Effect of perinatal malnutrition on the inactive behavior induced by long-term shock and conditioned analgesia

Modifications in avoidance reactions of mice, on a second exposure to the hot plate, resist to various amnesia-inducing treatments

The avoidance responses of mice exposed to the hot plate (55 degrees C) were found to be modified when tested a second time. In fact, when forepaws licking was no longer observed, the rearing was clearly anticipated (7 s instead of 15 s) as well as jumping (24 s instead of 55 s). These modifications of avoidance strategies as well as their latencies were still observed even 24 days after the first exposure. Avoidance responses were prevented by morphine or haloperidol injected prior to the first exposure, but not with scopolamine or diazepam. These modifications were not affected in mice injected with morphine or submitted to either a supramaximal electroshock or to ether anesthesia delivered immediately after the first hot plate exposure. Among the various known types of memory, these modifications could be linked to procedural memory.

Perinatal undernutrition: changes in brain opiate receptor density

The present work sought to study the binding properties of central mu-opiate receptors in whole brain and in different central areas in adult rats undernourished at perinatal age. Rats were undernourished with a hypoproteic diet containing 8% casein from day 14 of gestation until 50 days of age. The animals were thereafter fed a balanced commercial chow until 140 days of age. At this time point the experiments started. 3H-D-Ala2, N-Me-Phe4, Gly5-ol-enkephalin (3H-DAMGO) was used to selectively label the mu-receptors. The results obtained demonstrated that perinatal undernutrition induced, in the adult animal, a decreased mu-receptors density (Bmax) both in whole brain as well as in midbrain, without significant changes in affinity. In addition, no changes were found in mu-specific binding in the cortex of these undernourished animals. Taking into account that recent evidences from our laboratory have demonstrated a lower stress-induced analgesia following exposure to different stressful situations in rats undernourished in early life, the present findings seem to suggest that this lower analgesic response could be due, at least in part, to a lower density of mu-opiate receptors in the brain.