Connections of the parabrachial nucleus with the nucleus of the solitary tract and the medullary reticular formation in the rat

Mapping study of the parabrachial taste-responsive area for the anterior tongue in the golden hamster

The locations of taste-responsive areas within the brainstem parabrachial nucleus (PBN), an obligatory taste relay in the golden hamster (Mesocricetus auratus), were mapped in relation to cytoarchitectural boundaries. The PBN was systematically searched for multiunit neural activity in response to a taste mixture composed of 0.1 M sucrose, 0.03 M NaCl, and 0.1 M KCl applied to the anterior tongue. Taste responses were located exclusively in one of three subdivisions of the medial PBN, which is thought to be specialized for gustatory processing, and in one of six subdivisions of the lateral PBN, which is thought to be specialized for general visceral processing. Based on Nissl-stained material, both the medial and lateral PBN subdivisions in the hamster were similar to those reported for the rat PBN. The largest group of taste-responsive cells encompassed two-thirds of the central medial subdivision, while a smaller group of taste cells was exclusively located within the ventral lateral subdivision. The two taste-responsive subdivisions are separated by the superior cerebellar peduncle and contain diverse cell types. The finding that anterior tongue taste may be exclusively represented in circumscribed cytoarchitecturally defined parts of two PBN divisions suggests that taste information from the anterior tongue is required for both specific gustatory and general visceral functions.

Effects of parabrachial stimulation on angiotensin and blood pressure sensitive area postrema neurons

Subpopulations of neurons in the area postrema (AP) and commissural nucleus tractus solitarius (NTS) have been identified according to their responses to systemic angiotensin-II (ANG-II) and increases in blood pressure (BP). In order to further define the functional connections of these subpopulations of cells, electrophysiological single unit recording studies have been done to determine the orthodromic effects of parabrachial nucleus (PBN) stimulation on these functionally defined cell groups. Orthodromic effects were seen in a similar proportion of ANG-II sensitive neurons in the AP (31.5%) and NTS (31%). PBN stimulation influenced a similar percentage of BP sensitive neurons in the AP (35%), although a larger proportion of this group of NTS cells was affected (55.5%). Twenty-five percent of ANG-II/BP sensitive neurons in the AP were orthodromically influenced, and 71.5% of this group of NTS neurons were affected by PBN stimulation. Small proportions of the neurons in the unaffected subpopulation of AP (10%) and NTS (27%) were also orthodromically affected by PBN stimulation. The remaining neurons in each group were not affected. This study suggests that there is no apparent preferential distribution of excitatory or inhibitory PBN efferents to any of the identified subpopulations of AP and NTS neurons.

Autonomic responses and efferent pathways from the insular cortex in the rat

The anatomical distribution of autonomic, particularly cardiovascular, responses originating in the insular cortex was examined by using systematic electrical microstimulation. The localization of these responses to cell bodies in the insular cortex was demonstrated by using microinjection of the excitatory amino acid, D,L-homocysteic acid. The efferents from the cardiovascular responsive sites were traced by iontophoretic injection of the anterograde axonal tracer Phaseoleus vulgaris leucoagglutinin (PHA-L). Two distinct patterns of cardiovascular response were elicited from the insular cortex: an increase in arterial pressure accompanied by tachycardia or a decrease in arterial pressure with bradycardia. The pressor responses were obtained by stimulation of the rostral half of the posterior insular cortex while depressor sites were located in the caudal part of the posterior insular area. Both types of site were primarily located in the dysgranular and agranular insular cortex. Gastric motility changes originated from a separate but adjacent region immediately rostral to the cardiovascular responsive sites in the anterior insular cortex. Tracing of efferents with PHA-L indicated a number of differences in connectivity between the pressor and depressor sites. Pressor sites had substantially more intense connections with other limbic regions including the infralimbic cortex, the amygdala, the bed nucleus of the stria terminalis and the medial dorsal and intralaminar nuclei of the thalamus. Alternatively, the depressor region of the insular cortex more heavily innervated sensory areas of the brain including layer I of the primary somatosensory cortex, a peripheral region of the sensory relay nuclei of the thalamus and the caudal spinal trigeminal nucleus. In addition, there were topographical differences in the projection to the lateral hypothalamic area, the primary site of autonomic outflow for these responses from the insular cortex. These differences in connectivity may provide the anatomic substrate for the specific cardiovascular responses and behaviors integrated in the insular cortex.

