Cervical control of posture and movements

Unilateral section of the dorsal roots C1-C3 in rabbits produces rotation of the head towards the contralateral side 11, hypotonia of the ipsilateral limbs with lateropulsion, and a tendency of the animal to fall towards the side of the denervation 3. The conclusion of these experiments, i.e. that the postural asymmetry produced by unilateral deafferentation of the neck is similar to that elicited by ipsilateral labyrinthectomy 3, contrasts with the results of stimulation experiments, which show an antagonistic integration of the cervical and tonic labyrinthine inputs in the control of posture 9. Ataxia of the hindlimbs associated with defects of gait and difficulty in turning have also been observed in cats and monkeys after cervical deafferentation or denervation of the neck musculature; however, no indication about the type of postural asymmetry in the limb musculature has been reported in these studies1, ~,7,17. The main aim of the present experiments was to investigate the mechanisms responsible for the postural and motor deficits which occur in cats following unilateral section of the upper cervical dorsal roots. The experiments were carried out on 13 cats subjected, under Nembutal anesthesia (35 mg/kg i.p. of sodium pentobarbital) to unilateral section of the dorsal roots C1-Cs. All procedures and observations were defined as ipsilateral or contralateral with reference to the side of the cervical deafferentation. Unilateral section of the dorsal roots C1-Cz produced a slight tilt of the head to the contralateral side, due to asymmetric innervation of the dorsal neck musculature (Fig. 1A). Moreover, marked motor deficits involving the entire body were observed. In particular one day after the operation the cats tended to lie on the contralateral side, with the corresponding limbs flexed and the ipsilateral limbs extended (Fig. 1A, B). They began to right themselves and stand within 1-2 days; however, they showed much bodily sway, often interrupted by falling in the contralateral direction. By the third to the fifth day these effects disappeared and the animals were able to walk without apparent impairment, although the direction of the locomotor activity was still oriented towards the intact side. Seventeen days after deafferentation, the animals