Evidence Against Amplification of Four Genes in Giant Cells Induced by Meloidogyne incognita

Giant-cell DNA was isolated from pea (Pisum sativum) inoculated with Meloidogyne incognita and used in slot blots to test for selective sequence amplification. Four sequences representing low (ribulose 1,5-bisphosphate carboxylase and actin), mid-level (histone 3), and highly repetitive (large ribosomal repeat) sequence DNA were used as probes. Known amounts of root-tip DNA and giant-cell DNA were blotted onto hybridization membranes and probed. The signal strength on autoradiographs containing equal amounts of root-tip DNA and giant-cell DNA were compared with a scanning densitometer. No difference in signal strength between equal amounts of root-tip DNA and giant-cell DNA was found. Thus, for the probes tested, there is no difference in copy number and, hence, no selective DNA sequence amplification has occurred.     

Effects of chorda tympani nerve anesthesia on taste responses in the NST

Human clinical and psychophysical observations suggest that the taste system is able to compensate for losses in peripheral nerve input, since patients do not commonly report decrements in whole mouth taste following chorda tympani nerve damage or anesthesia. Indeed, neurophysiological data from the rat nucleus of the solitary tract (NST) suggests that a release of inhibition (disinhibition) may occur centrally following chorda tympani nerve anesthesia. Our purpose was to study this possibility further. We recorded from 59 multi- and single- unit taste-responsive sites in the rat NST before, during and after recovery from chorda tympani nerve anesthesia. During anesthesia, average anterior tongue responses were eliminated but no compensatory increases in palatal or posterior tongue responses were observed. However, six individual sites displayed increased taste responsiveness during anesthesia. The average increase was 32.9%. Therefore, disinhibition of taste responses was observed, but infrequently and to a small degree in the NST At a subset of sites, chorda tympani-mediated responses decreased while greater superficial petrosal-mediated responses remained the same during anesthesia. Since this effect was accompanied by a decrease in spontaneous activity, we propose that taste compensation may result in part by a change in signal-to-noise ratio at a subset of sites.