Topography of visual and somatosensory inputs to the pontine nuclei in zebra finches (Taeniopygia guttata)

Birds have a comprehensive network of sensorimotor projections extending from the forebrain and midbrain to the cerebellum via the pontine nuclei, but the organization of these circuits in the pons is not thoroughly described. Inputs to the pontine nuclei include two retinorecipient areas, nucleus lentiformis mesencephali (LM) and nucleus of the basal optic root (nBOR), which are important structures for analyzing optic flow. Other crucial regions for visuomotor control include the retinorecipient ventral lateral geniculate nucleus (GLv), and optic tectum (TeO). These visual areas, together with the somatosensory area of the anterior (rostral) Wulst, which is homologous to the primary somatosensory cortex in mammals, project to the medial and lateral pontine nuclei (PM, PL). In this study, we used injections of fluorescent tracers to study the organization of these visual and somatosensory inputs to the pontine nuclei in zebra finches. We found a topographic organization of inputs to PM and PL. The PM has a lateral subdivision that predominantly receives projections from the ipsilateral anterior Wulst. The medial PM receives bands of inputs from the ipsilateral GLv and the nucleus laminaris precommisulis, located medial to LM. We also found that the lateral PL receives a strong ipsilateral projection from TeO, while the medial PL and region between the PM and PL receive less prominent projections from nBOR, bilaterally. We discuss these results in the context of the organization of pontine inputs to the cerebellum and possible functional implications of diverse somato-motor and visuomotor inputs and parcellation in the pontine nuclei.     

Thyrotropin-releasing hormone-immunoreactive projections to the dorsal motor nucleus and the nucleus of the solitary tract of the rat.

Thyrotropin-releasing hormone-immunoreactive nerve terminals heavily innervate the dorsal motor nucleus and nucleus of the solitary tract, whereas cell bodies containing thyrotropin-releasing hormone residue most densely in the hypothalamus and raphe nuclei. By using double-labeling techniques accomplished by retrograde transport of Fluoro-Gold following microinjection into the dorsal motor nucleus/nucleus of the solitary tract combined with immunohistochemistry for thyrotropin-releasing hormone, it was demonstrated that thyrotropin-releasing hormone-immunoreactive neurons projecting to the dorsal motor nucleus/nucleus of the solitary tract reside in the nucleus raphe pallidus, nucleus raphe obscurus, and the parapyramidal region of the ventral medulla, but not in the paraventricular nucleus of the hypothalamus. The parapyramidal region includes an area along the ventral surface of the caudal medulla, lateral to the pyramidal tract and inferior olivary nucleus and ventromedial to the lateral reticular nucleus. Varying the position of the Fluoro-Gold injection site revealed a rostral to caudal topographic organization of these raphe and parapyramidal projections.     

Rostral wulst of passerine birds: II. Intratelencephalic projections to nuclei associated with the auditory and song systems.

We have previously shown that the hyperstriatum accessorium (HA) of the rostral wulst in zebra finches and green finches is the origin of a pyramidal-like tract with substantial projections to the brainstem and cervical spinal cord. Here, we show that the HA also is the origin of a set of intratelencephalic projections with terminal fields in the lateral part of the frontal neostriatum, the shell surrounding the lateral magnocellular nucleus of the anterior neostriatum, the lobus parolfactorius surrounding area X, the nucleus interface, auditory fields L1 and L3, the shelf underlying the high vocal center, the dorsolateral caudal neostriatum, the dorsocaudal part of the nucleus robustus archistriatalis, and the ventral archistriatum. The cells of origin of these projections are located predominantly laterally in the HA, close to and sometimes within the intercalated HA, which receives somatosensory projections from the dorsal thalamus. The specific implications of these findings for auditory and vocal function are unclear, but the apparent overlap of auditory and somatosensory inputs in several of these regions suggests the possibility of mechanisms for stimulus enhancement or depression, depending on the congruence of stimuli within a cell's "in-register" multiple receptive fields.     

Projections from the commissural subnucleus of the nucleus of the solitary tract: an anterograde tracing study in the cat.

