The aim of this study was to investigate changes in gene expression after tactile stimulation (tickling) accompanied by positive emotion in the adolescent rat brain. We observed a positive emotional response (50-kHz ultrasonic vocalizations) after tickling using a modified version of the Panksepp method, and then comprehensively compared gene expression levels in the hypothalamus of the tickled rats and control rats using the microarray technique. After 4 weeks of stimulation, the expression levels of 321 of the 41,012 genes (including transcripts) were changed; 136 genes were up-regulated (>1.5-fold) and 185 were down-regulated (>0.67-fold) in the tickled rat group. Upon ontology analysis, the up-regulated genes were assigned to the following Gene Ontology (GO) terms: feeding behavior, neuropeptide signaling pathway, biogenic amine biosynthesis and catecholamine biosynthesis. Down-regulated genes were not assigned to any GO term categorized as a biological process. In conclusion, repeated tickling stimulation with positive emotion affected neuronal circuitry directly and/or indirectly, and altered the expression of genes related to the regulation of feeding in the adolescent rat hypothalamus.

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