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.     

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.     

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.     

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.     

Distribution of neuropeptide Y-like immunoreactivity in the hypothalamus of the adult golden hamster

The distribution of neuropeptide Y (NPY)-like immunoreactivity within the hypothalamus of the adult golden hamster was investigated with conventional immunohistochemical techniques. Neuropeptide Y immunoreactive cell bodies were found in greatest numbers in the arcuate nucleus while a few stained perikarya were seen in the internal and subependymal zones of the median eminence. Isolated perikarya were observed in the anterior commissure and supracommissural portion of the interstitial nucleus of the stria terminalis. Immunoreactive axons were located throughout the hypothalamus with the highest concentrations in the subependymal and internal zones of the median eminence, the interstitial nucleus of the stria terminalis, the medial preoptic area, and in the following nuclei: periventricular, suprachiasmatic, paraventricular, perifornical, median preoptic, and arcuate. Moderate to dense plexuses of immunoreactive fibers were observed in the anterior, lateral, and posterior hypothalamic areas and in the infundibular stalk. The supraoptic nucleus and lateral preoptic area displayed a small number of labeled axons whereas the ventromedial nucleus contained only a few fibers. NPY immunoreactive fibers were present in the optic tract and in the dorsomedial aspect of the optic chiasm. Labeled fibers penetrated the ependymal lining of the third ventricle throughout the ventral aspect of the periventricular zone. Additional fibers were observed in the pia lining the ventral aspect of the hypothalamus. This systematic analysis of hypothalamic NPY immunoreactivity in the adult golden hamster suggests that a portion of the labeled fibers display a distribution that is similar to previously described noradrenergic fibers in the hypothalamus.     

An autoradiographic study of projections ascending from the midbrain central gray, and from the region lateral to it, in the rat

Ascending projections from the midbrain central gray (CG) and from the region lateral to it were traced in the rat using tritiated amino acid autoradiography. Leucine or a cocktail of amino acids (leucine, proline, lysine, histidine, and tyrosine) were used as tracers. In addition to projections within the midbrain, ascending fibers follow three trajectories. The ventral projection passes through the ventral tegmental region of Tsai and the medial forebrain bundle to reach the hypothalamus, preoptic area, caudoputamen, substantia innominata, stria terminalis, and amygdala. There are labeled fibers in the diagonal bands of Broca and medial septum, and terminal labeling in the lateral septum, nucleus accumbens, olfactory tubercle, and frontal cortex. The dorsal periventricular projection terminates in the midline and intralaminar thalamic nuclei. The ventral periventricular projection follows the ventral component of the third ventricle into the hypothalamus, passing primarily through the dorsal hypothalamic area and labeling the rostral hypothalamus and preoptic area. Projections from the region lateral to the CG are similar, but exhibit stronger proximal, and weaker distal, projections. Rostral levels of the CG send heavier projections to the fields of Forel and the zona incerta, but fewer fibers through the supraoptic decussation, than do caudal levels. Ascending projections from the CG are both strong and widespread. Strong projections to the limbic system and the intralaminar thalamic nuclei provide an anatomical substrate for CG involvement in nociception and affective responses.     

Forebrain afferents to the cat posterior hypothalamus: a double labeling study

Using a double immunostaining technique with cholera toxin (CT) as a retrograde tracer, we examined the cells of origin and the histochemical nature of afferents to the cat posterior hypothalamus. After injection in the tuberomamillary nucleus, a number of CT-labeled cells were observed in: medial preoptic area, nuclei of the septum and the stria terminalis, amygdaloid complex, anterior hypothalamic, ventromedial hypothalamic and premamillary nuclei. CT injections in the lateral hypothalamic area gave an additional heavy labeling of neurons in: lateral preoptic area, nuclei of the diagonal band of Broca, substantia innominata, and nucleus accumbens. The posterior hypothalamus receives: 1) cholinergic inputs from the septum, the lateral preoptic area and the nuclei of the diagonal band of Broca; 2) dopaminergic afferents from A11, A13, and A14 groups; 3) histaminergic afferents from the posterior hypothalamus; and 4) peptidergic afferents such as methionin-enkephalin, galanin and neurotensin, substance P and corticotropin-releasing factor from the medial preoptic area, the nucleus of the stria terminalis and/or the posterior hypothalamic structures.     