The commissural subnucleus (COM) of the nucleus of the solitary tract (NTS) is known to receive primary afferents from the lungs and other viscera innervated by the vagus nerve, and thus to participate in central autonomic and respiratory control. The aim of the present study was to identify the areas of terminal arborizations of COM neurons in order to examine brainstem sites which may be involved in reflex responses mediated by these neurons. The projections were studied in cats, using biocytin as an anterograde tracer. Labeled fibers and terminal boutons were visualized by horseradish-peroxidase histochemistry, 2-3 days after microinjection of the tracers into the COM 1-2 mm caudal to the obex. Labeled axons were examined in the brainstem from the rostral pons to the caudal medulla and were found bilaterally, with an ipsilateral predominance, mainly in the following regions: (1) The dorsolateral rostral pons. Terminal boutons were observed in the lateral and medial parabrachial nuclei, K?lliker-Fuse nucleus, and around the mesencephalic trigeminal tract. This area corresponds to the pontine respiratory group also known as the "pneumotaxic center." (2) The pontine area dorsolateral to the superior olivary nucleus. This region contains the A5 noradrenergic cell group; (3) Near the ventral surface, below the facial nucleus. This area overlaps with the 'retrotrapezoid nucleus.' (4) Respiration-related areas of the medulla, including the dorsal and ventral respiratory groups, and the B?tzinger complex. (5) The dorsal motor nucleus of the vagus. These results suggest that the COM is involved in reflex arcs, which have both respiratory functions and autonomic functions. The pathway to the dorsolateral pons, which has been identified in our recent electrophysiological study is likely to play a role in mediating respiratory responses from pulmonary rapidly adapting receptors. Other pathways may represent additional projections from second-order neurons receiving input from this group of lung receptors, or projections from as yet unidentified neurons that relay information from different afferents terminating in the COM.     

Projections of the dorsomedial nucleus of the intercollicular complex (DM) in relation to respiratory-vocal nuclei in the brainstem of pigeon (Columba livia) and zebra finch (Taeniopygia guttata)

Injections of neuronal tracers were made into the dorsomedial nucleus of the intercollicular complex (DM) of pigeons and zebra finches in order to investigate the projections of this nucleus which has long been implicated in respiratory-vocal control. Despite the fact that pigeons are nonsongbirds and zebra finches are songbirds, the projections were very similar in both species. Most descended throughout the brainstem, taking ventral and dorsal trajectories, which merged in the medulla. Those descending ventrally terminated upon the ventrolateral parabrachial nucleus (PBvl), the nucleus infraolivaris superior, a nucleus of the rostral ventrolateral medulla (RVL), and the nucleus retroambigualis (RAm). Those taking a dorsal trajectory via the occipitomesencephalic tract terminated in the tracheosyringeal part of the hypoglossal nucleus (XIIts), the suprahypoglossal region, and nucleus retroambigualis. There were also substantial projections throughout an arc extending, between XIIts and RVL rostrally, and XIIts and RAm caudally. Neurons throughout this arc, which include inspiratory premotor neurons at levels straddling the obex and expiratory premotor neurons more caudally (in RAm), were retrogradely labeled from spinal injections. The DM projections were predominantly ipsilateral, but there were distinct contralateral projections to all the homologous nuclei in both species. All but the projections to PBvl and XIIts were reciprocal. In summary, the projections of DM suggest that it is able to influence all the key motor and premotor nuclei involved in patterned respiratory-vocal activity. J. Comp. Neurol. 377:392–413, 1997. © 1997 Wiley-Liss, Inc.     

The organization of projections from the cortex, amygdala, and hypothalamus to the nucleus of the solitary tract in rat

