Immunohistochemical and biochemical studies on Lys8‐Asn9‐neurotensin8–13(LANT6)‐related peptides in the basal ganglia of pigeons, turtles, and hamsters

Abstract

The distribution of the neurotensin‐related hexapeptide LANT6 within the basal ganglia and its projection targets was studied in turtles, pigeons, and hamsters by using immunohistochemical techniques, radioimmunoassay (RIA), gel chromatography, and high performance liquid chromatography (HPLC). The results in turtles and pigeons were fundamentally similar. Within the basal ganglia, LANT6‐like immunoreactivity (LLI) was observed in a population of large striatal neurons (comprising 1–5% of the total number of striatal neurons) and in essentially all of the medium‐large pallidal neurons. In addition, LLI was observed in neurons of such other “striatal” and “pallidal” cell groups as the olfactory tubercle and ventral pallidum, respectively. Within the dopaminergic cell fields of the tegmentum, to which the pallidal cell groups project, LLI‐containing fibers were abundant. Knife‐cut studies confirmed that the majority of these LLI‐containing fibers arise from telencephalic levels. Biochemical studies with RIA and HPLC showed large amounts of immunoreactive LANT6 (iLANT6) in the basal telencephalon (477 pmol/g) and tegmentum of pigeons (259 pmol/g), and this material was indistinguishable from the synthetic peptide. Lower levels of iLANT6 were demonstrated in the basal telencephalon (82 pmol/g) and tegmentum (156 pmol/g) of turtles, and the majority of this activity appeared to be associated with larger molecular forms of LANT6 or a peptide related to LANT6. In addition, one or more substances resembling Neuromedin N (NMN), a mammalian counterpart to LANT6, were detected in the turtle nervous system. The labeling patterns in hamsters were similar to those in pigeons and turtles, except that in hamsters fewer neurons were labeled and the labeling was generally lighter. The lighter level of labeling may reflect a difference between the LANT6‐like material present in hamster nervous system and authentic LANT6. Biochemical studies revealed that a Neuromedin N‐like substance, as well as high molecular weight forms of a LANT6‐like substance, are present in hamster brain. In hamsters, neurons within globus pallidus, the entopeduncular nucleus, the ventral pallidum, and the poly‐morph layer of the olfactory tubercle were labeled for the presence of LANT6. Fiber labeling for LANT6 in the dopaminergic tegmental cell groups that receive pallidal input was, however, light. Thus, the present results establish that LANTG in pigeons and LANT6‐related peptides in turtles and hamsters are present within many pallidal neurons. In pigeons and turtles, these pallidal neurons give rise to a major LLI‐containing projection to the dopaminergic cell groups of the tegmentum. Thus, LANT6 in birds and related peptides in reptiles and mammals may used as a neurotransmitterheurornodulator by pallidal neurons of the basal ganglia, particularly in their projections to the dopaminergic cell groups of the tegmentum. This suggestion is consistent with recent studies that show neurotensin and neurotensin‐related substances, such as Neuromedin N, activate dopaminergic tegmental neurons (Kalivas, '85; Kalivas and Richardson‐Carlson, '85; Kalivas et at., '86).