Afferent projections related to attack sites in the pontine tegmentum

Attack by a cat on a rat was elicited by electrical stimulation of the ventral parabrachial nucleus or the paralemniscal pontine reticular formation. The attack was quiet and it differed from similar behavior elicited at other sites in that the cat not only bit the rat but struck it with its paw.Horseradish peroxidase was deposited at the attack sites. Cells sending projections to the attack sites were located in gyrus proreus, anterior, central, and medial amygdala, the bed nucleus of the stria terminalis, lateral, dorsal and perifornical hypothalamus, as well as the central gray matter, superior colliculus, midbrain reticular formation, locus coeruleus, nucleus of the lateral lemniscus, and nucleus interpositus. Additional sites of cells of origin appeared with less regularity. This distribution of sites correlates well with the sites from which attack can be elicited or modulated.     

Afferent projections to affective attack sites in cat hypothalamus

Quiet biting attack by a cat on a rat was elicited by electrical stimulation of sites in the cat's lateral hypothalamus.Horseradish peroxidase was deposited at the attack sites. Cells containing reaction products were found in gyrus proreus, anterior and central medial amygdaloid nuclei, lateral and medial preoptic areas, substantia innominata, the bed nuclei of stria terminalis, and anterior commissure. The dorsomedial area of the hypothalamus, paraventricular nucleus, suprammamillary region, and posterior hypothalamic area also contained reactive cells. In the midbrain the ventral tegmental area of Tsai, the dorsal and superior central nuclei of the raphe, central gray matter and interpeduncular nucleus were regions with reactive cells. In the pontine region, the locus coeruleus, parabrachial nuclei, nucleus of the lateral lemniscus, and the dorsal tegmental nucleus of Gudden all had reactive cells.There are many structures which send afferent projections to quiet attack sites located in the hypothalamus and the pontine tegmentum. The commonality of afferents to attack sites lends credence to the notion that a complex, distributed, interactive network underlies the neural basis of attack behavior.     

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.     

CNS cell groups projecting to pancreatic parasympathetic preganglionic neurons

The CNS cell groups that project to the pancreatic parasympathetic preganglionic neurons were identified by the viral retrograde transneuronal labeling method. Pseudorabies virus (PRV) was injected into the pancreas of C8 spinal rats and after 6 days survival, the animals were perfused and their brains processed for immunohistochemical detection of PRV. Parasympathetic preganglionic neurons of the dorsal vagal nucleus were retrogradely labeled with PRV. Several CNS cell groups consistently contained transneuronally labeled neurons. In the medulla oblongata, labeled neurons were found in the nucleus tractus solitarius, area postrema, paratrigeminal nucleus, lateral paragigantocellular reticular nucleus, raphe pallidus and obscurus nuclei, C3 region and scattered cells in the ventral medullary reticular formation. In the pons, the A5 cell group, Barrington's nucleus and the subcoeruleus region contained labeled neurons. Only an occasional labeled cell was identified in the parabrachial nucleus. In the midbrain, almost no labeling was found except for an occasional neuron in the central gray matter. In the diencephalon, labeling was found in the paraventricular hypothalamic nucleus (PVN) as well as in the lateral hypothalamic nucleus at two levels (one at the level of the PVN and the other at the level of the subthalamic nucleus). in addition, the perifornical and dorsal hypothalamic nuclei contained labeled neurons. A few cells were found in the peripheral part of the dorsomedial hypothalamic nucleus. No labeling was seen in the ventromedial hypothalamic nucleus. In the telencephalon, the central amygdaloid nucleus and the bed nucleus of the stria terminalis were labeled.     

