Bruce P. Halpern

Sensitivity and Behavioral Responses to the Pheromone Androstenone Are Not Mediated by the Vomeronasal Organ in Domestic Pigs

Based largely on results of studies of laboratory rodents, the vomeronasal or accessory olfactory system is believed to function mainly in social communication, mediating the effects of stimuli such as urine or glandular secretions on the behavior or endocrine response of conspecifics. In the domestic pig (Sus scrofa), the steroid androstenone has been identified as a pheromone that facilitates expression of both attraction to the male and a receptive mating stance in estrous females. Though the domestic pig is one of the few vertebrate species in which the identity of a compound that functions as a pheromone is known, the role of the vomeronasal system in domestic pigs has never been investigated. We have examined the role of the vomeronasal organ in mediating the pheromonal effects of androstenone in pigs. In addition, we have examined the structure of the vomeronasal organ at the gross and light-microscopic levels. The vomeronasal organ appears functional, with sensory epithelium lining the medial wall, and has access to stimuli from both the oral and nasal cavities. To determine whether the vomeronasal organ is necessary for androstenone detection or attraction or receptive behavior in female pigs, access to the vomeronasal organ was blocked with surgical cement, and androstenone detection threshold and sexual behavior were measured. Experimental animals did not differ significantly in androstenone sensitivity, measured behaviorally, from untreated controls. Vomeronasal organ-blocked animals also did not differ from untreated controls in either androstenone-mediated receptive standing behavior or attraction to the odor of androstenone. We conclude that in the domestic pig, the vomeronasal organ is not necessary for androstenone detection or androstenone-mediated sexual behavior in estrous females.

Taste Stimuli: Quality Coding Time

Rats conditioned to avoid drinking 300 millimolar NaCl recognized and rejected this solution within 250 to 600 milliseconds of onset of stimulus, a period containing the phasic portion of the peripheral neural response. They generalized to 500 millimolar NaCl but not to 500 millimolar sucrose. Rejection was based on quality identification neurally encoded within this brief period.

Taste Stimuli: A Behavioral Categorization

The selective patterns of generalization to various chemicals, obtained in rats after radiation-induced gustatory-avoidance conditioning against single chemicals, were used to evaluate qualitative similarities among taste stimuli. DL-Alanine, glycine, and sodium saccharin were classed together, but not with D-glucose or potassium chloride. Groupings such as these may serve as a basis for determining the dimensions along which taste quality is represented.

Enhancement of taste intensity through pulsatile stimulation

Abstract Human magnitude estimates of a 500 mM NaCl solution increased with time when alternating pulses of NaCl and H 2 O (2 sec-2 sec to 1 sec-1 sec) were deliverd to the tongue, but decreased with a continuous NaCl flow. Normal human drinking, and intermittant liquid intake in other species, may be similar enhancement situations.

Human taste perception

The recent literature in human taste research is critically reviewed. Special emphasis is placed on the qualities of taste and on taste intensity measurements. The underlying theme throughout the review is taste research methods. Phenomena receiving special attention are taste adaptation and taste mixtures.

Amiloride and vertebrate gustatory responses to NaCl

Amiloride at < or = 1 microM may block epithelial Na+ channels without affecting other cellular mechanisms, and attenuates gustatory responses to lingual NaCl from the chorda tympani nerves (CT) of gerbil, hamster, rhesus monkey, and several strains of laboratory rat and mouse, and from glossopharyngeally innervated frog taste-receptor cells; at 5 microM to 50 microM, also from Wistar rat and mongrel dog CT. Affected units responded more to NaCl than to KCl. Suppression of CT responses to KCl, HCl, NH4Cl, or saccharides also occurred in some mammals, but amiloride did not elicit responses. Taste-dependent behaviors towards NaCl or KCl were altered. DBA and 129/J laboratory mice, and mudpuppy, were unaffected by amiloride. In humans, 10 microM amiloride both produced taste reports and reduced total intensity of NaCl and LiCl by 15-20%. NaCl and LiCl sourness, and KCl and QHCl bitterness declined, but saltiness generally did not change. Effects on sweetness were inconsistent. Amiloride-sensitive gustatory mechanisms were prominent in some mammals, were not necessary for responses to NaCl, and were of minor importance for human taste.

Functional Anatomy of the Tongue and Mouth of Mammals

The static and dynamic characteristics of the jaws, tongue, and other structures surrounding the oral cavity of mammals strongly affect the types of environments in which a particular mammal can successfully function. A highly specialized mouth and tongue, such as that noted in anteaters by Sonntag (1925), is an extreme example of an ingestive apparatus that sets very narrow limitations on usable habitats. With reference to the primary focus of this chapter, liquid ingestion, less dramatic but equally significant constraints are found in adult animals unable to suck liquids, presumably because of their mouth characteristics. (See pp. 62–80, Drinking Behavior, especially p. 72 and Table 4). A specific liquid intake and intraoral manipulation mechanism may have great adaptive advantage for a given ecological niche. However, the possibility of evolutionary modification in the event of major, relatively rapid changes in habitat may be greatly reduced. Nonspecialized omnivores, having ingestive apparatus usable with a wide range of foods and liquid sources, avoid these problems, as Hiiemae and Crompton (1971) and Jolly (1972) have noted. It may be that omnivores may not be able to exploit some habitats as efficiently as specialized feeders.

Centrifugal control of gustatory responses.

Abstract The effect of gastric distention upon responses to lingual stimulation with NaCl, quinine hydrochloride and dextrose was recorded from a glossopharyngeal nerve of toads. The multiunit neural responses were quantified with a digitallized electronic summator. Maximum response magnitude, time to maximum, and magnitude at 10 sec after maximum were measured. With both glossopharyngeal nerves intact, maximum magnitude increased for NaCl during distention, decreased with quinine hydrochloride, but did not change for dextrose. No significant changes in rise or fall times occurred. After both glossopharyngeal nerves were mechanically blocked, gastric distention produced no changes in magnitude or time course of responses. It is hypothesized that these effects of gastric distention may modify gustatory selection of food intake.

Taste Stimuli: Time Course of Peripheral Nerve Response and Theoretical Models

The responses of a taste nerve in rats to sodium chloride were integrated over successive 10-millisecond intervals and averaged. The time course of the mean responses consisted of a 30-millisecond latency, a rapid rise to a maximum, and a slower decline to a sustained level. The chemoreceptor theories of Beidler and Paton failed to predict the relation between phasic response and time or concentration.

Effect of Vitamin A Deficiency on Taste.

Summary Rats in the advanced stages of vit. A depletion showed abnormal taste responses. A marked decrease in rejection of quinine and selection of NaCl solutions occurred. Administration of vit. A resulted in rapid recovery of NaCl selection but not of quinine rejection. These data suggest that vit. A may have a direct effect on the functioning of the taste cells.