Tactile discrimination following analgesia-producing brainstem stimulation in the rat

Abstract

Female albino rats were trained on a standard tactile discrimination and implanted with subcutaneous heating coils and stimulating electrodes aimed at analgesia-producing sites in brainstem. The effectiveness of brain stem stimulation in producing analgesia was assessed by measuring increase in latency offace wiping elicited by heating the subcutaneous coils about 30 sec after brain stimulation. Stimulation was then introduced 15 sec before or at the start of one of the six daily massed tactile discrimination trials. Errors and response latencies on the test discrimination trials were compared with errors and latencies on the immediately preceding and subsequent trials. Eight rats increased latency of face wiping and had electrodes in dorsal periaqueductal gray (P AG). Their performance on the tactile discrimination was disrupted on trials immediately following stimulation. Four other rats also showed increased face-wiping latencies but had electrodes outside dorsal PAG. Their discrimination performance was less consistently affected by brain stimulation. The remaining seven rats did not show increased face-wiping latencies. Their electrodes were also outside dorsal PAG, and they showed latency increases only when stimulation occurred at the start oftest trials. These data indicate that analgesia-producing brainstem stimulation can affect performance on a tactile discrimination task as well as on the reaction to noxious stimulation.