Fujita, I.1, Koyama, Y.1*, YOSHIMATSU, H.2, Aou, S., Nishino, H.1,2 and Oomura,
1 Natl. Inst. Physiol. Sci., Okazaki 444;
2 Toyama Med. Pharmaceut. Univ., Toyama 930-O1;
3 Dept. Physiol., Fac. Med., Kyushu Univ., Fukuoka 812 (Japan)
Allogrooming (AG) is the most common form of social behavior performed by non-human primates. It establishes and maintains a variety of relationships, reduces tension and promotes alliances between individuals. However, the neural substrate implicated in AG is largely unknown compared to other social behaviors including vocal communication, aggression and sexual behavior. We report here that the hypothalamus contains a neural system which facilitates AG. Two male and one ovariectomized, estrogen-treated female rhesus monkeys were acquired and used in accordance with the NIH Guide (1985). Allogrooming was reproducibly evoked by electrical stimuli (0.5 ms, 50 Hz, 10-300 μA, 2.5 sec) to the lateral preoptic area (LPOA), lateral hypothalamic area (LHA) and dorsomedial hypothalamic nucleus (DMH). When we removed the partner monkey, or replaced it with a non-living object or an experimenter, stimulation did not elicit any behavior. This exclude the possibility that electrical stimuli evoke simple arm extension which accidentally results in AG. Selfgrooming (SG) was not evoked from any sites. Sodium-glutamate solution of either 10, 33 or 100 mM injected at a rate of 0.5 μl/min for 6 min markedly facilitated AG without affecting SG, when infused into the loci where electrical shocks evoked AG in the LHA or DMH. No behavioral effect was observed after injection of saline into these sites. Extracellular unit recording in behaving monkeys showed that some neurons in the LPOA, LHA and DMH changed their activity during spontaneous AG. In some of the neurons examined, the activity- change seemed specific to AG, i.e., they changed their activity during AG, but not during sexual behavior neither in response to passive arm movement forced by an experimenter or tactile stimuli to the hand. The present study provide the first unequivocal evidence for the neural substrate involved in AG that the lateral and dorsomedial hypothalamus facilitates this behavior. Supported by Itoh Science Foundation and the Ministry of Education, Science and Culture.