Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Clinical Trial
Luminance neurons in the pretectal olivary nucleus mediate the pupillary light reflex in the rhesus monkey.
In humans and other primates, an increase in luminance in either eye elicits bilateral pupilloconstriction that is essentially equal in both eyes. Current models of the neural substrate for this clinically important light reflex propose that a retinorecipient pretectal nucleus projects bilaterally to the Edinger-Westphal nucleus (EW), which contains the parasympathetic, preganglionic neurons controlling pupilloconstriction. Based on single-unit recording studies in anesthetized cats and rats, it has been further suggested that luminance neurons in only one pretectal nucleus, the pretectal olivary nucleus, mediate this reflex. ⋯ These studies demonstrated that the primate pretectum contains luminance neurons with the characteristics appropriate for mediating the pupillary light reflex and that these neurons are located in one retinorecipient pretectal nucleus, the pretectal olivary nucleus. Electrical microstimulation at the site of these neurons often elicited pupilloconstriction. Our results provide clear evidence for the involvement of the pretectum, and more specifically the pretectal olivary nucleus, in mediating the pupillary light reflex in primates.
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Comparative Study
Early and late stretch responses of human foot muscles induced by perturbation of stance.
In eight subjects standing on a movable platform, surface EMG activity was recorded from the foot muscles extensor digitorum brevis (EDB) and flexor digitorum brevis (FDB) and from the leg muscles soleus (Sol) and tibialis anterior (TA) during perturbations of upright stance. Perturbations inducing foot dorsiflexion (upward tilt and backward translation) evoked a short-latency response (SLR) and a medium-latency response (MLR) to stretch in the physiological extensors FDB and Sol, and a long-latency response (LLR) in the physiological flexors EDB and TA. Perturbations inducing plantar-flexion (downward tilt and forward translation) evoked the MLR in EDB and TA, and the LLR in FDB and Sol. ⋯ All responses were modulated by perturbation type (tilt vs translation) and body posture (normal stance vs forward leaning). Both the large amplitude of the foot muscle responses and their temporal pattern indicate that the muscles acting on the toes play a major role in stabilising posture. Their action increases in amplitude and extends in time the foot-ground reaction force, thereby improving the efficiency of the superimposed action of the leg muscle responses.
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Comparative Study
The expression of different cytochemical markers in normal and axotomised dorsal root ganglion cells projecting to the nucleus gracilis in the adult rat.
Rat lumbar dorsal root ganglion neurones projecting to the nucleus gracilis in the brainstem were retrogradely labelled with Fluoro-Gold and analysed immunocytochemically for their expression of substance P-, calcitonin gene-related peptide-, galanin-, galanin message-associated peptide-, neuropeptide Y-, nitric oxide synthase- and carbonic anhydrase-like immunoreactivity as well as affinity to Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4, RT97 and to choleragenoid. The analysis was made both in uninjured rats and in rats which had been subjected to unilateral sciatic nerve transection and partial resection 3 weeks earlier. The data showed that 6% of the L4 and L5 lumbar dorsal root ganglion cells that projected to the nucleus gracilis showed substance P-like immunoreactivity. ⋯ Choleragenoid-like immunoreactivity was found in 99% of the Fluoro-Gold-labelled dorsal root ganglion cells normally and 81% after injury. Immunohistochemical visualisation of choleragenoid transganglionically transported from the injured sciatic nerve combined with neuropeptide Y immunocytochemistry showed that primary afferent fibres and terminals in the nucleus gracilis contain neuropeptide Y following peripheral nerve transection. Taken together, the results indicate that peripherally axotomised nucleus gracilis-projecting neurones undergo marked alterations in their cytochemical characteristics, which may be significant for the structural and functional plasticity of this system after injury.
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We studied changes in retinogeniculate transmission that occur during variation of modulatory brainstem input and during variation of stimulus contrast. Responses of single cells in the dorsal lateral geniculate nucleus (dLGN) to a stationary flashing light spot of varying contrast were measured with and without electrical stimulation of the peribrachial region (PBR) of the brainstem. PBR stimulation increased the contrast gain (slope of response versus contrast curve) and the dynamic response range (range between spontaneous activity and maximal firing). ⋯ PBR stimulation increased the transfer ratio, particularly at moderate input firing rates. The increased transfer ratio, caused by increasing input firing rates, enhanced the response versus contrast characteristics through an increase in contrast gain and dynamic response range. The modulatory input from the PBR further enhanced these characteristics.
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The flow of information in the sensorimotor cortex may determine how somatic information modulates motor cortex neuronal activity during voluntary movement. Electrophysiological recordings and neuroanatomical tracing techniques were used to study the connections between the primary somatosensory cortex (SI) and the vibrissal representation of the primary motor cortex (MI) in rodents. Intracortical microstimulation (ICMS) was applied to the vibrissal region of the motor cortex to identify a site from which stimulation evoked movements of the vibrissae. ⋯ A single narrow column of labeled fibers was found in the motor cortex following such injections. Thus, the sensory cortex appears to relay somatic information from the vibrissae to restricted regions of the motor cortex in a somatotopically organized manner. Furthermore, the stimulus-evoked whisker movements suggest that certain features of the output map of the motor cortex are discretely organized.(ABSTRACT TRUNCATED AT 400 WORDS)