Fractionation of the cataleptic bracing response in rats.

In haloperidol-treated rats, bracing, i.e., resistance to displacement along a horizontal surface, was found to involve four components: gripping by the digits, extension by the limbs, stiffening of the body axis and arching the vertebral column towards the displacing force. Labyrinthectomy weakened the bracing of the forequarters as did application of a head bandage. Labyrinthectomy, when combined with head bandage, completely abolished all forequarter bracing responses. Neither manipulation affected the bracing responses of the hindquarters. The hindquarter bracing reaction was abolished by application of an abdominal bandage, which left most of the forequarter responses intact. Isolation of fore- and hindquarter bracing responses revealed that whereas gripping by the digits and extension by the limbs could occur independently in either part of the body, stiffening of the body axis and arching of the vertebral column originated in the hindquarters. However, although these latter components of bracing originate in the hindquarters, as evidenced by their abolition with application of an abdominal bandage, their recruitment into the anterior of the body only occurred when the bracing of the forequarters was unimpaired. Either labyrinthectomy or head bandage prevented stiffening and arching of the vertebral column from occurring in the forequarters, even though these procedures had no effect on the hindquarters. Labyrinthectomy, head bandage and abdominal bandage all fractionated the bracing response over a wide range of haloperidol dosages (0.5, 1.0, 2,5, 5,0 and 7.5 mg/kg).