Effects On Synaptic Plasticity Of Hippocampus And Visual Pathway In Rats Prenatally Exposed To Morphine

More and more research focused on the damages to opiates abuse, especially to the abuse among pregnant women. Besides, prenatal exposure to opiates has becoming a sever problem as more and more medication were used nowadays. Hence, prenatal opiates exposure induced dysfunction in offspring is gradually becoming of major concern. Opiates, such as morphine, can cross the placenta to affect the development of the central nervous system and thereby result in a series of physical and behavioral dysfunctions, especially the deficits of learning and memory. The present study investigated the impaired spatial memory and hippocampal synaptic plasticity alteration, as well as synaptic plasticity alteration of visual pathway, induced by prenatal morphine exposure of SD rats, detected by in vivo local field potential (LFP) recording and behavioral test. Furthermore, we investigated the mechanisms of synaptic plasticity in hippocampus and visual pathway with morphological methods.We investigated the alterations of synaptic plasticity in the perforant path (PP) dentate gyrus (DG) pathway induced by prenatal morphine exposure in juvenile (postnatal day 21-31, PND 21-31) and adult offspring (three months) by LFP recording. We found that prenatal morphine exposure reduced depotentiation (DP), but not long-term potentiation (LTP), of the EPSP slope. However both LTP and DP of the EPSP slope were depressed in prenatal morphine exposed juvenile offspring. The basal synaptic transmission and the short-term synaptic plasticity in DG areas were almostly unaltered. The morphine group also showed poorer performance for the Y-maze task than the control group, suggesting a imapired spatial memory. Depressed PS LTP, but not EPSP LTP, in the morphine group suggested that prenatal morphine exposure changed GABAergic inhibition, which mediates EPSP-spike potentiation. Then a loss of GABA-containing neurons in the DG area of the morphine group was observed using immunohistochemistry.Behavior is highly controlled by different brain areas, especially the integration of signals from different sensory systems. However, the effects of prenatal morphine exposure on sensory systems remain unclear. Opiates receptors are abundant in rat visual cortex. So we investigated the short-term plasticity of geniculo-cortical visual pathway during critical period and adult offspring by LFP recording. We found that prenatal morphine exposure increased the paired pulse response ration (PPRS) of all interstimulus intervals (ISI) and the frequency depression ratio (FDR) of all frequencies. It also increased most of PPRS of PND 30 offspring, but not the PPRS and FDR of adult offspring.Taken together, our results suggest that prenatal morphine exposure impairs the juvenile offspring's dentate synaptic plasticity and spatial memory, and that decreased GABAergic inhibition may play a role in these effects. And also prenatal morphine exposure altered the short-term synaptic plasticity of geniculo-cortical visual pathway during critical period. These findings might contribute to an explanation for the cognitive deficits in children whose mothers abuse opiates during pregnancy.