Central effects of volleys in sensory and motor components of peripheral nerve in the stingray, Dasyatis sabina

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Abstract
The central effects of selective stimulation of the sensory and motor components of peripheral nerves were investigated in the unanesthetized spinal cords of stingrays (D. sabina) with a spinal transection at a high cervical level. The large myelinated fibers in the sensory component of the peripheral nerve produce an afferent volley which is readily recorded from the dorsal horn. This is followed by a negative field potential, the N1-wave, which is largest in the deep parts of the dorsal horn. The small myelinated afferent fibers evoke a late negative potential, the LN-wave, which is largest in the dorsalmost part of the dorsal horn. The central volley in the small afferents is difficult to detect. It may be demonstrated by anodally blocking the large afferents. Interneuronal activity can be evoked by large or small afferents or both. The excitation of interneurons underlies the N-waves. Antidromic field potentials are recorded in the ventral horn from motoneurons when the motor component of a peripheral nerve is stimulated. The antidromic invasion of motoneurons is facilitated by a conditioning volley in afferent fibers. The negative portion of the antidromic field potential shifts dorsolaterally with time, suggesting progressive invasion of the dorsolaterally oriented motoneuronal dendrites. Peripheral nerve stimulation evokes antidromic action potentials, monosynaptic and polysynaptic excitatory postsynaptic potentials and polysynaptic inhibitory postsynaptic potentials which can be recorded intracellularly from motoneurons of the stingray spinal cord. Reflex discharges are easily detected in motor nerves following stimulation of sensory nerves. Most of the discharge is polysynaptic Facilitation and posttetanic potentiation can be demonstrated.

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