Ascending projections of the locus coeruleus in the rat. II. Autoradiographic study.

The ascending projections of the locus coeruleus were studied using an autoradiographic method. The major projection of locus coeruleus neurons ascends in a dorsal pathway traversing the midbrain tegmentum in a position ventrolateral to the periaqueductal gray. At the caudal diencephalon the locus coeruleus axons descend to enter the medial forebrain bundle at a caudal tuberal hypothalamic level. They are jointed in the medial forebrain bundle by a much smaller locus coeruleus projection which takes a ventral course through the midbrain tegmentum and enters the medial forebrain bundle via the mammillary peduncle and ventral tegmental area. Terminal projections are evident in the midbrain to the periaqueductal gray, tegmentum and raphe nuclei. There are widespread projections to the dorsal thalamus. The heaviest of these are to the intralaminar nuclei, the anteroventral and anteromedial nuclei, the dorsal lateral geniculate and the paraventricular nucleus. In the hypothalamus the largest projections are to the lateral hypothalamic area, periventricular nucleus, supraoptic nucleus and paraventricular nucleus. As the locus coeruleus projection ascends in the medial forebrain bundle, fibers leave it to traverse the lateral hypothalamus and zona incerta and enter the internal capsule, the ventral amygdaloid bundle and ansa peduncularis. These appear to terminate in the amygdaloid complex and, via the external capsule, in the lateral and dorsal neocortex. At the level of the septum 4 projections are evident. One group of fibers enters the stria medullaris to terminate in the paraventricular nucleus and habenular nuclei. A second group joins the stria terminalis to terminate in the anygdaloid complex. The third group turns into the diagonal band and medial septum; some fibers terminate in the septal nuclei and others continue into the fornix to termimate in hippocampus. A large component continues around the corpus callosum into the cingulum to terminate in the cingulate and adjacent neocortex, the subiculum and hippocampus. The remaining fibers continue rostrally in the medial forebrain bundle to terminate in olfactory forebrain and frontal neocortex. Commissural projections arise at 4 locations. The first decussation occurs in the dorsal tegmentum just below the central gray rostral to the locus coeruleus. The crossing fibers enter the contralateral dorsal bundle. A second group of fibers leaves the ipsilateral dorsal pathway, crosses in the posterior commissure and enters the contralateral dorsal pathway at the level. The third commissural projection arises more rostrally and crosses in the dorsal supraoptic commissure to enter the contralateral medial forebrain bundle. The fourth commissural projection is through the anterior commissure. The termination of the contralateral projection appears similar to that of the ipsilateral projection.     

Afferent and efferent connections of the cholinoceptive medial pontine reticular formation (region of the ventral tegmental nucleus) in the cat

Following minor concussive brain injury when there is an otherwise general suppression of CNS activity, the ventral tegmental nucleus of Gudden (VTN) demonstrates increased functional activity (32). Electrical or pharmacological activation of a cholinoceptive region in this same general area of the medial pontine tegmentum contributes to certain components of reversible traumatic unconsciousness, including postural atonia (31, 32, 45). Therefore, in an effort to examine the neuroanatomical basis of the behavioral suppression associated with a reversible traumatic unconsciousness, the afferent and efferent connections of the VTN and putative cholinoceptive medial pontine reticular formation (cmPRF) were studied in the cat using the retrograde horseradish peroxidase (HRP), HRP/choline acetyltransferase (ChAT) double-labeling immunohistochemistry, and anterograde HRP and autoradiographic techniques. Based upon retrograde HRP labeling, the principal afferents to the VTN region of the cmPRF originated from the medial and lateral mammillary nuclei, and lateral habenular nucleus, and to a lesser extent from the interpeduncular nucleus, lateral hypothalamus, dorsal tegmental nucleus, superior central nucleus, and contralateral nucleus reticularis pontis caudalis. Other afferents, which were thought to have been labeled through spread of HRP into the medial longitudinal fasciculus (MLF), adjacent paramedian pontine reticular formation, or uptake by transected fibers descending to the inferior olive, included the nucleus of Darkschewitsch, interstitial nucleus of Cajal, zona incerta, prerubral fields of Forel, deep superior colliculus, nucleus of the posterior commissure, nucleus cuneiformis, ventral periaqueductal gray, vestibular complex, perihypoglossal complex, and deep cerebellar nuclei. In HRP/ChAT double labeling studies, only a very small number of cholinergic VTN afferent neurons were found in the medial parabrachial region of the dorsolateral pontine tegmentum, although the pedunculopontine and laterodorsal tegmental nuclei contained numerous single-labeled ChAT-positive cells. Anterograde HRP and autoradiographic findings demonstrated that the VTN gave rise almost exclusively to ascending projections, which largely followed the course of the mammillary peduncle (16,21) and medial forebrain bundle, or the tegmentopeduncular tract (4). The majority of fibers ascended to terminate in the medial and lateral mammillary nuclei, interpeduncular complex (especially paramedian subnucleus), ventral tegmental area, lateral hypothalamus, and the medial septum in the basal forebrain. Labeling that joined the mammillothalamic tract to terminate in the anterior nuclear complex of the thalamus was thought to occur transneuronally. Some projections were also observed to nucleus reticularis pontis oralis and caudalis, superior central nucleus, and dorsal tegmental nucleus adjacent to the VTN...     

