Neil E. Grunberg

The effects of nicotine and cigarette smoking on food consumption and taste preferences

Habitual cigarette smokers generally have lower body weights than comparably aged nonsmokers. In addition, habitual smokers who abstain from smoking often increase in body weight. Both psychological and physiological explanations have been suggested to account for this phenomenon. However, in the literature, there is no convincing research reason to prefer any of the alternatives. The effects of nicotine and cigarette smoking on food consumption and taste preferences are examined in rats and humans. For both species nicotine administration/cigarette smoking is accompanied by a decreased consumption of sweet-tasting high caloric foods. Consumption of other foods does not change. These findings may help to explain the changes in body weight which accompany cigarette smoking.

Effects of nicotine on body weight and food consumption in rats

Recent human and animal studies have found that cigarette smoking or nicotine administration is accompanied by decreased consumption of sweet-tasting, high caloric foods. Cessation of smoking or nicotine is accompanied by increased consumption of these foods. Changes in consumption of these specific foods may partially account for the inverse relationship between smoking or nicotine and body weight. The present research was designed to determine whether consumption of nonsweet food is affected by nicotine and whether continuous access to only nonsweet foods attenuates the body weight changes associated with nicotine administration and cessation of nicotine administration. Alzet miniosmotic pumps were implanted SC to administer saline or three different concentrations of nicotine to male Sprague-Dawley albino rats for 2–3 weeks. Two studies on a total of 80 rats found an inverse dose-response relationship between nicotine administration and body weight without changes in bland food or water consumption. After cessation of nicotine administration, there were no differences in food consumption or body weight changes between groups. The effects of nicotine on body weight, both during and after drug administration, were attenuated in comparison to the results of studies that provided sweet-tasting foods.

Effects of housing on male and female rats: Crowding stresses males but calms females

Housing conditions affect behavioral and biological responses of animals. Effects of same-sex grouped, crowded, or individually housed conditions on plasma corticosterone levels of male and female Wistar rats were examined in two experiments. Experiment 1 examined the effects of individual vs. crowded housing conditions on corticosterone, a biochemical index of stress, in seven male and seven female rats. Experiment 2 extended the findings of Experiment 1 by separately manipulating spatial and population aspects of housing with 50 male and 50 female rats. Male rats had higher corticosterone levels under crowded conditions. In contrast, female rats had higher levels when individually housed. Spatial crowding was the key variable for males, whereas the number of other animals was more important for females. These results indicate that investigators must consider housing conditions as an intervening variable that is likely to differentially affect behaviors of male and female rats.

Effects of social and physical enrichment on open field activity differ in male and female Sprague-Dawley rats.

Environmental enrichment affects performance of neurologically intact organisms and facilitates recovery of function following CNS injury. Only, a few recent studies have examined the extent to which physical versus social aspects of enriched environments separately contribute to superior performance [Pietropaolo S, Branchi I, Cirulli F, Chiarotti F, Aloe L, Alleva E. Long-term effects of the periadolescent environment on exploratory activity and aggressive behavior in mice: social vs. physical enrichment. Physiol Behav 2004;81:443-53; Schrijver NC, Bahr NI, Weiss IC, Wurbel H. Dissociable effects of isolation rearing and environmental enrichment on exploration, spatial learning and HPA activity in adult rats. Pharmacol Biochem Behav 2002;73:209-24] or the extent to which male and females differ in their response to enrichment [Bardo MT, Kiebaur JE, Valone JM, Deaton C. Environmental enrichment decreases intravenous self-administration of amphetamine in male and female rats. Psychopharm 2001;155:278-84; Daniel JM, Roberts S, Dohanich G. Effects of ovarian hormones and environment on radial maze and water maze performance of female rats. Physiol Behav 1999;66:11-20]. The current experiment examined the separate and combined effects of social enrichment (SE) and physical enrichment (PE) on locomotor activity of male and female Sprague-Dawley rats to determine what aspect of enrichment had the greatest effect to alter activity and to determine whether there were sex differences in these effects. Habituation in the open field was used as an index of simple information-processing and refers to the decrease in activity over time that occurs as an animal becomes acclimated to its environment. Faster habituation indicates greater information-processing. The major findings from the current study were: (1) social enrichment has the greatest effect to improve performance (i.e., increased habituation) for both males and females and (2) the effects of enrichment overall generally appear to be greater for males than for females.

Nicotine increases sensory gating measured as inhibition of the acoustic startle reflex in rats

Chronic nicotine administration has been reported to increase acoustic startle response (ASR) amplitude in rats, which has been offered as evidence that some dosages of nicotine can enhance attention. The present experiments examined effects of acutely administered nicotine on amplitude and pre-pulse inhibition (PPI) of acoustic startle in rats. PPI, the decrease in ASR amplitude by a stimulus preceding the startle-eliciting event, reflects pre-attentive neural processes underlying sensory gating. Nicotine had a biphasic dose effect on startle amplitude, with increases at lower dosages (0.01 mg/kg) and decreases at higher dosages (0.5–5.0 mg/kg SC). Lower dosages of nicotine (0.001–0.01 mg/kg) increased PPI and the increase at 0.001 mg/kg occurred independently of changes in ASR amplitude. These results confirm that increases in PPI are not dependent upon changes in ASR amplitude. Results are consistent with nicotines enhancements of performance on cognitive tasks in humans and are the first reported use of the PPI paradigm to model such effects. These findings indicate that ASR paradigms are useful to study effects of nicotine.

