Mechanisms of noradrenergic modulation of synaptic transmission and neuronal excitability in ventral horn neurons of the rat spinal cord

Abstract

Noradrenaline (NA) modulates the spinal motor networks for locomotion and facilitates neuroplasticity, possibly assisting neuronal network activation and neuroplasticity in the recovery phase of spinal cord injuries. However, neither the effects nor the mechanisms of NA on synaptic transmission and neuronal excitability in spinal ventral horn (VH) neurons are well characterized, especially in rats aged 7 postnatal days or older. To gain insight into NA regulation of VH neuronal activity, we used a whole-cell patch-clamp approach in late neonatal rats (postnatal day 7–15). In voltage-clamp recordings at −70 mV, NA increased the frequency and amplitude of excitatory postsynaptic currents via the activation of somatic α1- and β-adrenoceptors of presynaptic neurons. Moreover, NA induced an inward current through the activation of postsynapticα1- and β-adrenoceptors. At a holding potential of 0 mV, NA also increased frequency and amplitude of both GABAergic and glycinergic inhibitory postsynaptic currents via the activation of somatic adrenoceptors in presynaptic neurons. In current-clamp recordings, NA depolarized resting membrane potentials and increased the firing frequency of action potentials in VH neurons, indicating that it enhances the excitability of these neurons. Our findings provide new insights that establish NA-based pharmacological therapy as an effective method to activate neuronal networks of the spinal VH in the recovery phase of spinal cord injuries.