Direct projections from the forebrain to the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus in the rat medulla were mapped in detail using both retrograde axonal transport of the fluorescent tracer True Blue and anterograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). In the retrograde tracing studies, cell groups in the medial prefrontal cortex, lateral prefrontal cortex (primarily ventral and posterior agranular insular cortex), bed nucleus of the stria terminalis, central nucleus of the amygdala, paraventricular, arcuate, and posterolateral areas of the hypothalamus were shown to project to the NTS and in some cases also to the dorsal motor nucleus of the vagus. The prefrontal cortical areas projecting to the NTS apparently overlap to a large degree with those cortical areas receiving mediodorsal thalamic and dopaminergic input. The retrogradely labeled cortical cells were situated in deep layers of the rat prefrontal cortex. The anterograde tracing studies revealed a prominent topography in the mediolateral termination pattern of forebrain projections to the rostral part of the NTS and to the dorsal pons. The projections to the NTS were generally bilateral, except for projections from the central nucleus of the amygdala and bed nucleus of the stria terminalis which were predominantly ipsilateral. The prefrontal cortical projections to the NTS travel through the cerebral peduncle and pyramidal tract and terminate throughout the rostrocaudal extent of the NTS. Specifically, the prefrontal cortex innervates dorsal portions of the NTS (lateral part of the dorsal division of the medial solitary nucleus, dorsal part of the lateral solitary nucleus and the caudal midline region of the commissural nucleus), areas which receive relatively sparse subcortical projections. These dorsal portions of the NTS receive major primary afferent projections from the vagal and glossopharyngeal nerves. In contrast, the subcortical projections, which travel through the midbrain and pontine tegmentum, terminate most heavily in the ventral portions of the NTS, i.e., the area immediately dorsal and lateral to the dorsal motor nucleus of the vagus. Only the paraventricular hypothalamic nucleus has substantial terminals throughout the dorsal motor nucleus of the vagus. Hypothalamic cell groups innervate the area postrema and, along with the prefrontal cortex, innervate the zone subjacent to the area postrema.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neocortical projections to the pons and medulla of the nine-banded armadillo (Dasypus novemcinctus)

The pattern of neocortical projections to the pons and medulla was determined by employing the Nauta-Gygax technique ('54) on the brains of armadillos subjected to neocortical ablations. The results of this study indicate that the pretrigeminal basilar pontine gray receives input from a considerable portion of the neocortex. Degenerating fibers resulting from a lesion of the frontal tip of the neocortex terminated within the dorsal medial, the medial and the ventral medial areas of the rostral basilar pontine gray. Corticopontine fibers from the mid-presupraorbital neocortex ended throughout the rostral to caudal extent of the basilar pontine gray, and terminated within the dorsal medial, the medial and the ventral medial areas; whereas degenerating fibers resulting from a lesion of the neocortex immediately rostral to the supraorbital sulcus terminated within the medial, the ventral and the ventral lateral areas of the basilar pontine gray. The neocortex immediately caudal to the supraorbital sulcus distributed corticopontine fibers to the ventral, the ventral lateral, the dorsal lateral and to the dorsal areas of the basilar pontine gray, while degenerating fibers resulting from lesions of the caudal one-third and most caudal tip of the neocortex projected to the ventral and lateral portions of the basilar pontine gray. Neocortical projections to the pontine and medullary reticular formation originated mainly from cortical areas rostral and immediately caudal to the supraorbital sulcus. The neocortex rostral to the supraorbital sulcus distributed to the rostral and medial portions of the pontine reticular formation, whereas corticoreticular fibers from the neocortex immediately caudal to the suprarbital sulcus, also distributed degenerating fascicles to the spinal trigeminal nucleus, the nucleus of the solitary tract and to the nucleus cuneatus. No degenerating fibers were seen to terminate within motor nuclei of cranial nerves located within either the pons or medulla.     

Identification and connections of inspiratory premotor neurons in songbirds and budgerigar

Recordings of extracellular unit activity in the ventrolateral medulla and of electyromyographic activity in either the M. scalenus, a principal inspiratory muscle, or the abdominal expiratory muscles, were used to identify inspiratory related (IR) neurons. IR neurons extended from levels caudal to the obex through the caudal level of the descending vestibular nucleus. This distribution was found to correspond to that of a subset of cells retrogradely labeled from injections of neuronal tracers into the upper thoracic spinal cord, where motoneurons innervating the M. scalenus were located by retrograde transport. Injections of biotinylated dextran amine at the recording sites resulted in projections to the spinal cord and brainstem. Bulbospinal axons traveled in the lateral funiculus, predominantly contralaterally, and terminated in relation to the dendrites and cell bodies of motoneurons innervating the M. scalenus. Brainstem nuclei receiving projections from injections at IR loci included the retroambigualis, tracheosyringeal motor nucleus, ventrolateral nucleus of the rostral medulla, infra-olivaris superior, ventrolateral parabrachial nucleus, and the dorsomedial nucleus of the intercollicular complex. In the finches, there were also bilateral projections to nucleus uvaeformis of the posterior thalamus. The spinal and brainstem projections are similar to those found in pigeon (Reinke and Wild, [1997] J. Comp. Neurol. 379:347–362), and probably mediate the intricate coordination of the vocal (syringeal) and respiratory systems for the control of vocalization. The distribution of IR neurons in birds is similar to that of the rostral ventral respiratory group (rVRG) in mammals. J. Comp. Neurol. 391:147–163, 1998. © 1998 Wiley-Liss, Inc.     

