Inhibitory and excitatory effects of histamine on suprachiasmatic neurons in rat hypothalamic slice preparation.
The effects of histamine (HA) and serotonin (5-HT) on single neurons of the suprachiasmatic nucleus (SCN) in hypothalamic slices were investigated by iontophoretic application. Sixty-two of 181 cells were inhibited by HA, whereas 30 were excited. Forty-nine of 163 cells were inhibited by 5-HT, whereas 9 were excited. Pyrilamine, an H1-antagonist, slightly (2/7), and cimetidine, an H2-antagonist, strongly (10/13) antagonized the inhibitory effect of HA. The excitatory effect of HA was not antagonized by cimetidine (0/4), but was perfectly antagonized by pyrilamine (5/5). The present results suggest that HA and 5-HT play mainly an inhibitory role in the SCN neuronal activity, and that inhibition and excitation induced by HA may be mediated by H2- and H1-receptors, respectively.
D000818:Animals; D006632:Histamine / Q000008:administration & dosage / Q000494:pharmacology*; D006633:Histamine Antagonists / Q000494:pharmacology; D007478:Iontophoresis; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D051381:Rats / Q000502:physiology*; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000187:drug effects*
D006633:Histamine Antagonists; D012701:Serotonin; D006632:Histamine