Electrophysiological and Pharmacological Properties of Locomotor Activity-Related Neurons in cfos-EGFP Mice

Abstract

Electrophysiological and pharmacological properties of locomotor activityrelated neurons in cfos-EGFP mice. J Neurophysiol 102: 3365-3383, 2009. First published September 30, 2009 doi:10.1152/jn.00265.2009. Although locomotion is known to be generated by networks of spinal neurons, knowledge of the properties of these neurons is limited. Using neonatal transgenic mice that express enhanced green fluorescent protein (EGFP) driven by the c-fos promoter, we visualized EGFPpositive neurons in spinal cord slices from animals that were subjected to a locomotor task or drug cocktail [N-methyl-D-aspartate, serotonin (5-HT), dopamine, and acetylcholine (ACh)]. The activity-dependent expression of EGFP was also induced in dorsal root ganglion neurons with electrical stimulation of the neurons. Following 60 -90 min of swimming, whole cell patch-clamp recordings were made from EGFPϩ neurons in laminae VII, VIII, and X from slices of segments T 12 to L 4 . The EGFPϩ neurons (n ϭ 55) could be classified into three types based on their responses to depolarizing step currents: single spike, phasic firing, and tonic firing. Membrane properties observed in these neurons include hyperpolarization-activated inward currents (29/55), postinhibitory rebound (11/55), and persistent-inward currents (31/55). Bath application of 10 -40 M 5-HT and/or ACh increased neuronal excitability or output with hyperpolarization of voltage threshold and changes in membrane potential. 5-HT also increased input resistance, reduced the afterhyperpolarization (AHP), and induced membrane oscillations, whereas ACh reduced the input resistance and increased the AHP. In this study, we demonstrate a new way of identifying neurons active in locomotion. Our results suggest that the EGFPϩ neurons are a heterogeneous population of interneurons. The actions of 5-HT and ACh on these neurons provide insights into the neuronal properties modulated by these transmitters for generation of locomotion.

Using Motor Behavior during an Early Critical Period to Restore Skilled Limb Movement after Damage to the Corticospinal System during Development

“…Many are movement-related as they are active during fictive locomotion(Huang et al, 2000), and the Pitx2 group(Zagoraiou et al, 2009; Enjin et al, 2010) makes the M2-type muscarinic C-bouton on motoneurons (Miles et al, 2007) that may provide task-dependent regulation of motoneuronal excitability (Zagoraiou et al, 2009). Cholinergic agonists are potent modulators of spinal locomotor circuits(Dai et al, 2009; Dai and Jordan, 2010). Development of a cholinergic phenotype in most spinal interneurons occurs postnatally(Phelps et al, 1984; Chakrabarty et al, 2009a).…”

Tetrodotoxin-, dihydropyridine-, and riluzole-resistant persistent inward current: novel sodium channels in rodent spinal neurons

“…The sodium component of PIC (Na-PIC) is tetrodotoxin (TTX) sensitive, and the calcium component of PIC (Ca-PIC) is dihydropyridine (DHP) sensitive. In a series of studies for characterization of spinal interneurons activated by locomotor activity (Dai et al 2009a;Jordan 2010a, 2010b), we demonstrated the coexistence of Na-and Ca-PICs in these neurons through bath administration of TTX and/or DHP (Dai et al 2010a). However, our results also indicated that TTX and DHP did not completely block the PIC in some neurons, suggesting an existence of a new component of PIC, the TTX-and DHP-resistant PIC (TDR-PIC), in spinal neurons (Dai and Jordan 2007).…”

“…In the experiment with cfos-EGFP mice, a locomotor task (swimming) was induced in the animals before preparation of slices. Details for inducing locomotion were described in our recent study (Dai et al 2009a). Briefly, the mice were held in place with a length of paper tape 1 cm wide and 8 cm long placed around the animal's thorax.…”

“…The procedure for the preparation of mouse or rat spinal cord slices was similar to that previously reported (Dai et al 2009a(Dai et al , 2009b. Briefly, the animals were anesthetized with an intraperitoneal injection of ketamine (100 mg/kg).…”

Lighting Up Neuronal Pathways: The Development of a Novel Transgenic Rat that Identifies Fos-Activated Neurons Using a Red Fluorescent Protein

“…Surprisingly, the preparation of the slice alone did not induce fosGFP expression, and these animals have been used successfully to identify neurons in vitro that were activated by stimuli in vivo, e.g. whisker barrel stimulation (9 -11) and locomotor tasks, such as walking or swimming (12). The time course of activation of the mRFP1 and the half-life of the mRFP1 protein would also need to be established in these transgenic rats.…”