Distribution of neurotensin-like immunoreactive cell bodies and fibers in the brainstem of the adult male cat

Distribution of Neurotensin and Somatostatin-28 (1-12) in the Minipig Brainstem

Using an indirect immunoperoxidase technique, an in depth study has been carried out for the first time on the distribution of fibres and cell bodies containing neurotensin and somatostatin-28 (1-12) (SOM) in the minipig brainstem. The animals used were not treated with colchicine. The distribution of neurotensin- and SOM-immunoreactive fibres was seen to be quite similar and was moderate in the minipig brainstem: a close anatomical relationship between both neuropeptides was observed. The distribution of cell bodies containing neurotensin or SOM was quite different and restricted. Cell bodies containing neurotensin were found in four brainstem nuclei: nucleus centralis raphae, nucleus dorsalis raphae, in the pars centralis of the nucleus tractus spinalis nervi trigemini and in the nucleus ventralis raphae. Cell bodies containing SOM were found in six nuclei/regions of the brainstem: nucleus ambiguus, nucleus dorsalis motorius nervi vagus, formatio reticularis, nucleus parabrachialis medialis, nucleus reticularis lateralis and nucleus ventralis raphae. According to the observed anatomical distribution of the immunoreactive structures containing neurotensin or SOM, the peptides could be involved in sleep-waking, nociceptive, gustatory, motor, respiratory and autonomic mechanisms.

Mapping of neurotensin in the alpaca (Lama pacos) brainstem

We studied the distribution of cell bodies and fibres containing neurotensin (NT) in the brainstem of the alpaca using an indirect immunoperoxidase technique. Immunoreactive fibres were widely distributed throughout the brainstem, whereas the distribution of cell bodies was less widespread. Immunoreactive perikarya were only found in the mesencephalic and bulbar reticular formation, periaqueductal grey, nucleus of the solitary tract, laminar spinal trigeminal nucleus and in the inferior colliculus. A high density of fibres containing NT was found in the dorsal nucleus of the raphe, marginal nucleus of the brachium conjunctivum, locus coeruleus, inferior colliculus, inter-peduncular nucleus, substantia nigra, periaqueductal grey, reticular formation of the mesencephalon, pons and medulla oblongata, nucleus of the solitary tract, laminar spinal trigeminal nucleus, hypoglossal nucleus, inferior central nucleus and in the tegmental reticular nucleus. The widespread distribution indicates that NT might be involved in multiple physiological actions in the alpaca brainstem; this must be investigated in the future as alpacas lives from 0 m above sea level to altitudes of up 5000 m and hence the involvement of this neuropeptide in special and unique regulatory physiological mechanisms could be suggested.

Neurotensin and pain modulation

Neurotensin (NT) can produce a profound analgesia or enhance pain responses, depending on the circumstances. Recent evidence suggests that this may be due to a dose-dependent recruitment of distinct populations of pain modulatory neurons. NT knockout mice display defects in both basal nociceptive responses and stress-induced analgesia. Stress-induced antinociception is absent in these mice and instead stress induces a hyperalgesic response, suggesting that NT plays a key role in the stress-induced suppression of pain. Cold water swim stress results in increased NT mRNA expression in hypothalamic regions known to project to periaqueductal gray, a key region involved in pain modulation. Thus, stress-induced increases in NT signaling in pain modulatory regions may be responsible for the transition from pain facilitation to analgesia. This review focuses on recent advances that have provided insights into the role of NT in pain modulation.

Mapping of neurokinin b in the cat brainstem

We studied the distribution of neurokinin B-immunoreactive cell bodies and fibers in the cat brainstem using an indirect immunoperoxidase technique. The highest density of immunoreactive fibers was found in the motor trigeminal nucleus, the laminar and alaminar spinal trigeminal nuclei, the facial nucleus, the marginal nucleus of the brachium conjunctivum, the locus coeruleus, the cuneiform nucleus, the dorsal motor nucleus of the vagus, the postpyramidal nucleus of the raphe, the lateral tegmental field, the Kölliker-Fuse nucleus, the inferior central nucleus, the periaqueductal gray, the nucleus of the solitary tract, and in the inferior vestibular nucleus. Immunoreactive cell bodies containing neurokinin B were observed, for example, in the locus coeruleus, the dorsal motor nucleus of the vagus, the median division of the dorsal nucleus of the raphe, the lateral tegmental field, the pericentral nucleus of the inferior colliculus, the internal division of the lateral reticular nucleus, the inferior central nucleus, the periaqueductal gray, the postpyramidal nucleus of the raphe, and in the medial nucleus of the solitary tract. This widespread distribution of neurokinin B in the cat brainstem suggests that the neuropeptide could be involved in many different physiological functions. In comparison with previous studies carried out in the rat brainstem on the distribution of neurokinin B, our results point to a more widespread distribution of this neuropeptide in the cat brainstem.

