Functional Characterization of the Left Ventrolateral Premotor Cortex in Humans: A Direct Electrophysiological Approach.

In monkeys, motor outputs from premotor cortex (PM) involve cortico-cortical connections with primary motor cortex (M1). However, in humans, the functional organization of PM and its relationship with the corticospinal tract (CST) is still uncertain. This study was carried out in 21 patients undergoing intraoperative brain mapping prior to tumor resection. The left ventrolateral premotor cortex (vlPM-BA6) was identified preoperatively by functional magnetic resonance imaging, and then investigated intraoperatively using high frequency direct electrical stimulation (HF-DES) of the convexity of M1 and vlPM-BA6, with simultaneous recording of motor-evoked potentials (MEPs) from oro-facial, hand and arm muscles. The somatotopy, organization of evoked responses, latency of MEPs, and cortical excitability of vlPM-BA6 were compared with reference data from M1. vlPM-BA6 was found to be less excitable, with significantly longer MEP latencies than M1. In addition to the pure oro-facial and hand-arm muscle representation, a "transition oro-hand zone" was identified in vlPM-BA6. The longer latency of vlPM-BA6 MEPs suggests that human vlPM could act on spinal motoneurons either directly through more slowly conducting CST fibers or via less direct pathways through M1, brainstem, or spinal mechanisms. The results help in disclosing the very different roles of vlPM and M1 in motor control.

Erythropoietin effect on sensorimotor recovery after contusive spinal cord injury: an electrophysiological study in rats.

Spinal cord injury (SCI) is a debilitating clinical condition, characterized by a complex of neurological dysfunctions. It has been shown in rats that the acute administration of recombinant human erythropoietin (rhEPO) following a contusive SCI improves the recovery of hindlimb motor function, as measured with the locomotor BBB (Basso, Beattie, Bresnahan) scale. This scale evaluates overall locomotor activity, without testing whether the rhEPO-induced motor recovery is due to a parallel recovery of sensory and/or motor pathways. Aim of the present study was to utilize an electrophysiological test to evaluate, in a rat model of contusive SCI, the transmission of both ascending and descending pathways across the damaged cord at 2, 5, 7, 11, and 30 days after lesion, in animals treated with rhEPO (n=25) vs saline solution (n=25). Motor potentials evoked by epicortical stimulation were recorded in the spinal cord, and sensory-evoked potentials evoked by spinal stimulation were recorded at the cortical level. In the same animals BBB score and immunocytochemical evaluation of the spinal segments caudal to the lesion were performed. In rhEPO-treated animals results show a better general improvement both in sensory and motor transmission through spared spinal pathways, supposedly via the reticulo-spinal system, with respect to saline controls. This improvement is most prominent at relatively early times. Overall these features show a parallel time course to the changes observed in BBB score, suggesting that EPO-mediated spared spinal cord pathways might contribute to the improvement in transmission which, in turn, might be responsible for the recovery of locomotor function.

Protein kinase C modulates NMDA receptors in the myenteric plexus of the guinea pig ileum during in vitro ischemia and reperfusion.

BACKGROUND: Ischemic episodes lead to profound functional and structural alterations of the gastrointestinal tract which may contribute to disorders of intestinal motility. Enhancement of glutamate overflow and the consequent activation of NMDA (N-methyl-D-aspartate) receptors may participate to such changes by modulating different enteric neurotransmitter systems, including cholinergic motor pathways. METHODS: The molecular mechanism/s underlying activation of NMDA receptors in the guinea pig ileum were investigated after glucose/oxygen deprivation (in vitro ischemia) and during reperfusion. KEY RESULTS: The number of ileal myenteric neurons positive for NR1, the functional subunit of NMDA receptors, and its mRNA levels were unchanged after in vitro ischemia/reperfusion. In these conditions, the protein levels of NR1, and of its phosphorylated form by protein kinase C (PKC), significantly increased in myenteric neurons, whereas, the levels of NR1 phosphorylated by protein kinase A (PKA) did not change, with respect to control values. Spontaneous glutamate overflow increased during in vitro ischemia/reperfusion. In these conditions, the NMDA receptor antagonists, D(-)-2-amino-5-phosphonopentanoic acid [(D)-AP5] (10 µmol L(-1)) and 5,7-dichlorokynurenic acid (5,7-diClKyn acid) (10 µmol L(-1)) and the PKC antagonist, chelerythrine (1 µmol L(-1)), but not the PKA antagonist, H-89 (1 µmol L(-1)), were able to significantly depress the increased glutamate efflux. CONCLUSIONS & INFERENCES: The present data suggest that in the guinea pig ileum during in vitro ischemia/reperfusion, NR1 protein levels increase. Such event may rely upon posttranscriptional events involving NR1 phosphorylation by PKC. Increased NR1 levels may, at least in part, explain the ability of NMDA receptors to modulate a positive feedback on ischemia/reperfusion-induced glutamate overflow.