Organization of medullary adrenergic and noradrenergic projections to the periaqueductal gray matter in the rat.

The periaqueductal or midbrain central gray matter (CG) in the rat contains a dense network of adrenergic and noradrenergic fibers. We examined the origin of this innervation by using retrograde and anterograde axonal tracers combined with immunohistochemistry for the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT). Following injections of the fluorescent tracers Fast Blue or Fluorogold into the CG, double-labeled neurons in the medulla were identified mainly in the noradrenergic A1 group in the caudal ventrolateral medulla (VLM) and A2 group in the medial part of the nucleus of the solitary tract (NTS); and in the adrenergic C1 group in the rostral ventrolateral medulla and C3 group in the rostral dorsomedial medulla. Injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) into these cell groups resulted in a distinct pattern of axonal labeling in various subdivisions of the CG. Anterogradely labeled fibers originating in the medial NTS were predominantly found in the lateral portion of the dorsal raphe nucleus and in the adjacent part of the lateroventral CG (CGlv). Following PHA-L injections into the C3 region the anterogradely labeled fibers were diffusely distributed in the CGlv and the dorsal raphe nucleus at caudal levels, but rostrally tended to be located laterally in the CGlv. In contrast, ascending fibers from the caudal and rostral VLM terminated in the rostral dorsal part of the CGlv and in the dorsal nucleus of the CG, whereas ventral parts of the CG, including the dorsal raphe nucleus, contained few afferent fibers. Double-label studies with antisera against DBH and PNMT confirmed that noradrenergic neurons in the A1 and A2 groups and adrenergic neurons in the C1 and C3 groups contributed to these innervation patterns in the CGlv. Noradrenergic and adrenergic projections from the medulla to the CG may play an important role in a variety of autonomic, sensory and behavioral processes.     

Brainstem projections to the major respiratory neuron populations in the medulla of the cat

Efferent and afferent connections of the dorsal and ventral respiratory groups in the medulla of the cat were mapped by axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase. Injections of wheat germ agglutinin-horseradish peroxidase into the dorsal respiratory group and the three principal subdivisions of the ventral respiratory group (caudal, rostral, and B?tzinger Complex) revealed extensive interconnections between these regions and with a limited number of other brainstem neuron populations. Major neuron populations with efferent projections to the regions of the dorsal and ventral respiratory groups include the parabrachial nuclear complex (medial parabrachial, lateral parabrachial, and K?lliker-Fuse nuclei), subregions of the lateral paragigantocellular reticular nucleus, subregions of the lateral and magnocellular tegmental fields, inferior central and postpyramidal nuclei of the raphe, and sensory trigeminal nuclei. A previously unidentified neuron population with extensive efferent projections to the dorsal and ventral respiratory groups was found near the ventral surface of the rostral medulla; we refer to this group as the retrotrapezoid nucleus. The results suggest that the dorsal and ventral respiratory groups form an extensively interconnected neuronal system receiving convergent inputs from the same brainstem nuclear groups, consistent with the hypothesis that the dorsal and ventral groups are primarily sites for integration of sensory and premotor respiratory drive inputs. Neuron populations in the rostral ventrolateral medulla with projections to both the dorsal and ventral respiratory groups, particularly the retrotrapezoid nucleus and neighboring subregions of the lateral paragigantocellular reticular nucleus, are candidate sites for participation in respiratory rhythmogenesis or other critical functions of the brainstem respiratory control system such as intracranial chemoreception.     

Projections of the parabrachial nucleus in the pigeon (Columba livia).

