Primary culture of cerebellar granular cells was prepared from 8- day old Sprague Dawley rats. We found that these cells possess adrenergic alpha 1, histaminergic H1, 5-HT2 and muscarinic cholinergic receptors linked to phospholipase C. The response of muscarinic receptors stimulated by carbachol was particularly robust; this receptor agonist increased by about 30-fold the hydrolysis of phosphoinositide hydrolysis measured by the accumulation of inositol monophosphate (IP), in the presence of lithium. This muscarinic receptor response can be desensitized by pretreatment with carbachol or oxotremorine, another muscarinic receptor agonist. This receptor desensitization can be dissected into fast and slow components. The fast component is complete within one hr of stimulation and appears to involve receptor uncoupling. The slow component involves receptor loss assessed by using 3H-QNB and 3H-N-methyl-scopolamine (NMS) as the receptor ligand. The responses of adrenergic alpha 1, histaminergic H1 and 5-HT2 receptors can also be desensitization by stimulation with their respective agonist. However, no heterologous desensitization was found when these receptors were stimulated with their selective agonist for as long as 18 hrs. Cerebellar granular cells also express GABAB receptor which is linked to inhibition of adenylate cyclase. We found that stimulation of these GABAB receptors leads to inhibition of voltage sensitive calcium uptake. Moreover, inhibition of this calcium uptake appears to result in attenuation of the release of preloaded D-aspartate from granule cells. These results suggest that voltage sensitive calcium channel rather than the receptor- coupled phospholipase C system plays a major role in regulating the release of the excitatory neurotransmitter from granule cells.