Diencephalic projections from the pontine reticular formation: autoradiographic studies in the cat

Ascending projections to the diencephalon from the pontine reticular formation were studied in the cat by autoradiographic techniques. Projections from both rostral and caudal pontine regions ascend to the caudal diencephalon and divide into two components; a dorsal leaf terminates primarily in the thalamic intralaminar complex and a ventral leaf terminates in the subthalamic region. The relative densities of the two terminal regions vary with the injection site. Fibers originating in the caudal pons (nucleus reticularis pontis caudalis) terminate relatively heavily in the intralaminar nuclei of the dorsal thalamus, particularly the centre median, central lateral, central dorsal and paracentral nuclei, and also the dorsal medial nucleus. Relatively sparse termination occurs in the subthalamic region. In contrast, fibers from the rostral pons (nucleus reticularis pontis oralis) terminate relatively heavily in the subthalamic region, including the zona incerta, the fields of Forel, the ventral part of the thalamic reticular complex, and the lateral hypothalamus. Relatively sparse termination occurs in the dorsal thalamus, but includes the centre median, parafascicular, central lateral, paracentral and dorsal medial nuclei. These data are discussed with regard to reticular control of forebrain activity and the role of the classic dorsal and ventral components of ascending reticular projections.     

Cerebellothalamic projections in the rat: An autoradiographic and degeneration study

The purpose of this study was to determine the topographical organization of cerebellothalamic projections in the rat. Following stereotaxic injections of ³H-leucine or electrolytic lesions in the cerebellar nuclei, efferent fibers were observed to emerge from the cerebellum through two discrete routes. Fibers from the fastigial nucleus decussated within the cerebellum, formed the crossed ascending limb of the uncinate fasciculus, ascended in the dorsal part of the midbrain tegmentum, and entered the thalamus. Cerebellothalamic fibers from the interpositus and dentate nuclei coursed in the ipsilateral brachium conjuctivum, decussated in the caudal midbrain, and ascended to the thalamus via the crossed ascending limb of the brachium conjunctivum. Cerebellar terminations were observed in the intralaminar, lateral, and ventral tier thalamic nuclei as well as in the medial dorsal nucleus. Projections to the intralaminar nuclei were more pronounced from the dentate and posterior interpositus than from the anterior interpositus and fastigial nuclei. The lateral thalamic nuclei received a projection from the dentate and posterior interpositus nuclei while the fastigial nucleus projected to the medial dorsal nucleus. Within the rostral ventral tier nuclei fastigiothalamic terminations were localized in the medial parts of the ventral medial and ventral lateral nuclei, whereas dentatothalamic projections were concentrated in the lateral parts of the ventral medial nucleus and the medial half of the ventral lateral nucleus. Terminations from the posterior interpositus nucleus were observed ventrally and laterally within the caudal two-thirds of the ventral medial nucleus and throughout the ventral lateral nucleus, where they were densest in the lateral part of its lateral wing and within the central part of its cap. The anterior interpositus nucleus also projected to the central and lateral parts of the ventral lateral nucleus, but these terminations were considerably less dense than those from the posterior interpositus. A few fibers from the interpositus nuclei terminated in the medial part of the rostral pole of the ventral posterior nucleus. A prominent recrossing of cerebellothalamic fibers from the fastigial, posterior interpositus, and dentate nuclei occurred through the central medial nucleus of the internal medullary lamina. These terminated within the ipsilateral ventral lateral and intralaminar nuclei. These results show that each of the cerebellar nuclei project to the thalamus and that their terminations are topographically organized in the rostral ventral tier nuclei. The clustering of autoradiographic silver grains or terminal degeneration observed in the thalamic nuclei suggests a medial-to-lateral organization of this cerebellothalamic system.     

