than by vestibular and visual inputs. The contribution of sensory signals from different limbs to the generation of PTN postural responses was examined in the present study. In β-Sitosterol standing quadrupeds, each of the four limbs participates in supporting the body weight. When the animal,s posture is perturbed, each of the limbs contributes to the generation of a corrective motor response. To join the efforts of individual limbs, they have to be accurately coordinated. Thus, the postural control system performs two main functions the intralimb coordination based on local reflexes in each of the limbs, and the interlimb coordination based on interlimb influences. If the motor cortex participates in the interlimb coordination, the PTN activity would reflect the postural activity of other limbs.
To assess a contribution of input from a given limb to the Rolipram PTN activity, in the present study we used the recently developed method of varying the number of limbs supporting the body. In the cat balancing on the tilting platform, we lifted one limb or a group of limbs from the platform, and compared the PTN responses to the platform tilts in control and in the limb lifted condition. These experiments have shown that the tilt related modulation of the activity in a PTN depended primarily on the sensory input from the corresponding contralateral limb. The input from the ipsilateral limb, as well as the inputs from the limbs of the other girdle made a much smaller contribution to the PTN modulation.
These findings strongly suggest that, in the postural task, the PTNs are primarily involved in the feedback control of their own limb and, to a lesser extent, in the coordination of activity between the two limbs within a girdle, and between the two girdles. It is known that, in the resting animal, the PTNs controlling a given limb usually receive excitatory or inhibitory influences from a certain group of receptors of this particular limb, and respond to different manipulations with the limb such as touch, muscle palpation, flexion of joints, etc. Do the sensory signals from the receptive field, observed in the resting animal, contribute to the generation of PTN responses in the postural task, or are these responses caused by other signals? To answer this question, for individual PTNs we compared the pattern of responses to tilt with that expected from the data on their receptive fields at rest.
We have found that sensory input from the receptive field could be responsible for the tilt related modulation in only a proportion of PTNs, whereas in other PTNs the modulation was caused by another sensory input. Abrief account of a part of this study has been published in abstract form. Methods Recordings were obtained from two adult cats, a male and a female. Some of the methods have been described andwill be reported briefly here. Experiments were conducted in accordance with NIH guidelines and were approved by the Barrow Neurological Institute Animal Care and Use Committee. Surgical procedures Surgery was performed using aseptic procedures. Anaesthesia was induced using ketamine, which was followed by 2 5% isofluorane mixed with oxygen administered by inhalation for the length of the surgical procedure. The skin and fascia were removed from the dorsal surface of the sku