Modulation Of α₂-adrenergic Receptors On Inputs From Schaffer Collaterals To Hippocampal Ca1 Stratum Radiatum Of Rats Both In Vivo And In Vitro

Aim: This experiment was designed to investigate the modulation ofα2-adrenergic receptors on synaptic transmission from Schaffer collaterals to hippocampal CA1 radiatum stratum in rat hippocampus.Methods: 1. The extracellular recordings techniques were used to record the field excitatory postsynaptic potentials (fEPSPs) from Schaffer collaterals to hippocampal CA1 stratum radiatum in vivo. (1) Selectiveα2-adrenoceptors agonist clonidine (0.625μg/kg, 1.25μg/kg, 2.50μg/kg) and selectiveα2-adrenoceptors antagonist yohimbine (2.66μg/kg, 8.00μg/kg, 24.00μg/kg) were used to observe the effect ofα2-adrenoceptor agonist/antagonist on synaptic transmission efficiency by lateral ventricle injections in vivo. Long term potentiation (LTP) recorded in hippocampal CA1 stratum radiatum by stimulating Schaffer collaterals was performed in vivo to observe the effects of clonidine and yohimbine. (2) Paired pulse ratio (PPR) was adopted to determinne the function of clonidine and yohimbine are pre-sypanptic or post-synaptic. 2. Selectiveα2-adrenoceptors agonist clonidine (5μM) and selectiveα2-adrenoceptors antagonist yohimbine (2μM) were used to observe the effect ofα2-adrenoceptor agonist/antagonist on basal synaptic transmission efficiency from Schaffer collaterals to hippocampal CA1 stratum radiatum in rat slices.Results: 1. Clonidine could reduce LTP in a dos-dependent fashion, while yohimbine could dos-dependently improve the synaptic transmission efficiency indicated as enhanced LTP. 2. Contrast to the PPR of control group, yohimbine could increase the PPR, while clonidine exerts inhibition on PPR when LTP was induced succecessfully. 3. Both clonidine (5μM) and yohimbine (2μM) have very little effect on basal synaptic transmission from Schaffer collaterals to CA1 stratum radiatum in slices (no statistic difference at P<0.05). Conclusion: 1. Clonidine and yohimbine could modulate the synaptic transmission efficiency in LTP from Schaffer collaterals to hippocampal CA1 stratum radiatum respectively. 2. The modulation of clonidine and yohimbine on LTP are pre-synaptic or partial pre-synaptic at least. 3. Low dosage conidine (5μM) and yohimbine (2μM) could exert very little effect (no statistics difference at P<0.05) on basal synaptic transmission of the Schaffer collaterals input to CA1 stratum radiatum in slices.