Histamine reduces firing and bursting of anterior and intralaminar thalamic neurons and activates striatal cells in anesthetized rats.

Histamine is known to play a role in the regulation of waking behavior as well as in processes of memory and reinforcement. The striatum and thalamic nuclei as the intralaminar complex and the anterior group can be involved in these functions. Little is known about the action of histamine on neurons of these brain structures. Single unit activity was extracellularly recorded in rats anesthetized with urethane. Firing of anterior and intralaminar thalamic neurons that responded to iontophoretically administered histamine was predominantly reduced (Wilcoxon test (Wt), P<0.05, n=49 and 63, respectively), whereas striatal neurons were mainly activated by the drug (Wt, P<0.05, n=29). Thalamic neurons also significantly reduced the number of burst discharges and the proportion of spikes involved in bursts. The histaminergic effects could be blocked by H1 or H2 receptor antagonists. In conclusion, histamine may control waking behavior also via nonspecific thalamic nuclei and basal ganglia circuits. Through modulation of the transmission in the anterior thalamus it may exert an influence on learning and emotional processes.