Dorsal Subnuclei Research Articles

Distribution of bombesin‐like immunoreactivity in the nucleus of the solitary tract and dorsal motor nucleus of the rat and human: Colocalization with tyrosine hydroxylase

Bombesin is a peptide neurotransmitter/neuromodulator with important autonomic and behavioral effects that are mediated, at least in part, by bombesin-containing neurons and nerve terminals in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV). The distribution of bombesin-like immunoreactive nerve terminals/fibers and cell bodies in relation to a viscerotopically relevant subnuclear map of this region was studied by using an immunoperoxidase technique. In the rat, bombesin fiber/terminal staining was heavy in an area that included the medial subnucleus of the NTS and the DMV over their full rostral-caudal extent. Distinctly void of staining were the gelatinous, central, and rostral commissural subnuclei and the periventricular area of the NTS, regions to which gastric, esophageal, cecal, and colonic primary afferents preferentially project. The caudal commissural and dorsal subnuclei had light bombesin fiber/terminal staining, as did the intermediate, interstitial, ventral, and ventrolateral subnuclei. With colchicine pretreatment, numerous cell bodies were stained in the medial and dorsal subnuclei, with fewer neurons in the caudal commissural, intermediate, interstitial, ventral, and ventrolateral subnuclei. Bombesin-like immunoreactive neurons were found in numerous other areas of the brain, including the ventrolateral medulla, the parabrachial nucleus, and the medial geniculate body. In the human NTS/DMV complex, the distribution of bombesin fiber/terminal staining was very similar to the rat. In addition, occasional bombesin-like immunoreactive neurons were labeled in a number of subnuclei, with clusters of neurons labeled in the dorsal and ventrolateral subnuclei. Double immunofluorescence studies in rat demonstrated that bombesin colocalizes with tyrosine hydroxylase in neurons in the dorsal subnucleus of the NTS. Bombesin does not colocalize with tyrosine hydroxylase in any other location in the brain. In conclusion, the distribution of bombesin in the NTS adheres to a viscerotopically relevant map. This is the anatomical substrate for the effects of bombesin on gastrointestinal function and satiety and its likely role in concluding a meal. The anatomic similarities between human and rat suggest that bombesin has similar functions in the visceral neuraxis of these two species. Bombesin coexists with catecholamines in neurons in the dorsal subnucleus, which likely mediate, in part, the cardiovascular effects of bombesin. © 1996 Wiley-Liss, Inc.

Distribution and quantitative characterization of NADPH-diaphorase-reactive neurons in analgesic zones of the rat midbrain

The distribution of nitric oxide synthase (nicotinamide adenine dinucleotide phosphate diaphorase, NADPH-d)-containing neurons in the rat midbrain was studied. We found that NADPH-d-reactive neurons were predominantly concentrated in the dorsolateral part of the periaqueductal gray (PAG) and the dorsal raphe nucleus, which are implicated in the control of nociceptive transmission. Such neurons were also present in the supraoculomotor cap and laterodorsal tegmental nuclei. In the dorsolateral part ofPAG, the moderately stained small fusiform cells were revealed. In the dorsal raphe nucleus and laterodorsal tegmental nuclei, the densely stained multipolar or oval cells of larger size dominanted. The NADPH-d-reactive cells were not found in the ventrolateral part of central gray, which is considered the main source of antinociceptive descending influences. Quantitative analysis of histochemically revealed neurons showed that their number is somewhat higher in the caudal parts of dorsolateral central gray and considerably higher in the rostral regions of some dorsal raphe subnuclei. This peculiarity was expressed in significant accumulation of the NADPH-d-reactive neurons at the midbrain levels from Fr −7.6 to −8.0. The possible involvement of the NO-synthase-containing class of neurons in the functional organization of analgesic zones and formation ofPAG antinociceptive output signals is discussed.

Complementary expression of parvalbumin and calbindin D-28k delineates subdivisions of the rabbit medial geniculate body.

