POSTNATAL-DEVELOPMENT OF SYNAPTIC PLASTICITY IN THE CA3 HIPPOCAMPAL REGION OF CONTROL AND LEAD-EXPOSED WISTAR RATS

The object of this study was to compare the postnatal development of m essy fiber potentiation (MFP) and paired-pulse facilitation in the CA3 region of control and lead-exposed rats. The postnatal development of MFP was not influenced by the chronic pre- and postnatal lead exposur e nor did we find a statistically significant impairment of MFP in reg ion CA3 following lead exposure in the four age groups studied. In con trast to the adult animals, in the three immature groups of the contro l as well as of the lead-exposed animals MFP was preceded by a posttet anic depression after which MFP developed slowly. The results of the p aired-pulse procedure depended both on the age and on the interstimulu s interval (ISI) in control and lead-exposed animals. The differences between control and lead-exposed rats were statistically significant o nly in the adult animals at an ISI of 10 ms. In this case paired-pulse stimulation resulted in an increase of the second evoked response rel ative to the first response in the lead-exposed animals while the same procedure decreased the second evoked response in the control animals . It is concluded that although low level lead exposure had no effect on the expression of MFP in hippocampal CA3 region, inhibitory mechani sms as revealed by paired-pulse stimulation are impaired by lead in ad ult rats.