An immunocytochemical mapping of methionine-enkephalin-Arg6-Gly7-Leu8 in the cat brainstem

The distribution of methionine-enkephalin-Arg6-Gly7-Leu8-immunoreactive cell bodies and fibres was studied in the brainstem of the cat using an indirect immunoperoxidase technique. In the mesencephalon, immunoreactive cell bodies were observed in the periaqueductal grey, the dorsal raphe nucleus, the central and pericentral nuclei of the inferior colliculus and the pericentral division of the dorsal tegmental nucleus. In the pons, immunoreactive cell bodies were observed in the dorsolateral division of the pontine nucleus; below the central division of the dorsal tegmental nucleus; above the dorsolateral division of the pontine nucleus, and close to the superior cerebellar peduncle. In the medulla oblongata, immunoreactive cell bodies were observed in the laminar spinal trigeminal nucleus and in the lateral tegmental field; the dorsal motor nucleus of the vagus; the prepositus hypoglossal nucleus; the medial nucleus of the solitary tract; the rostral division of the cuneate nucleus, and close to the parvocellular division of the alaminar spinal trigeminal nucleus. The highest (moderate) density of immunoreactive fibres was observed in the periaqueductal grey; the parvocellular and magnocellular divisions of the alaminar spinal trigeminal nucleus; the laminar spinal trigeminal nucleus; the rostral division of the cuneate nucleus; the dorsal motor nucleus of the vagus; the lateral nucleus of the solitary tract, and in the midline between the central divisions of the reticulotegmental pontine nucleus. The widespread distribution of methionine-enkephalin-Arg6-Gly7-Leu8 in the cat brainstem indicates that the peptide might be involved in several physiological functions.

Neurotensin-like immunoreactivity in the brain of the chicken, Gallus domesticus

The distribution of neurons containing neurotensin in the central nervous system of the chicken was studied immunohistochemically. The majority of the neurotensin-immunoreactive (-ir) cell bodies were located in the hypothalamus. Extensive groups of labelled perikarya were found in the hypothalamic periventricular nucleus and in the magnocellular periventricular nucleus. In addition, ir-perikarya were scattered throughout the lateral hypothalamic area and in the ventromedial hypothalamic nucleus. The only extrahypothalamic site of ir-perikarya was in the region immediately under the lateral forebrain bundle. Immunoreactive fibres were detected in the hippocampus, the parahippocampal area, the hypothalamus, the region of the tractus corticohabenular and corticoseptal tracts, the median eminence, the region above the posterior commissure and in the intercollicular nucleus. The distribution pattern of the neurotensin-ir neurons suggests that neurotensin-like peptides are involved in the hypophysiotropic functions.

Neurotensin and the serotonergic system

The serotonergic system, because of very diffuse projections throughout the central nervous system, has been implicated in numerous functions including nociception, analgesia, sleep-wakefulness and autonomic regulation. Despite an abundant literature indicating the presence of neurotensin-containing (neurotensinergic) neurons, fibres and terminals in most areas containing serotonergic neurons, little is known about the possible relationship between serotonergic and neurotensinergic systems. The purpose of this review is (i) to summarize current knowledge on the anatomical relation between neurotensinergic and serotonergic system, (ii) to summarize current knowledge on the action of neurotensin on serotonergic neurons and (iii) to discuss the possible physiological relevance of this action. Neurotensin-containing cell bodies can be found in the most rostral raphe nuclei. There are neurotensin-containing fibres and terminals in all raphe nuclei. Raphe nuclei have also been shown to contain neurotensin-receptor binding sites. In the dorsal raphe nucleus, neurotensin induces a concentration-dependent increase in the firing rate of a subpopulation of serotonergic neurons. The neurotensin-induced excitation, which is selectively blocked by the non-peptide neurotensin receptor antagonist SR 48692, is observed mainly in the ventral part of the nucleus. Most serotonergic neurons show marked desensitization to neurotensin, even at low concentrations. In intracellular experiments, neurotensin induces an inward current, associated in some cases with a decrease in apparent input conductance, which is occluded by supramaximal concentrations of the alpha 1-adrenoceptor agonist phenylephrine. In rare cases, neurotensin induces an excitation of GABAergic or glutamatergic neurons. Since the neurotensinergic system has also been implicated in nociception, analgesia, sleep-wakefulness, and autonomic regulation, the review discusses the possibility that part of this regulation could involve the activation of the serotonergic system.