The complementary pattern of immunohistochemical staining for the calcium-binding proteins parvalbumin (PV) and calbindin D-28k (CB) was used to delineate four major subdivisions of the rabbit medial geniculate body (MGB). PV immunoreactivity predominates in the ventral and medial divisions, whereas CB-immunoreactive cells characterize the dorsal and internal divisions. The ventral nucleus is strongly PV+ due to dense neuropil labeling and moderately labeled somata. The medial nucleus contains both medium-sized and large PV+ somata, as well as thick PV+ axons and terminals. The wedge-shaped internal nucleus composed of densely labeled CB+ cells, separates the dorsal and ventral nuclei rostrally, and expands caudally to encapsulate the posterior MGV. Large multipolar CB+ neurons with radiate dendrites characterize the dorsal nucleus. The differential expression of PV and CB also distinguishes the deep dorsal and superficial dorsal subnuclei in the dorsal division and a ventrolateral component in the ventral division. A comparison with studies of MGB connectivity in a variety of species suggests that PV immunoreactivity is highest in subdivisions that receive a substantial input from the central nucleus of the inferior colliculus and that project to primary auditory cortex. In contrast, CB immunoreactivity characterizes nuclei that receive input primarily from other sources, such as the paracentral nuclei of the inferior colliculus, the lateral tegmentum, and the spinal cord, and that project to secondary auditory areas. The ability of calcium-binding protein immunohistochemistry to delineate neuronal compartments across indistinct cytoarchitectonic borders makes it a powerful tool for guiding future connectional and physiological studies of the MGB.

Colchicine induces the GAP-43 gene expression in rat hypothalamus.

Injection of colchicine, a mitogen inhibitor, in the dorsal third ventricle induced the expression of the growth associated protein-43 (GAP-43) mRNA in some groups of cells of the adult rat brain. These mRNAs were detected by in situ hybridization histochemistry using an alkaline phosphatase labeled oligonucleotide probe. A substantial up-regulation of GAP-43 mRNA was noticed by the increase of both the number of positive cells and the intensity of the hybridization signal. These changes were observed in the hypothalamic nuclei located near the ventral third ventricle, namely the preoptic area, the supraoptic nucleus, the peri- and the paraventricular nuclei of the hypothalamus, the dorsal subnucleus of the ventromedial nucleus, the arcuate nucleus and the posterior part of the peri-mammillary region. Such abundant GAP-43 mRNA positive cells have not been observed in control adult rat hypothalamus. Since the positive cell number and shape initially suggested that these were neurons or astrocytes, double labeling in situ hybridization using both radioactive (for the detection of GFAP mRNA as a marker of astrocyte) and non-radioactive (for the detection of GAP-43 mRNA) probes was carried out. This demonstrated that these GAP-43 mRNA positive cells were not astrocytes. In addition enhanced GAP-43 mRNA expression was also found in some neuronal component, particularly in neurosecretory magnocells of the pareaventricular and the supraoptic nuclei. This up-regulation was further confirmed by the Northern blot analysis. About five fold increase in GAP-43 mRNA in the colchicine-treated hypothalamic tissue was shown.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory and excitatory projections prom the dorsal raphe nucleus to neurons in the dorsolateral periaqueductal gray matter in slices of midbrain maintained in vitro