The efferent projections of the subfornical organ of the rat: A circumventricular organ within a neural network subserving water balance

The efferent projections of the subfornical organ (SFO) of rats were traced using the autoradiographic method of following anterograde transport of labelled proteins through axons.The efferents of the SFO go to two different areas. The first is the anteroventral third ventricular area of the preoptic region and the second is the hypothalamus particularly the neurosecretory, magnocellular nuclei. Specifically, the apparent terminal fields in the first area are in the nucleus medianus of the medial preoptic area (NM), the organum vasculosm of the lamina terminalis (OVLT), and the anterior periventricular area (PeV). Many efferent fibers to this area emerge from the rostral SFO, pass anteriorly over the anterior commissure in the midline and either descend along the anterior border of the NM or enter the PeV dorsally just beneath the anterior commissure. The apparent terminal fields within the hypothalamus are in the anterior and tuberal supraoptic nuclei (SON_a and SON_t), the paraventricular nucleus (PVN) including its rostral accessory cluster, the nucleus circularis (NC), the dorsal perifornical area (PFd), and in both the lateral preoptic area and lateral hypothalamus adjacent to the SON. Many efferent fibers to the hypothalamus emerge from the rostral SFO and enter the columns of the fornix, diverge with the ventral stria medullari to disperse medially and laterally over the columns of the fornix and along their dorsal border at the anterior dorsal level of the columns trajectory through the hypothalamus.These findings are discussed in terms of the SFO's role within a neural network mediating water balance behaviorally and physiologically.     

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.     

Distribution of galaninlike immunoreactivity in the rat central nervous system

The localization of galanin (GAL) immunoreactive (IR) neuronal structures in the rat central nervous system has been investigated by using the indirect immunofluorescence technique. GAL-IR structures were seen in high concentrations in the hypothalamus, medulla oblongata, and spinal cord. Less extensive systems were detected in the telencephalon, thalamus, mesencephalon, and pons, while virtually no GAL-positive structures were seen in the olfactory bulb and cerebellum. Major populations of cell bodies staining for GAL-like material were seen in many areas. In the telencephalon somata were revealed in the bed nucleus of stria terminalis, in the nucleus of the diagonal band, medial septum, and in the medial aspects of the central amygdaloid nucleus, and in small numbers in cortical areas. The anterodorsal and periventricular nuclei of the thalamus contained positive cell bodies. In the hypothalamus GAL-IR somata were seen in the medial and lateral preoptic nuclei, arcuate nucleus, periventricular nucleus, in the dorsomedial nucleus, in the medial forebrain bundle area, in the tubular, caudal, accessory, supraoptic, and paraventricular magnocellular nuclei and lateral to the mammillary recess. The dorsal raphe nucleus hosted a large number of GAL-positive somata. Locus coeruleus of the pons contained a large number of GAL-IR perikarya. In the medulla oblongata positive somata were found in the caudal spinal trigeminal nucleus, the nucleus of the solitary tract, and in the ventral lateral area just rostral to area postrema. Small cell bodies were detected in the superficial layers of the dorsal horn of the spinal cord at all levels and in lamina X at lumbar levels. Analysis of GAL-positive fibers in the telencephalon revealed highly or medium-dense networks in the lateral septal nucleus, in the bed nucleus of stria terminalis, and in the central and medial amygdaloid nuclei. Positive fibers were found in the thalamus in and around the periventricular nucleus as well as in the lateral habenular nucleus and extending in a lateral, caudal direction from the third ventricle and fasciculus retroflexus to the lateral tip of the medial lemniscus. In the hypothalamus the external layer of the median eminence contained a very dense fiber network. Dense or medium-dense GAL-IR networks were detected in the periventricular nucleus, throughout the medial and lateral preoptic areas, in the medial forebrain bundle area, in the dorsomedial nucleus, and lateral to the mammillary recess. In the pons GAL-IR fibers were seen in the parabrachial nuclei, dorsal to the superior olive, and in the periaqueductal central gray.(ABSTRACT TRUNCATED AT 400 WORDS)     

Afferent connections to the lateral hypothalamus: A horseradish peroxidase study in the rat

Horseradish peroxidase, 13% Sigma Type VI, was administered iontophoretically to the mid lateral hypothalamus (LH) of male hooded rats. Animals were perfused intracardially on the following day and brains were removed and sliced in the coronal or sagittal planes into 30–50 μm sections. Sections were processed with DAB and BDH for the brown and blue reaction products and later examined by bright and dark field microscopy for the presence and location of retrogradely labeled neurons. Results indicate that a significant number of afferent connections to the LH originate in the olfactory and accumbens nuclei, pyriform cortex, olfactory tracts, magnocellular and medial preoptic and anterior hypothalamic regions, stria terminalis, stria hypothalamic tract, diagonal tract of Broca, caudate-putamen and globus pallidus, internal capsule, lateral septal nuclei, lateral preoptic area and anterior medial forebrain bundle, the various amygdaloid nuclei, zona incerta, perifornical region, dorsal and ventral medial hypothalamic areas, supraoptic, paraventricular and periventricular nuclei, posterior hypothalamus and medial forebrain bundle, ventral thalamic nuclei, the fields of Forel, arcuate and mammillary nuclei, adjacent to the fasciculus retroflexus, in the ventral tegmental area of Tsai, interpeduncular nucleus, substantia nigra, mesencephalic reticular formation, periaqueductal gray, locus coeruleus and parabrachial region. Results are discussed in terms of previous anatomical and neurophysiological data, probable pathways, and the function of LH neurons.     

