Kenneth V. Anderson

Jaw depression elicited by tooth pulp stimulation.

Abstract Stimulation of tooth pulpal nerves in both anesthetized and alert cats elicited a vigorous jaw depression reflex. The threshold for jaw depression in the chronic preparation remained stable for as long as 4 months. Disappearance of the jaw depression response following endodontic therapy indicated that the response was not caused by spread of current to extrapulpal nerve fibers. Strength-duration curves were plotted for the jaw depression reflex and were found to vary with the depth of anesthesia. The jaw depression response followed stimulation frequencies of 13–23 cycle/sec in both the alert and anesthetized animals. Summation of the sensory input from the two upper canine teeth was demonstrated in all acute preparations.

Photically evoked responses in the visual system of rats exposed to continuous light

Abstract The influence of environmental light on the cyclicity of brain amines and neuroendocrine function of animals is most likely mediated through the retina and higher visual centers, and constant illumination modifies some aspects of this cyclicity. The photoreceptor cells in the retina of albino rats selectively degenerate after exposure to continuous, low intensity, fluorescent illumination at normal body and room temperatures, while cyclic light has no effect. Damage to the outer segments of these cells can be detected during the first 4 days of constant light exposure. By 14 days of exposure, most of the receptor cells are destroyed, especially in the posterior part of the retina. After 30 days of exposure, normal receptors are completely absent. The pigment cell layer and the innermost layers of the retina are not damaged by this treatment. The functional integrity of the visual system of rats with degenerated photoreceptors was assessed by examining the characteristics of photically evoked potentials in the optic tract, lateral geniculate nucleus, and visual cortex. Evoked responses in the visual system of rats that had been exposed to 4 days of light varied according to the recording site and were typically of low amplitude and had long latencies of onset. Only responses of low amplitude and with long latencies were recorded after 14 days of exposure, and no photically evoked potentials could be recorded from the optic tract and lateral geniculate nucleus. Similar responses were recorded in the visual system of rats exposed to 30 days of light, although, more commonly, no potentials could be evoked by flash stimuli. The limited retinal degeneration described, resulting from exposure of rats to low intensity illumination, provides a model for examining visual function in the absence of photoreceptor cells in the retina, but without apparent damage to other cellular components of the system.

Black-white and pattern discrimination in rats without photoreceptors

Abstract The discrimination performance of rats whose retinas lacked receptor cells was compared with the performance of normal, control rats. Retinal degeneration was produced by exposing animals to 30 days of constant light at 18 ft-c intensity. Both control rats and those with retinal degeneration were trained and tested in a T-maze on a black-white discrimination and two pattern discriminations. In the pattern tasks, the discriminanda consisted of targets with alternating black-and-white stripes oriented either horizontally or vertically. In the easier pattern discrimination the black-and-white stripes were 0.8 cm wide and in the more difficult pattern task they were 0.4 cm wide. The general finding was that rats without receptor cells were not impaired on any of the discrimination tests used in this experiment, but could readily perform at high levels on both black-white and pattern tasks. They could not only retain a visual habit learned prior to the degeneration, but could learn new discriminations at rates indistinguishable from control animals. The results strongly suggest that retinal elements other than receptor cells are sensitive to light.

Photoreceptor degeneration after exposure of rats to incandescent illumination

SummaryThe retina of the albino rat undergoes degenerative changes when exposed to low intensity incandescent light. The retinal degeneration is limited specifically to the photoreceptor cells, and the pigment epithelium is unaffected. Early changes in the receptors included fragmentation of the inner and outer segments and pyknosis of the receptor cell nuclei. Phagocytic cells invaded and occupied the central retinal area of degeneration, between the receptor layer and the pigment epithelium, in the 4 and 5 day exposure periods. They were absent centrally after 14 and 30 days of exposure, but were present at these time periods in the peripheral retina, where photoreceptor destruction was still in progress. The destruction of photoreceptor cells, including the receptor and outer nuclear layers of the retina, by incandescent light progressed at a slightly reduced rate as compared to that after exposure to fluorescent light of the same intensity. These experiments indicate that exposure to either low intensity incandescent or fluorescent light will cause a selective degeneration of retinal photoreceptor cells, and therefore provide an easily reproducible model for the study of retinal structure and function in the absence of the receptors.

Transmedian innervation of canine tooth pulp in cats

Abstract The present study was designed to determine the extent to which the pulpal nerves of teeth in the cat receive a bilateral innervation from first order trigeminal afferent fibers. Bipolar electrodes were implanted into the predentin of upper and lower canine and premolar teeth on both sides of the jaw and into the left and right trigeminal nerves. Stimulation of the pulp of single canine teeth was found to evoke large-amplitude, short-latency responses in both the right and left trigeminal nerves. Conversely, stimulation of the trigeminal nerve on one side led to evoked responses in all canine teeth. The conduction velocities were similar for ipsilateral and contralateral responses. Bilateral responses were not observed when stimulating or recording from premolar teeth. These findings indicate the existence of an extensive transmedian innervation of the teeth in the cat; an innervation which extends at least as far laterally as the first premolar teeth and which is particularly dense in the canine teeth.

