A Study of the Effects of Dopaminergic Manipulations and Stress on Dynorphin Concentrations in Midbrain and Forebrain Regions of Rat Brain

Abstract

In the present study, the effects of stress and dopaminergic manipulations on dynorphin peptides were investigated in the striatum (Str), substantia nigra (SN), nucleus acumbens (NA), and ventral tegmental area (VTA) of rat brain because of a recent history of conflicting reports regarding the effects of stress and dopaminergic manipulations on these brain regions. Male Sprague-Dawley rats were given repeau() injections of the dopamine (DA) agonist, apomorphine, followed by a 30 minute exposure to swimming stress over a course of 14 days; repeated injections of haloperidol, a DA antagonist, and swim for 14 days; and repeated swim for 7 days followed by an acute amphetamine challenge. Animals treated simultaneously with swim and apomorphine showed significant elevations in strlatallevels of Dyn AI-17 and Dyn B, suggesting that an interaction between swimming stress and apomorphine causes increases in dynorphin levels. Also, across the brain regions, large differences in peptide concentrations were noted. The SN exhibited 2 to 12-fold greater concentrations over VTA, and that NA consistently contained 2 to 3-fold greater concentrations than Str in all four Prodyn peptides. Dyn AI-8:Dyn AI-17 ratios were approximately 10:1 and 12:1 in Str and SN, respectively, and approximately 4: 1 and 2: 1 in NA and VT A, respectively, which implies the existence of separate dopamine/dynorphin loops between SN and Str and between VT A and NA.