Coronal slices of midbrain from adult rats, maintained in an interface chamber at 33–35°C, were used to investigate projections from the dorsal raphe nucleus to the dorsolateral periaqueductal gray matter. Extracellular recordings were made from neurons in the dorsolateral periaqueductal gray matter. The majority of cells were silent but activity could readily be induced by iontophoretic application of d,l-homocysteic acid from the recording pipette. Neuronal perikarya in the dorsal raphe nucleus were activated either by topical application of 15–100 ni droplets of 1 or 10 mM d,l-homocysteic acid or by iontophoresis into the dorsal raphe nucleus of 0.l M d,l-homocysteic acid from a five-barrelled glass micropipette. Both forms of stimulation evoked increases or decreases in firing in neurons in the dorsolateral periaqueductal gray matter. The excitatory responses were evoked only from stimulation sites in the dorsal subnucleus of the dorsal raphe nucleus, whilst inhibitory responses could be evoked by stimulating throughout the nucleus. 5-Hydroxytryptamine was applied by iontophoresis to 55 neurons in the dorsolateral periaqueduetal gray matter. Of these, 89% were inhibited whilst the remaining 11% were excited. No unresponsive cells were found. In a second series of experiments anterograde transport of biocytin was used to study projections from the dorsal raphe nucleus to the periaqueductal gray matter in vitro. Following injections of pellets of biocytin into the dorsal subnucleus of the dorsal raphe nucleus, two types of labelled axons could be distinguished which had either smooth or beaded profiles. Both types of axon could be followed into the region of the dorsolateral periaqueductal gray matter, from which recordings were made in the electrophysiological experiments. In contrast, following deposits of biocytin into the ventral half of the periaqueductal gray matter, very few labelled axons were found in the dorsolateral periaqueductal gray matter, although the ventrolateral periaqueductal gray matter was heavily labelled. We conclude that both excitatory and inhibitory projections from the dorsal raphe nucleus to the dorsolateral periaqueductal gray matter are present in the coronal midbrain slice preparation. Excitatory projections originate from the dorsal subnucleus of the dorsal raphe nucleus and may be mediated by a direct pathway. The inhibitory effects evoked from the ventral half of the dorsal raphe nucleus are probably mediated indirectly, perhaps by activation of inhibitory interneurons in the ventrolateral periaqueductal gray matter.

Distribution of substance P‐like immunoreactive neurons and terminals throughout the nucleus of the solitary tract in the human brainstem

The anatomical distribution of substance P-like immunoreactivity across the subnuclear divisions of the nucleus of the solitary tract has been examined in the human medulla oblongata. A differential distribution of neurons, fibres, and terminals was observed throughout the ten subnuclear divisions of this nucleus. Substance P-like immunoreactive neurons were observed most frequently in the nucleus gelatinosus, with moderate numbers in the medial, intermediate subnuclei and very few in the commissural, ventral, dorsal, and dorsolateral subnuclei. The paracommissural, ventrolateral, and interstitial subnuclei did not contain substance P-like-immunoreactive neurons. These neurons were typically bipolar and moderate-sized to large, except for the neurons in the nucleus gelatinosus, which were substantially smaller. The highest densities of fibres and terminals were observed in the gelatinosus, medial, and intermediate nuclei, with moderate densities in the paracommissural and dorsal subnuclei. Sparse substance P-like-immunoreactive fibres and terminals were seen in the ventral and interstitial nuclei as well as within the solitary tract. The dorsolateral nucleus was characterized by a light distribution of fibres and terminals, except for a dense aggregation along its lateralmost border. A prominent innervation of pigmented neurons by substance P-like-immunoreactive terminals and fibres was also observed in the dorsolateral nucleus. The results reveal that the subnuclear complexity of the nucleus of the solitary tract is richly reflected by its differential pattern of substance P-like-immunoreactive structures.

Dendritic architecture of hypoglossal motoneurons projecting to extrinsic tongue musculature in the rat.

The tracer, cholera toxin-horseradish peroxidase, was used to determine the dendritic architecture and organization of hypoglossal motoneurons in the rat. In 22 animals, the tracer was injected unilaterally into either the geniohyoid, genioglossus, hyoglossus, or styloglossus muscle. Within the hypoglossal nucleus, motoneurons innervating the extrinsic tongue muscles were functionally organized. Geniohyoid and genioglossus motoneurons were located within the ventrolateral and ventromedial subnuclei, respectively, while hyoglossus and styloglossus motoneurons were located within the dorsal subnucleus. Motoneurons located in all subnuclear divisions were found to have extensive dendrites that extended laterally into the adjacent reticular formation and medially to the ependyma. Less extensive extranuclear dendritic projections were found in the dorsal vagal complex and median raphe. Prominent rostrocaudal and mediolateral dendritic bundling was evident within the ventral subnuclei and dorsal subnucleus, respectively. Dendritic projections were also found extending inter- and intrasubnuclearly with a distinct pattern for each muscle. These data suggest that the varied and extensive dendritic arborizations of hypoglossal motoneurons provide the potential for a wide range of afferent contacts for, and interactions among, motoneurons that could contribute to the modulation of their activity. Specifically, the prominent dendritic bundling may provide an anatomic substrate whereby motoneurons innervating a specific muscle receive and integrate similar afferent input and are thus modulated as a functional unit. In contrast, the extensive intermingling of both inter- and intrasubnuclear dendrites within the hypoglossal nucleus may provide a mechanism for the coordination of different muscles, acting synergistically or antagonistically to produce a tongue movement.

