Neurotensin-like Immunoreactive Fibers Research Articles

The neurotensinergic synaptic innervation of vasopressin containing neurons in the rat hypothalamic paraventricular nucleus

A recent physiological report suggested that neurotensin could inhibit the vasopressin releasing from vasopressin-producing neurons in the hypothalamic paraventricular nucleus but not in the supraoptic nucleus. In the present study, the synaptic relationship between the neurotensin-like immunoreactive and vasopressin-like immunoreactive neurons has been examined using a pre-embedding double immunostaining technique in the rat hypothalamic paraventricular nucleus. At the light microscopic level, many neurotensin-like immunoreactive fibers were found near the vasopressin-like immunoreactive neurons. At the electron microscopic level, the neurotensin-like immunoreactive fibers were identified as axon terminals that made many synapses on the vasopressin-like immunoreactive perikarya and dendrites. The synapses were both asymmetrical and symmetrical. These findings of the present study suggest that the inhibitory effect of neurotensin on the vasopressin neurons in the hypothalamic paraventricular nucleus may be due to the direct synapses made by neurotensin-like immunoreactive axon terminals on the vasopressin-like immunoreactive neurons.

Postnatal changes in the density and distribution of neurotensin‐like immunoreactive fibers in the mediodorsal nucleus of the thalamus in the rat

A previous report (Inagaki et al., Brain Res. 260:143-146, '83) suggested that the peptide neurotensin is contained in neurons of the piriform cortex that project to the mediodorsal thalamic nucleus (MD) in young rats. To confirm this, we have studied the distribution of neurotensin-like immunoreactive (NTIR) fibers in MD during development, using three antisera directed at different parts of the neurotensin molecule (Emson et al., J. Neurochem. 38:992-999, '82). In adult rats, NTIR fibers in MD are sparse. They are located mostly at the medial edge of MD and in the adjacent midline thalamic nuclei, with a few poorly stained NTIR fibers in the central part of MD. In contrast, during the first postnatal week, both the medial and central portions of MD stain heavily for neurotensin. The density of NTIR fibers in MD then progressively decreases until the density typical of adult rats is reached, at about 5 weeks. Changes in the distribution of NTIR fibers in MD also occur. In 7-day-old rats, the patches of NTIR fibers in the medial and central parts of MD are contiguous, but by 10 days a sparsely immunoreactive zone forms between them. With maturation, this zone enlarges as the density of neurotensin staining decreases, until the medial contingent of NTIR fibers reaches its adult position at the medial edge of MD. From a comparison of the distribution of NTIR cells with that of cells that can be retrogradely labeled from MD or the midline thalamus, the probable source of the NTIR fibers to the central part of MD is in the deep layer of the piriform cortex, while the NTIR fibers to the medial edge of MD and the midline nuclei may arise from the preoptic region and the medial amygdala. In neonatal rats, neurons are found in the piriform cortex, the preoptic region, and the medial amygdala, which can be double-labeled both for neurotensin and with a retrograde tracer injected into MD and the midline thalamus. Projections of the preoptic region to the thalamus have a distribution similar to that of the medial population of NTIR fibers, whereas the distribution of piriform cortical afferents in central MD matches the central patch of NTIR fibers.

Heterogeneous distribution of neurotensin-like immunoreactive neurons and fibers in the midbrain periaqueductal gray of the rat

The midbrain periaqueductal gray (PAG) has been shown to be a site where various manipulations induce pain suppression. Recent physiological evidence (Behbehani and Pert, 1984; Behbehani et al., 1987) suggests that neurotensin has pronounced physiological actions in PAG and effects pain suppression. We have performed immunohistochemical studies in order to determine the magnitude and distribution of neurotensin-like immunoreactive (NT-IR) cell bodies and fibers in PAG. NT-IR cell bodies were common throughout PAG, although there were more in the caudal than the rostral half. NT-IR neurons were much more numerous in the ventral than the dorsal half of PAG, and some appeared to be located within the dorsal raphe nucleus. The pattern of NT-IR fibers was analyzed with the aid of image enhancement/analysis and densitometry. The fibers were found to be heterogeneously distributed, being most heavily concentrated in the region adjacent to the cerebral aqueduct in the caudal two-thirds of PAG. The distribution of NT fibers closely matches sites where exogenously applied NT elicits long-lasting excitation of PAG neurons (Behbehani et al., 1987). Based on the known physiological and behavioral actions of NT in PAG, the present anatomical results suggest that NT acts on elements located predominantly in the medial and ventrolateral parts of PAG. Neurons activated by NT may project directly to the nucleus raphe magnus and adjacent ventral medulla (Behbehani and Pert, 1984) to activate neurons that project to the spinal cord and modulate nociceptive circuits.

Distribution of neurotensin-like immunoreactivity in the diencephalon of the Japanese monkey (Macaca fuscata).

