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Several studies have reported differences in the morphological characteristics of motoneurons and the contractile properties of motor units of male and female rats. However, differences in spinal motoneuron activity between the sexes are not well understood. This study investigates the electrophysiological properties of spinal α-motoneurons in male and female Wistar rats under pentobarbital anaesthesia. Fast and slow types of tibial motoneurons were recorded intracellularly in 15 male and 15 female rats, and the measured parameters were compared statistically using two-way ANOVA and Tukey post hoc tests. The membrane properties, action potential parameters and firing characteristics were not different between sexes, though significant differences were observed in the properties of fast and slow motoneuron types within both sex groups. We conclude that the sex-related differences observed in motor performance between male and female rats are largely due to differences in muscle mass, the proportion of muscle fibre types and the related motor unit contractile properties, while the mechanisms of motor control dependent on the electrophysiological activity of motoneurons are similar between the sexes. These findings are significant, as they indicate that results of experiments investigating electrophysiological properties can be reliably compared between sexes.

Transcranial direct current stimulation (tDCS) affects neurons at both cortical and subcortical levels. The subcortical effects involve several descending motor systems but appeared toberelativelyweak,asonlysmallincreasesintheamplitudeofsubcorticallyinitiateddescending volleys and a minute shortening of latencies of these volleys were found. The aim of the present study was therefore to evaluate the consequences of facilitation of these volleys on the ensuing muscle activation. The experiments were carried out on deeply anaesthetized rats without neuro- muscular blockade. Effects of tDCS were tested on EMG potentials recorded from neck muscles evoked by weak (20-60 μA) single, double or triple stimuli applied in the medial longitudinal fascicle (MLF) or in the red nucleus (RN). Short latencies of these potentials were compatible with monosynaptic or disynaptic actions of reticulospinal and disynaptic or trisynaptic actions of rubrospinal neurons on neck motoneurons. Despite only weak effects on indirect descending volleys, the EMG responses from both the MLF and the RN were potently facilitated by cathodal tDCSanddepressedbyanodaltDCS.Boththefacilitationandthedepressiondevelopedrelatively rapidly (within the first minute) but both outlasted tDCS and were present for up to 1 h after tDCS.Thestudythusdemonstrateslong-lastingeffectsoftDCSonsubcorticalneuronsintherat, albeit evoked by an opposite polarity of tDCS to that found to be effective on subcortical neurons in the cat investigated in the preceding study, or for cortical neurons in the humans.