Anthony R. Caggiula - US grants

Drugs such as cocaine, the opiates and nicotine lose much of their effectiveness--that is, show tolerance--after repeated administration. It was once thought that the development of drug tolerance depended exclusively only on exposure to the drug. However, it is now quite clear that learned associations with the environmental conditions within which drugs are taken, referred to as drug-related cues, can greatly influence this tolerance process. Dr. Caggiula and his colleagues have recently demonstrated that tolerance to both the analgesic and appetite- suppressant effects of nicotine are strongly influenced by learned associations with environmental cues signaling drug delivery. Administering the drug in the absence of these cues reverses the tolerance, and, renders the drug significantly more effective. Dr. Caggiula is now extending and complementing this work with more detailed learning analyses. The first series of studies focuses on pharmacological and learning variables that control the maintenance of tolerance, using rats that had previously been made tolerant to the anorectic effects of nicotine. The second series of experiments are investigating which factors that are responsible for the development of tolerance in drug-naive rats.

Evidence from the experimental animal literature indicates that gonadal hormones such as estrogen alter immunologic function. Similar, though less conclusive human evidence has led to the idea that differences between males and females in the levels of these hormones are responsible for sex differences in immunologically-related disorders, such as some forms of autoimmune and neoplastic disease. However, the underlying hypothesis that gonadal hormones modulate immune function in humans has never been tested in an experimental paradigm which enables systematic, long term experimenter control over physiological levels of gonadal hormones in a nonclinical population. The present proposal provides such a test. Our currently funded research program, which will assess the relationship between gonadal hormones and cardiovascular response to acute stress, includes a powerful experimental paradigm uniquely suited to study the effects of ovarian hormones on physiological function. Beginning in July of 1991, naturally cycling, healthy women will be assessed for baseline values and stress-induced changes in several cardiovascular, endocrine and lipid functions before and during a complete suppression of ovarian hormones, which is produced by administration of a GnRH analogue. The contribution of estrogen to such changes will be determined by comparing women who are subsequently allowed to resume their cycle with those kept on the GnRH suppression and given estradiol replacement. The major aim of this proposal is to extend the above study to the immune system by incorporating measures of humoral and cell-mediated immunity into the protocol for the same subject population. We will ask whether suppression of ovarian hormones in healthy women alters baseline and stress-induced changes in immunologic function and whether such changes can be reversed by estrogen replacement. We will also determine the relationship among the immunologic, cardiovascular and neuroendocrine responses to reproductive hormones and to stress. This proposal is significant because it addresses an important question of women's health dealing with the relationship between ovarian hormones and immune function.

The development of tolerance to nicotine parallels, and may be causally linked to the development of dependent smoking behavior. Understanding the mechanisms that underlie tolerance is thus an important step in understanding drug taking behavior. While it was once thought that tolerance depended exclusively on repeated drug exposure per se, it is now clear that learned associations with environmental cues that predict drug delivery can influence the tolerance process for a number of drugs. Thus chronic tolerance can include both environment-dependent and drug-dependent components. Recently, this laboratory has demonstrated that tolerance to the behavioral and endocrine effects of nicotine in rats also includes a learned component, and, that an anticipatory release of corticosterone (CORT), conditioned to environmental cues that signal drug delivery, may participate in this component of tolerance by reducing sensitivity to nicotine. Studies are planned to determine the contribution of this cue-triggered, anticipatory CORT response to the development of tolerance to the behavioral, endocrine and immunologic effects of nicotine. A method of drug delivery, intravenous infusion, will be used which increases greatly both the degree of control of drug-related cues and the temporal resolution of drug effects.

