Participation of the medial and anterior hypothalamus in the modulation of tonic immobility in guinea pigs.
Tonic immobility (TI) is an inhibitory behavioral response during which the animal presents profound physical inactivity and a relative lack of response to the environment. This response is induced in the laboratory by postural inversion of the animal and brief postural contention of its movements. In nature, the response occurs when there is physical contact between prey and predator. In this case, the physical inactivity of the prey may prevent the continuation of the attack. The neural substrate of this response is not well known and the objective of the present study was to investigate the effect of cholinergic stimulation of hypothalamic regions on TI modulation in guinea pigs (Cavia porcellus). Microinjection of carbachol (1.0 microg/0.2 microL) into the anterior hypothalamus promoted an increase in the duration of TI episodes. Microinjection of carbachol into the ventro- and dorsomedial hypothalamus, however, promoted a reduced duration of TI episodes. Pretreatment with atropine (0.5 microg/0.2 microL) showed that the action of carbachol is mediated by muscarinic receptors in the anterior and ventromedial hypothalamus but not in the dorsomedial hypothalamus. The results suggest that the hypothalamic regions may play different roles in the organization of defensive behavioral responses such as TI.
De Oliveira
L
L
Department of Physiology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Brazil.
Hoffmann
A
A
Menescal-de-Oliveira
L
L
D000818:Animals; D001931:Brain Mapping; D002799:Cholinergic Fibers / Q000502:physiology; D004302:Dorsomedial Hypothalamic Nucleus / Q000502:physiology; D005239:Fear / Q000502:physiology*; D006168:Guinea Pigs; D007032:Hypothalamus, Anterior / Q000502:physiology*; D007033:Hypothalamus, Middle / Q000502:physiology*; D007103:Immobilization / Q000502:physiology*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D012018:Reflex / Q000502:physiology; D014697:Ventromedial Hypothalamic Nucleus / Q000502:physiology