Role of cannabinoid receptor type 1 in tibial and pudendal neuromodulation of bladder overactivity in cats.

The role of cannabinoid type 1 (CB1) receptors in tibial and pudendal neuromodulation of bladder overactivity induced by intravesical infusion of 0.5% acetic acid (AA) was determined in α-chloralose anesthetized cats. AA irritation significantly (P < 0.01) reduced bladder capacity to 36.6 ± 4.8% of saline control capacity. Tibial nerve stimulation (TNS) at two or four times threshold (2T or 4T) intensity for inducing toe movement inhibited bladder overactivity and significantly (P < 0.01) increased bladder capacity to 69.2 ± 9.7 and 79.5 ± 7.2% of saline control, respectively. AM 251 (a CB1 receptor antagonist) administered intravenously at 0.03 or 0.1 mg/kg significantly (P < 0.05) reduced the inhibition induced by 2T or 4T TNS, respectively, without changing the prestimulation bladder capacity. However, intrathecal administration of AM 251 (0.03 mg) to L7 spinal segment had no effect on TNS inhibition. Pudendal nerve stimulation (PNS) also inhibited bladder overactivity induced by AA irritation, but AM 251 at 0.01-1 mg/kg iv had no effect on PNS inhibition or the prestimulation bladder capacity. These results indicate that CB1 receptors play an important role in tibial but not pudendal neuromodulation of bladder overactivity and the site of action is not within the lumbar L7 spinal cord. Identification of neurotransmitters involved in TNS or PNS inhibition of bladder overactivity is important for understanding the mechanisms of action underlying clinical application of neuromodulation therapies for bladder disorders.

Electrical muscle stimulation elevates intramuscular BDNF and GDNF mRNA following peripheral nerve injury and repair in rats.

Despite advances in surgery, patients with nerve injuries frequently have functional deficits. We previously demonstrated in a rat model that daily electrical muscle stimulation (EMS) following peripheral nerve injury and repair enhances reinnervation, detectable as early as two weeks post-injury. In this study, we explain the enhanced early reinnervation observed with electrical stimulation. In two groups of rats, the tibial nerve was transected and immediately repaired. Gastrocnemius muscles were implanted with intramuscular electrodes for sham or muscle stimulation. Muscles were stimulated daily, eliciting 600 contractions for one hour/day, repeated five days per week. Sixteen days following nerve injury, muscles were assessed for functional reinnervation by motor unit number estimation methods using electromyographic recording. In a separate cohort of rats, surgical and electrical stimulation procedures were identical but muscles and distal nerve stumps were harvested for molecular analysis. We observed that stimulated muscles had significantly higher motor unit number counts. Intramuscular levels of brain-derived and glial cell line-derived neurotrophic factor (BDNF and GDNF) mRNA were significantly upregulated in muscles that underwent daily electrical stimulation compared to those without stimulation. The corresponding levels of trophic factor mRNA within the distal stump were not different from one another, indicating that the intramuscular electrical stimulus does not modulate Schwann cell-derived trophic factor transcription. Stimulation over a three-month period maintained elevated muscle-derived GDNF but not BDNF mRNA. In conclusion, EMS elevates intramuscular trophic factor mRNA levels which may explain how EMS enhances neural regeneration following nerve injury.

Acupuncture plus low-frequency electrical stimulation (Acu-LFES) attenuates denervation-induced muscle atrophy.

