Journal of neurophysiology
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Interaction of GABAB-mediated inhibition with voltage-gated currents of pyramidal cells: computational mechanism of a sensory searchlight. J. Neurophysiol. 80: 3197-3213, 1998. ⋯ Hyperpolarizing inhibition removes inactivation of IA to prevent subsequent inputs from driving the cell to threshold. Established depolarizing inputs, having allowed IA to inactivate, enable the cell to be highly sensitive to further depolarizing input. The term "conditional inhibition" is proposed to describe the general phenomenon where synaptic inhibition interacts with voltage-sensitive intrinsic currents.
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Inhibition of calcium currents in rat colon sensory neurons by kappa- but not mu- or delta-opioids. J. Neurophysiol. 80: 3112-3119, 1998. ⋯ Pretreatment with pertussis toxin (PTX) prevented the inhibition by U50,488. These results suggest that kappa-opioid receptors are coupled to multiple HVA Ca2+ channels in colon sensory neurons by a PTX-sensitive G protein pathway. We conclude that inhibition of Ca2+ channel function likely contributes in part to the peripheral analgesic action of kappa-ORAs in visceral nociception.
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Contribution of supragranular layers to sensory processing and plasticity in adult rat barrel cortex. J. Neurophysiol. 80: 3261-3271, 1998. ⋯ Proportionately fewer neurons in layer IV (52 vs. 64%) and in the infragranular layers (55 vs. 68%) exhibited a clear response bias to paired whiskers. We conclude that receptive-field plasticity can occur in layers IV-VI of barrel cortex in the absence of the supragranular layer circuitry. However, layer I-III circuitry does play a role in normal receptive-field generation and is required for the full expression of whisker pairing plasticity in granular and infragranular layer cells.
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Modulation of sacral spinal dorsal horn neurons by the ventrolateral PAG was studied by extracellular recording combined with microiontophoretic applications of alpha-adrenergic agonists or antagonists. Bicuculline (BIC, 15 ng) microinjected into the ventrolateral PAG produced a consistent inhibition of the responses of nociceptive dorsal horn neurons. After PAG-BIC applications, the total number of spikes per heat stimulation period was significantly decreased to a mean of 37 +/- 19% (n = 8) of the pre-BIC control. ⋯ Activation of the alpha1 adrenoceptors by iontophoresis of methoxamine often led to a marked increase in the responses to kainic acid and, to a lesser extent, to NMDA iontophoresis or noxious heat. Together with previously reported work, the current experiments demonstrate that PAG neurons inhibit nociceptive dorsal horn neurons primarily through an indirect alpha2 adrenoceptor mechanism. In this same population of dorsal horn neurons, norepinephrine has a direct alpha1-mediated excitatory effect.
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The cortical processing of vestibular information is not hierarchically organized as the processing of signals in the visual and auditory modalities. Anatomic and electrophysiological studies in the monkey revealed the existence of multiple interconnected areas in which vestibular signals converge with visual and/or somatosensory inputs. Although recent functional imaging studies using caloric vestibular stimulation (CVS) suggest that vestibular signals in the human cerebral cortex may be similarly distributed, some areas that apparently form essential constituents of the monkey cortical vestibular system have not yet been identified in humans. ⋯ Although undetected in previous imaging-studies using CVS, involvement of these areas could be predicted from anatomic data showing projections from the anterior ventral part of area 6 to the inner vestibular circle and the vestibular nuclei. Using a simple paradigm, we showed that GVS can be implemented safely in the fMRI environment. Manipulating stimulus waveforms and thus the GVS-induced subjective vestibular sensations in future imaging studies may yield further insights into the cortical processing of vestibular signals.