Effects of Neonatal Treatments on Pain and Audiogenic Sensitivity and Brain Content of Monoamines in Adult Rats

In adult Wistar, KM, and Wag/Rij rats, the threshold of pain sensitivity (tail-flick test) and audiogenic sensitivity were estimated after neonatal administration of Semax (analog of ACTG_4–10 fragment) or after placebo (administration of saline for the control of the effect of neonatal pain stimulation). These neonatal treatments did no affect the rates of sensomotor development at an early age (Fox tests), i.e., did not affect directly the physiological activity of rat pups at the age of up to 21 days. In all control rats injected with saline (pain stimulation), the latencies of audiogenic fits increased reliably, while their degree decreased. Administration of Semax raised these parameters to the level of those in intact animals, i.e., increased the sensitivity to sound. Neonatal administration (per os) of caffeine to KM rats increased reliably the latency of audiogenic fits. The thresholds of pain sensitivity in the rats of all strains were significantly lower saline injected animals than in the intact control, just as the level of dopamine in the hippocampus of KM rats. These data are interpreted as an evidence of changes in the development of some brain systems in response to neonatal treatments.