Electron microscopic study of GABAergic synaptic innervation of neurotensin-immunoreactive neurons in the dorsal raphe nucleus

A double immunocytochemical method combining the preembedding avidin-biotin-peroxidase-complex technique and the postembedding immunogold technique was used to examine synaptic interactions between GABAergic and neurotensin-containing neurons in the same tissue sections of the dorsal raphe nucleus of the rat. Whereas the neurotensin-like immunoreactive perikarya rarely received synapses from GABA-like immunostaining axon terminals, the neurotensin-like immunoreactive dendrites frequently received synapses from GABA-like immunoreactive neurons. These results suggest that GABAergic neurons could modulate neurotensinergic neurons in the dorsal raphe nucleus through synaptic relations. The immunocytochemically identified local synaptic circuit in the dorsal raphe was discussed.

Functional characteristics of the midbrain periaqueductal gray

The major functions of the midbrain periaqueductal gray (PAG), including pain and analgesia, fear and anxiety, vocalization, lordosis and cardiovascular control are considered in this review article. The PAG is an important site in ascending pain transmission. It receives afferents from nociceptive neurons in the spinal cord and sends projections to thalamic nuclei that process nociception. The PAG is also a major component of a descending pain inhibitory system. Activation of this system inhibits nociceptive neurons in the dorsal horn of the sinal cord. The dorsal PAG is a major site for processing of fear and anxiety. It interacts with the amygdala and its lesion alters fear and anxiety produced by stimulation of amygdala. Stimulation of PAG produces vocalization and its lesion produces mutism. The firing of many cells within the PAG correlates with vocalization. The PAG is a major site for lordosis and this role of PAG is mediated by a pathway connecting the medial preoptic with the PAG. The cardiovascular controlling network within the PAG are organized in columns. The dorsal column is involved in pressor and the ventrolateral column mediates depressor responses. The major intrinsic circuit within the PAG is a tonically-active GABAergic network and inhibition of this network is an important mechanism for activation of outputs of the PAG. The various functions of the PAG are interrelated and there is a significant interaction between different functional components of the PAG. Using the current information about the anatomy, physiology, and pharmacology of the PAG, a model is proposed to account for the interactions between these different functional components.

Distribution of neurotensin-containing neurons in the central nervous system of the dog

The distribution of neurotensin-containing cell bodies and fibers was examined in the central nervous system of the dog using light microscopic immunohistochemistry. A very large population of neurotensin-containing cell bodies was observed in the septal nuclei, nucleus accumbens septi, preoptic areas, bed nucleus of the stria terminalis, olfactory tubercle, entorhinal cortex, ventral subiculum, anterodorsal thalamic nucleus, anteroventral thalamic nucleus, nucleus reuniens, lateral habenular nucleus, parabrachial nucleus, and nucleus of the solitary tract. Extremely dense networks of neurotensin-containing fibers were found in the globus pallidus, hypothalamus, infundibular stalk, ventral tegmental area, periaqueductal gray, interpeduncular nucleus, and spinal nucleus of the trigeminal nerve and substantia gelatinosa. However, the cerebral neocortex and cerebellum were negative for neurotensin in the present study. When the present findings are compared with those in other animals, it is clear that the major species-specific differences in distribution involve three immunonegative regions and four immunopositive regions in the dog: The former are the cerebral neocortex, mammillary body, and hippocampus; the latter are the cell bodies in the pyramidal layer of the olfactory tubercle, the superficial and middle layers of the entorhinal cortex and ventral subiculum, and the nerve fibers in the interpeduncular nucleus. The present study indicates a rather extensive network of neurotensin neurons in the central nervous system of the dog.

