Fatemeh Aghighi - Physiology Research Center, Institute for Basic Sciences, Kashan University of Medical Sciences, Kashan, Iran
Mohammad Shabani - Student Research Committee, Kashan University of Medical Sciences, Kashan, Iran
Sayyed Alireza Talaei - Physiology Research Center, Institute for Basic Sciences, Kashan University of Medical Sciences, Kashan, Iran

Background: Facing environmental factors during early postnatal life, directly or indirectly via mother-infant relationships, profoundly affects the structure and function of the mammals’ Central Nervous System (CNS). Objectives: This study aimed to evaluate the effect of morphine consumption during the lactation period on short-term synaptic plasticity of the hippocampal Cornu Ammonis ۱ (CA۱) neurons in rat offspring. Materials & Methods: In addition to a group of control mother rats (CO), three groups subcutaneously received ۵ (M۵), ۱۰ (M۱۰), or ۲۰ (M۲۰) mg/kg morphine every ۱۲ hours during the lactation period. At ۴۵ days old, following the stimulation of the Schaffers’ collaterals, basic field Excitatory Post-Synaptic Potentials (fEPSPs) were recorded in their offspring’s hippocampal CA۱ neuronal circuits. After the construction input/output curve, paired-pulse stimulations with the inter-stimulus intervals of ۲۰, ۸۰, and ۲۰۰ ms were applied to determine the short-term synaptic plasticity, and the paired-pulse ratio was evaluated. Results: The baseline synaptic responses of the rats CA۱ neurons whose mothers received ۱۰ and ۲۰ mg/kg morphine twice daily during the lactation period decreased compared to the CO animals (P<۰.۰۱ & P<۰.۰۰۱, respectively). Furthermore, compared to the controls, the Paired-Pulse Ratio (PPR) of the CA۱ neural circuits of M۱۰ and M۲۰ rats at ۲۰ and ۸۰ ms Inter-Stimulus Intervals (ISI) decreased (P<۰.۰۱). Conclusion: Morphine exposure during the lactation period has a detrimental impact on the primary synaptic activity and short-term synaptic plasticity of the hippocampal CA۱ neuronal circuits of rats’ offspring.

Morphine, Lactation, Neuronal plasticity, Hippocampus, Rats