Objective: 

The dentate gyrus of hippocampal formation receives the strongest histaminergic innervation and also contains the highest density of H3 receptor binding sites. The histamine H3 receptor is a presynaptic autoreceptor which controls histamine release. Thioperamide, H3 receptor antagonist, blocks the effect of histamine. We aimed to investigate whether histamine acts on long term potentials through H3 receptor or other histaminergic receptor and neurotransmitters. For this purpose, we infused histamine and thioperamide in the dentate gyrus of rats to evoke excitatory postsynaptic potentials, in vivo.

Methods: 

The approval from Erciyes University Local Ethical Committee was obtained. A bipolar stimulating electrode was placed to the medial perforant path and a double-barrel glass micropipette was placed in the dentate gyrus as recording electrode. Artificial cerebrospinal fluid (to control group), histamine (10mM), thioperamide (10mM) or thioperamide+histamine (10mM) were infused to dentate gyrus. Three minutes after the infusion, high frequency stimulation protocol was applied to evoke long-term potentiation.

Results: 

The population spike amplitudes of the histamine group showed a depressed response when compared to control group; whereas thioperamide or thioperamide+histamine groups were not different than the control. When we compared the slope of excitatory postsynaptic potentials we observed no difference among the groups.

Conclusions: 

Our results showed the presence of a histaminergic tract ending at the dentate gyrus, that is activated that by stimulation of the perforant pathway. Although the predominantly presence of the H3 receptors on this tract, we need new studies to understand whether this occurs via direct or indirect mechanisms.