Extrageniculate projections to the visual cortex in the macaque monkey: an HRP study

Extrageniculate projections to the visual cortex were examined in the macaque monkeys by the horseradish peroxidase (HRP) method. Extrageniculate neurons sending fibers to the visual cortex were found in the lateral and inferior pulvinar nuclei, paracentral thalamic nucleus, claustrum, basal nucleus of Meynert, lateral part of the basal amygdaloid nucleus, lateral hypothalamus, locus coeruleus, and dorsomedial and midline regions of the pontine tegmentum.     

Distribution of phenylethanolamine-N-methyltransferase-immunoreactive perikarya and fibers in the brain of the lizard Gekko gecko

The distribution of phenylethanolamine N-methyltransferase (PNMT)-immunoreactive (PNMTi) cell bodies and fibers in the brain of the lizard Gekko gecko was studied by antibodies raised in rabbits against purified bovine adrenal PNMT. The PNMTi cell bodies were observed in the ventrolateral rhombencephalic tegmentum at the level of the obex. No immunoreactive perikarya were found in the nucleus of the solitary tract, the medial longitudinal fascicle or the hypothalamus. An extensive network of PNMTi fibers is present throughout the brain, extending rostrally as far as the olfactory peduncle. In the telecenphalon, moderate to dense plexuses of PNMTi fibers were observed in the medial part of the nucleus accumbens, the medial septal nucleus, the nucleus of the diagonal band, the caudoventral septal region and the central amygdaloid nucleus. In the diencephalon, the periventricular and lateral zones of the preoptic and hypothalamic areas, the medial forebrain bundle and the dorsomedial thalamic nucleus contain many PNMTi fibers. Brainstem structures innervated by PNMTi fibers are the ventral tegmental area, the substantia nigra, the periaqueductal gray, the locus coeruleus, the parabrachial region, the nucleus of the solitary tract, the dorsal motor nucleus of the vagus and the ventrolateral region of the caudal brainstem. Although the brain of Gekko appears to lack PNMTi cells in areas comparable to the C2 and C3 cell groups in rats, the distribution of PNMTi fibers is nevertheless strikingly similar in both groups.     

Projections to the pontine nuclei from choline acetyltransferase-like immunoreactive neurons in the brainstem of the cat

By use of retrograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) in combination with monoclonal antibodies against choline acetyltransferase (ChAT), we show that putative cholinergic inputs to the feline pontine nuclei originate from cells in the dorsolateral pontine tegmentum. These cells form a loosely arranged continuum that nevertheless may be subdivided into two groups on the basis of differences in cell morphology. One group consists of double-labeled cells in the periventricular gray substance medial to, and partly merging with, the nucleus locus coeruleus. The other group consists of double-labeled cells surrounding the brachium conjunctivum. In two cats with tracer injections in the pontine nuclei, 81% and 84%, respectively, of the retrogradely labeled cells in the dorsolateral pontine tegmentum are ChAT-like immunoreactive (ChAT-LI). In the same experiments, many ChAT-LI cells, but no retrogradely labeled cells, are seen in the basal telencephalon. The pontine nuclei contain a plexus of thin ChAT-LI fibers with varicosities resembling en passant as well as terminal boutons. These ChAT-LI fibers appear to branch extensively and cover all parts of the pontine nuclei. Following injections of rhodamine-B-isothiocyanate (RITC) in the thalamus and Fluoro-Gold in the pontine nuclei and surrounding regions in the same animal, all retrogradely labeled cells in the dorsolateral pontine tegmentum are labeled with both tracers, whereas most cells in the paramedian pontine reticular formation are labeled either with RITC or Fluoro-Gold. Thus it appears that all cells in the dorsolateral pontine tegmentum that project to the pontine nuclei also project to the thalamus. In analogy with findings by others in the dorsal lateral geniculate nucleus, we suggest that the putative cholinergic projections to the pontine nuclei may serve to modulate transmission of cerebellar afferent information in accordance with the behavioral state of the animal.     