Response patterns of cells in the feline caudal nucleus reticularis gigantocellularis after noxious trigeminal and spinal stimulation

Abstract Nucleus reticularis gigantocellularis has been shown, using both behavioral and physiological techniques, to be involved in the processing of nociceptive information in spinal systems. This investigation was designed to characterize the response patterns of nucleus reticularis gigantocellularis neurons to both spinal (superficial radial and sciatic nerve) and trigeminal (tooth pulp) noxious stimuli. One hundred and sixty-two neurons were studied using a poststimulus-time histogram analysis. Neurons in nucleus reticularis gigantocellularis were classified in four categories based on their responses to noxious stimuli: (i) 51% of the neurons responded to noxious stimuli delivered to all stimulus sites noted above with a short-latency, short-duration excitatory period, followed by a long-duration period of suppressed activity relative to control levels (“E-S cells”); (ii) 25% of the neurons studied responded to all noxious stimuli tested only with an excitatory response (“E cells”); (iii) 6% of the neurons responded to all noxious stimuli only with a period of suppressed activity (“S cells”) (some S cells had a period of increased activity after the period of suppression); (iv) 18% of the neurons had mixed responses, with the response depending on the site of stimulation (“M cells”). Except for M cells, each cell tended to respond with a characteristic response pattern, regardless of the site of stimulation.

Retinal degeneration produced by low-intensity colored light

Abstract The high-energy wavelengths of visible light were primarily responsible for light-induced retinal degeneration in the albino rat. Light of wavelengths passing through a blue filter were most effective in damaging photoreceptors.

Interaction of tooth pulp and periodontal ligament receptors in a jaw-depression reflex

Abstract Bipolar electrodes were implanted in the periodontal ligament space of the upper right and left canine teeth in eight cats to permit activation of periodontal ligament receptors, and in the predentin of each of these teeth, to permit activation of the pulpal nerves. Electrical stimulation of the periodontal ligament receptors of either canine tooth elicited a vigorous jaw-depression reflex. Tooth movement, which is known to stimulate the jaw-depression reflex, was completely avoided in this study. Summation of the sensory input from the two upper canine periodontal ligaments was demonstrated in every animal. In addition, summation was demonstrated between periodontal ligament receptors and tooth pulpal nerves.

The origin of spontaneous, rhythmic potentials in the visual system of rats

Abstract Spontaneous, rhythmic potentials recorded from the visual system of intact rats were compared with those recorded from enucleated rats and from rats with retinal degeneration. Three kinds of rhythmic potentials were recorded in intact rats anesthetized with pentobarbital or phenobarbital. The most predominant potential had a frequency of 10–25 cycle/sec and could be recorded from the optic tract (OT), lateral geniculate nucleus (LGN), and visual cortex (VC). A second kind of potential had a frequency of 100–150 cycle/sec and was most commonly found in the OT and LGN. The third kind of potential had a frequency of 0.3–0.5 cycle/sec and was restricted almost exclusively to the VC. The exact frequency and shape of the rhythmic potentials were found to depend upon the level of anesthesia and, to some degree, upon the lighting conditions present at the time of recording. No rhythmic potentials were found in enucleated rats. In rats with moderate retinal degeneration, spontaneous, rhythmic potentials were abolished or markedly disrupted. In rats with severe retinal degeneration, spontaneous, rhythmic potentials were completely absent. These results indicate that rhythmic, oscillatory potentials in the visual system of the rat originate in the retina.

Altered response latencies on visual discrimination tasks in rats with damaged retinas

Abstract The discrimination performance of rats whose retinas have no apparent receptor cells was compared with the performance of normal, control rats. Retinal degeneration was produced by exposing animals to 30 days of constant illumination at 18 ft-c (184 lux) intensity. Both control rats and those with retinal degeneration were trained and tested in a T-maze on a black-white discrimination. In the pattern task, the discriminanda consisted of targets with alternating black-and-white stripes (0.4 cm wide) oriented either horizontally or vertically. For each animal two measures were used to assess visual performance: the percentage of correct responses to the visual targets and the time taken to make a choice (latency of response). The results showed that latency of response was a more sensitive indicator of retinal damage than was the percentage of correct responses made on the visual task. The results confirmed the findings in previous studies that rats could not only retain a visual habit learned prior to the retinal degeneration, but could learn new discriminations after the retinas were damaged. The extent to which experimental design factors and other variables may influence the kind of results obtained in experiments with retinally damaged rats was discussed.