A natural peptide with NMDA inhibitory activity reduces tonic pain in the formalin model.

The aim of this study was to assess whether a natural peptide, histogranin, isolated from chromaffin cells and possessing NMDA receptor inhibitory activity, could reduce tonic pain. Rats received intrathecal injections of the stable analog [Ser1]histogranin (SHG), prior to induction of the formalin response. SHG markedly suppressed the second tonic phase of the formalin response compared with saline vehicle. A U-shaped dose-response curve was obtained. SHG had no effect on phase 1 acute pain responses. These findings indicate that SHG acts in a similar fashion as other, non-peptide, NMDA antagonists in suppressing tonic, but not acute pain. The presence of the natural peptide in chromaffin cells may contribute to the analgesic effects of adrenal medullary implants.

Pharmacologic characterization of opioid peptide release from chromaffin cell transplants using a brain slice superfusion method.

A simple chamber and an inexpensive superfusion system for studying mammalian brain slices containing neural transplants is described. With this method, rat brain slices containing bovine chromaffin cell transplants can be maintained for several hours, allowing for the determination of neurochemical characteristics and pharmacologic responsiveness of the grafted cells. Using this technique, basal and nicotine-stimulated release of metenkephalin from rat periaqueductal gray slices containing bovine chromaffin cell transplants were measured. Results showed that met-enkephalin release can be increased by nicotinic stimulation in slices containing chromaffin cell, but not control implants, for at least 8 weeks postimplantation. Furthermore, this response was dose-related. These results are in good agreement with previous behavioral studies and provide corroborative evidence for the mechanism of pain reduction by the release of opioid peptides from chromaffin cell transplants in the periaqueductal gray. This study demonstrates that neurochemical and pharmacologic analyses of neural transplants using a superfused brain slice method can be a complementary approach in determining the underlying mechanisms of neural transplants in the central nervous system.