Neonatal rat spinal cord slice preparation: postsynaptic effects of neuropeptides on dorsal horn neurons.

In the neonatal rat spinal cord slice preparation responses of the dorsal horn interneurons to iontophoretic or bath application of methionine-enkephalin (ME), substance P (SP) and somatostatin (SS) were qualitatively similar to those obtained in intact spinal cord. Thus, SP powerfully excited almost all neurons tested (15/16), while ME and SS depressed neuronal discharges in 13/14 and 4/6 units respectively. In some dorsal horn neurons the iontophoretic application of ME caused a marked depression of the SP-induced excitation. Angiotensin II (AgII) had no effect on dorsal horn units (n = 8). In the slices perfused with a Ca2+-free, Mg2+-high Krebs solution the extracellularly recorded effects of ME, SP and SS were not significantly modified, suggesting that the peptides were acting directly on postsynaptic sites. The results also indicate that the in vitro rat spinal cord slice preparation can be successfully utilized for further studies on the cellular mechanisms of actions of neuropeptides, particularly in relation to synaptic transmission processes in the dorsal horn.