KChIP1 and frequenin modify shal-evoked potassium currents in pyloric neurons in the lobster stomatogastric ganglion.

The transient potassium current (I(A)) plays an important role in shaping the firing properties of pyloric neurons in the stomatogastric ganglion (STG) of the spiny lobster, Panulirus interruptus. The shal gene encodes I(A) in pyloric neurons. However, when we over-expressed the lobster Shal protein by shal RNA injection into the pyloric dilator (PD) neuron, the increased I(A) had somewhat different properties from the endogenous I(A). The recently cloned K-channel interacting proteins (KChIPs) can modify vertebrate Kv4 channels in cloned cell lines. When we co-expressed hKChIP1 with lobster shal in Xenopus oocytes or lobster PD neurons, they produced A-currents resembling the endogenous I(A) in PD neurons; compared with currents evoked by shal alone, their voltage for half inactivation was depolarized, their kinetics of inactivation were slowed, and their recovery from inactivation was accelerated. We also co-expressed shal in PD neurons with lobster frequenin, which encodes a protein belonging to the same EF-hand family of Ca(2+) sensing proteins as hKChIP. Frequenin also restored most of properties of the shal-evoked currents to those of the endogenous A-currents, but the time course of recovery from inactivation was not corrected. These results suggest that lobster shal proteins normally interact with proteins in the KChIP/frequenin family to produce the transient potassium current in pyloric neurons.

Voltage-sensitivity of motoneuron NMDA receptor channels is modulated by serotonin in the neonatal rat spinal cord.

Both N-methyl-D-aspartate (NMDA) and serotonin (5-HT) receptors contribute to the generation of rhythmic motor patterns in the rat spinal cord. Co-application of these chemicals is more effective at producing locomotor-like activity than either neurochemical alone. In addition, NMDA application to rat spinal motoneurons, synaptically isolated in tetrodotoxin, induces nonlinear membrane behavior that results in voltage oscillations which can be blocked by 5-HT antagonists. However, the mechanisms underlying NMDA and 5-HT receptor interactions pertinent to motor rhythm production remain to be determined. In the present study, an in vitro neonatal rat spinal cord preparation was used to examine whether NMDA receptor-mediated nonlinear membrane voltage is modulated by 5-HT. Whole-cell recordings of spinal motoneurons demonstrated that 5-HT shifts the region of NMDA receptor-dependent negative slope conductance (RNSC) of the current-voltage relationship to more hyperpolarized potentials and enhances whole-cell inward current. The influence of 5-HT on the RNSC was similar to the effect on the RNSC of decreasing the extracellular Mg(2+)concentration. The results suggest that 5-HT may modulate this form of membrane voltage nonlinearity by regulating Mg(2+) blockade of the NMDA ionophore.

NMDA receptor-mediated oscillatory activity in the neonatal rat spinal cord is serotonin dependent.

The effect of serotonin (5-HT) receptor blockade on rhythmic network activity and on N-methyl--aspartate (NMDA) receptor-induced membrane voltage oscillations was examined using an in vitro neonatal rat spinal cord preparation. Pharmacologically induced rhythmic hindlimb activity, monitored via flexor and extensor electroneurograms or ventral root recordings, was abolished by 5-HT receptor antagonists. Intrinsic motoneuronal voltage oscillations, induced by NMDA in the presence of tetrodotoxin (TTX), either were abolished completely or transformed to long-lasting voltage shifts by 5-HT receptor antagonists. Conversely, 5-HT application facilitated the expression of NMDA-receptor-mediated rhythmic voltage oscillations. The results suggest that an interplay between 5-HT and NMDA receptor actions may be critical for the production of rhythmic motor behavior in the mammalian spinal cord, both at the network and single cell level.

NMDA receptor-mediated oscillatory properties: potential role in rhythm generation in the mammalian spinal cord.

Previous studies have demonstrated that (1) NMDA receptor activation occurs during locomotor network operation in lower and higher vertebrates and (2) NMDA induces active membrane properties that can be expressed as intrinsic voltage fluctuations in cells located in the spinal cord of lower vertebrates, as well as in neurons located in supraspinal regions of the mammalian nervous system. This paper reviews recent data showing that NMDA can induce similar inherent membrane potential behavior in synaptically isolated motoneurons and interneurons in the mammalian (in vitro neonatal rat) spinal cord. These TTX-resistant voltage fluctuations include rhythmic oscillations and plateau potentials, as well as low-frequency long-lasting voltage shifts (LLVSs). 5-HT facilitates the transformation of LLVSs into oscillatory events, and 5-HT receptor antagonists have the reverse effect. In the absence of TTX, locomotor-related rhythmic drive potentials in spinal cord neurons can display nonlinear voltage behavior compatible with NMDA receptor activation, although other voltage-activated conductances are not excluded. Suppression of the nonlinear voltage response associated with NMDA receptor activation, via removal of Mg2+, disrupts locomotor patterns of network activity. The potential role of NMDA receptor activation in the operation of mammalian locomotor networks is discussed in the context of these recent observations.

