Effects of the rate and volume of injection on the pharmacological response elicited by intranigral microapplication of drugs in the rat

Abstract

The effects of injecting fluid volumes of 0.1 μl and 2 μl over periods of 1 and 5 min into the substantia nigra were studied histologically and pharmacologically. A 2 μl injection spread rapidly throughout the whole of the nigra, however slowly it was given. This volume frequently produced mechanical lesions at the site of injection. The smaller 0.1 μl injection, however, could be confined to discrete areas of the nigra. Injecting 0.1 μl in 1 min caused dye to spread through a roughly threefold greater volume than when the injection was completed over a 5 min period. Differential behavioural (turning) responses were invariably produced with Substance P and picrotoxin injected slowly into different regions of the nigra (0.1 μl in 5 min), but not when these drugs were administered in a larger volume (2 μl) or more rapidly (over 1 min).