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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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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These experiments describe the responses of myelinated skin and muscle afferent nerve fibres at a neuroma to stretch, local pressure and vibration in the anaesthetised cat. The sural nerve and the nerve supplying the medial gastrocnemius were studied. Neuroma formation was encouraged by placing the cut end of the nerve in a cuff made of synthetic material (Gore-tex). ⋯ This result suggests that the disruption of orthograde axonal transport by colchicine leads to development of mechanically sensitive areas in axons further back from their cut ends. Local application of the drugs succinyl choline, tetra-ethyl ammonium and gadolinium had no effect on levels of resting activity or on mechanical sensitivity of afferents in the cuff. The potassium channel blocker 4-aminopyridine, on the other hand, produced an increase in the levels of resting activity and in the stretch responses of afferents.(ABSTRACT TRUNCATED AT 400 WORDS)
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In brainstem-spinal cord preparations isolated from newborn rats, intrinsic burst-generating properties of preinspiratory (Pre-I) neurons in the rostral ventrolateral medulla, which have been suggested to be primary respiratory rhythm-generating neurons, were studied by "perforated" whole-cell recordings using the antibiotic nystatin. Nystatin causes small pores to be formed in the cells, through which pass small monovalent ions. For blockade of chemical synaptic transmission, perfusate Ca2+ concentration was lowered to 0.2 mM and the Mg2+ concentration was increased to 5 mM. ⋯ In low Ca, burst-type neurons (n = 3) were also silent with 1 microM TTX perfusion. Inspiratory neurons either became silent (n = 4) or fired tonically (n = 1) in low Ca. The present study by "perforated" whole-cell recordings confirmed that some Pre-I neurons possess intrinsic burst-generating properties, which were not attributable to phasic synaptic inputs.