The subnuclear distribution of 5-HT 3 receptors in the human nucleus of the solitary tract and other structures of the caudal medulla

The distribution of 5-HT 3 receptors was examined in the human medulla using [ 3H]LY278584, a highly selective 5-HT 3 receptor antagonist. The highest density of 5-HT 3 receptors was found in the substantia gelatinosus subnucleus of nucleus of the solitary tract (NTS) throughout its rostrocaudal extent, followed by the dorsal subnucleus, the area postrema (AP), the commissural sub nucleus, the medial subnucleus, and in an arc correspondingto the gelatinosus of the spinal trigeminal nucleus (nSp5). The distribution of 5-HT 3 receptors in the brain may help explain some of the reported CNS activities of 5-HT 3-selective drugs. The anti-emetic and antinociceptive activities of 5-HT 3 antagonists may be mediated by receptors in sensory areas of the brainstem.

Potassium currents of neurons isolated from medical nucleus tractus solitarius

Voltage-dependent potassium currents of neurons enzymatically isolated from the medial and dorsal subnuclei of the solitary tract (mNTS) of adult guinea pig have been characterized with respect to their voltage dependence, time dependence, and sensitivity to specific blocking agents. This region of the medulla receives baroreceptor afferent input and is involved in cardiovascular regulation. Our results showed the presence of three types of potassium currents. First, in all neurons studied (n = 58) a slowly developing outward current was present at potentials more positive than -30 mV. The time to half-peak current decreased with depolarization [24.8 ms at 0 mV; 19.2 ms at +10 mV; 12.5 ms at +20 mV; 9.9 ms at +30 mV (n = 4)]. This current required 20 mM tetraethylammonium (TEA) for full block and failed to show significant inactivation for voltage commands up to 300 ms. Second, a rapidly activating, 4-aminopyridine (4-AP)-sensitive transient outward potassium current was present in 83% of the cells examined (n = 39/47). Threshold for activation was -30 mV. The current relaxation consisted of three components: tau 1 = 14-49 ms; tau 2 = 174-362; tau 3 = 1.1-2.4 s. Finally, in all cells tested calcium activated a large nontransient outward potassium current that was inhibited by charybdotoxin. The studies reported here will be used in conjunction with studies describing sodium and calcium currents to understand the basis for generation of activity in the mNTS in response to baroreceptor input.

Single-unit activity in the lateral nucleus of the amygdala and overlying areas of the striatum in freely behaving rats: rates, discharge patterns, and responses to acoustic stimuli.

Acoustic responses of single units were examined in awake, freely behaving rats in the lateral nucleus of the amygdala (AL). Recordings were made from a movable bundle of 9 microwires. Most cells had very low rates of spontaneous activity (about 3 spikes/s average). Firing rates increased during sleep states. Short-latency auditory responses (12-25 ms) were found in the dorsal subnucleus (ALd) of the AL. Cells in the ALd most typically responded in a sustained fashion. Some of the cells in the ALd showed preferences for high frequencies, tone bursts, or frequency-modulated stimuli with center frequencies above 12 kHz. Response latencies were considerably longer in other areas of the amygdala. Our results corroborate the main findings of a previous study (F. Bordi & J. LeDoux, 1992) that examined the acoustic response properties of single cells in the AL in anesthetized rats. Together the findings from awake and anesthetized rats provide the most precise information about sensory processing in amygdala neurons available to date.

