Contreras M, Carrasco M, Riveros M, Quispe M, Valdes J, Torrealba F (2007) Early activation of the tuberomammillary nucleus is a common factor in appetitive behaviors in rats. Neuroscience 2007 Abstracts 842.19/WW11. Society for Neuroscience, San Diego, CA.
Summary: Histamine neurons of the tuberomammillary nucleus show an earlier activation during the appetitive phase of feeding, compared to the other arousal system nuclei. To test if in different appetitive behaviors also these histaminergic neurons become active first, we studied changes in Fos-ir in arousal nuclei during sexual, drinking and drug-seeking behavior. Male rats were exposed to sexually receptive or to non-receptive female rats, allowing sensory but not sexual contact. Receptive females elicited increased sniffing time which positively correlated with Fos-ir in the dorsal raphe, laterodorsal tegmental nucleus, orexin hypothalamic neurons and tuberomammillary nucleus. Non receptive females induced less sniffing and no increased Fos-ir. Other male rats were deprived of water for 48 h and presented with an empty water bottle to induce appetitive behavior. The presentation of an empty water bottle to thirsty rats induced increased approaches to the bottle while they tried to drink. While water deprivation per se increased Fos-ir in the dorsal raphe and the locus coeruleus, the presentation of the bottle increased Fos-ir in the tuberomammillary nucleus and induced a further Fos-ir increase in the locus coeruleus. Other male rats were conditioned to amphetamine (1.5 mg/Kg i.p.) using a place preference task. Conditioned rats, but not rats injected with saline instead of amphetamine, showed a significant preference for amphetamine-paired room and increase in the number of Fos-ir in the tuberomammillary nucleus, orexin hypothalamic neurons and locus coeruleus. To evaluate the importance of the histaminergic neurons in the appetitive phase of these motivated behavior, we lesioned tuberomammillary nucleus using saporin conjugated to the hypocretin 2. The histaminergic neurons lesion blunted the appetitive phase in all motivated behaviors studied, without affecting general motor capacities. Taken together our results indicate that the histaminergic neurons become active at the onset of different motivated behaviors and they are key in the arousal that is essential in motivation. Other arousal nuclei may participate depending on the particular behavior.
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