Electrophysiological responses to muscarinic receptor stimulation in cultured hippocampal neurons

Electrophysiological recordings of responses to muscarinic receptor stimulation in cultured embryonic hippocampal neurons have been largely unsuccessful to date. In this study muscarinic receptor binding was demonstrated in 2-week-old embryonic rat hippocampal cultures. Using whole-cell patch-clamp recording we found that 1-5 microM carbachol produced multiple effects including depolarization, increased action potential firing rate, increased synaptic activity and a reduction in the amplitude of medium-duration afterhyperpolarizations. Voltage-clamp analysis revealed a time-dependent current relaxation with hyperpolarizing steps from a holding potential of about -40 mV which was inhibited by 10 microM muscarine or 50 microM carbachol and had characteristics similar to those of the m-current. Both atropine and pirenzepine inhibited all of these effects indicating that these cholinergic actions were mediated by muscarinic receptors. This study shows that muscarinic responses obtained classically in hippocampal brain slices can also be produced in cultured hippocampus.