Spinal and hindbrain structures involved in visceroception and visceronociception as revealed by the expression of Fos, Jun and Krox-24 proteins

We have used the evoked expression of the immediate early gene-encoded proteins (Krox-24, c-Fos, Fos B, Jun D, Jun B, c-Jun) to monitor visceral processing in both the spinal cord and hindbrain structures of rats undergoing either mechanical colorectal or chemical intraperitoneal stimulation. Experiments were conducted under controlled volatile anaesthesia to suppress affective reactions that visceral stimulations may induce. The results refer to the effects of anaesthesia alone, and of both innocuous and noxious stimulations. Non-nociceptive and nociceptive stimulation but not anaesthesia were effective in evoking c-Fos, c-Jun, Jun B and Krox-24 expressions in the spinal cord. Intraperitoneal injections labelled cells mostly at the thoracolumbar junction levels, while colorectal distension labelled cells mostly at the lumbrosacral junction levels. Labelling was widely distributed throughout the gray matter including superficial layers, deep dorsal horn, lamina X and sacral parasympathetic columns. Krox-24- and, to a lesser degree, c-Jun-labelled cells were quite numerous in the superficial layers of the dorsal horn; Jun B, and especially c-Fos, were very effective in demonstrating inputs to all parts of the spinal cord. Both anaesthesia and noxious visceral stimulation were effective in evoking c-Fos, Krox-24 and Jun B expressions in discrete hindbrain subregions. The structures which are primarily labelled under anaesthesia are the rostral ventrolateral medulla, the external medial and lateral nuclei of the parabrachial area, the medial and dorsal subnuclei of the nucleus of the solitary tract, the area postrema, the central gray including pars alpha and nucleus O, the nucleus beta of the inferior olive, the locus coeruleus, and the inferior colliculi and adjacent parts of central gray. The structures which are primarily labelled following noxious visceral stimulation are the caudal intermediate reticular nucleus as part of the caudalmost ventrolateral medulla and the superior lateral nucleus of the rostrolateral parabrachial area. Labelling in the caudal intermediate reticular nucleus was maximal for colorectal distension. Labelling in the superior lateral nucleus was specific to peritoneal inflammation. The Edinger-Westphal nucleus is a structure in which noxious-evoked labelling was superposed onto the anaesthesia-evoked labelling. Nociception-evoked overexpression in this nucleus was maximal for intraperitoneal inflammation. The present work demonstrates that the central effects induced by either anaesthesia or visceroception including pain can be effectively monitored through the induction of an array of immediate early genes. The variety of functionally distinct subregions involved at both spinal and hindbrain levels and their differential labelling under anaesthetic vs visceroceptive stimulating conditions could be related to the wide range of motor, emotional and behavioral patterns that neurovegetative inputs can elicit.

Development of glutamate and NMDA sensitivity of neurons within the cochlear nuclear complex of kittens

1. The effects of glutamate, N-methyl-D-aspartate (NMDA), and NMDA receptor antagonists, D-alpha-aminoadipate (D alpha AA) and 2-amino-5-phosphonovalerate (APV), microionophoretically applied onto neurons in the caudal divisions (posteroventral and dorsal subnuclei) of the cochlear nuclear complex (CN), were investigated during postnatal development in kittens with the use of extracellular techniques. From birth through postnatal day 7, microionophoretically applied glutamate elevated the acoustically evoked discharge rates of nearly 80% of neurons studied. Although fewer neurons were studied with the use of NMDA, approximately 65% of these responded to this glutamatergic agonist, and no developmental changes in the percentage of responsive neurons were observed. The actions of NMDA antagonists were studied in a relatively small number of neurons, and results support the supposition that glutamate, or a glutamate-like substance, acts as a CN neurotransmitter throughout postnatal life. 2. Approximately 64% of CN neurons encountered among neonatal animals were unresponsive to acoustic stimulation, even at the highest output levels available (> 120 dB SPL). That percentage declined monotonically during the next three postnatal days, such that approximately 23% of neurons encountered were unresponsive to acoustic stimulation on the third day. Essentially all encountered neurons were responsive to acoustic stimulation by the middle of the second postnatal week. Under conditions of simultaneous glutamate and acoustic stimulation, neurons in this general class of "acoustically unresponsive" neurons segregated into two groups. Glutamate increased spontaneous discharge rate in 45% of the neurons studied, however, these units remained acoustically unresponsive during combined sound and excitatory amino acid stimulation (group A1). In the second group (A2), 55% of the neurons that were acoustically unresponsive under control (sound alone) conditions responded to the acoustic component of the combined acoustic and glutamate stimulation (the experimental condition) in a frequency-dependent manner. A2 neurons exhibited temporal firing patterns characteristic of acoustically responsive neurons of corresponding age, suggesting that these neurons are functionally connected to the auditory periphery, whereas A1 neurons are not. 3. Dose-response curves were either sigmoidal or linear over the range that measurements were made, and maximum discharge rates evoked by high doses of glutamate in the youngest animals studied tended to be lower than those produced by acoustic stimulation alone in older animals. These results suggest that intrinsic properties contribute to the mechanism(s) that limits neuronal responsiveness. Average dose-response curve slopes were higher for neurons recorded from older animals, also indicating that intrinsic properties regulating dynamic response range are acquired postnatally in the kitten CN.(ABSTRACT TRUNCATED AT 400 WORDS)

