from those of the medial preoptic area (mPOA). For example, while AHA axons descended in a bundle ventromedial to the fornix, mPOA axons ran in the medial forebrain bundle. Such anatomical differences may underlie experimentally demonstrated functional differences between the mPOA and AHA, for instance, in mediation of male and female sex behaviors.     

Anatomical identification of neurons in selected brain regions associated with maternal behavior deficits induced by knife cuts of the lateral hypothalamus in rats

The present experiment identified neurons associated with maternal behavior deficits induced by damage to the lateral hypothalamus (LH) in rats. Fully maternal lactating rats received bilateral coronal knife cuts through either the dorsal or ventral LH at the level of the ventromedial nucleus. The blade of the wire knife used to make the cuts was coated with horseradish peroxidase (HRP). The maternal behavior of all females was studied for 4 days postoperatively and then the brains were processed for the localization of neurons retrogradely filled with HRP. The analysis focused on those brain regions thought to be important for maternal behavior. The dorsal LH cuts severely disrupted maternal behavior while the ventral LH cuts did not. The ventral cuts labeled more medial preoptic area (MPOA) and septal-diagonal band neurons with HRP than did the dorsal cuts. The dorsal LH cuts labeled more neurons with HRP in the lateral preoptic area (LPOA), magnocellular preoptic area, bed nucleus of the stria terminalis, ventral tegmental area (VTA), substantia nigra, and central gray than did the ventral cuts. Previous research has suggested that the lateral efferents of the MPOA interact with the VTA in the control of maternal behavior. The results of the present experiment suggest that MPOA axons which descend directly to the brainstem via the ventral LH are not essential for maternal behavior. Our results are consistent with the view that an MPOA-to-LPOA-to-VTA circuit may be important for maternal behavior.     

Anatomical evidence of direct projections from the nucleus of the solitary tract to the hypothalamus, amygdala, and other forebrain structures in the rat

Ascending projections from the caudal (general-visceroceptive) part of the nucleus of the solitary tract (NTS) were studied experimentally in the rat by the aid of the anterograde autoradiographic and the retrograde horseradish peroxidase (HRP) tracer techniques. Microelectrophoretic deposits of tritiated proline and leucine which involved the caudal part of the NTS, the dorsal motor nucleus of the vagus (dmX), and portions of the hypoglossal nucleus, nucleus intercalatus and/or nucleus gracilis were found to label ascending fibers that, besides going to numerous brain stem territories that included prominently the parabrachial area, could also be traced to serveral forebrain structures, namely, the bed nucleus of the stria terminalis (BST), the paraventricular (PA), dorsomedial (HDM) and arcuate (ARC) nuclei of the hypothalamus, the central nucleus of the amygdaloid complex (AC), the medial preoptic area (PM) and the periventricular nucleus of the thalamus (TPV). Smaller isotope injections almost completely confined to the NTS and dmX resulted in lighter labeling of a similar set of parabrachial and forebrain projections, whereas in another case, in which the deposit was almost exclusively limited to the nucleus gracilis, no label was seen in the aforementioned structures. In another series of experiments, aimed at further localizing the neurons of origin of the prosencephalic projections under consideration, small microelectrophoretic HRP injections confined almost totally to BST, PA, HDM, AC, PM or TPV, as well as both small and large injections involving ARC, resulted in labeled neurons situated in the dorsal medullary region, mainly in the medial portion of the NTS at the level of and caudal to the area postrema. Taken together, these observations indicate for the first time the existence of relatively direct conduction lines by which interoceptive information might be conveyed to limbic forebrain structures; some of the possible physiological correlates of these anatomical findings are discussed.