Vasoactive intestinal polypeptide excitation of central neurons

Vasoactive intestinal polypeptide (VIP) was tested on neurons in the rat sensory motor cerebral cortex and on the isolated hemisected toad spinal cord. Iontophoretically applied VIP excited deep, spontaneously active cortical neurons, including identified corticospinal neurons. The excitation had a latency of onset varying from several seconds to over 1 min and often lasted for a minute or longer after cessation of the application. Desensitization of the effect occurred with repeated applications. VIP caused a depolarization of motoneurons and dorsal root terminals in the isolated amphibian spinal cord. Threshold for this effect was about 10(-6) M. The effects of VIP on both preparations were comparable with those of another peptide, substance P.