Efferent connections of the ventral medulla oblongata in the rat

The efferent connections of the ventral medulla oblongata have been analyzed in the rat using the anterograde autoradiographic method and the HRP technique. Fibers originating from the nucleus interfascicularis hypoglossi (B1 serotonergic cell group) and nucleus reticularis gigantocellularis, pars a (B3 serotonergic cell group) innervate the intermediolateral cell column, ventral horn and intermediate gray matter of the spinal cord. Some fibers innervate the hypoglossal, dorsal motor vagal, and medial solitary nuclei. Ascending fibers project through the medullary and pontine reticular formation, providing inputs to the Kölliker-Fuse, lateral parabrachial, laterodorsal tegmental, subcoeruleus and locus coeruleus nuclei. In the midbrain, the fibers ascend in the central tegmental field and then divide into several fiber bundles. Some course medially to innervate the central gray matter. Others diverge laterally to innervate the external nucleus of the inferior colliculus and cuneiform nucleus as well as the deep layers of the contralateral superior colliculus. Still others course dorsally through the ventral pretectal region to reach the thalamus (laterodorsal, paraventri-cular, paracentral, and centrolateral thalamic nuclei). The remaining fibers innervate the hypothalamus (dorsal hypothalamic area, paraventricular nucleus, perifornical area, supraoptic nucleus, retrochiasmatic area, and median eminence). Some of these continue through the lateral preoptic region, shift medially as they course through the area of the nucleus of the diagonal band, septofimbrial nucleus, and medial septum, and arch around the genu of the corpus callosum to innervate the hippocampal formation.     

Some anatomical observations on the projections from the hypothalamus to brainstem and spinal cord: an HRP and autoradiographic tracing study in the cat

The hypothalamus is closely involved in a wide variety of behavioral, autonomic, visceral, and endocrine functions. To find out which descending pathways are involved in these functions, we investigated them by horseradish peroxidase (HRP) and autoradiographic tracing techniques. HRP injections at various levels of the spinal cord resulted in a nearly uniform distribution of HRP-labeled neurons in most areas of the hypothalamus except for the anterior part. After HRP injections in the raphe magnus (NRM) and adjoining tegmentum the distribution of labeled neurons was again uniform, but many were found in the anterior hypothalamus as well. Injections of 3H-leucine in the hypothalamus demonstrated that: The anterior hypothalamic area sent many fibers through the medial forebrain bundle (MFB) to terminate in the ventral tegmental area of Tsai (VTA), the rostral raphe nuclei, the nucleus Edinger-Westphal, the dorsal part of the substantia nigra, the periaqueductal gray (PAG), and the interpeduncular nuclei. Further caudally a lateral fiber stream (mainly derived from the lateral parts of the anterior hypothalamic area) distributed fibers to the parabrachial nuclei, nucleus subcoeruleus, locus coeruleus, the micturition-coordinating region, the caudal brainstem lateral tegmentum, and the solitary and dorsal vagal nucleus. Furthermore, a medial fiber stream (mainly derived from the medial parts of the anterior hypothalamic area) distributed fibers to the superior central and dorsal raphe nucleus and to the NRM, nucleus raphe pallidus (NRP), and adjoining tegmentum. The medial and posterior hypothalamic area including the paraventricular hypothalamic nucleus (PVN) sent fibers to approximately the same mesencephalic structures as the anterior hypothalamic area. Further caudally two different fiber bundles were observed. A medial stream distributed labeled fibers to the NRM, rostral NRP, the upper thoracic intermediolateral cell group, and spinal lamina X. A second and well-defined fiber stream, probably derived from the PVN, distributed many fibers to specific parts of the lateral tegmental field, to the solitary and dorsal vagal nuclei, and, in the spinal cord, to lamina I and X, to the thoracolumbar and sacral intermediolateral cell column, and to the nucleus of Onuf. The lateral hypothalamic area sent many labeled fibers to the lateral part of the brainstem and many terminated in the caudal brainstem lateral tegmentum, including the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus, and the solitary and dorsal vagal nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)     

Retinal projections in the freshwater butterfly fish, Pantodon buchholzi (Osteoglossoidei). I. Cytoarchitectonic analysis and primary visual pathways.