The ascending and descending projections of the parabrachial nuclear complex in the pigeon have been charted with autoradiographic and histochemical (WGA-HRP) techniques. The ascending projections originate from a group of subnuclei surrounding various components of the brachium conjunctivum, namely, the superficial lateral, dorsolateral, dorsomedial, and ventromedial subnuclei. The projections are predominantly ipsilateral and travel in the quintofrontal tract. They are primarily to the medial and lateral hypothalamus (including the periventricular nucleus and the strata cellulare internum and externum), certain dorsal thalamic nuclei, the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, the ventral paleostriatum, the olfactory tubercle, the nucleus accumbens, and a dorsolateral nucleus of the posterior archistriatum. There are weaker or more diffuse projections to the rostral locus coeruleus (cell group A8), the compact portion of the pedunculopontine tegmental nucleus, the central grey and intercollicular region, the ventral area of Tsai, the medial spiriform nucleus, the nucleus subrotundus, the anterior preoptic area, and the diagonal band of Broca. The parabrachial subnuclei have partially differential projections to these targets, some of which also receive projections from the nucleus of the solitary tract (Arends, Wild, and Zeigler: J. Comp. Neurol. 278:405-429, '88). Most of the targets, particularly those in the basal forebrain (viz., the periventricular nucleus and the strata cellulare internum and externum of the hypothalamus, the bed nucleus of the stria terminalis, and its lateral extension into the ventral paleostriatum, which may be comparable with the substantia innominata), have reciprocal connections with the parabrachial and solitary tract subnuclei and therefore may be said to compose parts of a "visceral forebrain system" analogous to that described in the rat (Van der Kooy et al: J. Comp. Neurol. 224:1-24, '84). The descending projections to the lower brainstem arise in large part from a ventrolateral subnucleus that may be comparable with the K?lliker-Fuse nucleus of mammals. They are mainly to the ventrolateral medulla, nucleus ambiguus, and massively to the hypoglossal nucleus, particularly its tracheosyringeal portion. These projections are therefore likely to be importantly involved in the control of vocalization and respiration (Wild and Arends: Brain Res. 407:191-194, '87). Some of these results have been presented in abstract form (Wild, Arends, and Zeigler: Soc. Neurosci. Abst. 13:308, '87).     

Projections of the dorsal raphe nucleus to the brainstem: PHA-L analysis in the rat

Early studies that used older tracing techniques reported exceedingly few projections from the dorsal raphe nucleus (DR) to the brainstem. The present report examined DR projections to the brainstem by use of the anterograde anatomical tracer Phaseolus vulgaris leucoagglutinin (PHA-L). DR fibers were found to terminate relatively substantially in several structures of the midbrain, pons, and medulla. The following pontine and midbrain nuclei receive moderate to dense projections from the DR: pontomesencephalic central gray, mesencephalic reticular formation, pedunculopontine tegmental nucleus, medial and lateral parabrachial nuclei, nucleus pontis oralis, nucleus pontis caudalis, locus coeruleus, laterodorsal tegmental nucleus, and raphe nuclei, including the central linear nucleus, median raphe nucleus, and raphe pontis. The following nuclei of the medulla receive moderately dense projections from the DR: nucleus gigantocellularis, nucleus raphe magnus, nucleus raphe obscurus, facial nucleus, nucleus gigantocellularis-pars alpha, and the rostral ventrolateral medullary area. DR fibers project lightly to nucleus cuneiformis, nucleus prepositus hypoglossi, nucleus paragigantocellularis, nucleus reticularis ventralis, and hypoglossal nucleus. Some differences were observed in projections from rostral and caudal parts of the DR. The major difference was that fibers from the rostral DR distribute more widely and heavily than do those from the caudal DR to structures of the medulla, including raphe magnus and obscurus, nucleus gigantocellularis-pars alpha, nucleus paragigantocellularis, facial nucleus, and the rostral ventrolateral medullary area. A role for the dorsal raphe nucleus in several brainstem controlled functions is discussed, including REM sleep and its events, nociception, and sensory motor control. © Wiley-Liss, Inc.     

Specificity of spinal projections from hypothalamic and brainstem areas which innervate sympathetic preganglionic neurons

The specificity and topographic organization of afferent projections to the intermediolateral column (IML) were examined using retrograde transport of fluorescent tracers injected into pairs of thoracic spinal segments. Neurons within the hypothalamus (parvocellular paraventricular nucleus, dorsomedial nucleus and lateral hypothalamus), pons (Kolliker-Fuse and A5 nuclei) and medulla (ventrolateral nucleus of the solitary tract and rostral ventrolateral medulla) each appeared to innervate only a single spinal segment. Neurons in each cell group projecting to different spinal segments were intermixed and showed no evidence of topographic organization. These results provide a potential anatomical substrate for organ-specific autonomic responses to physiological and psychological stimuli.     

