Mephenesin blocks early inward currents and strychnine-induced multiple discharges of aplysia neurons

Excitatory and Inhibitory Descending Commissural Interneurons Differentially Integrate Supraspinal and Segmental Sensory Signals

The limited information about how descending inputs from the brain and sensory inputs from the periphery use spinal cord interneurons (INs) is a major barrier to understanding how these inputs may contribute to motor functions under normal and pathologic conditions. Commissural interneurons (CINs) are a heterogeneous population of spinal INs that has been implicated in crossed motor responses and bilateral motor coordination (ability to use the right and left side of the body in a coordinated manner) and, therefore, are likely involved in many types of movement (e.g., dynamic posture stabilization, jumping, kicking, walking). In this study, we incorporate mouse genetics, anatomy, electrophysiology, and single-cell calcium imaging to investigate how a subset of CINs, those with descending axons called dCINs, are recruited by descending reticulospinal and segmental sensory signals independently and in combination. We focus on two groups of dCINs set apart by their principal neurotransmitter (glutamate and GABA) and identified as VGluT2+ dCINs and GAD2+ dCINs. We show that VGluT2+ and GAD2+ dCINs are both extensively recruited by reticulospinal and sensory input alone but that VGluT2+ and GAD2+ dCINs integrate these inputs differently. Critically, we find that when recruitment depends on the combined action of reticulospinal and sensory inputs (subthreshold inputs), VGluT2+ dCINs, but not GAD2+ dCINs, are recruited. This difference in the integrative capacity of VGluT2+ and GAD2+ dCINs represents a circuit mechanism that the reticulospinal and segmental sensory systems may avail themselves of to regulate motor behaviors both normally and after injury.SIGNIFICANCE STATEMENT The way supraspinal and peripheral sensory inputs use spinal cord interneurons is fundamental to defining how motor functions are supported both in health and disease. This study, which focuses on dCINs, a heterogeneous population of spinal interneurons critical for crossed motor responses and bilateral motor coordination, shows that both glutamatergic (excitatory) and GABAergic (inhibitory) dCINs can be recruited by supraspinal (reticulospinal) or peripheral sensory inputs. Additionally, the study demonstrates that in conditions where the recruitment of dCINs depends on the combined action of reticulospinal and sensory inputs, only excitatory dCINs are recruited. The study uncovers a circuit mechanism that the reticulospinal and segmental sensory systems may avail themselves of to regulate motor behaviors both normally and after injury.

Block of deltamethrin-modified sodium current in cultured mouse neuroblastoma cells: local anesthetics as potential antidotes

Effects of local anesthetics and anticonvulsants on the pyrethroid-modified sodium current in cultured mouse neuroblastoma cells have been investigated using the suction pipette voltage clamp technique. In the presence of 10 microM of the pyrethroid deltamethrin the sodium current consists of an enhanced peak current during membrane depolarization and a slowly decaying, deltamethrin-induced tail current remaining after repolarization. At the onset of block the local anesthetics tetracaine, lidocaine and QX 314 reduced the deltamethrin-induced tail current more effectively than the peak current. Lidocaine, but not phenytoin, caused a time-dependent block of tail currents evoked by membrane depolarizations lasting 10-1000 ms. Both lidocaine- and phenytoin-induced blocks were independent of the membrane potential during the tail current. The anticonvulsants phenytoin, phenobarbital and valproate blocked the tail and the peak sodium current to the same extent, but diazepam, mephenesin and urethane blocked the peak current more effectively. Vitamin E, which suppresses pyrethroid-induced paresthesia of the skin, had no effect on the voltage-dependent sodium current. It is concluded that indirect effects of anticonvulsants on pyrethroid-induced toxic symptoms predominate, whereas local anesthetics preferentially block the pyrethroid-induced tail current. Therefore, local anesthetics are potentially useful pyrethroid antidotes.

DDT-induced tremor in rats: effects of pharmacological agents

Rats given a tremorigenic dose of DDT (75 mg/kg, PO) were treated with pharmacological agents either 30 min prior to DDT or 1-2 h prior to testing at the time of peak effect (12 h postdosing). The administration of mephenesin (a centrally acting muscle relaxant) or Dilantin (an anticonvulsant) prior to DDT significantly attenuated tremor. Pretreatment with pizotifen (a serotonergic receptor antagonist) had no significant effect on tremor. Administration of the same agents 1-2 h prior to measurement had minimal effects. Trihexyphenidyl (a muscarinic cholinergic receptor antagonist) exacerbated the tremor produced by DDT. These data suggest that cholinergic neurotransmitter systems may be involved in DDT-induced tremor. That DDT-induced tremor was significantly attenuated by mephenesin and Dilantin is in accord with the conclusion that DDT-induced tremor is a manifestation of repetitive discharge due to interference with ionic conductance.