The freshwater butterfly fish, Pantodon buchholzi, is a member of the most primitive radiation of teleosts. The retinofugal projections were studied in this fish with autoradiographic and horseradish peroxidase (HRP) methods, and the cytoarchitecture of the retinorecipient regions in the diencephalon and pretectum was analyzed with Bodian-, cresylecht-violet- and acetylcholinesterase-reacted sections. The rostral diencephalon of Pantodon contains a large retinorecipient nucleus, not previously identified in any other fish, i.e. nucleus rostrolateralis. Other nuclei that are described correspond to those previously recognized in other species. The majority of retinorecipient nuclei are positive for acetylcholinesterase, particularly those in the pretectum, as has been found in other species of teleosts. Most of the retinofugal fibers decussate in the optic chiasm. Some fibers project via the axial optic tract to preoptic nuclei and a region in the rostral hypothalamus. Fibers leave the medial optic tract to terminate in nucleus rostrolateralis and in dorsal and ventral thalamic nuclei, accessory optic and tubercular nuclei, periventricular and central pretectal nuclei, and sparsely in the deep tectal fascicle and terminal field. Dorsal optic tract fibers project to the dorsal accessory optic nucleus, superficial and central pretectal nuclei, and superficial and deep tectal layers. Ventral optic tract fibers project to the superficial pretectum, accessory optic nuclei, posterior tuberculum, nucleus corticalis in the central pretectum, and superficial tectal layer. Fibers that remain in the ipsilateral optic tract project to most of the targets reached by contralaterally projecting fibers. A few fibers in the contralateral medial optic tract redecussate via the posterior commissure to reach the ipsilateral periventricular pretectum. No labeled retinopetal cells caudal to the olfactory bulb were identified in any of the HRP cases.     

Long descending projections of the hypothalamus in the pigeon, Columba livia

An autoradiographic analysis was performed on the descending projections of nucleus periventricularis magnocellularis (PVM) of the hypothalamus in the pigeon. A PVM-medullospinal pathway was observed coursing posteriorly through the lateral hypothalamus, ventrolateral midbrain tegmentum, and into the spinal lemniscus (ls) in the ventrolateral pons and medulla. In the pons, some fibers course dorsomedially from ls and terminate at the lateral border of the locus coeruleus. At medullary levels, fibers from ls sweep dorsomedially in the plexus of Horsley and project to certain regions of the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (NX). Specifically, PVM fibers project heavily into NTS subnuclei medialis superficialis, medialis ventralis, and lateralis (sulcalis) dorsalis as well as into the ventral parvocellular subnucleus of NX. Fibers in ls were traced caudally into the lateral funiculus as far as upper cervical levels of the spinal cord. Although autoradiographs of lower cervical or thoracic spinal cord sections were not available, PVM fibers do descend to thoracic spinal cord levels, as evidenced by the retrograde transport of horseradish peroxidase. In addition to the medullospinal pathway, the autoradiographs demonstrated PVM projections to septum, diencephalon, and midbrain. Labeled PVM fibers are found in the lateral septal nucleus, nucleus of the anterior pallial commisure, dorsomedial thalamic nucleus, dorsolateral anterior thalamic nucleus (pars ventralis), median eminence, medial and lateral hypothalamus, medial mammillary area, and nucleus intercollicularis and central gray of the midbrain. The projection of fibers to medullospinal regions and median eminence suggests that PVM is homologous to the mammalian paraventricular nucleus. These projections to specific subnuclei of NTS and NX denote hypothalamic control over certain autonomic functions.     

Efferent projections from the mammillary complex of the guinea pig: an autoradiographic study

The efferent projections from the medial and lateral mammillary nuclei of the guinea pig were traced after injecting tritiated amino acid. The major efferent started as the principal mammillary tract, but soon divided into mammillothalamic and mammillotegmental tracts. The mammillothalamic tract projected anterodorsally and terminated in the anterior dorsal, anterior ventral and anterior medial thalamic nuclei. The mammillotegmental tract projected caudally and terminated in the dorsal tegmental nucleus and central gray. The mammillary efferents in the mammillary peduncle ran via the tegmentum of the midbrain and pons. It terminated in the dorsal and ventral tegmental nuclei, basal pontine nucleus and pontine tegmental reticular nucleus. A diffuse mammillary projection had fibers directed dorsally which distributed in the midline thalamic nuclei and in central gray. Rostral projections via the medial forebrain bundle from the medial mammillary nucleus were found in the septal area and diagonal band of Broca. The lateral mammillary nucleus sent fibers which also joined the mammillothalamic and mammillotegmental tracts. These terminated bilaterally mainly in the anterior dorsal and anterior ventral nuclei of the thalamus, and caudally in the dorsal and ventral tegmental nuclei and basal pontine nucleus.     

