Insulin-like growth factor-1 (somatomedin-C) receptors in the rat brain: distribution and interaction with the hippocampal cholinergic system.

The present work characterizes the autoradiographic distribution of insulin-like growth factor-1 (IGF-1)/somatomedin-C binding sites in neonatal and adult rat brain, and attempts to correlate the distribution of IGF-1 sites, in certain regions of the rat brain, with functional IGF-1 receptors. In neonatal brain, [125I]IGF-1 binding sites are especially concentrated in superficial cortical layers, nucleus accumbens and hippocampus. In the adult rat brain, the distribution of IGF-1 sites is broader, with a high density of sites observed in superficial and deep cortical layers, olfactory bulb, endopiriform nucleus, basomedial nucleus of the amygdala, thalamic nuclei and hippocampus. Specific binding of [125I]IGF-1 to its sites in these brain regions was almost completely inhibited by 100 nM nonradioactive IGF-1. In contrast, similar concentrations of either IGF-2 or insulin did not significantly alter [125I]IGF-1 binding to its sites. Therefore, under our incubation conditions, [125I]IGF-1 appears to label specifically the type-I IGF receptor. In the hippocampus, which is highly enriched with specific [125I]IGF-1 binding sites in both neonatal and adult rat brain, IGF-1 significantly altered the potassium-evoked (25 mM) release of acetylcholine (ACh) from slices of adult, but not immature (6- and 18-day-old), rat brain. This IGF-1-induced decrease in ACh release from adult rat brain slices was concentration-dependent and appeared to be specific to hippocampus; ACh release from frontal cortical slices was not affected by this GF. The spontaneous release of ACh in the presence of IGF-1 in either tissue was not significantly different from control.(ABSTRACT TRUNCATED AT 250 WORDS)