Oestradiol-induced taste avoidance is the result of a conditioned palatability shift.

Taste avoidances were conditioned in male rats by pairing ingestion of a novel sucrose (0.3 M solution) taste with injections of 17 beta oestradiol (100 micrograms kg-1, s.c.). Following conditioning and prior to a two-bottle choice test (sucrose vs water), taste reactivity responses to three 30 s intraoral sucrose infusions were quantified. A robust conditioned shift in palatability, consisting of reduced ingestive and increased aversive taste reactivity responses, was obtained in the oestradiol group but not the vehicle control group. This conditioned palatability shift was also reflected in subsequent strong avoidance of the sucrose solution in the two-bottle choice test. The findings that oestradiol can condition taste aversions and shift food preferences support a role for oestrogens in the production of anorexia.

Alcohol-induced conditioned taste aversions in chemically labyrinthectomized rats.

Male rats were chemically labyrinthectomized (n = 22) by intratympanic injections of sodium arsanilate, and control rats (n = 15) received intratympanic injections of isotonic saline. All rats were tested for labyrinthine integrity and then adjusted to a 23 h.d-1 water deprivation schedule. Both labyrinthectomized and control rats were exposed to a conditioned taste aversion (CTA) procedure or a control procedure. The CTA technique involved pairing a novel saccharin taste with subsequent intraperitoneal injection of ethanol (1.5 g.kg-1; 15% solution). The control CTA procedure paired a novel saccharin taste with injections of isotonic saline. Following two conditioning trials and 3 d of water only, saccharin preference ratios were obtained in two-bottle choice tests (saccharin vs. water) over 4 consecutive days. Control rats conditioned with ethanol exhibited a strong CTA (p < 0.01) relative to control rats injected with saline. Labyrinthectomized rats drinking saccharin followed by ethanol injections showed a strong CTA (p < 0.01) if conditioning occurred 29-30 d post-labyrinthectomy. However, CTA's were not apparent in labyrinthectomized rats conditioned with ethanol 19 d post-labyrinthectomy. Thus, ethanol-induced CTA formation varied across the post-labyrinthectomy time period.

Reductions in body temperature and spontaneous activity in rats exposed to horizontal rotation: abolition following chemical labyrinthectomy.

The effect of horizontal rotation of male rats (70 rpm) on core temperature and spontaneous motor activity levels was examined. In Experiment 1, subjects were chemically labyrinthectomized (VNX) by intratympanic (IT) injections of sodium arsanilate and control rats (VNS) received IT injections of saline. Half of the rats in each group were subsequently rotated and the other half sham rotated. Measurement of body temperature prior to, immediately after, and 20 min following rotation revealed significant (all p < 0.01) reductions in temperature immediately after treatment, and 20 min later, in VNS rats. Sham-rotated VNS and all VNX rats failed to exhibit any significant changes in temperature following treatment. In Experiment 2, motor activity level was monitored in chemically labyrinthectomized (VNX) and control (VNS) rats prior to, and following, horizontal rotation. The VNS rats exhibited large (all p < 0.01) depressions in measures of horizontal and vertical spontaneous motor activity following rotation treatment, whereas VNX rats exhibited similar levels of activity in the pre- and postrotation period. These experiments show that, as in humans, exposing rats to horizontal rotation results in reduction of body temperature and motor activity, and that these physiological and behavioral changes require a functional vestibular system.