Facilitation of short‐term memory by histaminergic neurons in the nucleus accumbens is independent of cholinergic and glutamatergic transmission

Abstract

Here, we have investigated whether learning and/or short-term memory was associated with release of ACh and glutamate in the rat nucleus accumbens (NAc). Additionally, neurotransmitter release in the NAc was assessed during facilitation of cognitive processes by antagonists of inhibitory histamine autoreceptors. The olfactory, social memory test was used in combination with push-pull superfusion of the NAc. A male, juvenile rat was exposed twice to an adult male rat at intervals of 60 or 90 min, and release of ACh and glutamate was determined in the NAc of the conscious adult rat. Histamine receptor antagonists were applied i.c.v. First exposure of a juvenile rat to an adult rat increased ACh and glutamate release in the NAc of the adult rat. Repetition of exposure after 60 min did not change release of ACh and glutamate, while contact time to recognition (CTR) was shortened. Repetition of exposure after an interval of 90 min prolonged CTR and enhanced accumbal ACh and glutamate release rates. Injection (i.c.v.) of thioperamide (histamine H3 receptor antagonist) together with famotidine (H₂ receptor antagonist), 80 min prior to second exposure, diminished CTR and abolished ACh and glutamate release when second exposure was carried out 90 min after the first one. Histaminergic neurons per se facilitated short-term memory, without activation of cholinergic and/or glutamatergic neurons in the NAc of rats. Cholinergic and glutamatergic neurons within the NAc contributed to learning but not to recall of memory.