Peptides: Pharmacological evidence for three forms of chemical excitability in cultured mouse spinal neurons

Intracellular recordings from mouse spinal neurons growing in monolayer culture were used to study the effects of opioid peptides and substance P on neuronal excitability. Three actions were observed: 1) transmitter-like actions, including a presumptive increase in Cl^- conductance and a rapidly desensitizing excitation; 2) modulation of amino acid responses in the absence of, or independent of any other membrane effects; and 3) alteration in spike threshold in the absence of, or independent of any other membrane effects. All three types of effect were observed on the same cell. The same general classes of chemical excitability have been observed with a variety of non-peptide substances, indicating that the multiple effects of peptides are superficially not unique.