NMDA receptor activation triggers voltage oscillations, plateau potentials and bursting in neonatal rat lumbar motoneurons in vitro.

Whole-cell recordings of lumbar motoneurons in the intact neonatal rat spinal cord in vitro were undertaken to examine the effects of N-methyl-D-aspartate (NMDA) receptor activation on membrane behaviour. Bath application of NMDA induced rhythmic voltage oscillations of 5.9+/-2.1 mV (SD) at a frequency of 4.4+/-1.5 Hz. Amplitude, but not frequency, of the voltage oscillations was membrane potential-dependent. Voltage oscillations could recruit action potentials and/or plateau potentials with or without superimposed bursting. Blockade of synaptic transmission with tetrodotoxin (TTX) sometimes resulted in a loss of oscillatory activity which could then be restored by increasing the NMDA concentration. After application of TTX, the trajectory of NMDA-induced oscillations was similar to the trajectory induced in the presence of intact synaptic networks, although the mean oscillation duration was longer and the oscillation frequency was slower (1.8+/-1.1 Hz). Current ramps delivered after bath application of NMDA demonstrated bistable membrane properties which may underlie the plateau potentials. Injection of intracellular current pulses could initiate, entrain and terminate individual plateau potentials. The results suggest that membrane depolarization produced by oscillations may activate other intrinsic conductances which generate plateau potentials, thereby providing the neuron with enhanced voltage sensitivity, compared to that produced by NMDA receptor activation alone. These oscillatory events may have a role in the regulation of motor output in a variety of rhythmic behaviours including locomotion.

Lamina VII neurons are rhythmically active during locomotor-like activity in the neonatal rat spinal cord.

The midsagittally-sectioned lumbar spinal cord with thoracic segments intact retains the capacity for locomotor-like activity. Intracellular recordings were used to characterize the activity and concurrently label lumbar neurons in lamina VII, an area previously implicated in the generation of locomotion. Sharp electrodes were shown to preferentially impale larger neurons. These neurons undergo rhythmic voltage oscillations, presumably synaptically driven, during locomotor-like activity induced by bath application of N-methyl-D-aspartate and 5-hydroxytryptamine. This supports the hypothesis that synaptic activity recruits neurons in lamina VII that are associated with locomotor behavior.

Long-duration, frequency-dependent motor responses evoked by ventrolateral funiculus stimulation in the neonatal rat spinal cord.

Three variations of the in vitro neonatal rat spinal cord preparation were used to investigate motor responses to stimulation of the ventrolateral funiculus (VLF). In a partially hemisected spinal cord preparation, stimuli elicited frequency-dependent activity in lumbar ventral roots that outlasted the stimulus train by up to 30 s. In a spinal cord-hindlimb preparation, trains of VLF stimuli elicited slow, step-like flexor-extensor hindlimb movement that also persisted for up to 30 s beyond the stimulus. Finally, in a partially hemisected spinal cord preparation where 5-hydroxytryptamine/N-methyl-D-aspartate was used to induce locomotor-like rhythmic activity, short trains of VLF stimuli were capable of perturbing the locomotor rhythm, transiently altering its frequency. Application of pharmacological antagonists suggests that these responses may be the result of stimulation of a descending pathway that includes glutamatergic and catecholaminergic fibres comprising part of a descending locomotor command path.

Necrotizing vasculitis in gynecological surgery.

Extensive clinical investigation of asymptomatic vasculitis found in routine histopathological studies following gynecological surgery may often be unnecessary. In 11 patients necrotizing angiitis was an incidental finding in surgically removed uterine and uterine adnexal tissues. Following irradiation for urinary bladder carcinoma, one patient died during radical surgery: vasculitis was found in surgically resected pelvic organs, colon and kidneys. In other patients, vasculitis may have been attributable to drugs, e.g. penicillin, or to local arthus-like reaction following cone biopsy of cervix. Available from 6 of these cases, follow-up data presented no evidence of progressive systemic vascular disease, supporting the view that incidentally encountered necrotizing angiitis of uterus and uterine adnexa, like that of the appendix, may be innocuous.