Three-dimensional structure of the gustatory cell in the mouse fungiform taste buds: a computer-assisted reconstruction from serial ultrathin sections

Taste buds in fungiform papillae of the mouse were examined with transmission electron microscopy and computer-assisted, three-dimensional reconstructions from serial ultrathin sections. In accord with observation by Murray (1971), four distinct cell types, type I, II, III and basal cells, were identified. Of these, only the type III cell made synaptic contacts with nerve terminals and contained both small, clear vesicles and dense-cored granules. The former vesicles were synaptic-type and accumulated in the cytoplasm just below the synaptic in membrane thickenings. This finding clearly indicates a sensory function for the type III cell. One to three type III cells were identified within a taste bud. The type III cell had at most eight synapses with nerve terminals. One nerve fiber making two synapses with the type III cell was occasionally observed in its terminal region.     

Selective suppression of judged sweetness by ziziphins

The effects of ziziphins and of control treatments upon judgments by human adults of the sweetness, sourness, bitterness, and saltiness of American apple cider or apple juice were measured with a category estimation method during repeated trials before, during (90 sec treatment duration only), and after, treatment. Sweetness was reduced after either a 10 sec or a 90 sec whole mouth treatment with ziziphins, but not after quinine sulfate or apple juice control treatment. No differences in after-treatment sourness, bitterness, or saltiness occurred between treatments. The reduction in sweetness was weak with 10 sec 3.5% W/V ziziphins treatment, but strong after 90 sec 0.88% W/V ziziphins treatment; duration of suppression was ca. 70 sec. The mechanism was identified as taste modification since adaptation, cross-adaptation, and mixture suppression were eliminated by control treatments and by post-treatment rests and rinse. Comparisons with known gumnemic acids effects suggest that net dissociation of ziziphins from taste receptor membranes and/or inactivation in the membrane may be much faster than with gymnemic acids.     

Ovariectomy fails to affect rats' quinine aversion

Three studies investigated the effects of ovariectomy on the intake of quinine solutions. Despite significant elevations of body weight due to surgery, no change in quinine preference was noted. Varying the age of surgery (prepuberty, postpuberty, and adulthood), age of testing, and time between these events did not alter the basic findings.     

The issue of primary tastes versus a taste continuum

The concept of four primary tastes has been used to direct research and organize data in gustation. The attractive simplicity of this formulation has directed attention away from critical examinations of its validity. The present article shows that arguments used to support the concept of four tastes are equivocal. It is also suggested that the data are more consistent with the hypothesis that gustatory data have a more continuous organization which includes the familiar primary four. Data are considered at the stimulus, receptor, neural, and psychophysical levels.     

Gonadal hormones and behavioral regulation of body weight

Gonadal hormones have important effects on the behaviors that determine body weight in laboratory rats (i.e., eating, locomotor activity, and thermoregulatory behavior). These effects are most evident in the female where there are consistent, predictable changes in these behaviors which are correlated with fluctuations in plasma hormone levels during estrous cycles, puberty, pregnancy, or after gonadectomy and replacement therapy. Estradiol, which seems to be the principal ovarian steroid affecting body weight, may act directly on separate neural loci to: (a) inhibit food intake and (b) stimulate locomotor activity, possibly by lowering the set-point of a hypothalamic lipostat. Estradiol does not affect eating and running in prepubertal female rats, perhaps because of influences of pituitary hormone(s) at this age. Ovarian hormones also alter the taste preferences of rats and may be responsible for the changes in self-selection of dietary components during different reproductive states. Some implications of this research are discussed and possible directions for future research suggested.     

Reduction of learned taste aversions by pre-exposure to drugs

Taste aversions are induced by a variety of psychotropic drugs. In the present experiments taste aversions induced by the barbiturate hypnotic drug, amobarbital, were dramatically reduced by prior exposure to the drug. Increasing numbers of pre-exposures were associated with larger reductions in taste aversions. Reductions in sleeping time (a widely accepted measure of tolerance to barbiturate drugs) were not correlated with reductions in taste aversions. Taste aversions induced by amobarbital were also impaired following pre-exposure to the pharmacologically dissimilar drug d-amphetamine. These results suggest that reduced taste aversions following pre-exposure to drugs may reflect habituation to drug-related stimuli and not solely the development of tolerance to those drugs.Presented in part to the Psychonomic Society, Boston, 1974.     

Using profiles of saccharin and water drinking to detect and discriminate actions of drugs and toxicants

Experiments were conducted to investigate the feasibility of using the pattern of saccharin and water drinking to detect acute and chronic administration of drugs and toxicants. Procedural variables were found to be crucial. When rats were naive for the saccharin drinking fluid, a single injection of LiCl or 2-deoxyglucose produced persistant saccharin aversion. Hypertonic saline produced only a transient saccharin aversion. If rats were pre-exposed to saccharin, the 2-deoxyglucose injection and hypertonic NaCl produced an increase in saccharin drinking but LiCl was without effect. Several types of chronic treatment were given to saccharin-experienced rats. Chronic 2-deoxyglucose, LiCl, and Pb administration produced gradually developing saccharin aversion and qualitatively different patterns of saccharin and water drinking. Chronic administration of hypertonic NaCl or insulin or chronic food deprivation had no impact on saccharin preference. It was concluded that patterns of saccharin and water drinking can be used to detect the administration of a drug or toxicant and perhaps even the time course of action, but may not detect a substance given previous to saccharin, perhaps because the animal cannot associate these now familiar perturbations with the novel saccharin solution. This means that existing toxic states may not be detected by using saccharin preference as a probe.     

Phencyclidine and behavior: I. Sensory-motor function,activity level,taste aversion and water intake

Phencyclidine (PCP) injections in rats at doses of 4 mg/kg increased activity level, which might have been a function of impaired habituation. At doses of 8 mg/kg PCP produced a marked reduction in activity level. At doses of 12 mg/kg and above there were profound disruptive effects in detection of odors, visual square and touch measures, and performance of placing reflexes requiring visuo-motor coordination, righting, grasping reflexes, and equilibrium. Decreases in water intake occurred only at higher dose levels of PCP (16 and 24 mg/kg). On a qualitative basis the changes observed in rats are similar to changes described for humans.     

Antagonism of morphine-induced aversive conditioning by naloxone.

In Experiment 1, 4 doses of morphine and 4 doses of naloxone were tested for their ability to induce a conditioned aversion to saccharin in rats. Morphine was much more potent than naloxone which had only weak effects at the highest dose (12.96 mg/kg). Based on the determinations of Experiment 1, doses of 0.096, 0.96 and 0.6 mg/kg of morphine in a second experiment. The highest dose of naloxone was an effective antagonist of morphine-induced aversion. The antagonism was incomplete, but this may have reflected the particular dose combinations that were employed. Although 12.96 mg/kg of naloxone induced only a weak conditioned aversion to saccharin in Experiment 1, 9.6 mg/kg had a substantial effect in Experiment 2. Thus naloxone was itself an agent of aversive conditioning at a dose which significantly antagonized the aversive effects of morphine. Because of the successful demonstraion of antagonism, it was suggested that there may be common pharmacological mechanisms involved in both positive reinforcement and aversive conditioning by drugs of the opiate class.