Organization of the pallium in the fire-bellied toad Bombina orientalis. I: Morphology and axonal projection pattern of neurons revealed by intracellular biocytin labeling

The cytoarchitecture and axonal projection pattern of pallial areas was studied in the fire-bellied toad Bombina orientalis by intracellular injection of biocytin into a total of 326 neurons forming 204 clusters. Five pallial regions were identified, differing in morphology and projection pattern of neurons. The rostral pallium receiving the bulk of dorsal thalamic afferents has reciprocal connections with all other pallial areas and projects to the septum, nucleus accumbens, and anterior dorsal striatum. The medial pallium projects bilaterally to the medial pallium, septum, nucleus accumbens, mediocentral amygdala, and hypothalamus and ipsilaterally to the rostral, dorsal, and lateral pallium. The ventral part of the medial pallium is distinguished by efferents to the eminentia thalami and the absence of contralateral projections. The dorsal pallium has only ipsilateral projections running to the rostral, medial, and lateral pallium; septum; nucleus accumbens; and eminentia thalami. The lateral pallium has ipsilateral projections to the olfactory bulbs and to the rostral, medial, dorsal, and ventral pallium. The ventral pallium including the striatopallial transition area (SPTA) has ipsilateral projections to the olfactory bulbs, rostral and lateral pallium, dorsal striatopallidum, vomeronasal amygdala, and hypothalamus. The medial pallium can be tentatively homologized with the mammalian hippocampal formation, the dorsal pallium with allocortical areas, the lateral pallium rostrally with the piriform and caudally with the entorhinal cortex, the ventral pallium with the accessory olfactory amygdala. The rostral pallium, with its projections to the dorsal and ventral striatopallidum, resembles the mammalian frontal cortex.     

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.     

Heart rate and blood pressure responses to electrical stimulation of the central nervous system in the pigeon (Columba livia)

An extensive stereotaxic stimulation study of the pigeon brain was conducted with monitoring of heart rate, arterial blood pressure and respiration. Rostrally, short latency tachycardia, hypertension and hyperpnea were elicited from the archistriatum, occipitomesencephalic tract and hypothalamus. In addition, blood pressure decreases followed by long latency tachycardia were elicited from the septal complex, although occasionally slight bradycardia occurred. Tachycardia, hypertension and hyperpnea were elicited from many midbrain sites including the lateral reticular formation, ventrolateral tegmentum, ventral area of Tsai, the midline region between nucleus interpeduncularis and the oculomotor complex, and nucleus mesencephalicus lateralis, pars dorsalis. In addition, moderate tachycardia and hypotension were elicited from the central gray and nucleus intercollicularis while tachycardia, hypertension and hyperpnea were elicited from the tegmental area in the region of the occipitomesencephalic tract. At pontine levels, hypertension and cardioacceleration were elicited from a sparsely celled region lateral to the nucleus abducens and from a ventrolateral tegmental region. With respect to respiratory responses, hyperpnea was elicited from the ventrolateral brainstem at all pontine levels and from the dorsomedial region at rostral pontine levels. In caudal pons apnea was the consistent respiratory response to stimulation of the dorsomedial brainstem. In addition, cardio-acceleration, hypertension and apnea were elicited from the region of the deep cerebellar nucleus cerebellus internus and from its major outflow, the uncinate fasciculus. Finally, stimulation in the medulla elicited bradycardia and hypotension from the vagal rootlets, solitary complex, descending vestibular nucleus and lateral aspect of the dorsal motor nucleus just rostral to the obex. Tachycardia and hypertension were elicited from the medial aspect of the dorsal motor nucleus, medullary reticular formation ventral to the vagal rootlets and ventrolateral medulla.     

Distribution and connections of inspiratory premotor neurons in the brainstem of the pigeon (Columba livia)