There is considerable evidence that stress can affect the immune system of animals. While similar data exist for men, less attention has been given to women. Perhaps one reason for this disparity is the potential complicating factor of ovarian hormones. Hormonal fluctuations associated with the menstrual cycle, pregnancy or menopause may modify the impact of stress on immune function and contribute to gender differences in immunologically-related disorders. Our first grant, for which this is a revised renewal, directly studies the relationship between hormonal state and the effects of psychological stress on the immune system of women. Using a unique A-B-A design, naturally cycling women are assessed for stress-induced changes in cardiovascular, endocrine and immunologic measures during the follicular stage and again, after complete pharmacologic suppression of ovarian hormones, produced by the GnRH agonist, Lupron. The contribution of estrogen is determined by comparing women who are allowed to resume their cycles with those kept on Lupron and given estradiol. In the 21 months since the start of this grant, 25 women, have completed or are currently enrolled. Analyses are presented on the first 24 women, 16 experimental and 8 controls, who have completed the A1- B stages. Subjects had similar baseline values for all measures at visit 1, although state, but not trait, anxiety was higher in experimentals at both visits. Stress reduced the response of peripheral blood lymphocytes to mitogens, the % of CD4+ cells, the CD4+/CD8+ ratio, and IgG production. NK activity, both % specific lysis and lytic units, was increased by stress. Unstressed controls did not show these changes. Stress elevated systolic and diastolic blood pressure, heart rate, plasma norepinephrine (NE) and epinephrine (E).The number and percentage of T-cells, percentage of CD4+ cells, CD4+/CD8+ ratio, number of B-cells, serum IL-1a, and basal plasma levels of NE and DBP increased significantly from the first (follicular) to the second (Lupron-suppressed) visit in experimentals but not controls. There was also a trend for the percentage of NK cells to decrease in visit 2. However, changes in several other cardiovascular, endocrine and immunologic measures from visit #1 to #2 suggested possible habituation or practice effects. We are asking for two more years of funding to complete the study as originally designed, with the addition of the measurement of IL-6, and include another, potentially important experimental group - B (Lupron Suppression)-A1 (follicular) A1 (follicular). This group would allow us to disentangle the effects of habituation to the stressors from the effects of suppressing hormonal levels.

The development of tolerance to nicotine parallels, and may be causally linked to the development of dependent smoking behavior. Understanding the mechanisms that underlie tolerance is thus an important step in understanding drug taking behavior. While it was once thought that tolerance depended exclusively on repeated drug exposure per se, it is now clear that learned associations with environmental cues that predict drug delivery can influence the tolerance process for a number of drugs. Thus chronic tolerance can include both environment-dependent and drug-dependent components. Recently, this laboratory has demonstrated that tolerance to the behavioral and endocrine effects of nicotine in rats also includes a learned component, and, that an anticipatory release of corticosterone (CORT), conditioned to environmental cues that signal drug delivery, may participate in this component of tolerance by reducing sensitivity to nicotine. Studies are planned to determine the contribution of this cue-triggered, anticipatory CORT response to the development of tolerance to the behavioral, endocrine and immunologic effects of nicotine. A method of drug delivery, intravenous infusion, will be used which increases greatly both the degree of control of drug-related cues and the temporal resolution of drug effects.

DESCRIPTION: (Applicant's Abstract) There is considerable evidence that behavioral factors such as smoking, drug-taking and psychological stress have an important impact on the risk of cardiovascular and immune-related diseases, including infectious and neoplastic disorders. Recent findings also suggest that these factors can promote viral infections and accelerate the development of some AlDS-related infections in HIV seropositive individuals. Given the potential health impact of these risk factors in both normal and at-risk (e.g., HIV positive) populations, there is need for more basic research on the mechanisms mediating their cardiovascular and immune actions. Moreover, these factors rarely occur individually outside of the laboratory, and a more realistic laboratory model should include their convergent, in addition to their isolated effects. Finally, considerably more research has been devoted to the effects of these variables in men and more information is needed on their consequences in women. Our research team has had considerable experience in studying the endocrine, cardiovascular and immunological effects of smoking and stress in men and women and the endocrine and immunological effects of nicotine in laboratory animals. On the basis of our research, and the findings of others, we propose that smoking and stress are convergent risk factors for cardiovascular and immune-related disease and that their convergent effects may be mediated by acute activation of the sympathetic nervous system. We now propose to extend our research to study the convergent effects in women of two of these factors, psychological stress and smoking. Specifically, we will determine: 1) how the effects of smoking and acute stress on the immune and sympathetic nervous systems converge in women and 2) how the convergent effects of smoking and stress in women are altered by smoking cessation. The first goal will be achieved by comparing the effects of acute laboratory stress on smokers, with and without concurrent smoking, to the effects of stress in non-smokers. The second will be approached by using an already planned and funded smoking treatment program to assess baseline and stress-induced changes in the function of the SNS and immune systems which accompany cessation of smoking in women.

