A reliable technique for the induction of locomotor-like activity in the in vitro neonatal rat spinal cord using brainstem electrical stimulation

Abstract

The use of brainstem electrical stimulation (BES) to evoke locomotion in in vivo preparations, such as the decerebrate cat, is well established. In contrast, despite the popularity of in vitro rodent spinal cord models, BES has not been adapted for routine induction of locomotion in these preparations. We describe a simple and reliable method of inducing locomotor-like activity in the in vitro neonatal rat spinal cord using BES. Relatively large amplitude (0.5–10 mA), long duration (4–20 ms) and low frequency (0.8–2.0 Hz) pulses were delivered through a metal-in-glass electrode placed in contact with the ventral surface of the brainstem, without the need for precise targeting of specific sites. During continuous BES, locomotor-like activity (0.15–0.63 Hz) persisted for over 45 min. Episodes of locomotor-like activity could be recruited repeatedly for hours, using short periods (60 s) of BES alternating with brief rest periods. Additional observations confirmed that the rhythmogenic effect of BES is mediated by excitation of spinal projections at the brainstem level, rather than spinal cord activation due to electrotonic spread of stimulus from the brainstem electrode. Endogenous activation of locomotor networks using BES offers important advantages over bath-applied application of neurochemicals to induce stepping in the in vitro rat model.