title: Cerebellar vermis H₂ receptors mediate fear memory consolidation in mice.
abstract: Histaminergic fibers are present in the molecular and granular layers of the cerebellum and have a high density in the vermis and flocullus. Evidence supports that the cerebellar histaminergic system is involved in memory consolidation. Our recent study showed that histamine injections facilitate the retention of an inhibitory avoidance task, which was abolished by pretreatment with an H2 receptor antagonist. In the present study, we investigated the effects of intracerebellar post training injections of H1 and H2 receptor antagonists as well as the selective H2 receptor agonist on fear memory consolidation. The cerebellar vermi of male mice were implanted with guide cannulae, and after three days of recovery, the inhibitory avoidance test was performed. Immediately after a training session, animals received a microinjection of the following histaminergic drugs: experiment 1, saline or chlorpheniramine (0.016, 0.052 or 0.16 nmol); experiment 2, saline or ranitidine (0.57, 2.85 or 5.07 nmol); and experiment 3, saline or dimaprit (1, 2 or 4 nmol). Twenty-four hours later, a retention test was performed. The data were analyzed using one-way analysis of variance (ANOVA) and Duncan's tests. Animals microinjected with chlorpheniramine did not show any behavioral effects at the doses that we used. Intra-cerebellar injection of the H2 receptor antagonist ranitidine inhibited, while the selective H2 receptor agonist dimaprit facilitated, memory consolidation, suggesting that H2 receptors mediate memory consolidation in the inhibitory avoidance task in mice.
authors.affiliation: Laboratory of Neuroscience, Physiotherapy Department, Center of Biological Sciences and Health, Federal University of Sao Carlos, 13565-905, Sao Carlos, Brazil. Electronic address: acgianlorenco@yahoo.com.br.
authors.forename: A C L
authors.initials: AC
authors.lastname: Gianlorenço
authors.affiliation: Laboratory of Neuroscience, Physiotherapy Department, Center of Biological Sciences and Health, Federal University of Sao Carlos, 13565-905, Sao Carlos, Brazil. Electronic address: alineriboldi@yahoo.com.br.
authors.forename: A M
authors.initials: AM
authors.lastname: Riboldi
authors.affiliation: Laboratory of Neuroscience, Physiotherapy Department, Center of Biological Sciences and Health, Federal University of Sao Carlos, 13565-905, Sao Carlos, Brazil. Electronic address: bruna_chii@hotmail.com.
authors.forename: B
authors.initials: B
authors.lastname: Silva-Marques
authors.affiliation: Laboratory of Neuroscience, Physiotherapy Department, Center of Biological Sciences and Health, Federal University of Sao Carlos, 13565-905, Sao Carlos, Brazil. Electronic address: mattioli@ufscar.br.
authors.forename: R
authors.initials: R
authors.lastname: Mattioli
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D065814:Cerebellar Vermis / Q000187:drug effects / Q000378:metabolism*; D002744:Chlorpheniramine / Q000494:pharmacology; D017259:Dimaprit / Q000494:pharmacology; D005239:Fear; D017442:Histamine Agonists / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D008297:Male; D008568:Memory; D051379:Mice; D008845:Microinjections; D011899:Ranitidine / Q000494:pharmacology; D011970:Receptors, Histamine H2 / Q000378:metabolism*
chemical_list: D017442:Histamine Agonists; D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D011970:Receptors, Histamine H2; D002744:Chlorpheniramine; D011899:Ranitidine; D017259:Dimaprit
keywords: Cerebellar vermis; H(2) receptors; Histaminergic system; Inhibitory avoidance; Memory consolidation; Mice