title: Dorsal hippocampal microinjection of chlorpheniramine reverses the anxiolytic-like effects of l-histidine and impairs emotional memory in mice.
abstract: Several findings have pointed to the role of histaminergic neurotransmission in the modulation of anxiety-like behaviors and emotional memory. The elevated plus-maze (EPM) test has been widely used to investigate the process of anxiety and also has been used to investigate the process of learning and memory. Visual cues are relevant to the formation of spatial maps, and as the hippocampus is involved in this task, experiment 1 explored this issue. Experiment 2 investigated the effects of intraperitoneal (i.p.) injections of l-histidine (LH, a precursor of histamine) and of intra-dorsal hippocampus (intra-DH) injections of chlorpheniramine (CPA, an H1 receptor antagonist) on anxiety and emotional memory in mice re-exposed to the EPM. Mice received saline (SAL) or LH i.p. and SAL or CPA (0.016, 0.052, and 0.16 nmol/0.1 μl) intra-DH prior to Trial 1 (T1) and Trial 2 (T2). No significant changes were observed in the number of enclosed-arm entries (EAE) in T1, an EPM index of general exploratory activity. LH had an anxiolytic-like effect that was reversed by intra-DH injections of CPA. T2 versus T1 analysis revealed that only the lower dose of CPA resulted in impaired emotional memory. Combined injections of LH and CPA revealed that higher doses of CPA impair emotional memory. Taken together, these results suggest that LH and H1 receptors present in the dorsal hippocampus are involved in anxiety-related behaviors and emotional memory in mice submitted to EPM.
authors.affiliation: Laboratório de Neurociências, Universidade Federal de São Carlos, Brazil; Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, 14040-901, Ribeirão Preto, Brazil. Electronic address: lucascanto@gmail.com.
authors.forename: L
authors.initials: L
authors.lastname: Canto-de-Souza
authors.affiliation: Universidade Tiradentes, Rua Lagarto, 264, 49010-390 Aracaju, Brazil. Electronic address: diogoufscar@yahoo.com.br.
authors.forename: D C
authors.initials: DC
authors.lastname: Garção
authors.affiliation: Universidade do Estado de Santa Catarina, Rua Pascoal Simone, 358, 88080-350 Florianópolis, Brazil. Electronic address: feromaguera@gmail.com.
authors.forename: F
authors.initials: F
authors.lastname: Romaguera
authors.affiliation: Laboratório de Neurociências, Universidade Federal de São Carlos, Brazil. Electronic address: mattioli@ufscar.br.
authors.forename: R
authors.initials: R
authors.lastname: Mattioli
mesh_terms: D000818:Animals; D001007:Anxiety / Q000378:metabolism / Q000523:psychology*; D002744:Chlorpheniramine / Q000494:pharmacology*; D004644:Emotions; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology / Q000502:physiology*; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D008297:Male; D008568:Memory; D051379:Mice; D008845:Microinjections
chemical_list: D006634:Histamine H1 Antagonists; D002744:Chlorpheniramine; D006632:Histamine
keywords: Anxiety; Chlorpheniramine; Dorsal hippocampus; Elevated plus-maze; Emotional memory; Mice