Serotonergic, adrenergic and histaminergic receptors coupled to phospholipase C in cultured cerebellar granule cells of rats

Abstract Phosphatidylinositol (Ptdlns) turnover has been studied in the primary culture of granule cells dissociated from the cerebellum of postnatal rat. Addition of serotonin (5-hydroxytryptamine, 5-HT) caused an increase (300–600% of control) of [ 3 H]inositol monophosphate (IP 1 ) accumulation in the presence of LiCl in cells prelabeled with [ 3 H]myo-inositol. The EC 50 and saturation concentrations of 5-HT were about 0.1 and 10 μM respectively. Some nonselective 5-HT receptor agonists, MK212, 5-methoxytryptamine, tryptamine and quipazine, were capable of stimulating IP 1 accumulation; a selective 5-HT 1A receptor agonist, 8-OH-DPAT, was ineffective. The 5-HT-induced response was potently blocked by several 5-HT 2 receptor antagonists such as ketanserin, mianserin, spiroperidol and pyzotyline. The 5-HT-induced accumulation was dependent on the culturing time of granule cells with the maximal response seen in an 8-day culture. Norepinephrine (NE) also promoted an increased IP 1 accumulation (300% of the control) with an EC 50 of about 1 μM, while prazosin inhibited this NE-induced response with a K i of about 0.2 nM. The responses induced by NE and 5-HT appeared to be additive. In addition, histamine in a dose-dependent manner enhanced the accumulation by about 100%; this histamine effect was blocked by triprolidine, an H 1 receptor antagonist, but not by cimetidine, an H 2 receptor antagonist. These results suggest that 5-HT, NE and histamine could be part of the neurotransmitter substances present in mossy fibers or other afferent nerve endings which innervate granule cells in vivo and that Ptdlns turnover regulated by their selective receptors on granule cells may play a role in modulating the excitatory function of these neurons.