Afferent and efferent connections of the oculomotor region of the fastigial nucleus in the macaque monkey.

Afferent and efferent connections of the fastigial oculomotor region (FOR) were studied in macaque monkeys by using axonal transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP). When injected HRP is confined to the FOR, retrogradely labeled cells appear in lobules VIc and VII of the ipsilateral vermis and in group b of the contralateral medial accessory olive (MAO). In reference to the maps of topographical organization, the extent of the effective site in the fastigial nucleus (FN) could be assessed from the distributions of labeled Purkinje cells (P cells) in the vermis and labeled olivary neurons in the MAO. In contrast to the unilateral nature of the P-cell and climbing-fiber projections, those from the other brainstem regions to the FOR were bilateral. Following the injection of HRP into the FOR, the largest number of retrogradely labeled cells appeared in the pontine nuclei. Although the number of labeled cells was greater on the contralateral side in both the peduncular and dorsomedial pontine nuclei (DMPN), the number of each side was virtually identical in the dorsolateral pontine nucleus (DLPN). In the nucleus reticularis tegmenti pontis (NRTP), labeled cells were located only in its medial and dorsolateral portions bilaterally. In the vestibular complex, labeled cells appeared in the superior (SVN), medial (MVN), and inferior vestibular nuclei (IVN) bilaterally. The lateral vestibular nucleus (LVN), including y group and the ventrolateral vestibular nucleus, were free of labeled cells. Labeled cells appeared also in the perihypoglossal nucleus (PHN) bilaterally. In the pontine raphe (PR) and paramedian pontine reticular formation (PPRF), labeled cells appeared bilaterally in the caudal third of the area between the oculomotor and abducens nuclei. Labeled cells appeared also in the mesencephalic and medullary reticular formation. Tracing of anterogradely labeled axons demonstrated that most fibers from the FOR decussated within the cerebellum and entered the brainstem via the contralateral uncinate fasciculus. Some crossed fibers ascended with the contralateral brachium conjunctivum and terminated in the midbrain tegmentum. A small contingent of fibers advanced further to the thalamus. In the mesodiencephalic junction, labeled terminals were found contralaterally in the rostral interstitial nucleus of medial longitudinal fasciculus (riMLF) and a medial portion of FOrel's H Field. They appeared also in the central mesencephalic reticular formation (cMRF), the periaqueductal gray (PAG), the posterior commissure nucleus, and the superior colliculus. The oculomotor and trochlear nuclei, the red nucleus, and the interstitial nucleus of Cajal were free of labeled terminals.(ABSTRACT TRUNCATED AT 400 WORDS)     

Projections from the 'cingular' vocalization area in the squirrel monkey.

In 5 squirrel monkeys the anatomical projections from the 'cingular' vocalization area were studied by the autoradiographic tracing technique. The 'cingular' vocalization area lies around the sulcus cinguli at the level of the genu of the corpus callosum; its electrical stimulation yields purring and cackling calls. The following efferent connections were found: corticocortical fibers could be traced into the orbital cortex (areas 10 and 11), dorsomedial frontal cortex (areas 9, 8 and 6), limbic cortex (areas 25, 24 and 23), Broca's area (area 44), frontal operculum (area 50), insula (areas 13 and 14), and auditory association cortex (area 22). Subcortical terminal fields within the telencephalon were found in the nucleus caudatus, putamen, claustrum, globus pallidus, olfactory tubercle, preoptic region and nucleus centralis and basolateralis amygdalae. Fibers reached most of these structures along different trajectories. In the diencephalon terminal fields lay in the dorsal hypothalamus, the subthalamus, lateral habenular nucleus, and the following thalamic nuclei: nucleus reticularis, ventralis anterior, centralis medialis, centralis superior lateralis, centralis inferior, submedius, medialis dorsalis and centrum medianum. In the midbrain, the periaqueductal gray was the only projection area, extending into the parabrachial nuclei at the pontomesencephalic transition. The most caudal terminal field was found in the medial pontine gray. No terminals were detected in the nucleus ambiguus, nucleus n. hypoglossi or in any other cranial motor nucleus involved in phonation processes. A comparison of this projection system with the whole of structures producing vocalization when electrically stimulated yielded only partial overlap. Not all vocalization areas lie within the 'cingular' projection system, and inversely, not the whole projection system yielded vocalization. Overlap took place in the anterior limbic cortex, preoptic region, central amygdaloid nucleus, midline thalamus, dorsal hypothalamus, periaqueductal gray and parabrachial nuclei. These structures are considered to compose a functionally coherent vocalization system. The projections into Broca's area, nucleus ventralis anterior thalami, frontoopercular cortex within the lateral fissure, pontine nuclei and superior temporal gyrus are discussed in their possible relationship to vocalization processes.     

