Odor of specific alcohol solutions selectively alters locomotor activity of alcohol-drinking P rats

Ethanol intake in the juvenile, adolescent, and adult rat: effects of age and prior exposure to ethanol

BACKGROUND

Initial ingestion of ethanol by naïve rats has seemed to decrease dramatically with age. During the preweanling period, infant rats consume large quantities of high concentrations of ethanol without initiating procedures, in some instances exceeding doses required for severe motor incoordination. During adulthood, however, initial ingestion of ethanol without initiation procedures is low and infrequent. In the present study, the ontogeny of ethanol intake was measured in juvenile, adolescent and adult rats using a technique [consume off the floor (COF)] similar to that used to study intake during infancy. How this initial experience with ethanol affected subsequent affinity for ethanol intake was later assessed using 2-bottle choice preference tests.

METHODS

Independent ingestion of ethanol was measured at 3 developmental periods, the juvenile period (P22-P28), adolescence (P30-P34) and adulthood (P60-P64), with systematic variation in ethanol concentration (15 or 30% v/v) and palatability (sweetness) of ethanol. Blood ethanol concentrations (BECs) were determined in all animals. This dependent variable served as an estimate of absolute ethanol ingestion. Three COF sessions were conducted for each age group. Following these sessions animals' ethanol consumption was also assessed using a 2-bottle choice test (water vs 15% v/v unsweetened ethanol).

RESULTS

In all experiments, groups consuming 30% v/v ethanol exhibited significantly higher BECs than those exposed to 15% v/v ethanol. Adding saccharin to the ethanol increased absolute ethanol ingestion in only the oldest animals. During the pre-exposure phase (COF sessions) of each experiment, absolute ethanol intake was found to decline with repeated exposures. Sex effects were particularly evident during later stages of ontogeny (adolescents and adults). The overall pattern of results indicated that juveniles relative to adults show a marked predisposition to consume highly concentrated ethanol solutions and that BECs derived from the COF sessions influenced ethanol acceptance patterns in the subsequent 2-bottle test.

CONCLUSIONS

Using the (COF) technique with BECs as an estimate of intake, absolute ethanol consumption seems to be quite high early in ontogeny and decline gradually into adulthood. Adding saccharin to ethanol solutions at the concentration used in the present study (0.1%) was generally not sufficient to increase absolute ethanol intake from the floor, except during adulthood. The experimental strategy employed in this study represents a novel approach for examining ethanol acceptance patterns across ontogeny and how experience with the process of intoxication affects subsequent ethanol preferences.

Craving for alcohol in the rat: adjunctive behavior and the lateral hypothalamus

A review of previous results and the new data in this report show clearly that the Falk model of adjunctive behavior is an adequate analogue of human alcoholism and can be applied to induce excessive ethanol consumption. New data on the consumption of sweet flavored ethanol solutions and, especially, sweet alone solutions during brief periods of ethanol withdrawal provide some significant insights concerning the possible physiological basis for cravings in humans. Because voluntary consumption of ethanol is the normal process by which alcoholism develops, a general set of environmental and other experimental conditions that produce behavioral excess; adjunctive behavior, electrical stimulation of the brain, and salt arousal of drinking are discussed in some detail. Neuronal circuits of the lateral hypothalamus are important because some of the cells are chemosensitive and monitor osmolality of the blood and initiate drinking in the normal regulation of body fluids. Alcohol in very small amounts has a direct effect on these cells that also project to lower spinal motor neurons and modulate the level of excitability in spinal reflexes and thereby reactivity to environmental stimulation. Taste and other sensory information from the mouth arrives in presynaptic endings on these same cells by a multitude of indirect multisynaptic pathways. A theoretical model is developed to explain how tactile and taste sensory information and what is initially a nonspecific general state of motor arousal interact together to produce an excessive consumption or craving for ethanol.

Interactions between perinatal and neonatal associative learning defined by contiguous olfactory and tactile stimulation

Tactile stimulation of the neonate, as performed by the mother during and after delivery, has been described as an effective unconditioned stimulus during early ontogeny (Leon, 1987; Ronca & Alberts, 1994). The present experiments examined the interaction between perinatal and neonatal learning determined by the explicit association between alcohol odor and vigorous body stimulation of the perinatal organism. In Experiment 1, rat fetuses were exposed to either alcohol or saline 10 min prior to cesarean delivery. The alcohol administration procedure here employed was sufficient to provide sensory contamination of the amniotic fluid but avoid fetal alcohol intoxication. Pups in the two prenatal treatments later experienced the smell of alcohol, tactile stimulation, or both stimuli explicitly paired or unpaired. Other postnatal groups were composed of pups that had no explicit experience with either experimental stimulus. Pups subjected to alcohol odor in utero displayed more overall motor activity in response to that odor than saline controls. The increased motor responses were further potentiated in pups that experienced additional postnatal alcohol odor paired with tactile stimulation. In Experiment 2, pups were exposed to alcohol in the amniotic fluid 10 or 30 min prior to birth. As previously demonstrated the memory acquired in utero appears highly dependent upon contingency between exposure to this particular scent and delivery procedures. Pups in both prenatal treatment groups were then exposed to alcohol odor paired or unpaired with tactile stimulation. Some control animals received no further experience with either stimuli. Those pups exposed to alcohol odor paired with tactile stimulation both pre- and postnatally later showed maximum motor activity elicited by the odor of alcohol. The results support the notion of fetal associative learning comprising alcohol's chemosensory cues and behaviorally activating stimuli. Furthermore, the conditioned response under analysis is potentiated whenever neonates are reexposed to contingent presentations of the elements that defined the original associative memory.