The use of brain slices for the study of enzymatic metabolism of Des-enkephalin-tau-endorphin (DEtauE) and its analogues.

Abstract

The present study utilized a newly developed rat brain slice and incubation techniques to determine the effects of peptide structural modifications and brain peptidase regional specificity on neuropeptide metabolism. Organon (Oss, The Netherlands) provided us with a series of $\tau$-endorphin analogues with structural and conformational changes. Differences between the half-lives of the endogenous peptide Des-enkephalin-$\tau$-endorphin (DE$\tau$E) and its analogues were estimated after time-course incubations with discrete, regionally dissected rat brain slices. Tissue viability was estimated as the ability of the slice to uptake ($\sp3$H) -GABA, or to release ($\sp3$H) -GABA following K$\sp+$ stimulation. Results demonstrated stability of uptake/release up to 5 hours of incubation, suggesting tissue viability over this period. Our results suggest that the peptides studied are metabolized at different rates in the individual brain regions tested. Changes in DE$\tau$E structure (Pro$\sp7$ substitution, and Lys$\sp9$ acetylation) appear to increase the half-life of DE$\tau$E. However, cyclization of DE$\tau$E, and substitutions with D-Thr and cyclohexylalanine did not appear to result in an increase in peptide half-life in the brain regions tested. In summary, these studies have shown that the brain slice technique is a valid and unique approach to study neuropeptide metabolism in small, discrete regions of the rat brain.