In vitro electrophysiological properties of rat dorsal column nuclei neurons

The dorsal column nuclei include the gracile and cuneate nuclei, which rece ive somatosensory information from the periphery and project to the ventrop osterior nucleus of the contralateral thalamus. The aim of this study was t o determine the electrophysiological and morphological characteristics of t he neurons of the dorsal column nuclei and to identify synaptic events evok ed by electrical stimulation of the dorsal column, using an in vitro slice preparation. The results show two types of neurons, termed type I and II. A repolarizing sag distinguished type I cells during hyperpolarizing current injection, suggesting the activation of a Q-current. Moreover, type I cell s, but not type II cells, were capable of maintaining spontaneous rhythmic activity at 9-15 Hz. Both types of cells displayed a delay in their return to the resting membrane potential following hyperpolarizing current pulses, indicating the existence of an A-current. Electrical stimuli applied to th e dorsal column elicited brief EPSPs and IPSPs in both cell types. EPSPs we re abolished by 6-cyano-7-nitroquinoxaline-2,3-dione, indicating that they were mediated through non-NMDA receptors. IPSPs were blocked by picrotoxin, implying the activation of GABAA receptors. Intracellular staining with ca rboxyfluoresceine revealed that type I neurons had elongated somas and prim ary dendrites that extended radially. Type II cells were smaller and had ro und somas with few primary dendrites, most of them emerging from one pole o f the soma, The axon of many type I neurons was stained and could be follow ed running ventrally and in rostral direction.