Localization of preproenkephalin mRNA in the rat brain and spinal cord by in situ hybridization

To determine the localization in rat brain and spinal cord of individual neurons that contain the messenger RNA coding for the opioid peptide precursor preproenkephalin, we performed in situ hybridization with a tritiated cDNA probe complementary to a protion of preproenkephalin mRNA. We observed autoradiographic signal over the cytoplasm of neurons of many regions of the central nervous system. Several types of controls indicated specificity of the labeling. Neurons containing preproenkephalin mRNA were found in the piriform cortex, ventral tenia tecta, several regions of the neocortex, nucleus accumbens, olfactory tubercle, caudate-putamen, lateral septum, bed nucleus of the stria terminalis, diagonal band of Broca, preoptic area, amygdala (especially central nucleus, with fewer labeled neurons in all other nuclei), hippocampal formation, anterior hypothalamic nucleus, perifornical region, lateral hypothalamus, paraventricular nucleus, dorsomedial and ventromedial hypothalamic nuclei, arcuate nucleus, dorsal and ventral premamillary nuclei, medial mamillary nucleus, lateral geniculate nucleus, zona incerta, periaqueductal gray, midbrain reticular formation, ventral tegmental area of Tsai, inferior colliculus, dorsal and ventral tegmental nuclei of Gudden, dorsal and ventral parabrachial nuclei, pontine and medullary reticular formation, several portions of the raphe nuclei, nucleus of the solitary tract, nucleus of the spinal trigeminal tract (especially substantia gelatinosa), ventral and dorsal cochlear nuclei, medial and spinal vestibular nuclei, cuneate and external cuneate nuclei, gracile nucleus, superior olive, nucleus of the trapezoid body, some deep cerebellar nuclei, Golgi neurons in the cerebellum, and most laminae of the spinal cord. In most of these brain regions, the present results indicate that many more neurons contain preproenkephalin mRNA than have been appreciated previously on the basis of immunocytochemistry.     

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.     

Afferent projections to the cholinergic pedunculopontine tegmental nucleus and adjacent midbrain extrapyramidal area in the albino rat. I. Retrograde tracing studies.

The afferent connections of the pedunculopontine tegmental nucleus (PPT) and the adjacent midbrain extrapyramidal area (MEA) were examined by retrograde tracing with wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Major afferents to the PPT originate in the periaqueductal gray, central tegmental field, lateral hypothalamic area, dorsal raphe nucleus, superior colliculus, and pontine and medullary reticular fields. Other putative inputs originate in the paraventricular and preoptic hypothalamic nuclei, the zona incerta, nucleus of the solitary tract, central superior raphe nucleus, substantia innominata, posterior hypothalamic area, and thalamic parafascicular nucleus. The major afferent to the medially adjacent MEA originates in the lateral habenula, while other putative afferents include the perifornical and lateral hypothalamic area, periaqueductal gray, superior colliculus, pontine reticular formation, and dorsal raphe nucleus. MEA inputs from basal ganglia nuclei include moderate projections from the substantia nigra pars reticulata, entopeduncular nucleus, and a small projection from the globus pallidus, but not the subthalamic nucleus. Dense anterograde labeling was observed in the substantia nigra pars compacta, entopeduncular nucleus, subthalamic nucleus, globus pallidus, and caudate-putamen only following WGA-HRP injections involving the MEA. The results of this study demonstrate that the PPT and MEA share many potential afferents. Remarkable differences were found that support distinguishing between these two nuclei in future studies regarding the functional organization of the midbrain and pons. The results, for example, confirm our previous observations that the largely reciprocal connections between the midbrain and basal ganglia distinguish the MEA from the PPT. Afferents from the lateral habenula and contralateral superior colliculus represent extensions of more traditional basal ganglion circuitry which further delineate the MEA from the PPT. The results are discussed with respect to the important role of the midbrain and pons in behavioral state control and locomotor mechanisms.     

Direct projections to the pretectum and the midbrain reticular formation from auditory relay nuclei in the lower brainstem of the cat

