Distribution of glucagon-like peptide-1 and other preproglucagon-derived peptides in the rat hypothalamus and brainstem
Section snippets
Animals
Fifty-five adult male Wistar rats (200–250 g; Panum Institute Colony) were used in this study. The rats had unlimited access to pellet chow and water, and they were housed under standard laboratory conditions with lights on from 6.00 a.m. to 6.00 p.m.
Chromatography
Thirty rats were decapitated between 9.00 and 10.00 a.m., and their brains were removed and rapidly frozen on dry ice. Tissue blocks containing the rostral portion of the hypothalamus and brainstem blocks were dissected and pooled. The two tissue
Gel chromatography
Upon gel filtration of the extracts of rat hypothalamus and brainstem, similar elution patterns of all measured moieties were found in the two areas (Fig. 2). The peptide concentrations/g tissue (wet weight), however, were significantly higher in the hypothalamus than in the brainstem (7 pmol/g vs 0.1 pmol/g). In both areas almost all GLP-1 immunoreactivity (as measured with antisera nos 2135 and 89390) eluted at the position of synthetic GLP-1 (7–36 amide) (Kd 0.60). The brain peptide must be
Discussion
The present study confirms the presence of a single population of GLP-1-synthesizing neurons in the caudal brainstem and provides evidence that this population of cells contributes to the terminal field of at least one hypothalamic target. Furthermore, the dual-labelling experiments indicate that this population of GLP-1 cells is distinct from the catecholaminergic cells of the NTS, supporting the view that the parvicellular neurons of the PVN receive neurochemically diversified inputs from
Conclusions
The present data clearly demonstrate that a population of non-catecholaminergic solitary tract neurons produces fully processed GLP-1 from the preproglucagon precursor. Furthermore, it is clear that this group of neurons projects to the PVN. Given the apparent absence of other GLP-1-IR neurons in the CNS, these neurons are the only source of central GLP-1-containing nerve fibres.
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