Subdivisions and neuron types of the nucleus of the solitary tract that project to the parabrachial nucleus in the hamster

The solitary nuclear complex (NST) consists of a number of subdivisions that differ in their cytoarchitectonic features as well as in the amounts of inputs they receive from lingual afferent axons. In this study horseradish peroxidase (HRP) was injected into the parabrachial nucleus (PBN) of the hamster to determine which of these subdivisions contain cells that project to the pons. In the rostral, gustatory division of the NST, the rostral central subdivision contains the greatest number of labelled pontine-projection neurons. The rostral lateral subdivision contains moderate numbers of labelled cells; progressively fewer labelled cells are in the ventral, medial, and dorsal subdivisions. In the caudal, general viscerosensory division of the NST, the caudal central subdivision contains the majority of labelled cells, although fewer than its rostral counterpart. Progressively fewer cells are labelled in the medial, laminar, ventrolateral, and lateral subdivisions; none in the dorsolateral subdivision. Small horseradish peroxidase injections into the pons revealed that cells of the rostral central and rostral lateral subdivisions of the NST project to the medial subdivision of the PBN, predominantly to caudal and ventral parts of the subdivision. Cells of the caudal central and medial subdivisions of the NST project to the central lateral subdivision of the PBN, predominantly to intermediate and rostral-dorsal parts of the subdivision. Outside the NST, cells in the spinal trigeminal nucleus and parvicellular reticular formation were also labelled after PBN injections. Within the rostral central and rostral lateral (gustatory) subdivisions of the NST at least two types of neurons, distinguished on the basis of dendritic and cell body morphology, were labelled after HRP injections that included the medial PBN. Elongate cells have ovoid-fusiform somata and dendrites oriented in the mediolateral plane parallel to primary afferent axons entering from the solitary tract. Stellate cells have triangular or polygonal cell bodies and three to five dendrites oriented in all directions, although one or two often extend mediolaterally. These results indicate that cytoarchitectonic subdivisions of the NST are distinguished by their efferent ascending connections. For each subdivision within the rostral, gustatory NST there is a correlation between the density of lingual inputs it receives and the density of pontine-projection neurons it contains.(ABSTRACT TRUNCATED AT 400 WORDS)

Relays from the spinal cord and solitary nucleus through the parabrachial nucleus to the forebrain in the cat

Projections from the spinal cord and solitary nucleus to the lateral parabrachial nucleus (PBN1) in the cat were directly compared using double anterograde tracing methods. The two inputs were found to overlap within a well-circumscribed zone in the rostral 2/3 of PBN1. This zone was flanked ventrally by a zone receiving only solitary nucleus input and dorsally by a zone receiving only spinal input. Other authors have shown that neurons within these three recipient zones (overlap area, solitary nucleus and spinal cord) project to different forebrain targets (hypothalamus, amygdala and thalamus, respectively). This orderly input-output organization is likely to provide part of the framework for PBN's complex involvement in the coordination of respiratory and cardiovascular activities and their association with pain, visceral sensation and emotion.

Organization of cortical, basal forebrain, and hypothalamic afferents to the parabrachial nucleus in the rat

In a previous study (Herbert et al., J. Comp. Neurol. [1990];293:540-580), we demonstrated that the ascending afferent projections from the medulla to the parabrachial nucleus (PB) mark out functionally specific terminal domains within the PB. In this study, we examine the organization of the forebrain afferents to the PB. The PB was found to receive afferents from the infralimbic, the lateral prefrontal, and the insular cortical areas; the dorsomedial, the ventromedial, the median preoptic, and the paraventricular hypothalamic nuclei; the dorsal, the retrochiasmatic, and the lateral hypothalamic areas; the central nucleus of the amygdala; the substantia innominata; and the bed nucleus of the stria terminalis. In general, forebrain areas tend to innervate the same PB subnuclei from which they receive their input. Three major patterns of afferent termination were noted in the PB; these corresponded to the three primary sources of forebrain input to the PB: the cerebral cortex, the hypothalamus, and the basal forebrain. Hypothalamic afferents innervate predominantly rostral portions of the PB, particularly the central lateral and dorsal lateral subnuclei. The basal forebrain projection to the PB ends densely in the external lateral and waist subnuclei. Cortical afferents terminate most heavily in the caudal half of the PB, particularly in the ventral lateral and medial subnuclei. In addition, considerable topography organization was found within the individual projections. For example, tuberal lateral hypothalamic neurons project heavily to the central lateral subnucleus and lightly to the waist area; in contrast, caudal lateral hypothalamic neurons send a moderately heavy projection to both the central lateral and waist subnuclei. Our results show that the forebrain afferents of the PB are topographically organized. These topographical differences may provide a substrate for the diversity of visceral functions associated with the PB.

