[Electrophysiologic analysis of the nociceptive system of the thalamus in the ontogenesis of the rabbit].

In acute experiments in rabbits, characteristics of the parafascicular complex EPs in response to peripheral nociceptive stimulation revealed that the waveform of the EP changes during the ontogenesis: from a marked variability in newborn rabbits to a stable biphasic positive-negative potential in adult rabbits. During the postnatal period the magnitudes of the latency and duration of phases of the EPs decrease. "Critical periods" in the formation of the parafascicular complex have been discovered. The 1st period (7-8 days of age) is characterized by the largest amplitude and the shortest duration; the 2nd period (18-40-50 days) involves a stable form of the basic negative long phase. It has been established that, during the ontogenesis, the threshold of the nociceptive response rose.