The development of chronic tolerance to nicotine (NIC) parallels, and may be causally linked to the development of smoking behavior. Understandably, considerable attention has been given to identify the mechanisms underlying tolerance. Theories relating tolerance to smoking behavior rely heavily on animal models of tolerance to NIC's effects. However, this vast literature has been based, amongst without exception, on experimenter-administered drug. While considerable evidence has been gained using this approach, extrapolation to human use is limited by the assumption that the effects of experimenter-administered (non- contingent) NIC are the same as self-administered (contingent) NIC. This assumption has been questioned recently by research on stimulants and opiates and by our recent data which show striking differences in both the acute and chronic effects of contingent versus non-contingent recent data which show striking differences in both the acute and chronic effects of contingent versus non-contingent NIC. We are focusing on gaps in the literature by determining whether the tolerance (or sensitization) that has been reported for non-contingent NIC is also obtained for self- administered NIC, for those effects that have been hypothesized as being important for the drug's abuse potential and/or health consequences. Using a limited access and triple-yoked paradigm, which contrasts self- administered NIC with non-contingent (yoked) NIC and vehicle, we will ask: (1) Does the induction of tolerance or sensitization by pre-exposure to NIC alter NIC SA in rats? (2) Do the reinforcing effects of NIC exhibit tolerance or sensitization? (3) Does NIC SA induce tolerance or sensitization for behavioral (anti-nociception and locomoter activation), endocrine (elevation of corticosterone) and sympathetic nervous system (increased heart rate, blood pressure and plasma catecholamines) effects previously reported for experimenter-administered NIC? (4) Does NIC SA produce the same changes in nicotinic cholinergic receptors in the brain as has been reported for experimenter-administered NIC?

[unreadable] DESCRIPTION (provided by applicant): Models of intravenous nicotine self-administration in laboratory animals are being used to investigate the behavioral and neurobiological consequences of nicotine reinforcement, and to aid in the development of novel pharmacotherapies for smoking cessation. Central to these models are the principles of contingency and primary reinforcement, which have been widely used to explain why people smoke tobacco - smoking results in the rapid delivery of nicotine to the brain, the consequences of which are to reinforce smoking behavior. However, there is mounting evidence that the primary reinforcement model of nicotine self-administration fails to fully explain existing data. Two other factors must be taken into account to attain a complete understanding of the contribution of nicotine to smoking. One is the role of environmental stimuli that accompany the intake of nicotine, and that contribute to the overall magnitude of reinforcement afforded to the behavior. In a series of experiments, we have shown that a compound visual stimulus that accompanies nicotine delivery is as important as nicotine in critical aspects of nicotine self-administration. The second factor is based on our recent finding that the non-contingent administration of nicotine is as effective as contingently delivered (self-administered) nicotine in maintaining high levels of operant responding for the compound visual stimulus. This finding suggests that nicotine can function as both a primary reinforcer when experienced contingently, and as an enhancer of the reinforcing properties of other stimuli, which does not require a contingent relationship between drug delivery and reinforced operant behavior. Understanding the independent and combined contribution of these two factors will help resolve paradoxes and contradictions in the literature regarding the role of nicotine reinforcement in nicotine self-administration and smoking. Using a yoked paradigm, which contrasts self-administered drug with non-contingent (yoked) drug, we will ask: (1) Can non-contingent nicotine enhance the reinforcing effects of other stimuli such as conditioned reinforcers and reinforcing drugs such as cocaine? (2) Can the reinforcement-enhancing effects of non-contingent nicotine be demonstrated using multiple measures of reinforcement and incentive motivation? (3) Are the dual actions of NIC -- as a primary reinforcer and an enhancer of the reinforcing properties of other stimuli -- exhibited by other drugs such as cocaine? [unreadable] [unreadable]