Cholecystokinin-, galanin-, and corticotropin-releasing factor-like immunoreactive projections from the nucleus of the solitary tract to the parabrachial nucleus in the rat

The parabrachial nucleus (PB) is the main relay for ascending visceral afferent information from the nucleus of the solitary tract (NTS) to the forebrain. We examined the chemical organization of solitary-parabrachial afferents by using combined retrograde transport of fluorescent tracers and immunohistochemistry for galanin (GAL), cholecystokinin (CCK), and corticotropin-releasing factor (CRF). Each peptide demonstrated a unique pattern of immunoreactive staining. GAL-like immunoreactive (-ir) fibers were most prominent in the "waist" area, the inner portion of external lateral PB, and the central and dorsal lateral PB subnuclei. Additional GAL-ir innervation was seen in the medial and external medial PB subnuclei. GAL-ir perikarya were observed mainly rostrally in the dorsal lateral, superior lateral, and extreme lateral PB. CCK-ir fibers and terminals were most prominent in the outer portion of the external lateral PB; some weaker labeling was also present in the central lateral PB. CCK-ir cell bodies were almost exclusively confined to the superior lateral PB and the "waist" area, although a few cells were seen in the Kölliker-Fuse nucleus. The distribution of CRF-ir terminal fibers in general resembled that of GAL, but showed considerably less terminal labeling in the lateral parts of the dorsal and central lateral PB, and the external medial and Kölliker-Fuse subnuclei. The CRF-ir cells were most numerous in the dorsal lateral PB and the outer portion of the external lateral PB; rostrally, scattered CRF-ir neurons were seen mainly in the central lateral PB. After injecting the fluorescent tracer Fast Blue into the PB, the distribution of double-labeled neurons in the NTS was mapped. GAL-ir cells were mainly located in the medial NTS subnucleus; 34% of GAL-ir cells were double-labeled ipsilaterally and 7% contralaterally. Conversely, 17% of the retrogradely labeled cells ipsilaterally and 16% contralaterally were GAL-ir. CCK-ir neurons were most numerous in the dorsomedial subnucleus of the NTS and the outer rim of the area postrema. Of the CCK-ir cells, 68% in the ipsilateral and 10% in the contralateral NTS were double-labeled, whereas 15% and 10%, respectively, of retrogradely labeled cells were CCK-ir. In the area postrema, 36% of the CCK-ir cells and 9% of the Fast Blue cells were double-labeled. CRF-ir neurons were more widely distributed in the medial, dorsomedial, and ventrolateral NTS subnuclei, but double-labeled cells were mainly seen in the medial NTS.(ABSTRACT TRUNCATED AT 400 WORDS)

Central neural control of esophageal motility: a review

We review recent studies on the central neural control of esophageal motility, emphasizing the anatomy and chemical coding of esophageal pathways in the spinal cord and medulla. Sympathetic innervation of the proximal esophagus is derived primarily from cervical and upper thoracic paravertebral ganglia, whereas that of the lower esophageal sphincter and proximal stomach is derived from the celiac ganglion. In addition to noradrenaline, many sympathetic fibers in the esophagus contain neuropeptide Y (NPY), and both noradrenaline and NPY appear to decrease blood flow and motility. Preganglionic neurons innervating the cervical and upper thoracic ganglia are located at lower cervical and upper thoracic spinal levels. The preganglionic innervation of the celiac ganglion arises from lower thoracic spinal levels. Both acetylcholine (ACh) and enkephalin (ENK) have been localized in sympathetic preganglionic neurons, and it has been suggested that ENK acts to pre-synaptically inhibit ganglionic transmission. Spinal afferents from the esophagus are few, but have been described in lower cervical and thoracic dorsal root ganglia. A significant percentage contain calcitonin gene-related peptide (CGRP) and substance P (SP). The central distribution of spinal afferents, as well as their subsequent processing within the spinal cord, have not been addressed. Medullary afferents arise from the nodose ganglion and terminate peripherally both in myenteric ganglia, where they have been postulated to act as tension receptors, and, to a lesser extent, in more superficial layers. Centrally, these afferents appear to end in a discrete part of the nucleus of the solitary tract (NTS) termed the central subnucleus. The transmitter specificity of the majority of these afferents remains unknown. The central subnucleus, in turn, sends a dense and topographically discrete projection to esophageal motor neurons in the rostral portion of the nucleus ambiguous (NA). Both somatostatin-(SS) and ENK-related peptides have been localized in this pathway. Finally, motor neurons from the rostral NA innervate striated portions of the esophagus. In addition to ACh, these esophageal motor neurons contain CGRP, galanin (GAL), N-acetylaspartylglutamate (NAAG), and brain natriuretic peptide (BNP). The physiological effect of these peptides on esophageal motility remains unclear. Medullary control of smooth muscle portions of the esophagus have not been thoroughly investigated.