Comparison of neuronal activity in the rostral supplementary and cingulate motor areas during a task with cognitive and motor demands.

A number of cortical motor areas have been identified on the medial wall of the hemisphere in monkeys. However, their specific role in motor control remains unclear. In this study, we sought to describe and compare the functional properties of the presupplementary (pre-SMA) and rostral cingulate (CMAr) motor areas in two monkeys performing a visually instructed, delayed, sequential movement. We recorded 134 task-related neurons in the pre-SMA and 149 in the CMAr. The main difference between the two areas was the abundance of responses to targets (46%) in the pre-SMA, while CMAr activity was more related to reward (28%). Neuronal responses to targets were more phasic and higher in frequency in the pre-SMA than in the CMAr. During the delay, the percentage of neuronal responses was similar in the two areas. The discharge pattern was different depending upon whether the delay duration was fixed or variable but in most neurons was the same regardless of the sequence performed. Movement-related changes were common in the pre-SMA (75%) and in the CMAr (81%) but they occurred earlier in the former. Neurons activated exclusively during movement were more numerous in the CMAr. Finally, neuronal activity in the pre-SMA was more related to the sequential aspect of the task compared to the CMAr. Our results suggest that although the two areas share functional properties, they also participate in different aspects of motor behaviour. Their functional properties reflect their anatomical positions, which give them the potential to integrate external stimuli (pre-SMA) and internal states (CMAr) during motor planning.

High-frequency stimulation produces a transient blockade of voltage-gated currents in subthalamic neurons.

The effect of high-frequency stimulation (HFS) of the subthalamic nucleus (STN) was analyzed with patch-clamp techniques (whole cell configuration, current- and voltage-clamp modes) in rat STN slices in vitro. A brief tetanus, consisting of 100-micros bipolar stimuli at a frequency of 100--250 Hz during 1 min, produced a full blockade of ongoing STN activity whether it was in the tonic or bursting mode. This HFS-induced silence lasted around 6 min after the end of stimulation, was frequency dependent, could be repeated without alteration, and was not synaptically induced as it was still observed in the presence of blockers of ionotropic GABA and glutamate receptors or in the presence of cobalt at a concentration (2 mM) that blocks voltage-gated Ca(2+) channels and synaptic transmission. During HFS-induced silence, the following alterations were observed: the persistent Na(+) current (I(NaP)) was totally blocked (by 99%), the Ca(2+)-mediated responses were strongly reduced including the posthyperpolarization rebound (-62% in amplitude) and the plateau potential (-76% in duration), suggesting that T- and L-type Ca(2+) currents are transiently depressed by HFS, whereas the Cs(+)-sensitive, hyperpolarization-activated cationic current (I(h)) was little affected. Thus a high-frequency tetanus produces a blockade of the spontaneous activities of STN neurons as a result of a strong depression of intrinsic voltage-gated currents underlying single-spike and bursting modes of discharge. These effects of HFS, which are completely independent of synaptic transmission, provide a mechanism for interrupting ongoing activities of STN neurons.

Interplay between Ca2+ release and Ca2+ influx underlies localized hyperpolarization-induced [Ca2+]i waves in prostatic cells.

Calcium seems to be a major second messenger involved in the regulation of prostatic cell functions, but the mechanisms underlying its control are poorly understood. We investigated spatiotemporal aspects of Ca2+ signals in the LNCaP cell line, a model of androgen-dependent prostatic cells, by using non-invasive external electric field pulses that hyperpolarize the anode facing membrane and depolarize the membrane facing the cathode. Using high-speed fluo-3 confocal imaging, we found that an electric field pulse (10-15 V/cm, 1-5 mA, 5 ms) initiated rapidly, at the hyperpolarized end of the cell, a propagated [Ca2+]i wave which spread through the cell with a constant amplitude and an average velocity of about 20 microns/s. As evidenced by the total wave inhibition either by the block of Ca2+ entry or the depletion of Ca2+ stores by thapsigargin, a specific Ca(2+)-ATPase inhibitor, the [Ca2+]i wave initiation may imply a localized Ca2+ influx linked to a focal auto-regenerative process of Ca2+ release. Using different external Ca2+ and Ca2+ entry blockers concentrations, Mn2+ quenching of fluo-3 and fura-2 fluorescence and inhibitors of InsP3 production, we found evidence that the [Ca2+]i wave progression required, in the presence of basal levels of InsP3, an interplay between Ca2+ release from InsP3-sensitive Ca2+ stores and Ca2+ influx through channels possibly activated by the [Ca2+]i rise.