Neural compensation for mechanical differences between hand and foot during coupled oscillations of the two segments.

(1) Rhythmic flexion-extensions of the hand and foot on one side were performed by ten male and nine female subjects. Limbs were rotated in the same direction (in-phase) or in opposite directions (anti-phase). Oscillation frequency ranged from 0.6 to 3.2 Hz for in-phase and to 2.2 Hz for anti-phase movements. In both genders, movement synchrony was more strictly maintained during anti-phase than during in-phase coupling. (2) EMG recordings showed that, in males, movement synchrony was achieved by activating hand movers in advance of foot movers. This phase advance increased as the oscillation frequency increased. In females, instead, muscles of the two limbs were activated almost simultaneously over most of the frequency range. Since the different timing of muscle activation in the two genders suggests that their limbs have different mechanical characteristics, the frequency response of each limb was estimated in either gender. The frequency response between 0.6 and 3.2 Hz was evaluated in five males and five females by measuring the phase delay between the onset of the EMG activity and the onset of the related movement, both when the limbs were moved in isolation and when they were coupled. (3) In uncoupled conditions, the hand and foot curves were roughly parallel in females, the phase delay being about 45 degrees larger in the hand than in the foot. In males, the curves were also separated by 45 degrees at the lowest frequencies but they further diverged when the frequency was raised, because of a faster increase in the phase delay in the hand than in the foot. These results indicate that, when the extremities have to be coupled, a nervous compensation is necessary and that it must be different in the two genders. (4) Analysis of the phase-response when limbs were coupled showed that synchrony was approached by two mechanisms: (a) an earlier EMG activation of the hand movers, preferentially utilised by males during in-phase coupling; and (b) a change in the viscoelastic properties of one extremity, which reduces (or eliminates) the difference between their frequency responses as well as between the EMG onsets of hand and foot movers. This second mechanism was utilised by both genders during anti-phase coupling.

Temporal analysis of adaptation in moth (Trichoplusia ni) pheromone receptor neurons.

The temporal pattern of response in chemoreceptor neurons reflects both the temporal distribution of stimuli and the timing of signal transduction, action potential generation and propagation. Here we analyze the temporal characteristics of the responses elicited in pheromone receptor neurons by computer-controlled rectangular pulses of odorant. Extracellular recordings from the HS sensilla trichodea on the antenna of male Trichoplusia ni reveal the activity of two neurons: the "A" neuron, which responds to the major component of the female pheromone blend, (Z)7-dodecenyl acetate and the "B" neuron, which responds to (Z)7-dodecenol. "B" neurons were divided into two classes (HR, LR), based on the magnitude and temporal pattern of their response to (Z)7-dodecenol. Most "A" and HR "B" neurons responded to rectangular pulses of various durations (0.1-40 s) with an initial phasic burst (approximately 100 ms), followed by a slowly declining tonic component. At moderate and elevated pheromone doses, prolonged stimulation resulted in significant reductions in the tonic response levels (adaptation); stimuli of increasing duration effected greater adaptation. Most LR "B" neurons lacked a phasic response component and showed virtually no adaptation with prolonged stimulation. Pheromone receptor neurons may differ in both their spectral and temporal response properties which may provide the animal with additional sensory information for blend discrimination and spatial orientation in complex natural pheromone plumes. The potential functional value of adaptation in the moth pheromone communication system is discussed.

Distribution of radionuclides in the environment in northern Italy after the Chernobyl accident.

Soon after the Chernobyl nuclear accident, the air-pumping stations in Pavia (northern Italy) were alerted. In a few days, a rapid increase in radionuclide concentration in air particulates was observed. Consequently, an environmental radioactivity monitoring programme was started in which several matrices such as soil, grass, vegetables and cows' milk were subjected to direct gamma-ray spectrometry. The radioactivity distribution and its variation with time is presented, discussed and compared with other available data. Detection limits, precision and accuracy are also reported, and depth profiles in soils for 137Cs are presented and correlated with soil quality parameters. A survey of environmental radioactivity in soil, in a search for residual Chernobyl fallout, was carried out and a map of the 137Cs distribution over a large area in northern Italy is presented and discussed.

