Farias P, Valdes J, Riveros M, Torrealba F (2006) The tuberomammillary nucleus is a key component of the arousal system for the appetitive phase of feeding. Neuroscience 2006 Abstracts 361.24. Society for Neuroscience, Atlanta, GA.
Summary: The histaminergic neurons from the tuberomammilary nucleus (TMN) are important in maintaining a high level of arousal or increased sensory alertness. We have seen TMN activation (assessed by Fos-ir) in three different motivated behaviors: feeding, drinking and sexual. The aim of this work is to prove that TMN neurons are essential to promote the arousal during the appetitive phase of feeding. We evaluated the effect of TMN lesion performed with the neurotoxin-saporin coupled to orexin-B on locomotor activity and on thermal responses during food presentation to hungry rats as well as changes in Fos-ir of arousal nuclei and subcortical regions involved in thermal responses. Rats were implanted with telemetric transponders to measure locomotor activity and body core temperature. The brains were processed for Fos-ir, and counterstained with appropriate antibodies to identify ascending arousal system (AAS) nuclei. Histaminergic neurons in the TMN were identified by adenosine deaminase (ADA)-ir. The lesions significantly decreased the number of ADA ir/mm2. The larger lesion (<54% surviving neurons) produced a significant decreased in locomotion and temperature responses to food enticing, compared to intact rats or rats with smaller lesion. Larger lesion abolished the increase in Fos-ir of the AAS nuclei (except the locus coeruleus), and the increase in Fos-ir in thermoregulatory nuclei observed in intact rats. The activation of the orexin neurons of the lateral hypothalamic area and the increase in locomotor activity during food presentation were correlated with the activation of the dorsal TMN. The increased Fos-ir in locus coeruleus and dorsal raphe, and the increase in body core temperature were correlated with the activation of the ventral TMN. In conclusion the TMN neurons seems to act as a “master switch” since they are necessary to initiate the increased arousal that characterizes motivated behaviors, and they likely engage other arousal nuclei as well as thermoregulatory nuclei during the appetitive phase of feeding.
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