OBJECTIVE: For understanding the neurochemical mechanism of neuropsychiatric conditions associated with cognitive deficits it is of major relevance to elucidate the influence of serotonin (5-HT) agonists and antagonists on memory function as well dopamine (DA) and 5-HT release and metabolism. In the present study, we assessed the effects of the 5-HT2A receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) and the 5-HT2A receptor altanserin (ALT) on object and place recognition memory and cerebral neurotransmitters and metabolites in the rat.
METHODS: Rats underwent a 5-min exploration trial in an open field with two identical objects. After systemic injection of a single dose of either DOI (0.1 mg/kg), ALT (1 mg/kg) or the respectice vehicle (0.9 % NaCl, 50 % DMSO), rats underwent a 5-min test trial with one of the objects replaced by a novel one and the other object transferred to a novel place. Upon the assessment of object exploration and motor/exploratory behaviors, rats were sacrificed. DA, 5-HT and metabolite levels were analyzed in cingulate (CING), caudateputamen (CP), nucleus accumbens (NAC), thalamus (THAL), dorsal (dHIPP) and ventral hippocampus (vHIPP), brainstem and cerebellum with high performance liquid chromatography.
RESULTS: DOI decreased rearing but increased head-shoulder motility relative to vehicle. Memory for object and place after both DOI and ALT was not different from vehicle. Network analyses indicated that DOI inhibited DA metabolization in CING, CP, NAC, and THAL, but facilitated it in dHIPP. Likewise, DOI inhibited 5-HT metabolization in CING, NAC, and THAL. ALT facilitated DA metabolization in the CING, NAC, dHIPP, vHIPP, and CER, but inhibited it in the THAL. Additionally, ALT facilitated 5-HT metabolization in NAC and dHIPP.
CONCLUSIONS: DOI and ALT differentially altered the quantitative relations between the neurotransmitter/metabolite levels in the individual brain regions, by inducing region-specific shifts in the metabolization pathways. Findings are relevant for understanding the neurochemistry underlying DAergic and/or 5-HTergic dysfunction in neurological and psychiatric conditions.

Both dopamine (DA) and serotonin (5-HT) play key roles in numerous functions including motor control, stress response and learning. So far, there is scarce or conflicting evidence about the effects of 5-HT1A and 5-HT2A receptor (R) agonists and antagonists on recognition memory in the rat. This also holds for their effect on cerebral DA as well as 5-HT release. In the present study, we assessed the effects of the 5-HT1AR agonist 8-OH-DPAT and antagonist WAY100,635 and the 5-HT2AR agonist DOI and antagonist altanserin (ALT) on rat behaviors. Moreover, we investigated their impact on monoamine efflux by measuring monoamine transporter binding in various regions of the rat brain. After injection of either 8-OH-DPAT (3 mg/kg), WAY100,635 (0.4 mg/kg), DOI (0.1 mg/kg), ALT (1 mg/kg) or the respective vehicle (saline, DMSO), rats underwent an object and place recognition memory test in the open field. Upon the assessment of object exploration, motor/exploratory parameters and feces excretion, rats were administered the monoamine transporter radioligand N-o-fluoropropyl-2b-carbomethoxy-3b-(4-[123I]iodophenyl)-nortropane ([123I]-FP-CIT; 8.9 ± 2.6 MBq) into the tail vein. Regional radioactivity accumulations in the rat brain were determined post mortem. Compared vehicle, administration of 8-OH-DPAT impaired memory for place, decreased rearing behavior, and increased ambulation as well as head-shoulder movements. DOI administration led to a reduction in rearing behavior but an increase in head-shoulder motility relative to vehicle. Feces excretion was diminished after ALT relative to vehicle. Dopamine transporter (DAT) binding was increased in the caudateputamen (CP), but decreased in the nucleus accumbens (NAC) after 8-OH-DPAT relative to vehicle. Moreover, DAT binding was decreased in the NAC after ALT relative to vehicle. Findings indicate that 5-HT1AR inhibition and 5-HT2AR activation may impair memory for place. Furthermore, results imply associations not only between recognition memory, motor/exploratory behavior and emotionality but also between the respective parameters and the levels of available DA in CP and NAC.