Adaptation in chemoreceptor cells. II. The effects of cross-adapting backgrounds depend on spectral tuning.

1. The cross-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using NH(4) receptor cells, of known spectral tuning from the lobster (Homarus americanus). 2. Spectrum experiments: The spectral tuning of NH(4) receptor cells was investigated using NH(4)C1 and 7 other compounds selected as the most stimulatory non-best compounds for NH(4) cells from a longer list of compounds tested in previous studies. Based on their responses to the compounds tested, 3 spectral subpopulations of NH(4) Bet cells which responded second-best to Betaine (Bet; and 'pure' NH(4) cells, which responded to NH(4)C1 only (Fig.1). 3. Cross-adaptation experiments: Overall, cross-adaptation with Glu and Bet backgrounds caused suppression of response of NH(4) receptor cells to various concentrations of NH(4)C1. However, the different subpopulations of NH(4) cells were affected differently: (a) The stimulus-response functions of NH(4)-Glu cells were significantly suppressed by both a 3 micrometre (G3) and 300 micrometre (G300) Glu backgrounds. (b) The stimulus-response functions of NH(4)-Bet cells was not affected by a 3 micrometre (B3), but significantly suppressed by a 300 micrometre (B300) Bet background. (c) The stimulus-response functions of pure NH(4) cells were not affected by any of the Glu or Bet back grounds (Figs. 3, 4). 4. The stimulus-response functions of 5 cells from all different subpopulations were enhanced by cross-adaptation with the G300 and B300 back-grounds (Fig 4, Table 1). 5. Whereas self-adaptation caused parallel shifts in stimulus-response functions (Borroni and Atema 1988), cross-adaptation caused a decrease in slope of stimulus-response functions. Implications of the results from cross- and self-adaptation experiments on NH(4) receptor cells, for a receptor cell model are discussed.

Adaptation in chemoreceptor cells. I. Self-adapting backgrounds determine threshold and cause parallel shift of response function.

1. The self-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using lobster (Homarus americanus) NH4 receptor cells. 2. These receptors responded for several seconds to the onset of the backgrounds, and then returned to their initial level of spontaneous activity (usually zero). The strongest response always occurred only during the steepest concentration change; the response then decayed back to zero or to the earlier spontaneous firing level, while the background concentration was still rising, and remained silent during the entire time that the background was maintained constant (20-30 min) 3. Exposure to constant self-adapting backgrounds eliminated the response of NH4 receptor cells to stimuli of concentration lower than the background, and reduced the responses to all higher stimulus concentrations tested by a nearly equal amount. This resulted in a parallel shift of the stimulus-response function to the right along the abscissa. 4. Since the response threshold was completely re-set by adaptation to backgrounds, NH4 receptors seem to function mostly as detectors of relative rather than absolute stimulus intensity across their entire dynamic range: the response to a given stimulus-to-background ratio remained the same over 3 log step increases of background concentration. 5. As in other sensory modalities, a parallel shift of response functions appears to be an important property of chemoreceptor cells, allowing for this sensory system to function over a wider stimulus intensity range than the instantaneous dynamic range of individual receptor cells.

The role of narrowly tuned taste cell populations in lobster (Homarus americanus) feeding behavior.

A whole-animal behavioral assay was developed to measure responses to chemical stimulation of the walking leg (taste) receptors of lobsters. Lesions of only the taste receptors abolished the dactyl clasping response, a result demonstrating that such receptors are necessary to elicit this response. Then the stimulatory effectiveness of natural and synthetic mixtures was determined, particularly of 6 single compounds (glutamate, glutamine, NH4Cl, betaine, aspartate, and taurine) for which the legs have prominent, narrowly tuned receptor cell populations. The results showed that a synthetic mixture of the 22 principal amino acids and amines present in mussel tissue is as powerful a stimulus as either a homogenate of such tissue or its purified extract. Of the single compounds, only NH4Cl was stimulatory at the behavioral level; glutamate was not despite the fact that glutamate receptors are the predominant cell population known in lobster legs. Even a mixture of the 6 single compounds in their natural mixture ratio was not very stimulatory (it was even less stimulatory than the sum of the responses to each single compound), a result suggesting the occurrence of suppressive interactions. The complementary mixture, that is, the synthetic mixture without the 6 single compounds, was equally unstimulatory. It is unlikely that mixture suppression alone is responsible for the poor behavioral responses to single compounds such as glutamate, and to the partial mixtures that were tested. Full response to the more complex mixture of 22 compounds demonstrates that special mixture combinations can "override" mixture suppression. Such signal mixtures may represent the lobster leg's picture of food.