Effects of thioproperazine and sulpiride on the locomotor rhythms in the decorticate cat

The decorticate cat develops sequences of locomotor movements, especially in the two posterior limbs: those appear either spontaneously, or following a single shock applied to L7 dorsal root. Using this preparation, we tested the effects of two neuroleptic agents, Thioproperazine (TZ) and Sulpiride (S), through either systemic administration or local injection into the lateral-posterior hypothalamus and into the lumbar spinal cord. TZ administered i.v. (0.5 mg/kg) suppressed all locomotor rhythms, while S induced unclear effects. The tested drugs clearly acted at the hypothalamic level, but the effects of the drugs were opposite; TZ (70 microgram) suppressed rhythms, while S (350 microgram) increased or even induced them. T2 (50 microgram) injected at the L7 cord-level abolished rhythms, and S (350 microgram) reduced their amplitude but increased the duration of locomotor sequences. The flexion reflex was never affected by these drugs. The two drugs seem to act at the spinal and the hypothalamic levels. The possible mechanisms involved in their action are discussed.