Muscle wasting occurs in a variety of clinical situations, including denervation. There is no effective pharmacological treatment for muscle wasting. In this study, we used a tibial nerve denervation model to test acupuncture plus low-frequency electric stimulation (Acu-LFES) as a therapeutic strategy for muscle atrophy. Acupuncture needles were connected to an SDZ-II electronic acupuncture device delivering pulses at 20 Hz and 1 mA; the treatment was 15 min daily for 2 wk. Acu-LFES prevented soleus and plantaris muscle weight loss and increased muscle cross-sectional area in denervated mice. The abundances of Pax7, MyoD, myogenin, and embryonic myosin heavy chain were significantly increased by Acu-LFES in both normal and denervated muscle. The number of central nuclei was increased in Acu-LFES-treated muscle fibers. Phosphorylation of Akt was downregulated by denervation leading to a decline in muscle mass; however, Acu-LFES prevented the denervation-induced decline largely by upregulation of the IGF-1 signaling pathway. Acu-LFES reduced the abundance of muscle catabolic proteins forkhead O transcription factor and myostatin, contributing to the attenuated muscle atrophy. Acu-LFES stimulated the expression of macrophage markers (F4/80, IL-1b, and arginase-1) and inflammatory cytokines (IL-6, IFNγ, and TNFα) in normal and denervated muscle. Acu-LFES also stimulated production of the muscle-specific microRNAs miR-1 and miR-206. We conclude that Acu-LFES is effective in counteracting denervation-induced skeletal muscle atrophy and increasing muscle regeneration. Upregulation of IGF-1, downregulation of myostatin, and alteration of microRNAs contribute to the attenuation of muscle atrophy in denervated mice.

Transcriptional upregulation of SCG10 and CAP-23 is correlated with regeneration of the axons of peripheral and central neurons in vivo.

We have compared SCG10 and CAP-23 expression with that of GAP-43 during axonal regeneration in the peripheral and central nervous systems (PNS, CNS) of adult rats. SCG10, CAP-23, and GAP-43 mRNAs were strongly upregulated by motor and dorsal root ganglion (DRG) neurons following sciatic nerve crush, but not after dorsal rhizotomy. When the sciatic nerve was cut and ligated to prevent reinnervation of targets, expression of all three mRNAs was prolonged. Neurons in the thalamic reticular nucleus and deep cerebellar nuclei transiently upregulated these mRNAs after axotomy, and showed prolonged upregulation of all three molecules when regenerating axons into peripheral nerve grafts inserted into the thalamus of cerebellum. Neurons in the dorsal thalamus and cerebellar cortex showed poor regenerative capacity and most did not upregulate any of these mRNAs. Thus, in both PNS and CNS neurons, the transcription of SCG10, CAP-23, and GAP-43 mRNAs is coregulated following axotomy and during regeneration. Signals from living peripheral nerve appear to maintain expression of all three mRNAs in regenerating neurons, and in PNS neurons downregulation correlates with target reinnervation. Thus, SCG10 and CAP-23, as well as GAP-43, are likely to be important neuronal determinants of regenerative ability.

A defect in sodium-dependent amino acid uptake in diabetic rabbit peripheral nerve. Correction by an aldose reductase inhibitor or myo-inositol administration.

A myo-inositol-related defect in nerve sodium-potassium ATPase activity in experimental diabetes has been suggested as a possible pathogenetic factor in diabetic neuropathy. Because the sodium-potassium ATPase is essential for other sodium-cotransport systems, and because myo-inositol-derived phosphoinositide metabolites regulate multiple membrane transport processes, sodium gradient-dependent amino acid uptake was examined in vitro in endoneurial preparations derived from nondiabetic and 14-d alloxan diabetic rabbits. Untreated alloxan diabetes reduced endoneurial sodium-gradient dependent uptake of the nonmetabolized amino acid 2-aminoisobutyric acid by greater than 50%. Administration of an aldose reductase inhibitor prevented reductions in both nerve myo-inositol content and endoneurial sodium-dependent 2-aminoisobutyric acid uptake. Myo-inositol supplementation that produced a transient pharmacological elevation in plasma myo-inositol concentration, but did not raise nerve myo-inositol content, reproduced the effect of the aldose reductase inhibitor on endoneurial sodium-dependent 2-aminoisobutyric acid uptake. Phorbol myristate acetate, which acutely normalizes sodium-potassium ATPase activity in diabetic nerve, did not acutely correct 2-aminoisobutyric uptake when added in vitro. These data suggest that depletion of a small myo-inositol pool may be implicated in the pathogenesis of defects in amino acid uptake in diabetic nerve and that rapid correction of sodium-potassium ATPase activity with protein kinase C agonists in vitro does not acutely normalize sodium-dependent 2-aminoisobutyric acid uptake.