GABA receptor-mediated inhibition of reflex deglutition in the cat.

In anesthetized cats, swallowing elicited by electrical stimulation of the superior laryngeal nerves (SLNs) was inhibited by the GABA-mimetic muscimol and by diazepam, an action that was reversed by picrotoxin and bicuculline. This inhibition supports the involvement of GABA receptors, specifically those of the GABAA subtype which both antagonists have been shown to block in various areas of the central nervous system. The inhibition of reflex swallowing and its reversal were unaltered by a transection of the brainstem at a midcollicular level. Stimulation of the SLNs also caused a bradycardia that was inhibited by both muscimol and diazepam and was restored by both GABA antagonists. Data from these experiments provide suggestive evidence for a role of GABA-ergic transmission in the central control of the deglutitory reflex.

Restoration of orbicularis oculi function by contralateral orbicularis oculi innervated muscle flap vs neuromuscular pedicle technique.

In preliminary experiments with dogs and cats, unilateral paralysis of the orbicularis oculi muscle group was produced by a section of the seventh nerve that included the posterior auricular branch. Either one of two procedures was then employed in attempts to reinnervate the paralyzed eyelid. In one group of animals, a neuromuscular pedicle was employed and in another, a contralateral orbicularis innervated muscle flap was used. Both methods restored synchronous, reflex blinking to the denervated eyelid. Of the two procedures, neurotization appears to offer the greater promise because the use of a neuromuscular pedicle requires an expendable nerve that is functional, and no such suitable substitute is available in humans.

Perineurial permeability to sodium during Wallerian degeneration in rat sciatic nerve.

In rat sciatic nerves, the effect of Wallerian degeneration on the rate of transperineurial passage of sodium between the endoneurium and the epineurial extracellular space was investigated. In nerves transected and ligated at the sciatic notch, an in situ technique was used to measure the permeability coefficient-surface area product (PS) of the mid-thigh portion of the perineurium to 22Na. Sampling times ranged from one day to sixteen weeks after the lesion. Additionally, endoneurial water content (an indicator of nerve edema) was also measured in transected, degenerating nerves at the same sampling times. Endoneurial water content increased significantly by the fourth day after transection, peaked at four weeks, and then remained elevated through 16 weeks of post-lesion measurement. The PS of the perineurium to 22Na on the 4th day after transection was significantly greater than that of control animals. This increase then declined to normal levels through the 2nd week, and finally increased to values that were 3-fold to 4-fold of control values for the remainder of the observation period. The earlier, short lasting increase in perineurial PS is probably associated with the inflammatory response to nerve section, and proliferation of perineurial layers and cells. The later increase in perineurial permeability is proposed to play a role in the dissipation of endoneurial hydrostatic pressure and clearance of myelin debris from the endoneurium. In view of the complex changes in perineurial permeability described herein, it would seem inappropriate to consider these phenomena merely as passive breakdowns of the barrier properties of the perineurium.

Interaction between primary afferent nerves in the elicitation of reflex swallowing.

In adult cats anesthetized with urethan, a number of observations were made that support the concept that some control over the rate of reflexly induced swallowing occurs in the intermediate network at the level of the nucleus of the solitary tract. It was shown that different nerves, e.g., the two superior laryngeal and glossopharyngeal nerves, when activated in sequence interact in such a manner as to facilitate reflex swallowing. It was also shown that the decrement in the reflex response observed to continuous stimulation of a primary afferent nerve, e.g., one superior laryngeal, can be reversed by switching the stimulation to another nerve either on the same or contralateral side. And finally, following discrete medullary lesions, it was observed that that portion of the nucleus of the solitary tract located 2 mm or more rostral to the rostralmost point of the dorsal medial sulcus appears to contain an integral component of the intermediate network that governs reflexly induced swallowing, whereas lesions restricted to the ventrolateral portion of the nucleus of the solitary tract have no effect on the reflex response.

Basal forebrain facilitation of reflex swallowing in the cat.

In adult cats anaesthetized with urethane, electrical and chemical stimulation of the basal forebrain facilitated reflex swallowing elicited by electrical stimulation of the superior laryngeal nerve. A systematic stereotaxic mapping study using electrical stimulation revealed that the facilitatory sites were distributed along the course of the ansa peduncularis, specifically its rostral forebrain and hypothalamic components associated with the anterior amygdalar area, substantia innominata, lateral preoptic area, anterior hypothalamus and nucleus accumbens. By means of acute discrete radiofrequency lesions, the descending pathways mediating facilitatory influences from the nucleus accumbens and the amygdala to the brain stem were found to traverse the lateral hypothalamus. Ventral tegmental facilitatory sites in the midbrain are likely to be associated with these descending pathways; however, there is evidence for independent participation of this region of the brain in the control of swallowing. Chemical stimulation by means of microinjections of dopamine and apomorphine into the amygdala and nucleus accumbens also enhanced reflex swallowing. It is concluded that the results of this investigation implicate the basal forebrain as a site of integration of viscero-olfacto-gustatory information needed for the enactment of ingestive behaviour.

The emetic action of L-dopa and its effect on the swallowing reflex in the cat.

In adults cats anesthetized with urethane it was shown that facilitation of reflexly-induced swallowing by dopaminomimetics is caused by a central action independent of the emetic of such drugs. It is suggested that this modulatory influence is mediated by dopamine receptors associated with the amygdala and ventral basal striatum.

Electroencephalographic and behavioral alterations produced by delta-1-tetrahydrocannabinol.

The administration of small doses of Delta(l)-tetrahydrocannabinol to cats with indwelling electrodes produced a disruption of both the electroencephalogram and behavior. Some of these alterations, including the appearance of a high-voltage slow wave electroencephalogram in the awake and moving animal, have been observed in cats that had been administered other drugs known to cause hallucinogenic states in man.