Synaptic relations of neurotensinergic neurons in the dorsal raphe nucleus

The ultrastructure and synaptic relations of neurotensinergic neurons in the rat dorsal raphe nucleus (DRN) were examined. The neurotensin-like immunoreactive (NT-L1) neurons in the DRN were fusiform or spherical. The NT-LI perikarya could only be detected in colchicine-treated animals whereas the immunoreactive axon terminals could only be found in the animals not treated with colchicine. Although many NT-LI dendrites received synapses from nonimmunoreactive axon terminals, the NT-LI perikarya received few synapses. NT-LI axon terminals also made synapses on nonimmunoreactive dendrites. Occasionally, synapses were found between the NT-LI axon terminals and NT-LI dendrites in the cases in which the animals were not treated with colchicine.

Distribution of gastrin-releasing peptide/bombesin-like immunoreactive cell bodies and fibres in the brainstem of the cat

Using an indirect immunoperoxidase technique, the location of gastrin-releasing/bombesin-like immunoreactive fibres and cell bodies in the cat brainstem was studied. A moderate or low density of immunoreactive cell bodies was observed in the nucleus of the brachium of the inferior colliculus, pericentral nucleus of the inferior colliculus, ventral nucleus of the lateral lemniscus and in the external division of the lateral reticular nucleus. The densest network of immunoreactive fibres was visualized in the interpeduncular nucleus, marginal nucleus of the brachium conjunctivum, alaminar and laminar spinal trigeminal nuclei and in the substantia nigra. The periaqueductal gray, brachium of the inferior colliculus, nucleus of the brachium of the inferior colliculus, locus coeruleus, nucleus incertus, Kölliker-Fuse nucleus, facial nucleus, medial nucleus of the solitary tract and the area postrema contained a moderate density of immunoreactive fibres, whereas the pericentral nucleus of the inferior colliculus, nucleus sagulum, cuneiform nucleus, dorsal nucleus of the raphe, superior central nucleus, central, lateral and paralemniscal tegmental fields, ventral nucleus of the lateral lemniscus, dorsal tegmental nucleus, postpyramidal nucleus of the raphe, nucleus ambiguus, accessory dorsal tegmental nucleus, dorsal motor nucleus of the vagus and the inferior olive had the lowest density of immunoreactive fibres.

Alpha-neo-endorphin-like immunoreactivity in the cat brain stem

This paper examines the distribution of fibers and cell bodies containing alpha-neo-endorphin in the cat brain stem by using an indirect immunoperoxidase technique. A high or moderate density of immunoreactive cell bodies was found in the superior central nucleus, nucleus incertus, dorsal tegmental nucleus, nucleus of the trapezoid body, and in the laminar spinal trigeminal nucleus, whereas a low density of such perikarya was observed in the inferior colliculus, nucleus praepositus hypoglossi, dorsal nucleus of the raphe, nucleus of the brachium of the inferior colliculus, and in the nucleus of the solitary tract. The highest density of immunoreactive fibers was found in the substantia nigra, dorsal motor nucleus of the vagus, nucleus coeruleus, lateral tegmental field, marginal nucleus of the brachium conjunctivum, and in the inferior and medial vestibular nuclei. These results indicate that alpha-neo-endorphin is widely distributed in the cat brain stem and suggest that the peptide could play an important role in several physiological functions, e.g., those involved in respiratory, cardiovascular, auditory, and motor mechanisms.

Neurokinin A-like immunoreactivity in the cat brainstem

We have studied the distribution of neurokinin A-like immunoreactive cell bodies and fibers in the cat brainstem. The densest clusters of perikarya containing the peptide were observed in the periaqueductal gray, inferior colliculus, postpyramidal nucleus of the raphe, medial nucleus of the solitary tract and in the lateral reticular nucleus. By contrast, the interpeduncular nucleus, magnocellular part of the red nucleus, central tegmental field, cuneiform nucleus, dorsal tegmental nucleus, nucleus sagulum and the medial and inferior vestibular nuclei had the lowest density, whereas a moderate density of immunoreactive cell bodies was found in the superior colliculus, medial division of the dorsal nucleus of the raphe, nucleus incertus, locus coeruleus and in the Kölliker-Fuse area. The highest density of immunoreactive fibers was observed in the substantia nigra, periaqueductal gray, marginal nucleus of the brachium conjunctivum, medial vestibular nucleus, medial nucleus of the solitary tract, laminar spinal trigeminal nucleus, inferior colliculus, medial division of the dorsal nucleus of the raphe, locus coeruleus, dorsal tegmental nucleus and in the spinal trigeminal tract. A moderate density of immunoreactive fibers was found in the dorsal motor nucleus of the vagus and in the postpyramidal nucleus of the raphe and a low density in the cuneiform nucleus, Kölliker-Fuse area, nucleus sagulum, inferior and superior central nuclei, lateral reticular nucleus and in the lateral and magnocellular tegmental fields.