Potassium conductance in the androgen-sensitive prostate cancer cell line, LNCaP: involvement in cell proliferation.

BACKGROUND: Very little is known about the expression of ion channels in prostate cells (both normal and malignant), and their possible role in physiological and pathological functions. We therefore studied ion conductances and their role in the proliferation of LNCaP cells, an androgen-sensitive human prostate cancer cell line. METHODS: We applied patch-clamp recording techniques for electrophysiological studies, and 3H-thymidine incorporation and protein content assays for cell growth studies. RESULTS: Only one type of voltage-dependent ion conductance, a potassium K+ conductance, was identified. This current, which was depressed by a rise in intracellular Ca2+, had a high sensitivity to tetraethylammonium (TEA) (with half-block at 2 mM) and was also inhibited by 2 nM alpha-dendrotoxin (DTX) and 20 nM mast-cell degranulating peptide (MCDP). K+ channel inhibitors inhibited [3H]thymidine incorporation and protein content, in a dose-dependent fashion, indicating that K+ channels are involved in cell growth. CONCLUSIONS: We conclude from our findings that the human cancer prostate cell line LNCaP has a new type of K+ channel, likely to play an essential role in the physiology of these cells and, more specifically, in cell proliferation.

Responses of substantia nigra pars reticulata neurons to intrastriatal D1 and D2 dopaminergic agonist injections in the rat.

Extracellular neuronal recordings were performed in the substantia nigra pars reticulata (SNr) of normal and 6-hydroxydopamine (6-OHDA)-lesioned rats during intrastriatal D1 and D2 dopaminergic-agonist injections. Three types of responses were observed, inhibition, excitation and/or regularization of neuronal discharge patterns. In normal rats, variable responses were observed after D2 injections and a predominance of inhibition after D1 injections. In lesioned rats, the percentage of neurons inhibited and that of neurons regularized increased following D2 injections. During sequential intrastriatal D1 and D2 agonist injections, a response to both dopaminergic agents was observed in 22.5% and 55.5% of SNr neurons in normal and lesioned rats, respectively. Our data suggests that the physiological relevance of direct and indirect pathways convergence upon a given SNr target neuron depends on their respective synaptic weight, the influence of surrounding SNr neurons and the state of dopamine depletion.

Intracellular pH in individual pituitary cells: measurement with a dual emission pH indicator.

Intracellular pH (pHi) can now be measured at the single cell level using dual emission wavelength microspectrofluorimetry with the fluorescent pH indicator SNARF 1 and its membrane permeant acetoxymethyl ester (SNARF 1/AM). We measured pHi of individual pituitary cells under both basal and stimulated conditions. The emitted fluorescence of SNARF 1 probe was calibrated following experimental manipulations of pHi in two types of rat pituitary cells. The calibration curves obtained in the two cell types were identical. We observed a Gaussian distribution of individual pHi with a wide dispersion (6.95 to 8) in the two cell populations. TRH (10(-7) M) and ionomycin (5 microM) induced a transient acidification followed by a sustained alkalinization, whereas K+ (50 mM) depolarization only exerted a transient acidification. These results show that the dual emission pH indicator SNARF 1 can be used to reliably investigate changes in pHi in individual endocrine cells.

Measurement of CA2+ transients using simultaneous dual-emission microspectrofluorimetry and electrophysiology in individual pituitary cells.

Cytosolic free calcium concentration, [Ca2+]i, was monitored in individual pituitary GH3B6 cells, loaded with the fluorescent Ca2+ indicator indo 1 either by internal perfusion through a patch clamp pipette or by exposure to indo 1 acetoxymethyl ester, with the use of a dual-emission apparatus for microspectrofluorimetry. This system was sensitive enough to allow on-line monitoring of [Ca2+]i (from the ratio of fluorescent intensities) which could be combined simultaneously with whole-cell patch clamp recordings. The following situations were examined: (a) [Ca2+]i oscillations due to action potential firing, and (b) rapid transient elevations of [Ca2+]i triggered by voltage-dependent Ca2+ current. The results indicate that monitoring of [Ca2+]i at the single cell level with indo 1 provides a powerful means to study the [Ca2+]i regulation in pituitary cells, which should be applicable to many other cell types.