Journal of neurophysiology
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1. Intraplantar injection of formalin (5%, 100 microliters in saline) was associated with a high level of spinal c-Fos immunoreactivity and a peripheral paw and ankle edema, as assessed at 3 h after formalin administration. For the two experimental series, the control number of formalin-evoked Fos-like immunoreactive (Fos-LI) neurons were 174 +/- 6 and 193 +/- 18 (means +/- SE) Fos-LI neurons per 40-microns section of the lumbar segment L4-L5 of the rat spinal cord. ⋯ Neither prior administration of intravenous RP67580 (0.05, 0.5, and 1.5 mg/kg) or RP68651 (1.5 mg/kg) or prior coadministration of RP67580) (0.5 mg/kg) and (+)-HA966 (2.5 mg/kg) influenced the extent of the paw or ankle-edema at 3 h after intraplantar injection of formalin. 6. Our results illustrate that NK1-receptor activation contributes to inflammatory-evoked spinal c-Fos expression and thus supports the current contention that NK1-receptor activation, and by inference SP, plays a role in spinal nociceptive processing. The second part of our study suggests that the previously reported NK1/NMDA-receptor interactions contribute to formalin-evoked spinal c-Fos expression and consequently may contribute to the longer term spinal neuroplasticity associated with inflammatory nociceptive processing.
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1. The purpose of this study was 1) to characterize the decrease observed in mean firing rates of motor units in the first 8-15 s of isometric constant-force contractions and 2) to investigate possible mechanisms that could account for the ability to maintain force output in the presence of decreasing motor unit firing rates. 2. The decrease in mean firing rates was characterized by investigating myoelectric signals detected with a specialized quadrifilar needle electrode from the first dorsal interosseus (FDI) and the tibialis anterior (TA) muscles of 19 healthy subjects during a total of 85 constant-force isometric contractions at 30, 50, or 80% of maximal effort. ⋯ As the contraction progresses, the twitch force of the muscle fibers undergoes a potentiation followed by a decrease. Simultaneously, the "late adaptation" property of the motoneuron decreases the firing rate of the motor unit. Findings of this study suggest that voluntary reduction in firing rates also cannot be ruled out as a means to augment the adaptation in motoneurons. (ABSTRACT TRUNCATED)
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1. The vestibular type I hair cell and its calyx ending can communicate in three ways. 1) In conventional synaptic transmission an excitatory neurotransmitter is released in multimolecular packets from the hair cell and depolarizes the ending. 2) Ephaptic transmission occurs because currents originating in one structure change the membrane potential of the other structure. 3) Potassium is released from the hair cell during transduction, accumulates in the intercellular space, and can depolarize both the hair cell and the ending. 2. A system of steady-state cable equations was used to analyze conventional and ephaptic transmission. ⋯ A transducer current of 100 pA can result in a delta x[K+] of 7 mM at the base and a possible 25-mV depolarization of the hair cell and the ending. 7. Intercellular K+ accumulation has kinetics with a dominant rate constant of 12 s-1, corresponding to a first-order low-pass filter with a corner frequency of 2 Hz. Kinetics is sufficiently fast for accumulation to participate in the transduction of normally occurring head movements. (ABSTRACT TRUNCATED)
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1. L4 and L5 dorsal root ganglia of rats aged 4-5 wk were isolated in vitro with their dorsal roots and sciatic nerves intact. With the use of intracellular microelectrodes, conduction velocity (CV) was determined along both peripheral and central axons and active and passive membrane properties were investigated with the use of a single-electrode switching clamp. 2. ⋯ This study shows that many of the electrical characteristics of isolated dorsal root ganglion neurons can be demonstrated in intact ganglia in which the neurons can be better identified functionally. The currents underlying the afterhyperpolarization in these cells are diverse across all subgroups and require further investigation. The electrical effects of retaining the axonal projections of the cells and the use of microelectrodes filled with 0.5 M KC1 are discussed in relation to the differences from data recorded in dissociated neurons.