Immunohistochemical evidence for a neurotensin striatonigral pathway in the rat brain

The distribution and origin of neurotensin-like immunoreactivity in the substantia nigra pars reticulata of the rat have been analysed using immunohistochemistry combined with different drug treatments and lesioning techniques. In normal rats, a distinct but weakly fluorescent network of neurotensin-immunoreactive fibers was found in the central part of the substantia nigra pars reticulata. When the animals were treated with reserpine, which suppresses dopamine transmission, a similar pattern of immunoreactivity was found, though the intensity of staining was slightly enhanced. However, when rats were treated with methamphetamine, a potent dopamine releaser, the intensity of immunoreactivity was dramatically increased. In particular, densely packed neurotensin-immunoreactive fibers were found at the dorsal border and at the ventral periphery of the substantia nigra pars reticulata. This pattern of immunoreactivity was found to be similar to that displayed by dynorphin. In the nucleus caudatus, several neurotensin-immunoreactive cell bodies were seen after reserpine treatment. Morphologically similar perikarya were observed in methamphetamine-treated rats, but they were less numerous, whereas no cell bodies were detectable in untreated animals. When a unilateral mechanical transection or an ibotenic acid injection was performed in the striatum, the patterns of neurotensin as well as dynorphin and substance P immunoreactivities in the substantia nigra pars reticulata were strongly affected. Both types of lesion caused a marked, parallel depletion of all three immunoreactive substances on the side ipsilateral to the lesion, where a restricted area was virtually devoid of immunoreactive elements. Thus the present study provides evidence for the existence of a unilateral neurotensin striatonigral pathway, terminating in the pars reticulata. The origin of the neurotensin fibers in the pars compacta has not been established but does not appear to be the caudate nucleus. These results together with evidence from the literature suggest that methamphetamine induced a massive release of dopamine from nigral dendrites acting on presynaptic D1 dopamine receptors located on neurotensinergic terminals leading to a marked increase in neurotensin-like immunoreactivity in the pars reticulata.

Neurotensin immunoreactivity in the colliculus inferior of cat: light and electron microscopic investigations

Neuronal perikarya with neurotensin-like immunoreactivity (NT-LI) are found in the pericentral and external nuclei and the dorsomedial part of the central nucleus of the inferior colliculus. On electron-microscopic examination, these neurons are characterized by a relatively large nucleus, a small amount of cytoplasm and paucity of organelles. NT-LI is observed in large and small dendrites and dendritic spines as well as in axon terminals which contain small round or elongated clear vesicles and/or dense core vesicles. The immunoreactive terminal boutons make asymmetrical axodendritic and symmetrical axo-somatic synapses mainly on non-immunoreactive elements.

Distribution of parvalbumin immunoreactivity in the cat brain stem

We studied the distribution of parvalbumin-immunoreactive cell bodies and fibers in the cat brain stem. A high or moderate density of perikarya containing parvalbumin was observed in the periaqueductal gray, interpeduncular nucleus, nucleus of the trapezoid body, superior and inferior colliculi, and in the substantia nigra. The nucleus ruber, cuneiform nucleus, preolivary nucleus, retrorubral nucleus, paracentral division of the tegmental reticular nucleus, central and lateral tegmental fields, and the pericentral division of the dorsal tegmental nucleus had the lowest density of immunoreactive cell bodies. Moreover, a high or moderate density of parvalbumin immunoreactive processes was visualized in the nucleus ruber, substantia nigra, superior and inferior colliculi, periaqueductal gray, nucleus sagulum, cuneiform nucleus, Kölliker-Fuse nucleus, nucleus of the trapezoid body, vestibular nuclei, dorsal motor nucleus of the vagus, and in the lateral reticular nucleus. Finally, a few immunoreactive fibers were observed in the pontine gray, nucleus coeruleus, marginal nucleus of the brachium conjunctivum, nucleus of the solitary tract, inferior olive, and in the tegmental fields.