Anesthesia of the chorda tympani nerve and taste phantoms.

The chorda tympani nerve innervates the anterior two-thirds and the glossopharyngeal nerve, the posterior one-third, of each side of the tongue. Previous work showed that anesthesia of one chorda tympani increased the perceived intensity of quinine applied to an area innervated by the contralateral glossopharyngeal nerve, but decreased the perceived intensity of NaCl applied to an area innervated by the ipsilateral glossopharyngeal nerve. The data presented here corroborate that earlier finding and show that if both chorda tympani nerves are anesthetized, the taste of quinine is intensified and the taste of NaCl diminished at areas innervated by the glossopharyngeal on both sides of the tongue. In about 40% of the subjects, tastes occurred in the absence of stimulation (we call these tastes phantoms). The phantoms were usually localized to the posterior tongue contralateral to the anesthesia and they were abolished when a topical anesthetic was applied to the area where they were perceived. Phantoms like these may be a source of clinical dysgeusia in patients with localized taste damage. The phantoms may result because the anesthesia releases inhibition normally occurring between the central projection areas of different taste nerves.

Fetal skeletal malformations associated with moderate zinc deficiency during pregnancy.

This study investigated the effects of moderate zinc deficiency on the development of rat fetal skeleton. Eighteen pregnant rats were fed zinc deficient diet (1.3 ppm) from days 3 to 15 of gestation. An additional 18 rats were pair fed the same diet supplemented with 100 ppm zinc and served as controls. The levels of zinc in plasma were determined on days 15 and 20 of gestation and in the amniotic fluid on day 20. The pregnant rats were killed on day 20 and fetuses were cleared and stained with alizarin red. The weight of zinc deficient fetuses was significantly less than that of controls. The uncleared, as well as stained zinc supplemented fetuses, showed no anomalies. The alizarin stained experimental fetuses showed severe anomalies of long bones, vertebrae, and ribs. The overall calcification of bones was also considerably less as compared to zinc supplemented controls. The zinc levels were significantly less in plasma (day 15) and amniotic fluid (day 20) of experimental dams. The results also indicated that although moderate zinc deficiency does not cause external craniofacial malformations, it severely affects the calcification and development of cranial bones.

Effects of a zinc deficient diet upon fluid intake in the rat.

Zinc deficient rats demonstrate an increased intake of sodium chloride (NaCl) containing solutions as compared to normal rats, presumably related to decreased taste acuity. The purpose of this study was to determine if zinc deficient rats would show altered intake of other solutions since changes in NaCl intake may be reflective of serious pathophysiologic processes not related to taste. Eight littermate pairs of inbred Fisher CDF rats, 29 days of age, were divided into two groups and individually housed in stainless steel cages. One group was pair-fed a zinc deficient diet supplemented with ZnSO4, 100 ppm, while the second group was fed the zinc deficient diet, ad libitum. Using a two-bottle preference test, the rats fed the zinc deficient diet showed significantly increased preferences for 5 X 10(-2), 1.5 X 10(-1) and 3 X 10(-1) M NaCl as compared to controls, supporting previous observations. In addition, they showed significantly increased mean preferences for 3.0 X 10(-2) M sucrose, 1.3 X 10(-6) M quinine sulfate and 2.5 X 10(-3) M hydrochloric acid. Analysis of the individual water and fluid intakes showed that the altered preferences were generally the result of increased fluid intake with variable differences observed in water intake. The results demonstrate that zinc deficient rats exhibit altered intake of several different chemical compounds, and support the hypothesis that zinc deficient animals may have alterations in taste acuity.