PLATEAU-GENERATING NEURONS IN THE DORSAL HORN IN AN IN-VITRO PREPARATION OF THE TURTLE SPINAL-CORD

1. In transverse slices of the spinal cord of the turtle, intracellula r recordings were used to characterize and analyse the responses to in jected current and activation of primary afferents in dorsal horn neur ones. 2. A subpopulation of neurones, with cell bodies located lateral ly in the deep dorsal horn and dendrites radiating: towards the pial s urface, was distinguished by the ability to generate plateau potential s. Activation of the plateau potential by a suprathreshold depolarizin g current pulse produced an increasing firing frequency during the fir st few seconds and a sustained after-discharge. 3. The plateau potenti al was assumed to be mediated by L-type Ca2+ channels since it was blo cked by Co2+ (3 mM)and nifedipine (10 mu M) and enhanced by Bay K 8644 (0.5 - 2 mu M). 4. The threshold for activating the plateau potential declined during the first few seconds of depolarization. The decline in threshold gradually subsided over 3 - 10 s after repolarization. 5. Frequency potentiation of the plateau potential contributed to wind-u p of the response to depolarizing current pulses and primary afferent stimuli repeated at frequencies higher than 0.1 - 0.3 Hz. 6. The susta ined after-discharge mediated by the plateau potential was curtailed b y a slow after-hyperpolarization (sAHP) evoked by strong depolarizatio ns. The relative strength of the plateau potential and sAHP varied amo ng cells. In some cells the plateau potential and sAHP interacted to p roduce damped oscillations upon depolarization. The sAHP was mediated by both apamin and tetraethylammonium (TEA)-sensitive K+ channels. 7. Our findings suggest that basic properties of sensory integration may reside with the specialized intrinsic response properties of particula r subtypes of neurones in the dorsal horn.