Stimulation-induced ingestion in neonatal rats

Rat pups, 3, 6, 10 and 15 days old, received 500 ms pulse trains of electrical stimulation to the medial forebrain bundle (MFB) at the level of the lateral hypothalamus in the presence of milk. Pups receiving stimulation ingested more milk than littermate controls during a 30-min test at 3, 6 and 10 days of age. Day 15 pups did not. Stimulated pups through day 10 were more active than controls and exhibited the organized behaviors of mouthing, licking, gaping, stretch and even lordosis. Stimulated pups that ingested more milk continued to show increased activity through the 30-min test period, while the activity of control pups demonstrated a satiety effect. Milk augmented the activation of stimulation alone, increasing the incidence of all behaviors in 3-day-old pups and channelled the behavior of older pups into ingestion. Behaviors incompatible with ingestion such as lordosis were selectively inhibited by the presence of milk in stimulated day 10 pups. These results suggest a high degree of behavioral organization in neonatal rats than can be elicited by MFB stimulation and that becomes more goal-directed with age.