Competition between lateral hypothalamus and ventromedial tegmentum in electrical self-stimulation in the rat.

Abstract

Rats with two bipolar electrodes, one in the lateral hypothalamus (LH), the other in the ventromedial tegmentum (VMT) were used. After training, bar-pressing rates for LH and VMT self-stimulation (ss) were studied separately by switching the stimulation alternately to LH and to VMT (single-bar test), or in a choice test where qninnaTg had to choose between UH and VMT stimulation by pressing two independent bars. In the single-bar test when threshold currents were used, rats self-stimulated significantly more in LH than in VMT, but the reverse was observed at high current intensities. Some negative behaviours observed in is with strong currents did not generalize when stimulation was switched to the VMT probe, suggesting a relative independence between ta and VMT. Furthermore, the comparison between the relative preference of animals for LB or VMT stimulation in the choice test and the bar-pressing rates in the single-bar test shows that in this last test bar-pressing rates reflect the rewarding value of stimulation only when weak current intensities are used.THIS WOBK IS THE LAST in a series of three studies comparing behaviours elicited by electrical stimulation from the lateral hypothalamus (us) and ventromedial tegmentum (VMT) in the rat (Miliaressis, 1972; Miliaressis &Cardo,1973).The purpose of the present experiment was to investigate problems relevant to the competition encountered when the opportunity is given to animals to choose between is. and VMT intracranial self-stimulation (ss). Studies concerning competition between ss and feeding have been conducted (Le Moal et cd., 1969; Miliaressis & Cardo, 1973; Routtenberg & Lundy, 1965;Spies, 1965;Stutz et al., 1971), but to our knowledge there exists only one reference concerning competition between two different brain sites for ss (Hodos & Valenstein, 1962). The relative importance attributed to the different brain regions in ss behaviour is usually based on the bar-pressing rates. Nevertheless, Hodos and Valenstein have shown •Supported in part by a grant (A8625) to T.E. Miliaressis from the National Research Council of Canada.