The distribution of neurotensin-like immunoreactive (NT-LI) neurons was examined in the thalamus and hypothalamus of the Japanese monkey (Macaca fuscata) by using the peroxidase-antiperoxidase immunocytochemistry technique. In the thalamus, NT-LI neuronal perikarya were distributed mainly in the midline nuclear group and the dorsomedial nucleus, and partially in the intralaminar nucleus: Immunoreactive fibers were mainly distributed in the midline nucleus, particularly in the nucleus rhomboidalis. Numerous immunoreactive fibers were also detected in the regions that contain the pathways to extrathalamic areas such as the stratum zonale and inferior thalamic peduncle. In the hypothalamus, many immunoreactive neuronal perikarya were distributed in the lateral hypothalamic area and in the arcuate nucleus. Immunoreactive fibers were disseminated throughout the hypothalamus, but they were dense in the preoptic area and sparse in the ventromedial nucleus. An accumulation of dense immunoreactive endings was also observed in the external layer of the median eminence. NT-LI fibers in the external layer of the median eminence were considered to represent nerve endings near portal vessels. Functional roles of neurotensin in the thalamus and hypothalamus are discussed from the anatomical point of view.

A neurotensin-immunoreactive pathway from the subiculum to the mammillary body in the rat

The existence of a neurotensin-like immunoreactive (NT-IR) pathway from the subiculum to the mammillary body was demonstrated in very young rats using immunocytochemistry, knife cut, electric lesion and retrograde tracer techniques. Unilateral hemitransection of the dorsal fornx caused a marked reduction of NT-IR fibers in the ipsilateral mammillary body. Unilateral electric lesion of the subiculum also resulted in ipsilateral reduction of NT-IR fibers in the mammillary body. Biotin-wheat germ agglutinin (B-WGA), injected into the mammillary body, labeled neurons in the ipsilateral subiculum which were shown by double staining to have NT-IR cytoplasm. These findings demonstrate the presence of a major NT-IR fiber pathway from the subiculum to the mammillary body via the fornix.

Distribution of neurotensin-like immunoreactivity in rat and cat area postrema

The distribution of neurotensin-like immunoreactive (NT-LI) fibers and cell bodies in the area postrema (AP) of rat and cat, utilizing the peroxidase, antiperoxidase (PAP) technique, is described. In the rat, the greatest accumulation of NT-LI fibers were present along the borders of the AP, while there were very few NT-LI fibers in central regions. In the cat, scattered NT-LI fibers occupied the majority of the central AP, while moderate numbers of NT-LI fibers were present at the ventromedial border. In more rostral cat AP levels, the number of NT-LI fibers decreased. NT-LI somata were present in rat AP, but were lacking in cat AP. The localization of NT within the AP suggests that the cardiovascular and gastric effects attributed to NT may be mediated, in part, through the AP.

Influence of ascending noradrenergic fibers on the neurotensin-like immunoreactive perikarya and evidence of direct projection of ascending neurotensin-like immunoreactive fibers in the rat central nucleus of the amygdala

The influence of ascending noradrenergic neuronal input on the neurotensin (NT)-like immunoreactive neuronal perikarya located in the dorsal part of the central nucleus of the amygdala (CNA) was examined using fluorescence histochemistry and peroxidase-antiperoxidase (PAP) immunocytochemistry. Unilateral hemitransection of the ascending noradrenergic pathway by injection of 6-hydroxydopamine into the caudal mesencephalon just rostral to the locus coeruleus caused a marked depletion of immunoreactivity in NT-like immunoreactive neuronal perikarya in the CNA. Ascending noradrenergic neuronal input, therefore, is considered to facilitate production of NT-like immunoreactive substances in neuronal perikarya and to influence on the functional role of the amygdaloid complex. In addition, we obtained evidence of unilateral direct ascending projections of NT-like immunoreactive neurons into the CNA since the disappearance of NT-like immunoreactive processes occurred mainly in the ventral part of the CNA after surgical hemitransection of the ascending neuronal pathway that interrupts the ascending NT-like immunoreactive pathway arising from the neurons in the brain stem.

Distribution and origins of neurotensin-containing fibers in the nucleus ventromedialis hypothalami of the rat: an experimental immunohistochemical study

The distribution and origins of neurotensin (NT)-containing fibers in the nucleus ventromedialis hypothalami (VM) of the rat were investigated experimentally using an indidrect immunofluorescence technique. A dense plexus of NT-like immunoreactive (NTI) fibers which was composed of very fine varicosities was identified in the VM. Although they were distributed throughout its entire rostrocaudal extent, the distribution was uneven. The highest density was identified in the dorsomedial part of the VM. In the central part, a less numerous but still moderate number of NTI fibers was detected in its dorsal part. But in a ventrolateral direction, they decreased in number and in the ventrolateral part only a few NTI fibers were seen. The present study demonstrated experimentally that these fibers originate from the medial nucleus of the amygdaloid complex (AM), since destruction of the AM resulted in a marked reduction of NTI fibers ipsilaterally in the VM. These findings suggest that the AM influences the VM's functions via neurotensin-like immunoreactive fibers.

Evidence for the existence of a neurotensin-containing pathway from the endopiriform nucleus and the adjacent prepiriform cortex to the anterior olfactory nucleus and nucleus of diagonal band (Broca) of the rat

The origin of neurotensin-like immunoreactive fibers to the anterior olfactory nucleus and nucleus of the diagonal band of Broca of the rat were elucidated experimentally using the indirect immunofluorescence method. Neurotensin-like immunoreactive fibers located in these areas decreased remarkably in numbers on the operated side after the destruction of the ventral part of the endopiriform nucleus and the adjacent prepiriform cortex where numerous cells with neurotensin-like immunoreactivity were detected. This strongly suggests that such cells located in the endopiriform nucleus and the adjacent prepiriform cortex send a neurotensin-like projection ipsilaterally to the anterior olfactory nucleus and to the nucleus of the diagonal band of Broca.