Organized behavioral responses to lateral hypothalamic electrical stimulation in infant rats.

Brief trains of electrical stimulation (500 msec) were administered to 3-, 6-, 10-, and 15-day-old rat pups through electrodes directed at the medical forebrain bundle (MFB) at the level of the lateral hypothalamus. Stimulation was given at three different frequencies: once per 30 sec, once per 20 sec, and once per 10 sec. Pups 10 days of age and younger became behaviorally activated by stimulation and reliably emitted a series of behavioral responses including mouthing, licking, pawing, gaping, probing, and stretch and lordosis responses. Behavior increased with increasing frequency of stimulation and became more organized with age. Sequences of organized behavior patterns are elicited by MFB stimulation which in their culmination take on the characteristics of motivational responses. Fifteen-day-old pups did not respond to these stimulation parameters. These findings indicate that the components of motivational systems are present and can be elicited at an early age. As development progresses, responses become more organized until stimulation parameters effective in rats 3 to 10 days of age become ineffective in activating behavior in day 15 pups.