Direct projections to the pretectum and the midbrain reticular formation from auditory relay nuclei in the lower brainstem were examined by the retrograde and anterograde tracer methods in the cat. After horseradish peroxidase (HRP) injection into the pretectomesencephalic reticular region (Pt-MRF), which includes caudoventral regions of the pretectum and rostrodorsal regions of the midbrain reticular formation, labeled neurons were seen in the dorsal nucleus of the lateral lemniscus (DLL), the pericentral (PC) and external (EN) nuclei of the inferior colliculus (IC), the rostral process of IC (RP) and the nucleus of the brachium of IC (NB); no labeled neurons were found in the main laminated portion of the central nucleus of IC. Subsequently, tritiated leucine was injected into DLL, EN, RP or NB for autoradiographic fiber tracing. After injection into DLL or EN, terminal labeling was confined to the ventral portions of the anterior pretectal nucleus. After injection into RP or NB, heavy terminal labeling was observed in the midbrain reticular formation, extending dorsally into the anterior pretectal nucleus. Thus, 3 sectors are distinguishable in Pt-MRF in terms of termination of fibers from the midbrain auditory relay nuclei; the dorsomedial, intermediate or ventrolateral Pt-MRF sector receives fibers arising from DLL, RP or NB, respectively. Fibers from EN terminate only in the dorsal portion (pretectal regions) of the intermediate sector.     

Subcortical projections to the centromedian and parafascicular thalamic nuclei in the cat

The primary objective of this study is to identify the totality of input to the centromedian and parafascicular (CM-Pf) thalamic nuclear complex. The subcortical projections upon the CM-Pf complex were studied in the cat with three different retrograde tracers. The tracers used were unconjugated horseradish peroxidase (HRP), horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP), and rhodamine-labeled fluorescent latex microspheres (RFM). Numerous subcortical structures or substructures contained labeled neurons with all three tracing techniques. These labeled structures included the central nucleus of the amygdala; the entopeduncular nucleus; the globus pallidus; the reticular and ventral lateral geniculate nuclei of the thalamus; parts of the hypothalamus including the dorsal, lateral, and posterior hypothalamic areas and the ventromedial and parvicellular nuclei; the zona incerta and fields of Forel; parts of the substantia nigra including the pars reticularis and pars lateralis, and the retrorubral area; the pretectum; the intermediate and deep layers of the superior colliculus; the periaqueductal gray; the dorsal nucleus of the raphe; portions of the reticular formation, including the mesencephalic, pontis oralis, pontis caudalis, gigantocellularis, ventralis, and lateralis reticular nuclei; the nucleus cuneiformis; the marginal nucleus of the brachium conjunctivum; the locus coeruleus; portions of the trigeminal complex, including the principal sensory and spinal nuclei; portions of the vestibular complex, including the lateral division of the superior nucleus and the medial nucleus; deep cerebellar nuclei, including the medial and lateral cerebellar nuclei; and lamina VII of the cervical spinal cord. Moreover, the WGA-HRP and rhodamine methods (known to be more sensitive than the HRP method) revealed several afferent sources not shown by HRP: the anterior hypothalamic area, ventral tegmental area, lateral division of the superior vestibular nucleus, nucleus interpositus, and the nucleus praepositus hypoglossi. Also, the rhodamine method revealed labeled neurons in laminae V and VI of the cervical spinal cord.     

Projections to the caudolateral medulla from the pons,midbrain, and diencephalon in the cat

Previous research implicated neurons in the caudolateral medulla in the expression of estrous behaviors triggered by genital stimulation in the female cat. The present study identified descending pathways through which the activity of neurons in estrogen-concentrating cellular regions of the diencephalon and anterior brain stem could be transmitted to caudolateral medullary neurons. Cats received medullary injections of 50% horseradish peroxidase (HRP) in or around nucleus ambiguus. After 1 to 3 days, retrograde transport of HRP was demonstrated using tetramethyl benzidine as a chromogen. In the pons, labeled cells were most numerous in the ipsilateral parabrachial nuclei, the Kölliker-Fuse nucleus, and lateral tegmental field. In the midbrain, the central gray contained many labeled neurons bilaterally, especially at trochlear and caudal oculomotor nuclear levels. Labeled cells were also found in the midbrain reticular formation bilaterally and in the contralateral deep tectum and red nucleus. In the diencephalon, some labeled neurons were in lateral and periventricular hypothalamic regions, usually posteriorly, and many paraventricular nucleus neurons were labeled. The existence of central gray and deep tectal projections to the lateral medulla was also verified electrophysiologically by antidromic invasion. The substantial projection from the central gray to the caudolateral medulla provides a potential route for the activity of estrogen-concentrating neurons to be transmitted to cells involved in genitally triggered estrous responses because some central gray cells bind estrogen and the central gray also receives strong projections from hypothalamic estrogen-concentrating neuronal regions.     

