Presynaptic inhibition by neuropeptide Y of slow inhibitory synaptic transmission in submucous neurones of guinea-pig caecum.

The occurrence and disposition of immunoreactivity for neuropeptide Y (NPY) was investigated in the submucosa of guinea-pig caecum. There were few NPY-immunoreactive neurones but intraganglionic varicose fibres were so numerous and strongly immunoreactive that some somata may have been obscured. In each neurone tested, exogenous application of NPY (1-100 nM) depressed the duration and amplitude of the slow inhibitory postsynaptic potential. In contrast, NPY (1-300 nM) had no effects on the resting membrane potential, input resistance and fast and slow excitatory synaptic transmission.