Neuroscience letters
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Neuroscience letters · May 2004
Methodologic factors which contribute to variations in experimental pain threshold reported for older people.
Using the same study groups and psychophysical methods, we have tested the hypothesis that variations in pain threshold with advancing age are best explained by variations in stimulus duration. Fifteen young adults and 15 older people without clinical evidence of neurologic disease or psychologic dysfunction had pain thresholds determined with heat and electrical stimuli using the method of limits; for electrical stimulation a double random staircase design was used. ⋯ It was found that older people have an increased threshold for thermal and electrically induced pain if the stimulus duration is kept short. This result explains much of the variability in age associated pain threshold in the literature.
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Spatial integration of cold pressor pain (CPP) in the hand was studied in healthy human subjects by measuring the latency to the ice water-induced first pain sensation with and without conditioning CPP. CPP alone showed a marked spatial summation effect. ⋯ A decrease in the test stimulus area increased the suppressive effect by conditioning CPP. Thus, CPP shows spatial summation or inhibition depending on experimental parameters.
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Neuroscience letters · May 2004
Single-trial detection of human brain responses evoked by laser activation of Adelta-nociceptors using the wavelet transform of EEG epochs.
The aim of this study was to identify EEG changes induced by Adelta-nociceptor activation in single trials. In a preliminary experiment, intense CO(2) laser stimuli were delivered to the hand dorsum of five volunteers. The average amplitude of EEG epochs was estimated in the time-frequency (TF) domain using the continuous Morlet wavelet transform (CMT). ⋯ After applying the TF filter, amplitudes within a predefined interval were summed. Whether this sum predicted the occurrence of Adelta-nociceptor activation was tested using the reaction-time to discriminate between Adelta- or C-fibre mediated detection. Results showed that this method accurately identified single-trial EEG responses to Adelta-nociceptor activation.
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Neuroscience letters · May 2004
Selective C-fiber deafferentation of the spinal dorsal horn prevents lesion-induced transganglionic transport of choleragenoid to the substantia gelatinosa in the rat.
The effect of neonatal capsaicin treatment, producing selective elimination of almost all unmyelinated C-fiber sensory axons, was studied on lesion-induced transganglionic labelling of the substantia gelatinosa of the spinal cord by choleragenoid. In both control and capsaicin-pretreated rats, the injection of choleragenoid-horseradish peroxidase conjugate into the intact sciatic nerves resulted in intense labelling only of the deeper layers of the spinal dorsal horn. In the control but not the capsaicin-pretreated rats, the injection of the tracer into sciatic nerves transected 2 weeks previously produced an intense homogeneous labelling of the substantia gelatinosa. It is concluded that the uptake and axonal transport of choleragenoid by capsaicin-sensitive C-fiber afferents may be accounted for by the lesion-induced transganglionic labelling of the substantia gelatinosa, rather than by A-fiber sprouting.
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Neuroscience letters · May 2004
Longterm stability and developmental changes in spontaneous network burst firing patterns in dissociated rat cerebral cortex cell cultures on multielectrode arrays.
Spontaneous action potentials were recorded longitudinally for 4-7 weeks from dissociated rat occipital cortex cells cultured on planar multi-electrode plates, during their development from isolated neurons into synaptically connected neuronal networks. Activity typically consisted of generalized bursts lasting up to several seconds, separated by variable epochs of sporadic firing at some of the active sites. ⋯ These findings indicate that after about a month in vitro these cultured neuronal networks have developed a degree of excitability that allows almost instantaneous triggering of generalized discharges. Individual neurons tend to fire in specific and persistent temporal relationships to one another within these network bursts, suggesting that network connectivity maintains a core topology during its development.