Distribution of cholecystokinin-like-immunoreactive neurons in the guinea pig forebrain

The distribution of cholecystokinin (CCK)-immunoreactive nerve fibers and cell bodies was studied in the forebrain of control and colchicine-treated guinea pigs by using an antiserum directed against the carboxyterminus of CCK octapeptide (CCK-8) in the indirect immunoperoxidase technique. Virtually all forebrain areas examined contained immunoreactive nerve fibers. A dense innervation was visualized in; neocortical layers II-III, piriform cortex, the medial amygdala, the medial preoptic area, a circumventricular organ-like structure located at the top of the third ventricle in the preoptic area, the subfornical organ, the posterior bed nucleus of the stria terminalis, the posterior globus pallidus (containing labeled woolly fiber-like profiles), the ventromedial hypothalamus, the median eminence, and the premammillary nucleus. A moderately dense innervation was visualized elsewhere excepted in the septum and thalamus where labeled axons were comparatively few. Immunoreactive perikarya were abundant in: neocortex (especially layers II-III), piriform cortex, amygdala, the median preoptic nucleus, the bed nucleus of the stria terminalis, the hypothalamic paraventricular (parvicellular part), arcuate, and dorsomedial (pars compacta) nuclei, the dorsal and perifornical hypothalamic areas, and throughout the thalamus. Areas also containing a moderate number of labeled cell bodies were the medial preoptic area, the globus pallidus, the caudate-putamen, and the periventromedial area in the hypothalamus. Immunostained perikarya were absent or only occasionally observed in the septum, the suprachiasmatic nucleus, the magnocellular hypothalamoneurohypophyseal nuclei, and the ventral mesencephalon. In the adenohypophysis, corticomelanotrophs were labeled in both males and females, and thyrotrophs were labeled in females only. This distribution pattern of CCK-8 immunoreactivity is compared to those previously recorded in other mammals. This shows that very few features are peculiar to the the guinea pig. It is discussed whether some interspecific differences in immunostaining are real rather than methodological.     

Neurons of origin and fiber trajectory of amygdalofugal projections to the medial preoptic area in Syrian hamsters

The amygdaloid neurons of origin and the trajectory of amygdaloid fibers to the medial preoptic area of the adult male Syrian hamster were identified by using horseradish peroxidase (HRP) histochemistry. After iontophoresis of HRP into the medial preoptic area, retrogradely labeled amygdaloid neurons were located in the dorsal and caudal parts of the medial amygdaloid nucleus and throughout the amygdalohippocampal area. No amygdaloid neurons were labeled after HRP applications confined to the most rostral portion of the medial preoptic area (anterior to the body of the anterior commissure). Following more caudal medial preoptic area injections (body of the anterior commissure to the suprachiasmatic nucleus) the distribution of retrogradely labeled cells in the medial amygdaloid nucleus and the amygdalohippocampal area revealed no topographic organization of the amygdalopreoptic connections. When amygdaloid neurons were labeled, the amygdalohippocampal area contained two to five times as many HRP-filled cells as the medial amygdaloid nucleus. Retrogradely transported HRP could be followed from the medial preoptic area to the amygdala through fibers in the dorsomedial quadrant of the stria terminalis. In addition, electrolytic lesions of the stria terminalis prior to iontophoresis of HRP into the medial preoptic area prevented retrograde transport to neurons in both the dorsocaudal medial amygdaloid nucleus and the amygdalohippocampal area. These results confirm earlier observations describing the location of autoradiographically labeled efferents from the medial amygdaloid nucleus to the medial preoptic area and provide new information about the restricted region within the medial amygdaloid nucleus from which these projections arise. They also suggest that, unlike the projections from the medial amygdaloid nucleus to the bed nucleus of the stria terminalis, the efferents to the medial preoptic area travel entirely in the stria terminalis.     

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.     

Distributions of spinothalamic, spinohypothalamic, and spinotelencephalic fibers revealed by anterograde transport of PHA-L in rats.