Efferent tectal pathways of the opossum (Didelphis virginiana)

Efferent tectal pathways have been determined for the opossum, Didelphis virginiana, by employing the Nauta-Gygax technique ('54) on animals with tectal lesions of varying sizes. The superior colliculus projected tectothalamic fascicles to the suprageniculate nucleus, the central nucleus of the medial geniculate body, the lateral posterior thalamus, the pretectal nucleus, the ventral lateral geniculate nucleus, the fields of Forel and zona incerta, the parafascicular complex, the paracentral thalamic nucleus and in some cases to restricted areas of the anterior thalamus. Degenerating fibers from superior collicular lesions showed profuse distribution to the deeper layers of the superior colliculus on both sides and to the midbrain tegmentum, but only minimally to the red nucleus and substantia nigra. Fibers of tectal origin did not distribute to the motor nuclei of the oculomotor or trochlear nerves. At pontine levels, efferent fascicles from the superior colliculus were present as an ipsilateral tectopontine and tectobulbar tract and as a crossed predorsal bundle. The tectopontine tract ended mostly within the lateral and ventral basal pontine nuclei, whereas the ipsilateral tectobulbar tract distributed to certain specific areas of the reticular formation throughout the pons and medulla, minimally to the most medial portion of the motor nucleus of the facial nerve and to the nucleus of the inferior olive. The predorsal tract contributed fascicles to certain nuclei of the pontine raphe, extensively to the medial reticular formation of the pons, to the central and ventral motor tegmental nuclei of the reticular formation within the pons and medulla, to the paraabducens region, minimally to cells within restricted portions of the motor nucleus of the facial nerve, to certail specific regions of the caudal medulla and to the cervical cord as far caudally as the fourth segment. The tectospinal fascicles were few but some ended related to the spinal accessory nucleus and the ventral medial nucleus of the ventral horn. Lesions of the inferior colliculus resulted in degenerating fibers which distributed rostrally to the rostral nucleus of the lateral lemniscus and parabrachial region, to the suprageniculate nucleus, the parabigeminal nucleus and to the central nucleus of the medial geniculate body. The inferior colliculus also contributed fibers to the ipsilateral tectopontine and tectobulbar tracts. The latter bundle was traced as far caudally as the medulla and may arise from cells of the superior colliculus which are situated dorsal to the nucleus of the inferior colliculus.     

Pontine sources of norepinephrine in the cat cochlear nucleus

In the current study, the distribution of noradrenergic neurons in the pontine tegmentum that project to the cochlear nucleus was determined with retrograde tract tracing combined with neurotransmitter immunohistochemistry in the cat. Double-labeled neurons were observed in all noradrenergic cell groups, in both the dorsolateral and the ventrolateral tegmentum. Half of the double-labeled cells were located in the locus coeruleus complex. Most of these were situated in its ventral division. Most other double-labeled cells were located in peribrachial regions, especially lateral to the brachium conjunctivum. Relatively few double-labeled cells were observed in both the A4 and the A5 cell groups, 2% and 0.4%, respectively, of the total. Except for neurons in A5, which projected only contralaterally, the projections were bilateral, with an ipsilateral preponderance. The results indicate that neurons located in the ipsilateral dorsolateral tegmentum, namely, in the locus coeruleus complex and the peribrachial region, are the primary source of pontine noradrenergic afferents to the cochlear nucleus of the cat.     

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.     

The origin of brainstem afferents of the paramedian pontine reticular formation in the cat

Transcannular microinjections of horseradish peroxidase (HRP) were made into the paramedian pontine reticular formation (PPRF) in adult cats to determine the origin of the principal sources of inputs to this important preoculomotor center for the production of saccadic eye movements. Retrogradely labeled cells were observed in numerous oculomotor-related structures, including the prerubral field (rostral interstitial nucleus of the medial longitudinal fasciculus), nucleus of Darkschewitsch, nucleus of the posterior commissure, deep superior colliculus, supraoculomotor ventral periaqueductal gray, contralateral paramedian pontine reticular formation, pontine raphe and dorsal medial pontine tegmentum medial to the abducens nucleus (purported to contain omnipause neurons), cell group Y, and the perihypoglossal complex (nucleus prepositus hypoglossi). Other sources of afferents to the region included the zona incerta, lateral and medial habenular nuclei, medial hypothalamus, medial mammillary nucleus, nucleus cuneiformis, medial medullary reticular formation, and the medial and lateral cerebellar nuclei. The results are discussed in terms of the potential influence of these nuclei on the control of eye movement.     