Effects of Nicotine and Stress on Startle Amplitude and Sensory Gating Depend on Rat Strain and Sex

We recently reported that 14 days of nicotine administration (12 mg/kg/day) reduced acoustic startle reflex amplitude and impaired prepulse inhibition (PPI) of startle in male and female Long-Evans rats. These findings contrasted with reports of nicotine-induced enhancement of startle and PPI in Sprague-Dawley (a different strain) male rats. The present experiment administered 0, 6, or 12 mg/kg/day nicotine via osmotic minipump for 14 days to 120 Sprague-Dawley rats (male and female) and to 120 Long-Evans rats (male and female) and examined ASR and PPI. Half of the subjects also were stressed by immobilization once each day to examine nicotine-stress interactions. Nicotine enhanced ASR and PPI responses of Sprague-Dawley rats but impaired these responses in Long-Evans rats, regardless of sex. Effects of stress were complex and depended on strain, sex, and drug dose. These findings indicate that effects of nicotine on measures of reactivity (ASR) and sensory gating (PPI) depend on genotype and that nicotine stress interactions depend on genotype, sex, and nicotine dosage.

Effects of nicotine on elevated plus maze and locomotor activity in male and female adolescent and adult rats

Over 4500 adolescents start smoking every day in the United States. Of these, one-third will die prematurely from smoking-related diseases. The current experiment examined the effects of repeated-acute nicotine administration (saline, 0.1, 0.5, or 1.0 mg/kg daily) on elevated plus maze (EPM) and locomotor behaviors of 160 adolescent and adult male and female Sprague-Dawley rats. Nicotines effects depended on age and sex of animal. On the EPM, nicotine exerted anxiolytic effects (increased percentage of time in the open arms) in adolescent males, but exerted anxiogenic effects (decreased percentage of time in the open arms) in adolescent females and in adult males and females. For adults, peak locomotor activity occurred at the 0.5-mg/kg dosage, and the 1.0-mg/kg dosage reduced activity below the saline level on Day 1 and below the 0.5-mg/kg level on Days 1, 3, and 5. For adolescents, peak locomotor activity occurred at the 1.0-mg/kg dosage and there were no activity-depressant effects. These findings suggest there are age differences in sensitivity to nicotine that may affect vulnerability to long-term tobacco use.

Adolescent and adult male rats differ in sensitivity to nicotine's activity effects.

More than 90% of cigarette smokers begin smoking during adolescence. This between-subjects repeated-measures experiment examined: (1) nicotines acute effects on activity in adolescent and adult female Sprague-Dawley rats (Drug Phase I); (2) the effects of age of initial nicotine exposure on activity when nicotine was not administered (Interim Phase); and (3) the effects of age of initial nicotine exposure on later responses to nicotine (Drug Phase II). The experiment consisted of three separate phases. In Drug Phase I, animals were administered either 0 (saline), 0.01, 0.10, 0.50, or 1.0 mg/kg nicotine via subcutaneous injections for 12 days and horizontal activity was measured daily. During the Interim Phase (no drug phase), activity was measured but nicotine was not administered. During Drug Phase II, the same animals were administered the same nicotine dosages as in Drug Phase I for 12 days and activity was measured daily. Drug Phase I revealed dose-response differences between adolescent and adult female rats. In addition, animals initially exposed to nicotine in adolescence exhibited greater sensitivity to nicotines activity-increasing effects than did females initially exposed to nicotine in adulthood (i.e., Drug Phase II).

Gender, stress, and health.

Studying men and women and differences between them has long been a goal for researchers in health psychology. Recent advances in this endeavor, reflected in this special issue on the topic, have led to important information about the relationships between health and behavior. Of particular interest are possible differences in psychophysiological response, stress, and immune function. Clearly, more inclusive research strategies hold great promise for future scientific discoveries.

Adult vs. adolescent rats differ in biobehavioral responses to chronic nicotine administration

More than 90% of smokers begin smoking during adolescence, suggesting that nicotines actions may differ in adults vs. adolescents in ways that render adolescents vulnerable to smoking initiation. This experiment tested the hypothesis that nicotines biobehavioral actions differ in adult and adolescent rats. Forty-two male (21 adolescents, 21 adults) and 41 female (21 adolescents, 20 adults) Sprague-Dawley rats were administered saline or 12 mg/kg/day nicotine via osmotic minipump for 21 days. Body weight, feeding, and locomotion (horizontal activity, vertical activity, center time) were measured before, during, and after saline or nicotine administration. Nicotines effects depended on age and sex. Nicotine reduced body weight and feeding of adult males and females, and of adolescent males, but not of adolescent females. In addition, adolescent males were more sensitive than adults or adolescent females to nicotines activity-enhancing effects. In cessation, nicotine-exposed adolescent males continued to exhibit greater activity than saline-exposed animals. Results indicate that nicotines biobehavioral actions differ depending on age and sex.