Location of motoneurons innervating the middle ear muscle of the chicken, ( Gallus domesticus)

The motoneuron pool for the musculus columellae, the avian equivalent to the m. stapedius, was identified by retrograde labeling with WGA-HRP. It consists of a discrete group of approximately 65 neurons located along the dorsolateral border in the ventral subnucleus of the facial nuclear complex. Other facial motoneurons were only labeled when diffusion of the tracer into neighbor structures was not excluded. The dorsal subnucleus of the facial nerve innervates the m. depressor mandibulae.

Subnuclear organization of the human caudal nucleus of the solitary tract

The caudal human nucleus of the solitary tract (NTS) is composed of 10 subnuclei. The commissural subnucleus spans the midline below the obex, merging rostrally into the medial subnucleus. The other subnuclei of the NTS are best seen just above the obex. The ventrolateral subnucleus contains large, darkly staining neurons. The interstitial subnucleus consists of neurons lying in groups intermingled with the fibers of the tract. The lateral subnucleus is small at caudal levels, merging with the interstitial subnucleus more rostrally. The dorsal subnucleus contains large melanotic neurons and encircles the substantia gelatinosus. a round, cell-poor subnucleus. The ventromedial subnucleus curls around the medial and ventral edge of the tract. The intermediate subnucleus, laying ventrolateral to the dorsal motor nucleus of the vagus, also contains melanotic neurons. The subpostremal subnucleus separates the area postrema from the NTS proper. The medial subnucleus is the largest subnucleus in the caudal NTS, containing medium-sized fusiform neurons. Adoption of a uniform cytoarchitectural map of the caudal NTS will permit more accurate comparisons between human and nonhuman studies.

The organization of the crossed geniculogeniculate pathway of the rat: A Phaseolus vulgaris-leucoagglutinin study

The intergeniculate leaflet of the thalamus is known to give rise to neuronal projections to the suprachiasmatic nuclei and the rostral part of the pineal gland. Via these projections the intergeniculate leaflet is considered to play a role in regulation of circadian rhythms. Iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were placed in various subnuclei of the lateral geniculate nucleus in order to study the topographical organization of the crossed geniculogeniculate pathway in the rat. Injections involving neurons in the intergeniculate leaflet or the medial subpart of the ventral nucleus (which presumably is part of the intergeniculate leaflet of the thalamus too) gave rise to labeled nerve fibers in the opposite lateral geniculate nucleus. The axons contained in this pathway were followed either medially via the posterior commissure, or via the optic tracts and optic chiasm, to the contralateral hemisphere. In the contralateral lateral geniculate nucleus, the intergeniculate leaflet was most densely innervated, but a substantial innervation of the ventral lateral geniculate nucleus was observed as well. Only a few labeled fibers were observed in the dorsal subnucleus. However, the dense innervation of the contralateral intergeniculate leaflet not only covered the small zone between the dorsal and ventral nuclei, but also a dorsomedial part of the ventral nucleus that merged caudally with the lateral part of the zona incerta. In the remaining part of the ventral nucleus, single Phaseolus vulgaris-leucoag-glutinin-labeled fibers surrounded specific cells. The demonstration of a divergent projection between the intergeniculate leaflet and specific subparts of the contralateral geniculate nuclei indicates that the two lateral geniculate nuclei are regulating each other. The function of this pathway is suggested to be related to the regulation of circadian rhythmicity, but experimental evidence for this hypothesis is still lacking.

