Locomotion‐related variations in excitability of spino‐olivocerebellar paths to cat cerebellar cortical c2 zone.

Abstract

SUMMARY1. Cutaneous nerve stimulation was used to study the excitability of the spinoolivocerebellar pathways (SOCPs) to the c2 zone of the paravermal cerebellar cortex in the cat. Non-noxious single-shock stimulation of the right and left superficial radial (SR) nerves via implanted cuff electrodes was used to evoke field potentials in the cerebellar cortex via the SOCPs.2. The evoked potentials were recorded extracellularly either in lobule V of the anterior lobe (three cats) or within the paramedian lobule of the posterior lobe (one cat) with glass-coated tungsten microelectrodes. Measurement of the amplitudes of the responses was used to monitor transmission in the SOCPs in cats at rest and during walking.3. A total of eleven c2 recording sites were investigated in detail. At seven of these sites, responses were recorded both during locomotion and at rest. For all seven sites responses during locomotion were smaller, more variable in amplitude and less securely evoked (average reduction 59%). 4. At five out of the eleven recording sites (45 %) the mean amplitude of responses elicited during different tenths of the step cycle fluctuated sufficiently that the largest response was more than twice the smallest. In the majority of these cases (4/5) the responses were largest in either mid-stance or late swing. These fluctuations in response size occurred without parallel fluctuation in the amplitude of the peripheral nerve volley. At the remaining sites fluctuation of the cerebellar field size was less and in some cases practically absent.5. At six recording sites it was possible to record the climbing fibre potentials evoked by stimulation of both the ipsilateral and contralateral superficial radial nerves. In all six cases the fluctuations in size of the response during locomotion occurred in phase, despite the fact that the two limbs move out of phase.6. The probability that an individual stimulus would evoke any cerebellar response also varied between the different tenths of the step cycle and such variations occurred in parallel with the fluctuations in response size. This shows that the SOCP regulatory mechanisms) must, at least in part, operate at a precerebellar level.MS 8015 R. APPS, M. LIDIERTH AND D. M. ARMSTRONG

Central regulation of motor cortex neuronal responses to forelimb nerve inputs during precision walking in the cat

“…SR volleys were therefore presumably confined almost entirely to Aâ fibres connected to cutaneous mechanoreceptors, while UL volleys presumably involved similar afferents together with IA and IB muscle afferents and perhaps some group II afferents. As in previous studies from this laboratory (see Apps et al 1990 the amplitudes of the NCAPs used to monitor nerve volley size did not differ systematically (or substantially) between rest and walking, nor did they usually vary during the step cycle. When variation was present it did not in any instance parallel in its temporal pattern the variation present in the responses of the cortical neurone simultaneously under study.…”

“…NCAP data are not presented routinely (though see Figs 1, 5 and 8) because the findings were entirely similar to those in several previous studies in our laboratory (see Apps et al 1990. NCAPs evoked during walking were sometimes unchanged in mean amplitude relative to rest, and sometimes modestly increased or decreased.…”

Changes in Excitability of Ascending and Descending Inputs to Cerebellar Climbing Fibers during Locomotion

“…All leads were fed subcutaneously to connectors that were attached to the skull with dental acrylic cement, forming a lightweight headpiece. For additional details of the methods, see the research of Apps et al (1990), Drew (1993), and Apps and Lee (1999).…”

“…Thus, it is safe to conclude that the step-related changes in size of climbing fiber responses evoked by SR or CP stimulation are likely to be attributable to central changes in excitability rather than any steprelated changes in efficacy of the probe stimulus (cf. Apps et al, 1990;Apps and Lee, 1999) (also see Discussion for additional comments).…”

Gating of cutaneous input to cerebellar climbing fibres during a reaching task in the cat

“…Upon termination of the experiment (ca 6 weeks after the initial operation) animals were killed by an overdose of anaesthetic, the cerebellum was removed and the folial location of the microwires (in lobule Va-c) was verified by inspection of the dorsal surface of the cerebellum. For further details of implants see Apps et al (1990).…”