Subcortical afferents to the hippocampal formation in the monkey

The distribution of neurons in the basal telencephalon, the diencephalon, and the brainstem that project to the hippocampal formation has been analyzed in mature cynomolgus monkeys (Macaca fascicularis) by the injection of horseradish peroxidase into different rostro-caudal levels of the hippocampal formation. After injections which involve Ammon's horn, the dentate gyrus, and the subicular complex, retrogradely labeled neurons are found in the following regions: in the amygdala (specifically in the anterior amygdaloid area, the basolateral nucleus, and the periamygdaloid cortex); in the medial septal nucleus and the nucleus of the diagonal band; in the ventral part of the claustrum; in the substantia innominata and the basal nucleus of Meynert; in the rostral thalamus (specifically in the anterior nuclear complex, the laterodorsal nucleus, the paraventricular and parataenial nuclei, the nucleus reuniens, and the nucleus centralis medialis); in the lateral preoptic and lateral hypothalamic areas, and especially in the supramammillary and retromammillary regions; in the ventral tegmental area, the tegmental reticular fields, the raphé nuclei (specifically in nucleus centralis superior and the dorsal raphé nucleus), in the nucleus reticularis tegmenti pontis, the central gray, the dorsal tegmental nucleus, and in the locus coeruleus.     

Mesencephalic and diencephalic afferents to the superior colliculus and periaqueductal gray substance demonstrated by retrograde axonal transport of horseradish peroxidase in the cat

The mesencephalic and diencephalic afferent connections to the superior colliculus and the central gray substance in the cat were examined by means of the retrograde transport of horseradish peroxidase (HRP). After deep collicular injections numerous labeled cells were consistently found in the parabigeminal nucleus, the mesencephalic reticular formation, substantia nigra pars reticulata, the nucleus of posterior commissure, the pretectal area, zona incerta, and the ventral nucleus of the lateral geniculate body. A smaller number of cells was found in the inferior colluculus, the nucleus of the lateral lemniscus, the central gray substance, nucleus reticularis thalami, the anterior hypothalamic area, and, in some cases, in the contralateral superior colliculus, Forel's field, and the ventromedial hypothalamic nucleus. Only the parabigeminal nucleus and the pretectal area showed labeled cells following injections in the superficial layers of the superior colliculus. In the cats submitted to injections in the central gray substance, labeled cells were consistently found in the contralateral superior colliculus, the mesencephalic reticular formation, substantia nigra parts reticulata, zona incerta and various hypothalamic areas, especially the ventromedial nucleus. In some cases, HRP-positive cells were seen in the nucleus of posterior commissure, the pretectal area, Forel's field, and nucleus reticularis thalami. A large injection in the mediodorsal part of the caudal mesencephalic reticular formation, which included the superior colliculus and the central gray substance, resulted in numerous labeled cells in nucleus reticularis thalami. The findings are discussed with respect to the suggested functional division of the superior colliculus into deep and superficial layers. Furthermore, the possible implications of labeled cells in zona incerta and the reticular thalamic nucleus are briefly discussed.     

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.     

A PHA-L analysis of ascending projections of the dorsal raphe nucleus in the rat.

