Nora Gray 07
Although Zingiber officinale (ginger) has been used for centuries among Asian cultures as an antiemetic, research directly assessing the effects of this herb in a variety of clinical as well as animal models remains sparse. In those few studies reported, however, ginger has been shown to attenuate symptoms of nausea and vomiting in both clinical and laboratory settings. The senior honors thesis project of Nora Gray evaluated the capacity of ginger to alleviate nausea as measured through an established laboratory paradigm. The efficacy of intragastric (i.g.) ginger to block the formation of a conditioned taste aversion (CTA) was evaluated in intact and vagotomized rats. In Experiment 1 intact rats were exposed to 0.1% saccharin solution in a lickometer for 30 min over 3 consecutive days. After each trial, rats received an i.g. infusion of either a ginger rhizome solution (200 mg/kg) or equivolumetric dH2O as a control, followed by a LiCl injection (3 mEq/kg, i.p.). Thereafter, rats received 3 daily 30-min two-bottle preference tests (dH2O vs. 0.1% saccharin). The control group exhibited classic CTA behavior with a marked decline in saccharin intake across single-bottle tests and a strong preference for water in 2-bottle tests. In contrast, the ginger-treated group showed no decline in saccharin intake and expressed a preference for saccharin in subsequent 2-bottle tests. Ginger treatment also prevented changes in licking microstructure associated with CTA formation: where LiCl treatment increased the proportion of brief (<2s) interlick intervals and decreased the initial rate of licking, average ingestion rate, and mean lick burst size for saccharin in the i.g. water group, these effects were absent in the i.g. ginger group.
To explore neurophysiological underpinnings of this effect, we reasoned that the efferent vagus nerve (which controls gastrointestinal motility) was important in mediating ginger’s anti-emetic effect, as ginger treatment has been shown to alter the rate of gastric emptying, ileal motility, and to induce longitudinal contractions of the guinea pig fundus in vitro. Therefore, for Experiment 2 rats received bilateral subdiaphragmatic vagotomy prior to a replication of Experiment 1. Each rat was anesthetized using a ketamine HCl:xylazine HCl mixture (50:10 mg/kg) and the abdomen was shaved. The rat was then placed on a warm plate and a 1” laparotomy was made on the left side approximately 1” lateral to the midline. The liver and stomach were gently retracted using hooks and clamps so as to visualize the subdiaphragmatic esophagus under a surgical microscope. Approximately 3mm sections of the left and right trunks of the vagus were then teased from the esophagus dorsal to the gastric branches and two 6-0 silk ligatures were applied to each trunk, approximately 2mm apart. Each trunk was then severed between the ligatures using microscissors. The stumps were then glued with cyanoacrylate to prevent regeneration. The stomach and liver were then gently repositioned, the laparotomy sutured, and the rat was placed under a warm lamp until it regained activity.
To confirm the vagotomies, rats were injected with the retrograde tracer FluorogoldTM (0.5mg/12.5μL; Biotium Inc., Hayward, CA) into the abdomen (i.p.). Four intact rats without surgery or testing were also injected, to provide positive control tissue (Figure A). Three days after Fluorogold injection, all rats were anesthetized with an overdose of sodium pentobarbital (100mg/kg) and transcardially perfused with 10% formalin. Brains were kept in 10% formalin for 24 hours and then transferred to a 20% sucrose/formalin solution until sectioning 7-10 days later. Brains were blocked and the hindbrains were sectioned into 50 μm slices and mounted on microscope slides in two series. One series was counterstained in neutral red to facilitate localization of the dorsal motor nucleus of the vagus (mX). The extent of each vagotomy was then evaluated under ultraviolet light using a Zeiss Axioscope with a FITC filter or a Zeiss Pascal confocal microscope. The number of fluorescent cells visible in the mX of vagotomized rats and intact controls was then compared. All intact rats exhibited substantial cell body labeling in mX (more than approximately 30 cells; see Figure B). If no more than 1 labeled cell body was observed in the mX of a vagotomized rat, the vagotomy was deemed successful. Based on this criterion, vagotomies were confirmed in 7 of the 9 rats that underwent fluorogold analysis. Vagotomized rats displayed classic CTA learning regardless of whether they received i.g. ginger or water pretreatment. We concluded that the vagus nerve plays a critical role in mediating the capacity of i.g. ginger to block a LiCl-induced CTA. These results were present by Nora Gray at the Society for Neuroscience meeting in Washington, DC. As a post-script, recent follow-up work in our laboratory has encountered difficulty replicating one of the main findings of the studies above, therefore additional work must be undertaken to explore this discrepancy.