Evidence for the existence of histamine H1- and H2-receptors on astrocytes of cultured rat central nervous system.

By means of intracellular microelectrodes we have studied the action of histamine H1- and H2-agonists and -antagonists on the membrane potential of astrocytes in cultured rat brainstem and spinal cord. Histamine at high concentrations (10(-4) and 10(-5) M) mainly depolarized the glial membrane, whereas at low concentration (10(-6) M) it usually caused hyperpolarizations. The histamine-induced depolarizations were reversibly blocked by the H1-antagonist pyrilamine, whereas the H2-antagonist cimetidine antagonized the hyperpolarizations. The H1-agonist thiazolethylamine mainly produced depolarizations while impromidine, a H2-agonist, predominantly caused hyperpolarizations. Our findings, together with autoradiographic binding studies, provide strong evidence for the existence of histamine H1- and H2-receptors on astrocytes.