Ascending projections from the dorsal raphe nucleus (DR) were examined in the rat by using the anterograde anatomical tracer, Phaseolus vulgaris leucoagglutinin (PHA-L). The majority of labeled fibers from the DR ascended through the forebrain within the medial forebrain bundle. DR fibers were found to terminate heavily in several subcortical as well as cortical sites. The following subcortical nuclei receive dense projections from the DR: ventral regions of the midbrain central gray including the 'supraoculomotor central gray' region, the ventral tegmental area, the substantia nigra-pars compacta, midline and intralaminar nuclei of the thalamus including the posterior paraventricular, the parafascicular, reuniens, rhomboid, intermediodorsal/mediodorsal, and central medial thalamic nuclei, the central, lateral and basolateral nuclei of the amygdala, posteromedial regions of the striatum, the bed nucleus of the stria terminalis, the lateral septal nucleus, the lateral preoptic area, the substantia innominata, the magnocellular preoptic nucleus, the endopiriform nucleus, and the ventral pallidum. The following subcortical nuclei receive moderately dense projections from the DR: the median raphe nucleus, the midbrain reticular formation, the cuneiform/pedunculopontine tegmental area, the retrorubral nucleus, the supramammillary nucleus, the lateral hypothalamus, the paracentral and central lateral intralaminar nuclei of the thalamus, the globus pallidus, the medial preoptic area, the vertical and horizontal limbs of the diagonal band nuclei, the claustrum, the nucleus accumbens, and the olfactory tubercle. The piriform, insular and frontal cortices receive dense projections from the DR; the occipital, entorhinal, perirhinal, frontal orbital, anterior cingulate, and infralimbic cortices, as well as the hippocampal formation, receive moderately dense projections from the DR. Some notable differences were observed in projections from the caudal DR and the rostral DR. For example, the hippocampal formation receives moderately dense projections from the caudal DR and essentially none from the rostral DR. On the other hand, virtually all neocortical regions receive significantly denser projections from the rostral than from the caudal DR. The present results demonstrate that dorsal raphe fibers project significantly throughout widespread regions of the midbrain and forebrain.     

Efferent projections of the infralimbic (area 25) region of the medial prefrontal cortex in the rat: an anterograde tracer PHA-L study

The efferent projections of the infralimbic region (IL) of the medial prefrontal cortex of the rat were examined by using the anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L). Major targets of the IL were found to include the agranular insular cortex, olfactory tubercle, perirhinal cortex, the whole amygdaloid complex, caudate putamen, accumbens nucleus, bed nucleus of the stria terminalis, midline thalamic nuclei, the lateral preoptic nucleus, paraventricular nucleus, supramammillary nucleus, medial mammillary nucleus, dorsal and posterior areas of the hypothalamus, ventral tegmental area, central gray, interpeduncular nucleus, dorsal raphe, lateral parabrachial nucleus and locus coeruleus. Previously unreported projections of the IL to the anterior olfactory nucleus, piriform cortex, anterior hypothalamic area and lateroanterior hypothalamic nucleus were observed. The density of labeled terminals was especially high in the agranular insular cortex, olfactory tubercle, medial division of the mediodorsal nucleus of the thalamus, dorsal hypothalamic area and the lateral division of the central amygdaloid nucleus. Several physiological and pharmacological studies have suggested that the IL functions as the 'visceral motor' cortex, involved in autonomic integration with behavioral and emotional events. The present investigation is the first comprehensive study of the IL efferent projections to support this concept.     

Projections from the rhomboid nucleus of the bed nuclei of the stria terminalis: implications for cerebral hemisphere regulation of ingestive behaviors

The basic organization of an exceptionally complex pattern of axonal projections from one distinct cell group of the bed nuclei of the stria terminalis, the rhomboid nucleus (BSTrh), was analyzed with the PHAL anterograde tract-tracing method in rats. Brain areas that receive a strong to moderate input from the BSTrh fall into nine general categories: central autonomic control network (central amygdalar nucleus, descending hypothalamic paraventricular nucleus, parasubthalamic nucleus and dorsal lateral hypothalamic area, ventrolateral periaqueductal gray, lateral parabrachial nucleus and caudal nucleus of the solitary tract, dorsal motor nucleus of the vagus nerve, and salivatory nuclei), gustatory system (rostral nucleus of the solitary tract and medial parabrachial nucleus), neuroendocrine system (periventricular and paraventricular hypothalamic nuclei, hypothalamic visceromotor pattern generator network), orofaciopharyngeal motor control (rostral tip of the dorsal nucleus ambiguus, parvicellular reticular nucleus, retrorubral area, and lateral mesencephalic reticular nucleus), respiratory control (lateral nucleus of the solitary tract), locomotor or exploratory behavior control and reward prediction (nucleus accumbens, substantia innominata, and ventral tegmental area), ingestive behavior control (descending paraventricular nucleus and dorsal lateral hypothalamic area), thalamocortical feedback loops (medial-midline-intralaminar thalamus), and behavioral state control (dorsal raphé and locus coeruleus). Its pattern of axonal projections and its position in the basal telencephalon suggest that the BSTrh is part of a striatopallidal differentiation involved in modulating the expression of ingestive behaviors, although it may have other functions as well.     