We have recorded extracellular, inspiratory-related (IR) unit activity in the medulla at locations corresponding to those of neurons retrogradely labeled by injections of retrograde tracers in the lower brachial and upper thoracic spinal cord, injections that covered cell bodies and dendrites of motoneurons innervating inspiratory muscles. Bulbospinal neurons were distributed throughout the dorsomedial and ventrolateral medulla, from the spinomedullary junction through about 0.8 mm rostral to the obex. Almost all of the 104 IR units recorded were located in corresponding parts of the ventrolateral medulla, rostral to nucleus retroambigualis, where expiratory related units are found. Injections of biotinylated dextran amine at the recording sites labeled projections both to the spinal cord and to the brainstem. In the lower brachial and upper thoracic spinal cord, bulbospinal axons traveled predominantly in the contralateral dorsolateral funiculus and terminated in close relation to the dendrites of inspiratory motoneurons retrogradely labeled with cholera toxin B-chain. In the brainstem, there were predominantly ipsilateral projections to the nucleus retroambigualis, tracheosyringeal motor nucleus (XIIts), ventrolateral nucleus of the rostral medulla, infraolivary superior nucleus, ventrolateral parabrachial nucleus, and dorsomedial nucleus of the intercollicular complex. In all these nuclei, except XIIts, retrogradely labeled neurons were also found, indicating reciprocity of the connections. These results suggest the possibility of monosynaptic connections between inspiratory premotor neurons and inspiratory motoneurons, which, together with connections of IR neurons with other brainstem respiratory-vocal nuclei, seem likely to mediate the close coordination that exists in birds between the vocal and respiratory systems. The distribution of IR neurons in birds is similar to that of the rostral ventral respiratory group (rVRG) in mammals. J. Comp. Neurol. 379:347–362, 1997. © 1997 Wiley-Liss, Inc.     

Amygdalo-hypothalamic projections in the lizard Podarcis hispanica: A combined anterograde and retrograde tracing study

The cells of origin and terminal fields of the amygdalo-hypothalamic projections in the lizard Podarcis hispanica were determined by using the anterograde and retrograde transport of the tracers, biotinylated dextran amine and horseradish peroxidase. The resulting labeling indicated that there was a small projection to the preoptic hypothalamus, that arose from the vomeronasal amygdaloid nuclei (nucleus sphericus and nucleus of the accessory olfactory tract), and an important projection to the rest of the hypothalamus, that was formed by three components: medial, lateral, and ventral. The medial projection originated mainly in the dorsal amygdaloid division (posterior dorsal ventricular ridge and lateral amygdala) and also in the centromedial amygdaloid division (medial amygdala and bed nucleus of the stria terminalis). It coursed through the stria terminalis and reached mainly the retrochiasmatic area and the ventromedial hypothalamic nucleus. The lateral projection originated in the cortical amygdaloid division (ventral anterior and ventral posterior amygdala). It coursed via the lateral amygdalofugal tract and terminated in the lateral hypothalamic area and the lateral tuberomammillary area. The ventral projection originated in the centromedial amygdaloid division (in the striato-amygdaloid transition area), coursed through the ventral peduncle of the lateral forebrain bundle, and reached the lateral posterior hypothalamic nucleus, continuing caudally to the hindbrain. Such a pattern of the amygdalo-hypothalamic projections has not been described before, and its functional implications in the transfer of multisensory information to the hypothalamus are discussed. The possible homologies with the amygdalo-hypothalamic projections in mammals and other vertebrates are also considered. J. Comp. Neurol. 384:537–555, 1997. © 1997 Wiley-Liss, Inc.     

The distribution and morphological characteristics of serotonergic cells in the brain of monotremes

The distribution and cellular morphology of serotonergic neurons in the brain of two species of monotremes are described. Three clusters of serotonergic neurons were found: a hypothalamic cluster, a cluster in the rostral brainstem and a cluster in the caudal brainstem. Those in the hypothalamus consisted of two groups, the periventricular hypothalamic organ and the infundibular recess, that were intimately associated with the ependymal wall of the third ventricle. Within the rostral brainstem cluster, three distinct divisions were found: the dorsal raphe nucleus (with four subdivisions), the median raphe nucleus and the cells of the supralemniscal region. The dorsal raphe was within and adjacent to the periaqueductal gray matter, the median raphe was associated with the midline ventral to the dorsal raphe, and the cells of the supralemniscal region were in the tegmentum lateral to the median raphe and ventral to the dorsal raphe. The caudal cluster consisted of three divisions: the raphe obscurus nucleus, the raphe pallidus nucleus and the raphe magnus nucleus. The raphe obscurus nucleus was associated with the dorsal midline at the caudal-most part of the medulla oblongata. The raphe pallidus nucleus was found at the ventral midline of the medulla around the inferior olive. Raphe magnus was associated with the midline of the medulla and was found rostral to both the raphe obscurus and raphe pallidus. The results of our study are compared in an evolutionary context with those reported for other mammals and reptiles.     

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

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