Calbindin‐D28K (CaBP28k)‐like Immunoreactivity in Ascending Projections

This study concerns the involvement of calbindin-D28K (CaBP28k)-containing neurons in the efferent projections of both the trigeminal nucleus caudalis and the dorsal vagal complex (nucleus of the solitary tract and area postrema) in rats. Recent evidence has shown that these projections are particularly important for the processing of visceroception and/or nociception at central levels. The trigeminal nucleus caudalis has dense projections to both the nucleus of the solitary tract and the parabrachial area; the dorsal vagal complex is intimately connected to the parabrachial area. CaBP28k is a calcium-binding protein the function of which could be a determining factor in controlling the excitability of cells by acting on intrinsic calcium metabolism. CaBP28k content of projections was ascertained using a double labelling approach that combined the retrograde transport of a protein - gold complex to identify projection cells and immunocytochemistry to identify CaBP28k-positive cells. The trigeminal nucleus caudalis is rich in both CaBP28k-immunoreactive cells and cells projecting to the parabrachial area or the nucleus of the solitary tract. Cells containing both the protein and the retrograde tracer, however, were mostly restricted to the superficial layers (laminae I and outer II) and to their rostral extensions, the dorsal paramarginal and paratrigeminal nuclei. These trigeminal subdivisions are targets for nociceptive, visceroceptive and thermal inputs of peripheral origins. The dorsal vagal complex is rich in CaBP28k. Dense populations of immunoreactive cells are observed in the ventrolateral part of the area postrema and all of the three main subdivisions of the nucleus of the solitary tract (rostral gustatory, ventrolateral respiratory and medial cardiovascular subregions). The subnucleus commissuralis, subnucleus centralis and dorsal subnuclei are particularly densely stained. The subnucleus centralis, which is involved in regulating food and water intake, does not project to the parabrachial area. The area postrema, subnucleus commissuralis and dorsal subnuclei, which are implicated in cardiovascular and/or ingestive behaviours, have dense projections to the parabrachial area, many of which contain CaBP28k. The present results demonstrate that CaBP28k-containing cells form a major part of the solitary and trigeminal projection systems, including subregions that are involved in visceroception and/or nociception processing. The location of solitary nucleus projection cells overlaps those of some neuropeptidergic projecting populations, suggesting colocalization. Consequently, certain neuropeptidergic actions may be CaBP28k-dependent.

Distribution of axons showing calcitonin gene-related peptide- and/or substance P-like immunoreactivity in the sensory trigeminal nuclei of the cat

Distribution of axons with calcitonin gene-related peptide (CGRP)-like and/or substance P (SP)-like immunoreactivity (LI) within the sensory trigeminal nuclei was examined in the cat before and after trigeminal rhizotomy. Axons with CGRP-LI or SP-LI were seen throughout the principal sensory trigeminal nucleus (Vp) and spinal trigeminal nuclei, including the medullary dorsal horn (MDH). They were densely distributed particularly in the dorsolateral part of the dorsal subnucleus of the Vp, ventromedial marginal zone of the ventral subnucleus of the Vp, dorsomedial and ventromedial parts of the oral spinal trigeminal nucleus, ventromedial and lateral marginal zones of the interpolar spinal trigeminal nucleus, and lamina I, outer part of lamina II and lamina V of the MDH. Most of the CGRP-LI axons exhibited SP-LI, while many SP-LI axons did not show CGRP-LI. After trigeminal rhizotomy, almost all CGRP-LI axons disappeared from the ipsilateral sensory trigeminal nuclei, while a considerable number of SP-LI axons remained intact throughout the nuclei: these SP-LI axons did not show CGRP-LI. The results indicate that CGRP-LI axons within the sensory trigeminal nuclei exhibit SP-LI and are of peripheral origin, and that SP-LI axons without CGRP-LI are of central origin.

