Experimental neurology
-
Experimental neurology · Sep 1988
Properties of functionally identified nociceptive and nonnociceptive facial primary afferents and presynaptic excitability changes induced in their brain stem endings by raphe and orofacial stimuli in cats.
The activity of 221 single primary afferent units was recorded extracellularly in the trigeminal (V) ganglion of chloralose-anaesthetized cats to examine the receptive field properties of nonnociceptive and nociceptive cutaneous afferents and the effect of conditioning stimulation of the raphe system and orofacial afferents on the antidromic excitability of their brain stem endings in V subnucleus caudalis. In addition to slowly adapting and rapidly adapting low-threshold mechanosensitive afferents, we functionally identified three classes of cutaneous nociceptive afferents: these included A-delta high-threshold mechanoreceptive afferents (A-delta HTMs), C-fiber high-threshold mechanoreceptive afferents (C-HTMs), and C-polymodal nociceptive afferents (CPNs). ⋯ We noted that orofacial conditioning stimulation could produce an increase in antidromic excitability which was considered a reflection of primary afferent depolarization (PAD) in both nociceptive and nonnociceptive afferents innervating the cat's facial skin; nonnoxious mechanical stimuli and electrical stimuli were particularly effective in the low-threshold mechanosensitive afferents and noxious mechanical and high-intensity electrical stimuli were especially effective in the cutaneous nociceptive afferents. Raphe conditioning stimulation also was very effective in inducing PAD in these nociceptive afferents; however, the raphe conditioning effects were not limited to these nociceptive afferents since PAD was also frequently demonstrated in the low-threshold mechanosensitive afferents.
-
Experimental neurology · Jan 1987
Comparative StudyTooth pulp-evoked activity in the spinal trigeminal nucleus caudalis of cat: comparison to primary afferent fiber, reflex, and sensory responses.
Tooth pulp-evoked single-neuron responses were recorded in the spinal trigeminal nucleus caudalis of the cat. The thresholds to monopolar electric pulses of various durations (0.2 to 20 ms) were determined using a constant current stimulator. With stimulus pulse durations of 10 to 20 ms, the thresholds were comparable with those of primary afferent A-fibers, although the most sensitive primary afferent fibers had lower thresholds. ⋯ The results indicate that the activation of postsynaptic trigeminal neurons requires a considerable temporal summation of primary afferent impulses. The jaw reflex thresholds cannot be explained by the properties of the neurons in the subnucleus caudalis of the trigeminal tract. The results support the concept that dental pain is based on the activation of spinal trigeminal nucleus caudalis neurons receiving their input from intradental A-fibers.
-
Experimental neurology · Apr 1986
Histopathologic evaluation of prolonged intracortical electrical stimulation.
Chronic stimulating microelectrodes fabricated from platinum-30% iridium (Pt-30%Ir) or activated iridium were implanted in assemblies of three in the left sensorimotor cortex of the cat and pulsed continuously at currents of 10 to 320 microA (100 to 3200 microC/cm2 X ph, 2 to 64 nC/ph) for periods of 24 h or for 23 h/day for 7 days. The microelectrodes had beveled tips with uninsulated geometric surface areas of 20 X 10(-6) cm2. Neuronal activity evoked by the focal stimulation was monitored by recording compound action potentials from the ipsilateral pyramidal tract. ⋯ Electrode dissolution appears to be best correlated with charge density and current density. Dissolution of the Pt-30%Ir microelectrode tip was observed by scanning electron microscopy at charge densities as low as 200 microC/cm2 X ph (1 A/cm2), whereas erosion of activated iridium microelectrodes occurred only at the highest charge and current densities (3200 microC/cm2 X ph, 16 A/cm2). Thus, the activated iridium electrode is superior to Pt-30%Ir for chronic stimulations, from the standpoint of electrode tip stability, because with the former, in contrast to the alloy, detectable erosion occurred only at an intensity well above that required for activation of nearby neurons.
-
Experimental neurology · Apr 1986
Respiratory functions of the inferior pharyngeal constrictor and sternohyoid muscles during sleep.
We studied the respiratory activity of the inferior pharyngeal constrictor and sternohyoid muscles of the rat during non-rapid eye movement (non-REM) and REM sleep. Each animal carried chronically implanted electrodes for recording the integrated EMG activity of respiratory muscles as well as the electrocorticogram (ECoG) and postural tone (dorsal neck EMG). The latter permitted polygraphic identification of sleep states. ⋯ During REM sleep, the inferior pharyngeal constrictor and sternohyoid muscles retained their inspiratory activity. No tonic activity could be detected in either muscle. We conclude that the inferior pharyngeal constrictor and sternohyoid muscles safeguard upper airway patency in the two main sleep states.
-
Experimental neurology · Aug 1985
Reversal of deficits in axonal transport and nerve conduction velocity by treatment of streptozotocin-diabetic rats with myo-inositol.
This study examined the effects of myo-inositol treatment on the deficits of motor nerve conduction velocity and of axonal transport of choline acetyltransferase in rats with streptozotocin-induced diabetes. Motor nerve conduction velocity was measured in seven groups of male rats. Two groups formed nondiabetic controls; one survived for 3 and the other for 6 weeks, then motor nerve conduction velocity was again measured and the accumulation of choline acetyltransferase activity proximal to a 24-h sciatic nerve constriction was estimated. ⋯ At death, choline acetyltransferase accumulation was measured and the remainder of the sciatic nerves was assayed for sorbitol and myo-inositol. In the two untreated diabetic groups we found reduced motor nerve conduction velocity, a deficit in the accumulation of choline acetyltransferase proximal to the sciatic nerve constriction, and a marked build-up of nerve sorbitol and a depletion of nerve myo-inositol. All three treated groups showed a reversal of this myo-inositol depletion without a reduction in the nerve sorbitol content.(ABSTRACT TRUNCATED AT 250 WORDS)