Efferent connections of the lateral hypothalamic area of the rat: An autoradiographic investigation

The efferent projections of the lateral hypothalamic area (LHA) at mid-tuberal levels were examined with the autoradiographic tracing method. Connections were observed to widespread regions of the brain, from the telencephalon to the medulla. Ascending fibers course through LHA and the lateral preoptic area and lie lateral to the diagonal band of Broca. Fibers sweep dorsally into the lateral septal nucleus, cingulum bundle and medial cortex. Although sparse projections are found to the ventromedial hypothalamic nucleus, a prominent pathway courses to the dorsal and medial parvocellular subnuclei of the paraventricular nucleus. Labeled fibers in the stria medullaris project to the lateral habenular nucleus. The central nucleus of the amygdala is encapsulated by fibers from the stria terminalis and the ventral amygdalofugal pathway. The substantia innominate, nucleus paraventricularis of the thalamus, and bed nucleus of the stria terminalis also receive LHA fibers. Three descending pathways course to the brainstem: (1) periventricular system, (2) central tegmental tract (CTT), and (3) medial forebrain bundle (MFB). Periventricular fibers travel to the ventral and lateral parts of the midbrain central gray, dorsal raphe nucleus, and laterodorsal tegmental nucleus of the pens. Dorsally coursing fibers of CTT enter the central tegmental field and the lateral and medial parabrachial nuclei. The intermediate and deep layers of the superior colliculus receive some fibers. Fibers from CTT leave the parabranchial region by descending in the ventrolateral pontine and medullary reticular formation; some of these fibers sweep dorsomedially into the nucleus tractus solitarius, dorsal motor nucleus of the vagus, and nucleus commissuralis. From MFB, fibers descend into the ventral tegmental area and to the border of the median raphe and raphe magnus nuclei.     

Demonstration of topographically organized projections from the hypothalamus to the pontine nuclei: an experimental anatomical study in the cat

In 22 cats implantations and injections of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) or Fluoro-Gold were placed in the pontine nuclei or the hypothalamus. The occurrence and distribution of labeled cells in the hypothalamus and of labeled terminal fibers in the pontine nuclei were mapped. Following implantations of HRP-WGA ventromedially in rostral parts of the pontine nuclei, 22-44% of all labeled cells in the brainstem and diencephalon are found in the medial mamillary nucleus ipsilateral to the implantation. Some labeled cells are also found in the supramamillary, premamillary, anterior mamillary, and tuberomamillary nuclei. Thus, labeled cells in the hypothalamus make up 33-54% of all labeled cells in the brainstem and diencephalon in such cases. In contrast, implantations and injections in mediocaudal parts of the pontine nuclei result in labeling of cells mainly in the posterior, dorsal, and lateral hypothalamic areas (terminology of Bleier: The Hypothalamus of the Cat. Baltimore: Johns Hopkins Press, '61). In these cases the labeled cells in the hypothalamus make up 16-25% of all labeled cells in the brainstem and diencephalon. Implantations in more lateral parts of the pontine nuclei label only a few cells in the hypothalamus. Following implantations of HRP-WGA in restricted parts of the hypothalamus, fibers from the medial mamillary nucleus were found to terminate ventromedially at all rostrocaudal levels of the pontine nuclei, ipsilateral to the implantation. In the rostralmost part of the pontine nuclei, the terminal labeling forms a dense, transversely oriented, c-shaped band. Fibers from the posterior and dorsal hypothalamic areas terminate medially and dorsomedially in the caudal third of the pontine nuclei. Sparse terminal labeling is also seen in lateral parts of the pontine nuclei and medially at more rostral levels. In two cases with small implantations of HRP-WGA ventromedially in rostral parts of the pontine nuclei, labeled cells are found both in the medial mamillary nucleus and the cingulate gyrus. Thus, it seems possible that fibers from the medial mamillary nucleus and the cingulate gyrus converge upon a restricted area ventromedially in rostral parts of the pontine nuclei.