Fibers projecting from several levels of the spinal cord to the diencephalon and telencephalon were labeled anterogradely with Phaseolus vulgaris leucoagglutinin injected iontophoretically. Labeled fibers in the thalamus confirmed projections previously observed. In addition, many labeled fibers were seen in the hypothalamus and in telencephalic areas not generally recognized previously as receiving such projections. In the hypothalamus, these areas included the lateral hypothalamus (including the medial forebrain bundle), the posterior hypothalamic area, the dorsal hypothalamic area, the dorsomedial nucleus, the paraventricular nucleus, the periventricular area, the suprachiasmatic nucleus, and the lateral and medial preoptic areas. In the telencephalon, areas with labeled fibers included the ventral pallidum, the globus pallidus, the substantia innominata, the basal nucleus of Meynert, the amygdala (central nucleus), the horizontal and vertical limbs of the diagonal band of Broca, the medial and lateral septal nuclei, the bed nucleus of the stria terminalis, the nucleus accumbens, infralimbic cortex, and medial orbital cortex. These results suggest that somatosensory, possibly including visceral sensory, information is carried directly from the spinal cord to areas in the brain involved in autonomic regulation, motivation, emotion, attention, arousal, learning, memory, and sensory-motor integration. Many of these areas are associated with the limbic system.     

An autoradiographic study of the efferent connections of the ventromedial nucleus of the hypothalamus

Efferent projections from the ventromedial nucleus of the hypothalamus (VMN) were traced using tritiated amino acid autoradiography in albino rats. Ascending fibers passed through the anterior hypothalamus. Labelled fibers and terminal fields were seen in the preoptic area, bed nucleus of the stria terminalis, substantia innominata, the anterior amygdaloid area, diagonal bands of Broca and lateral septum. Fibers also projected laterally from VMN and entered the supraoptic commissures and zona incerta. These lateral projections were responsible for the fibers observed in the cerebral peduncle, the amygdala, the thalamus and the reticular formation. Fibers descending in a medial position projected through the posterior hypothalamus and then swept dorsally to terminate in the mesencephalic and pontine central grey. A projection from VMN into the median eminence was noted. The overall patterns of projection from different parts of VMN were similar; differences that existed were primarily in the relative strengths of the different projections. The efferent projections from VMN are extensive, well organized, and would appear capable of supporting significant physiological actions on extra-hypothalamic structures.     

The efferent projections of the periaqueductal gray in the rat: A Phaseolus vulgaris-leucoagglutinin study. I. Ascending projections

This study has examined the ascending projections of the periaqueductal gray in the rat. Injections of Phaseolus vulgaris-leucoagglutinin were placed in the dorsolateral or ventrolateral subregions, at rostral or caudal sites. From either region, fibers ascended via two bundles. The periventricular bundle ascended in the periaqueductal and periventricular gray matter. At the posterior commissure level, this bundle divided into a dorsal component that terminated in the intralaminar and midline thalamic nuclei, and a ventral component that supplied the hypothalamus. The ventral bundle formed in the deep mesencephalic reticular formation and supplied the ventral tegmental area, substantia nigra pars compacta, and the retrorubral field. The remaining fibers were incorporated into the medial forebrain bundle. These supplied the lateral hypothalamus and forebrain structures, including the preoptic area, the nuclei of the diagonal band, and the lateral division of the bed nucleus of the stria terminalis. The dorsolateral subregion preferentially innervated the centrolateral and paraventricular thalamic nuclei and the anterior hypothalamic area. The ventrolateral subregion preferentially innervated the parafascicular and central medial thalamic nuclei, the lateral hypothalamic area, and the lateral division of the bed nucleus of the stria terminalis. Although the dorsolateral and ventrolateral subregions gave rise to differential projections, the projections from both the rostral and caudal parts of either subregion were similar. This suggests that the dorsolateral and ventrolateral subregions are organized into longitudinal columns that extend throughout the length of the periaqueductal gray. These columns may correspond to those demonstrated in recent physiological studies. © 1995 Willy-Liss, Inc.     

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.     

Differential projections of habenular nuclei

Lesions were made in the lateral and medial habenular nuclei of the cat. Subsequent degeneration of nerve fibers and terminalis was studied using Nauta-Gygax silver technique. The medial and lateral habenular nuclei project differentially to the septum, olfactory, tubercle, thalamus, midbrain tegmentum and tectum. The diffuse part of the habenulopeduncular tract rises from the lateral habenular nucleus and the compact part rises from both nuclei. Degenerating terminals were seen caudally in the following nuclei: interpeduncular, central superior, dorsal raphae, ventral tegmental (from the medial habenular nucleus), dosral tegmental (from the lateral habenular nucleus), pretectal area, superior colliculus and inferior colliculus (from the lateral habenular nucleus). Rostral projections course in the medial part of the stria medullaris from the medial habenular nucleus and in the lateral part of the stria medullaris from the lateral habenular nucleus: Degenerating terminals were seen rostrally in the following nuclei: dorsomedial, anteroventral, anterodorsal, paraventricular, posterior medial septal (from the medial habenular nucleus) and preoptic area (from the lateral habenular nucleus). Projections occur from the medial habenular nucleus to the amygdala via the stria terminalis. The habenular nuclei are considered to be structures of the limbic system which are differentially related to midbrain, thalamic, amygdaloid, septal and preoptic structures via feedback circuits.