The efferent connections of the lateral septal nucleus in the guinea pig: intrinsic connectivity of the septum and projections to other telencephalic areas

The distribution of efferent fibers originating in the lateral septal nucleus was investigated in guinea pigs by means of anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Special emphasis was placed on the intraseptal fiber systems. The fibers originating from the different subnuclei of the lateral septal nucleus formed massive horizontal connections in the rostrocaudal axis. Projections to the contralateral, congruent subnuclei were also detected. In the medial septum/diagonal band of Broca complex the largest number of PHA-L-stained fibers was found after application of the tracer into the dorsal subnucleus of the lateral septal nucleus; the density of the efferent fibers decreased progressively after injection into the intermediate or ventral subnuclei. In all cases the diagonal band contained a much higher number of efferent fibers from the lateral septal nucleus than from the medial septal nucleus. In the medial septal nucleus, terminal labeling was generally sparse. Other telencephalic areas (organum vasculosum of the lamina terminalis, nucleus accumbens, bed nucleus of the stria terminalis, amygdala, hippocampal complex, and other cortical areas) contained varying numbers of labeled projections. In double-labeling experiments, a close spatial relationship between PHA-L-stained fibers and vasoactive intestinal polypeptide-immunoreactive perikarya was observed in several of these target areas.

Enkephalin and serotonin innervation of somatostatin-immunoreactive medullary reticular formation neurones

Somatostatin cells in the rat medullary reticular formation (Md) have been studied using peroxidase-antiperoxidase immunocytochemistry. Large fusiform and multipolar somatostatin immunoreactive cells were observed in the ventral subnucleus (MdV) running in a band close to the border with the dorsal subnucleus (MdD). In the same region somatostatin-, serotonin- and enkephalin-immunoreactive fibres occur and double staining revealed that these all contact the somatostatin-immunoreactive cells, with enkephalin making a particularly dense innervation.

A Golgi Study on the Afferent Fibers to the Habenular Ganglion in the Red Stingray, Dasyatis akajei

Afferent fibers to the habenular ganglion (HG) were derived mainly from the stria medullaris thalami (SM), which was roughly divided into a dorsal and ventral bundle. In the left ganglion seen at the level of the rostrocaudal middle, the dorsal bundle gave off collaterals to the lateral habenular nucleus (LH) and dorsal subnucleus of the medial habenular nucleus (MH), while the ventral bundle innervated the intermediate and ventral subnuclei of the MH. On the other hand, in the right ganglion at the level of the rostrocaudal middle, the dorsal subnucleus of the MH was innervated by collaterals from the dorsal bundle of the SM, whereas in the intermediate and ventral subnucleus fibers from the ventral bundle were seen. In the left ganglion at the caudal level, the dorsal and ventral bundle extended medially and joined the same bundle of the opposite side to constitute a dorsal and intermediate component of the habenular commissure, respectively. A third component of the HC, a ventral component, was seen to run between the fasciculus retroflexus of both sides. As in the case of the rostral level, the dorsal bundle of the SM emitted collaterals to the LH and dorsal subnucleus of the MH, while the intermediate and ventral subnuclei of the MH were projected upon by collaterals from the ventral bundle of the SM. At the caudal level of the right ganglion, the dorsal bundle gave off collaterals to the dorsal subnucleus of the MH. In contrast, the LH and the intermediate and ventral subnuclei of the MH were innervated by fibers from the ventral bundle. With regard to terminal patterns of the SM, fibers to the MH gave off many short fine branchlets forming the glomerular structures, whereas those to the LH branched out into numerous terminals to form a dense fiber plexus. Thus, the afferent fibers to the HG in the red stingray exhibited a striking left-right asymmetry.