The effects of histaminergic agents in the dorsal hippocampus of rats in the elevated plus-maze test of anxiety.
High levels of histamine are found in the hippocampus. The central histamine system is involved in many physiological behavioural processes including anxiety-related behaviours both in animals and humans. In the present study, we investigated the effects of intra-hippocampal CA1 (intra-CA1) microinjection of histaminergic agents on anxiety-related behaviours in rats, using elevated plus-maze test of anxiety. Intra-CA1 administration of histamine (at the dose of 10 microg/rat) increased open arm time (%OAT) and open arm entry (%OAE) but not locomotor activity, thus showing an anxiolytic response. Intra-CA1 microinjection of pyrilamine (H1 receptor antagonist; at the doses of 10, 20 and 40 microg/rat) in combination with histamine (10 microg/rat) showed a decrease in the %OAT and %OAE. Higher dose of the antagonist (40 microg/rat) by itself increased both %OAT and %OAE, but not locomotor activity, indicating an anxiolytic effect. Intra-CA1 microinjection of ranitidine (H2 receptor antagonist), at the doses of 10, 20 and 40 microg/rat, also reduced the histamine response. Furthermore, the H2 receptor antagonist by itself reduced %OAT and %OAE without affecting locomotor activity. The results may indicate an anxiogenic effect for the antagonist. Our results showed that histamine may modulate anxiety via H1 and H2 receptors in the CA1 region of hippocampus of the rat.
Zarrindast
Mohammad-Reza
MR
Department of Pharmacology, School of Medicine and Iranian National Center for Addiction Studies, Tehran University of Medical Sciences, Tehran, Iran. zarinmr@ams.ac.ir
Torabi
Monirsadat
M
Rostami
Parvin
P
Fazli-Tabaei
Soheila
S
D000818:Animals; D001007:Anxiety / Q000139:chemically induced / Q000188:drug therapy*; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D006632:Histamine / Q000494:pharmacology*; D008297:Male; D018782:Maze Learning / Q000187:drug effects*; D009043:Motor Activity / Q000187:drug effects; D011738:Pyrilamine / Q000494:pharmacology; D011899:Ranitidine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011969:Receptors, Histamine H1 / Q000502:physiology; D011970:Receptors, Histamine H2 / Q000502:physiology
D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D006632:Histamine; D011899:Ranitidine; D011738:Pyrilamine