Effects of histamine on spontaneous electrical activity of neurons in rat suprachiasmatic nucleus.
The hypothalamic suprachiasmatic nucleus (SCN) is thought to be a light-entrained pacemaker in mammals, inducing a wide range of endogenous circadian events. In rat brain, histaminergic (HAergic) fibres are particularly rich in the hypothalamus. This prompted an investigation of the influence of bath-applied HAergic compounds on the spontaneous electrical activity of SCN neurons, recorded extracellularly in the hypothalamic slice preparation. Cells activated by bath application of HA (n = 28) outnumbered those inhibited by HA (n = 6). 48% of cells tested (n = 28) were unresponsive to HA application. HA-induced activation of SCN neurons' discharge rate could be suppressed by the H1-antagonist mepyramine, but not by the H2-antagonist cimetidine. HAergic effects were still present when synaptic transmission was blocked, indicating a postsynaptic site of action for HA within SCN. Due to the anatomical distribution of HA-responsive SCN neurons and the independence of HA-effects with respect to circadian time, HA seems not to endow a pivotal role within generation and maintenance of circadian rhythm. Although data were obtained from SCN deprived of neural input, results show clear evidence for a modulatory impact of HA on the spontaneous electrical activity of part of SCN neurons.
Stehle
J
J
Department of Physiology and Pathophysiology, University of Mainz, F.R.G.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002927:Cimetidine / Q000494:pharmacology; D002940:Circadian Rhythm / Q000502:physiology; D006632:Histamine / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000187:drug effects*; D011738:Pyrilamine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013493:Suprachiasmatic Nucleus / Q000187:drug effects*
D002927:Cimetidine; D006632:Histamine; D011738:Pyrilamine