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

Abstract

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.

Neurotensin afferents of the ventral tegmental area in the rat: [1] re‐examination of their origins and [2] responses to acute psychostimulant and antipsychotic drug administration

“…Although no tracing study devoted specifically to the ventral endopiriform area appears to exist (Behan & Haberly, 1999), it nonetheless has been demonstrated that neurons in this area receive olfactory information via a substantial projection from the superficial layer of the piriform cortex (Luskin & Price, 1983) and convey this information to the mediodorsal and submedial thalamic nuclei (Price & Slotnick, 1983). A subpopulation of the mediodorsal‐projecting neurons utilize NT as a neurotransmitter (Inagaki et al ., 1983; Ray & Price, 1990). Whether these neurons also project to the VTA or whether the NT‐containing VTA‐projecting neurons constitute a different population of neurons remains to be investigated.…”

Review of the cytology and connections of the lateral habenula, an avatar of adaptive behaving

“…Modern studies have consistently demonstrated non-uniform LHb distributions of immunoreactivity against various neuropeptides, mainly due to peptidergic enrichments in a small-celled (Pert and Atweh, 1976; Iwahori, 1977) medial core (e.g., opiates – Pert and Atweh, 1976; Atweh and Kuhar, 1977; substance P – Cuello, 1978; vasopressin – Buijis, 1978; Sofroniew and Weindl, 1978; somatostatin - Vincent et al, 1985; neurotensin - Ray and Price, 1990). Aside from the peptides, LHb neurons are reported to be mainly glutamatergic, expressing either vesicular glutamate transporter 2 (Geisler et al, 2007; Brinschwitz et al, 2010) or vesicular glutamate transporter 3 (Herzog et al, 2004).…”

Subnuclear organization of the rat habenular complexes

“…The evidence for this association, however, appears to be vague. A variety of investigations based on morphologic demonstrations of neuropeptides (e.g., neurotensin: Ray and Price, 1990;somatostatin: Vincent et al, 1985;vasopressin: Sofroniew and Weindl, 1978), metabolically activated neurons (Chastrette et al, 1991;Nagao et al, 1993;Wirtshafter et al, 1994), and neurons or fibers visualized subsequent to anterograde or retrograde axonal tracing (Pasquier et al, 1976;Skagerberg et al, 1984;Behzadi et al, 1990;Hazrati and Parent, 1991;Steininger et al, 1992) have yielded ample evidence for the heterogeneous composition of the LHb. Unfortunately, the localization of the activated or immunoreactive neurons with respect to the subnuclear compositions of the LHb cannot be appreciated.…”