Actions of single sensory fibres on cat dorsal column nuclei neurones: vibratory signalling in a one‐to‐one linkage.

Abstract

1. The synaptic linkage between single, identified sensory fibres associated with Pacinian corpuscle (P.c.) receptors and central neurones of the dorsal column nuclei was examined in decerebrate or anaesthetized cats. Paired recordings were made from individual neurones in the gracile division of the dorsal column nuclei and from the hind‐limb interosseous nerve in which it is possible to identify and monitor the activity of each P.c. fibre activated when recording from the intact nerve with a platinum hook electrode. Individual P.c. fibres were activated by vibration delivered with an 0.2 mm diameter probe to the interosseous P.c. receptors. 2. Thirty‐five P.c. fibre‐gracile neurone pairs were isolated in which activity in the single, identified P.c. fibre evoked suprathreshold responses (mean latency +/‐ S.D., 10.3 +/‐ 1.5 ms) in the gracile neurone. A single impulse arriving over one P.c. fibre could generate pairs or triplets of output spikes from several target neurones thus revealing a potent synaptic organization within the dorsal column nuclei for the transmission and amplification of weak sensory signals. 3. The potency of the linkage for some pairs resulted in post‐synaptic response levels of up to 400 impulses s‐1 when a single input fibre was discharging one impulse on each vibration cycle at 200‐400 Hz. 4. Gracile neurones driven by single P.c. fibres had phase‐locked responses to vibration at frequencies of up to 400‐500 Hz. However, the responses displayed much greater phase dispersion than those of P.c. fibres, indicating that a major component of phase dispersion in the vibration‐induced responses of dorsal column nuclei neurones is attributable to the properties of the synaptic linkage between an individual fibre and the target neurone. 5. The potent actions of single, identified P.c. fibres on their target neurones are consistent with the hypothesis that phase‐locked responses in dorsal column nuclei neurones to vibration at 100‐400 Hz may reflect the functional domination of the target neurone's output by one or a few of its converging fibres.

Integrative processing of vibratory information in cat dorsal column nuclei neurones driven by identified sensory fibres.

“…inputs were carried out on cats from the earlier series (Ferrington et al 1987b) and all procedures with the exception of those outlined below were described in that paper. Five additional experiments were performed in adult cats, to investigate whether convergent P.c.…”

An intact peripheral nerve preparation for monitoring inputs from single muscle afferent fibres

“…This capacity for selective recruitment of different fibres together with the excellent signal-to-noise ratio attainable from the indicis proprius nerve in continuity, permitted unequivocal monitoring and identification of each active fibre. These attributes make this limb nerve preparation just as suitable as those we have used previously for the purpose of examining the central actions of single identified sensory nerve fibres of other classes, in particular the PC, SAI, SAII and joint afferent fibre classes (Ferrington et al 1987;Vickery etal. 1994;Gynther etal.…”

“…As recorded fibres were sensitive to manual stretch applied longitudinally to the muscle tendon they were assumed to be associated with muscle spindles, whose locations were then identified by mechanical probing of the muscle by means of a fine (0.5-2 mm diameter) glass probe. Once the receptor's location was established, a mechanical stimulator (Ferrington et al 1987;Mackie et al 1995) was used to apply controlled stimuli (steady displacement or trains of sinusoidal vibration) to the focus of maximum sensitivity. It appeared that all fibres studied were of the group la class of account of their high sensitivity to both longitudinal and focal vibration (Brown et al 1967).…”

“…The first instance in which a preparation of this type was achieved for a peripheral nerve in the limb was for sensory fibres associated with Pacinian corpuscles (PCs) of the hindlimb interosseous membrane. When the interosseous nerve is freed and placed in continuity over a hook electrode, it becomes possible to identify and monitor, from the intact nerve, the impulse activity of each PC fibre activated (Mclntyre et al 1967;Ferrington et al 1987). Similar preparations that retain continuity of the peripheral nerve have been achieved to monitor inputs to the central nervous system from individual slowly adapting type I and II (SAI and SAIl) fibres (Brown and Ritz 1985;Vickery et al 1994;Gynther et al 1995) and for individual kinaesthetic fibres of the joint afferent class (Mackie et al 1995).…”

Responses of slowly adapting type II afferent fibres in cat hairy skin to vibrotactile stimuli.

“…Should these reliable signals of vibrotactile events in the SAII fibres not be used for the behavioural aspects of vibrotactile sensibility in hairy skin it may mean that the central transmission of their signals is poorer than that for other classes such as the PC fibres. We have shown that the latter group has a remarkable security of transmission that preserves temporal patterning across the synaptic linkage of the dorsal column nuclei (Ferrington et al 1986(Ferrington et al , 1987a. The issue of central transmission of SAII and SAI signals is currently under investigation in our laboratory.…”