Hypothalamic,other diencephalic,and telencephalic neurons that project to the dorsal midbrain

Neurons in the hypothalamus, other diencephalic regions, and the telencephalon which project to the mesencephalic central gray (CG) and the region lateral to it were demonstrated, in the rat, by the horseradish peroxidase retrograde neuroanatomical tracing method with diaminobenzidine and tetramethyl benzidine visualization reactions. The greatest concentrations of neurons that project to the dorsal mesencephalon were found in the ventromedial nucleus, particularly the anterior and ventrolateral subdivisions, in the dorsal premammillary nucleus, and in the zona incerta. Neurons that project to or lateral to the CG were also found in the laterocaudal hypothalamus, the dorsomedial hypothalamus, regions of the anterior hypothalamic area, specific areas of the cerebral cortex (32, 29, 8, 8A, 13, 14), and the central nucleus of the amygdala. Some neurons that project were also found in the preoptic area, septum, bed nucleus of the stria terminals, and the habenula. More neurons in the mediocaudal quadrant of the hypothalamus project to the mesencephalon than do those in laterocaudal, mediorostral, or laterorostral quadrants. More neurons in the medial than the lateral half, and more in the caudal than the rostral half of the hypothalamus project to the mesencephalon. More neurons project to the central gray, or the region lateral to it, at the inferior colliculus. These descending connections to the midbrain, particularly from the hypothalamus and zona incerta, are probably components of neural networks that regulate nociception, certain neuroendocrine functions, sexual and other behaviors, and certain autonomic functions.     

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.     

Connections of the lobus inferior hypothalami of the clearnose skate Raja eglanteria (Chondrichthyes)

The afferent and efferent connections of the lobus inferior hypothalami of the clearnose skate were demonstrated by the anterograde and retrograde transport of horseradish peroxidase. The main source of afferents is from the midbrain tegmentum and telencephalon. The major midbrain input is from cells of the ipsilateral nucleus tegmentalis lateralis and the caudal tegmental area. Another prominent, mostly ipsilateral, projection arises from nucleus F of the isthmic region. A few labeled cells also occur in the nucleus interpeduncularis, nucleus raphes superior, and lateral reticular formation. Afferents from the telencephalon arise from cells of the area preoptica, area superficialis basalis, striatum, nucleus septalis lateralis, and area subpallialis 1. Of the pallial structures, the pallium mediale and anterior as well as posterior subdivisions of the pallium dorsale pars centralis appear to have strong projections to the inferior lobe. Efferent connections of the inferior lobe consist of ascending and descending pathways. Fibers of the main ascending efferent pathway course within the basal forebrain bundle and distribute to subpallial areas. The descending efferent pathways course within the tractus lobobulbaris and tractus lobocerebellaris. Of these, the former is traceable to the level of the facial motor nucleus, issuing fibers enroute to the midbrain tegmentum and to the lateral reticular formation. The lobocerebellar tract courses dorsolateral to the lobobulbar tract, and its fibers terminate within the ipsilateral granular ridge of the rostral pole of the cerebellar corpus. There appears to be a topological organization of the inferior lobe connections. In general, pallial areas project mainly to the lateral subdivision of the inferior lobe nucleus at midlobic levels, whereas connections with the brainstem arise from or terminate within the dorsal and intermediate subdivisions at midlobic as well as caudal levels. The widespread ascending and descending connections indicate that the hypothalamic inferior lobe of the clearnose skate is a major relay center between the telencephalon and brainstem.     

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.