Journal of neurophysiology
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Spinal serotonin is derived entirely from bulbar sources and plays an important role in spinal modulatory processes, including pain modulation. Establishing the electrophysiological properties of SEROTONERGIC bulbospinal neurons in the pontomedullary raphe and reticular formation is critical to understanding the physiological role of serotonin in the spinal cord. Neurons were characterized by their responses to noxious stimulation and their background discharge pattern in the lightly anesthetized rat. ⋯ The probability of misclassification with the use of this discriminant function was estimated to be < 10%. Employing the discriminant function on a test group of cells whose immunochemical content was unknown revealed a population of SEROTONERGIC-LIKE cells that resembled the labeled SEROTONERGIC cells in background discharge pattern, response to noxious stimulation, and nuclear location. The discharge of pontomedullary SEROTONERGIC neurons is slow and steady, suggesting that these neurons may have a role in the tonic, rather than phasic, modulation of spinal processes.
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Clinical Trial
Motor task difficulty and brain activity: investigation of goal-directed reciprocal aiming using positron emission tomography.
Differences in the kinematics and pattern of relative regional cerebral blood flow (rCBF) during goal-directed arm aiming were investigated with the use of a Fitts continuous aiming paradigm with three difficulty conditions (index of difficulty, ID) and two aiming types (transport vs. targeting) in six healthy right-handed young participants with the use of video-based movement trajectory analysis and positron emission tomography. Movement time and kinematic characteristics were analyzed together with the magnitude of cerebral blood flow to identify areas of brain activity proportionate to task and movement variables. Significant differences in rCBF between task conditions were determined by analysis of variance with planned comparisons of means with the use of group mean weighted linear contrasts. ⋯ Differences in unimanual aiming task difficulty lead to dissociable activation of cortical-subcortical networks. Further, these data suggest that when more precise targeting is required, independent of task difficulty, a cortical-subcortical loop composed of the contralateral motor cortex, intraparietal sulcus, and caudate is activated. This is consistent with the role of motor cortex
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The cellular mechanisms that underlie transient synaptic potentiation were studied in visual cortical slices of adult guinea pigs (> or = age 5 wk postnatal). Postsynaptic potentials (PSPs) elicited by stimulation of the white matter/layer VI border were recorded with conventional intracellular techniques from layer II/III neurons. Transient potentiation (average duration 23 +/- 3 min, mean +/- SE) was evoked by 60 low-frequency (0.1 Hz) pairings of weak afferent stimulation with coincident intracellular depolarizing pulses (80 ms) of the postsynaptic cell. ⋯ It did, however, block subsequent enhancement for several cells (2 of 4) that had previously had their inputs potentiated. Moreover, LNA increased the overall average magnitude of synaptic potentiation (with an additional +28%) when induction was successful. These results suggest that endogenous cortical nitric oxide production can both positively and negatively modulate this NMDA receptor-mediated type of synaptic plasticity.
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In our previous study, pairing-induced transient synaptic potentiation in supragranular layers of the visual cortex was described in mature guinea pigs. In the present study, the development of this type of synaptic plasticity and the underlying cellular mechanisms that mediate it were evaluated in animals from postnatal day (PND) 5 to 180. Potentiation is more reliably evoked in younger animals (likelihood: 75%, PND 5-30; 51%, PND > or = 34), and the magnitude of the effect is greater (+40 +/- 3%, mean +/- SE, PND 5-30; +26 +/- 3%, PND > or = 34). ⋯ Synaptic potentiation was prevented (8 of 11 cases) or was replaced by synaptic depression (3 of 11 cells) in experiments in which postsynaptic calcium levels were reduced by intracellular application of 1,2-bis-2-aminophenoxy ethane-N,N,N',N'-tetraacetic acid (BAPTA) in the cortex of young (PND 7-14) animals, or in which the extracellular calcium concentrations was lowered. Inhibition of postsynaptic calcium-induced calcium release blocked synaptic potentiation (4 of 4 cells). Prolonged superfusion (3 h) of the nitric oxide synthase inhibitor L-nitro-arginine (LNA) did not significantly affect the likelihood (in LNA, 81%; 13 of 16 cells), or the magnitude (+38 +/- 7% increase in LNA vs. +40 +/- 3% in control cases) of potentiation, in contrast to its effects in the mature cortex.
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Most communication sounds and most echolocation sounds, including those used by the big brown bat (Eptesicus fuscus), contain frequency-modulated (FM) components, including cyclical FM. Because previous studies have shown that some neurons in the inferior colliculus (IC) of this bat respond to linear FM sweeps but not to pure tones or noise, we asked whether these or other neurons are specialized for conveying information about cyclical FM signals. In unanesthetized bats, we tested the response of 116 neurons in the IC to pure tones, noise with various bandwidths, single linear FM sweeps, sinusoidally amplitude-modulated signals, and sinusoidally frequency-modulated (SFM) signals. ⋯ The SFM-selective neurons in the IC responded to a lower and more limited range of SFM rates than do neurons in the nuclei of the lateral lemniscus of this bat. Because the FM components of biological sounds usually have low rates of modulation, we suggest that the tuning of these neurons is related to biologically important sound parameters. The tuning could be used to detect FM in echolocation signals, modulations in high-frequency sounds that are generated by wing beats of some beetles, or social communication sounds of Eptesicus.