Role of dynorphin-containing neurons in the presynaptic inhibitory control of the acetylcholine-evoked release of dopamine in the striosomes and the matrix of the cat caudate nucleus

The roles of acetylcholine and dynorphin (1–13) in the presynaptic control of the release of [ 3H]dopamine continuously synthesized from [ 3H]tyrosine were examined in a prominent striosomal enriched area and in an adjacent matrix enriched area of the cat caudate nucleus. This was achieved using microsuperfusion devices applied vertically onto coronal slices of cat brain. These devices were placed in a striosomal enriched area located in the core of the structure (acetylcholinesterase-poor zone) and in an adjacent matrix enriched area (acetylcholinesterase-rich zone). [ 3H]Tyrosine was delivered continuously to each microsuperfusion device and [ 3H]dopamine released was estimated in the superfusate. As previously shown, in the presence of tetrodotoxin (1 μM), acetylcholine (50 μM) induces a prolonged stimulation of [ 3H]dopamine release in both compartments through an interaction with muscarinic receptors. Our present study indicates that both dynorphin 1−13 (1 μM) and the selective kappa agonist trans-3,4-dichloro-N-methyl-N[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamine (U50488) (1 μM) inhibit the tetrodotoxin-resistant acetylcholine-evoked release of [ 3H]dopamine, these effects being slightly more pronounced in the matrix than in the striosomal enriched area. Naloxone (1 μM) reversed the inhibitory effect of U50488 in both areas. These results suggest that dynorphin exerts an inhibitory presynaptic control of dopamine release through kappa opioid receptors located on dopamine nerve terminals in the striosome as well as in the matrix. However, the presynaptic cholinergic control of dopamine release is much more complex in the matrix than in the striosomal enriched area. Besides its tetrodotoxin-resistant stimulatory effect, acetylcholine exerts two opposing tetrodotoxin-sensitive effects on [ 3H]dopamine release, one facilitatory and the other inhibitory. We demonstrate here that in the superfused matrix enriched area, the indirect acetylcholine inhibitory response is mediated by dynorphin-containing neurons. Indeed, the short-lasting stimulatory effect of acetylcholine on [ 3H]dopamine release was converted into a long-lasting response in the presence of naloxone (1 μM), and, in this latter condition, the co-application of dynorphin 1–13 (1 μM) restored the short-lasting stimulatory effect.