Hindlimb Inputs Research Articles

Limb input to the cat vestibular nuclei.

The input from fore- and hindlimbs to the vestibular nuclear complex (VNC) was investigated in awake cats. Electrical stimulus was given to the sciatic, radial and vestibular nerves bilaterally and single unit responses were recorded in the VNC with extracellular technique. The position of the microelectrode was histologically confirmed. All four major vestibular nuclei received fore- as well as hindlimb input. Forty per cent of the neurons with limb input also received vestibular afferents. No major distinguishing features appeared between the different nuclei with regard to response characteristics. Certain differences in laterality of response, quantitative fore-hindlimb ratio and somatosensory-labyrinthine convergence were observed however. Response latencies to sciatic and radial nerve stimuli always exceeded a 3 msec and were grouped around 8 and 16 msec. A third population of vestibular neurons had latencies over 20 msec. Both excitatory and inhibitory responses were recorded, with the latter not always following an activation. The findings illustrate the complex nature of the ascending pathway to the VNC and the integrative properties of this complex.

Somatotopic studies on red nucleus: spinal projection level and respective receptive fields.

The somatotopic inputs into red nucleus (RN) neurons have been studied with special reference to their level of projection in the spinal cord. As inputs we employed either volleys in predominantly cutaneous nerves of forelimb and hindlimb or cutaneous mechanoreceptor discharges evoked by taps to footpads of forelimb and hindlimb. There has been physiological confirmation of the anatomical findings that RD neurons projecting to the lumbar cord are located in the ventrolateral zone of the pars magnocellularis, whereas in the dorsomedial zone are RN neurons with cervical but not lumbar projection. Somatotopically there was found to be a differentiation of input to RN neurons according as they projected to the lumbar or only to the cervical cord. This finding was presented in the form both of tables and of somatotopic maps. As expected, this discrimination was more restrictive for the more selective inputs from pad taps than for nerve inputs. Nevertheless, forelimb inputs often had a considerable excitatory and inhibitory action on lumbar-projecting RN neurons, and vice versa for cervical-projecting neurons. There were two notable somatotopic findings that suggest specificities of connectivities. First, despite the large convergence of IP neurons onto RN neurons (about 50-fold), the degree of somatotopic discrimination was about the same for interpositus and RN neurons with two testing procedures: between inputs from forelimb and hindlimb; and between inputs from pads on one foot. Second, although there was in the interpositus nucleus a considerable topographical admixture of neurons with dominant forelimb or hindlimb inputs, the axonal projections of these neurons were apparently unscrambled on the way to the target RN neurons, so as to deliver the somatotopic specificities observed for two classes of RN neurons; those projecting down the spinal cord beyond L2 level, and those projecting to C2 but not L2. Finally, there is a general discussion of motor control with reference to the pathway; pars intermedia of anterior lobe of cerebellum leads to interpositus nucleus leads to red nucleus leads to rubrospinal tract leads to spinal motoneurons.

Somatotopically organized inputs from fore- and hindlimb areas of sensorimotor cortex to cerebellar Purkynĕ cells.

The patterns of convergence of nerve and cortical inputs representing the forelimb and hindlimb were studied in Purkyně cells of the cat. The most important inputs to Purkyně cells of the pars intermedia come from peripheral nerves and the areas of the sensorimotor cortex concerned with the same limb. In lobule V, the forelimb nerve and cortical inputs are dominant, while in lobules III and IV the hindlimb inputs are dominant. Lobules IVa–Va represent a zone of hindlimb-forelimb overlap, with the nerve and cortical inputs making parallel transitions from the hindlimb dominance of IVa to the forelimb dominance of Va. Furthermore, within the nerve and cortical projections to the pars intermedia, mossy fiber and climbing fiber systems have similar projection patterns. In addition to the hindlimb-forelimb overlap in lobules IVa–Va, nearly half (44%) of the Purkyně cells throughout lobules III, IV, and V of the pars intermedia respond with weak or moderate responses to cortical or nerve inputs from the non-dominant limb, some of which are clearly important physiologically.

Physiology of peripheral neurons innervating semicircular canals of the squirrel monkey. II. Response to sinusoidal stimulation and dynamics of peripheral vestibular system.

A CENTRAL PROBLEM in vestibular physiology has been the elucidation of the dynamics of the peripheral vestibular apparatus. Following the development of the torsion-pendulum model by Steinhausen (24, 25), many efforts have been directed toward the determination of the time constants of the model. That the model, itself, might not adequately describe the transfer characteristics of the peripheral system has seldom been questioned. Further, the procedures employed to estimate the time constants have had their drawbacks. The dynamics of the system have sometimes been deduced from hydrodynamic principles (5, 6, 15, 17, 22, 23). Such an analysis permits the inference of only some of the relevant variables. In the torsionpendulum model, it will be recalled, the angular deflection of the cupula g(t) is related to the angular acceleration a(t) by the equation