Prenatal morphine alters the synaptic complex of postsynaptic density 95 with N-methyl-d-aspartate receptor subunit in hippocampal CA1 subregion of rat offspring leading to long-term cognitive deficits

Abstract

Infants who are passively exposed to morphine or heroin through their addicted mothers usually develop neurobiological changes. The postsynaptic density 95 (PSD-95) protein, a submembranous cytoskeletal specialization, is dynamically linked with N-methyl-d-aspartate receptors (NMDARs) to form a synaptic complex in postsynaptic neurons. This complex serves important neurobiological functions, including mammalian learning and memory. However, the effects of prenatal morphine exposure on this synaptic complex are not well understood. In this study, we determined whether prenatal morphine exposure altered the synaptic complex association between PSD-95 and three major NMDAR subunits (NR1, NR2A, and NR2B), at the mRNA and protein levels, within the hippocampal CA1 subregion (an important integration area for mammalian learning and memory) of rat offspring along with the performance of long-term cognitive functions. Sprague–Dawley rat offspring from morphine-addicted mothers were studied at a younger age (postnatal day 14; P14) and at an older age (P45). Subsequently, an eight-arm radial maze task was applied to analyze the working and cued reference memory in such offspring (P45). The real-time polymerase chain reaction results showed that prenatal morphine exposure caused significant decreases in mRNA levels of the PSD-95 and three NMDAR subunits (NR1, NR2A, and NR2B) in offspring (P14 and P45). Similarly, at the protein level, immunoblotting showed that decreased whole levels of PSD-95 and NMDAR subunits were seen in offspring subjected with prenatal morphine. Furthermore, the protein interaction of the synaptic complex between the PSD-95 and NMDAR subunit, as indicated by coimmunoprecipitation, was less in prenatal morphine samples than in vehicle controls (P14 and P45). The prenatal morphine group also showed poorer performance for an eight-arm radial maze task than the vehicle-control group. These results are particularly important for a better understanding of certain opioid-mediated neurobehavioral cognitive changes in offspring associated with altered protein interaction between PSD-95 and NMDAR subunits within the developing brain.