Conan Kornetsky - US grants

My future research will continue with a major commitment to the study of abuse substances as well as provide a laboratory for the training of both pharmacology and psychology students. The immediate research plan is divided into three sets of interrelated experiments in the rat directed toward furthering our understanding of the neurobehavioral bases of the rewarding effects of abuse substances. The first of these is designed to test further the hypothesis that drug-induced changes in the threshold for rewarding electrical stimulation of the brain of the rat is predictive of abuse liability and that it is an animal model for drug-induced euphoria. The second series of experiments is directed toward the development of a model that allows for the prediction of analgesic efficacy as well as abuse liability of various drugs by means of the effects of these drugs on the threshold for aversive as well as rewarding electrical stimulation of the brain. The third set of experiments is designed to determine if the extent of the effects of abuse substances on the threshold for both rewarding and aversive stimulation is correlated with the specific brain area stimulated. For rewarding stimulation we will compare effects from the medial forebrain bundle (MFB), the periaquaductal grey, and the zona compacta of the substantia nigra. For aversive stimulation we will compare effects from the mesencephalic reticular formation (RF) and the spinal trigeminal nucleus caudalis. In addition, we will determine the effects of single doses and daily administration of morphine on the threshold for brain-stimulation detection (using brain stimulation as a cue) from the MFB and the RF. This procedure allows for the study of drug effects on the perceptual properties of brain stimulation independent of effects on motivational properties. The threshold for three types of electrical stimulation to the brain will be determined in these experiments: brain-stimulation reward, brain-stimulation escape and brain-stimulation detection. The drugs investigated will include opioids, cannabinoids, pentobarbital, combinations of drugs such as d-amphetamine and morphine, tripelennamine and pentazocine, as well as some non abuse substances such as the analgesic, methotrimeprazine.

The proposed experiments build on previous work that found that a few high doses of morphine (MS) administered within a 24 to 36 hour period in the rat will result in marked oral stereotypy that can be reexpressed up to 6 months later. The experiments will determine if this MS sensitizing treatment will increase the rewarding effects of MS as measured by intracranial rewarding electrical stimulation, MS self-administration or conditioned place preference. Because changes in basal rates of glucose metabolism in the brain have been found 6 days after the high dose MS treatment, some experiments will focus on determining the duration of this effect and the role that conditioning plays in the observed changes. By the use of various antagonists, the contribution of the excitatory amino acids in the development and expression of sensitization to oral stereotypy will be determined. Parallel experiments will be carried out with cocaine. Additionally, the extent to which cross-sensitization between morphine and cocaine occurs will be studied. If these effects are related to the brain reward system, then these experiments have the potential to increase our understanding of the long- term effects of abused substances, and possibly contribute to the understanding of the neurobiology of craving. A final question regarding long-term effects will be addressed by an experiment comparing the effects of self-administered cocaine to experimenter-administered cocaine on rewarding brain stimulation. The experimental techniques to be used are brain-stimulation reward, drug self-administration, conditioned place preference, observational ratings, and the quantitative 2-deoxy-D[14C] glucose method for determining local cerebral metabolic rates for glucose.

The proposed research is divided into three groups of interrelated experiments that are directed toward furthering our understanding of the neurobehavioral basis of the rewarding effects of ethanol. The first of these is designed to determine if ethanol will cause changes in the threshold for rewarding brain stimulation (electrodes in the medial forebrain bundle-lateral hypothalamic area) in the rat and if these changes are a relevant model for ethanol induced euphoria or "high". In these experiments the effects of ethanol will be compared to those of a benzodiazepine, a barbiturate and Delta9-THC. Also the effects of ethanol in combination with each of these drug will be determined. Similarly the effects of naloxone on ethanol induced changes in responding for brain-stimulation reward will be investigated. The second group of experiments is designed to determine if ethanol effects on the threshold for rewarding brain stimulation are related to the specific area of the brain that is being stimulated. Brain sites to be compared are those that are relatively high or low in either norepinephrine, dopamine or acetylcholine. The third group of experiments will determine the effects of ethanol on the threshold for detection of stimulation (using brain stimulation as a cue) from the same brain sites studied in the experiments above. Since changes in detection threshold are probably related to changes in attentional and cognitive processes, while changes in reward threshold are probably related to changes in motivational and emotional processes, these two procedures will allow for a direct comparison of the effects of ethanol on these two functional systems and their putative underlying neuronal substrates.

This is a continuation of a research program that has been supported by NIMH and NIDA for a number of years. The purpose of this research is to delineate some of the pharmacological characteristics of tolerance and dependence to the narcotic analgesics. The experiments outlined will continue work on the characteristics and properties of tolerance and dependence and explore several avenues of approach to this problem. We propose to continue an investigation of the factors involved in the appearance, maintenance and loss of tolerance and physical dependence as they relate to dose, dose intervals and the chemical structures of the narcotic analgesics administered. The study also proposes to further explore the interrelationship of tolerance and physical dependence with respect to onset, duration and disappearance. We shall carry out these studies using analgesic assays and temperature changes as measurements of tolerance and weight loss, and behavioral changes and temperature changes as indicators of physical dependence. As part of these studies we will expand the exploration of the feasibility of using one parameter of drug effect, namely temperature, as a measure of both tolerance and dependence. We will use the complex interrelationship of agonist and antagonist to further investigate the nature of the drug-receptor occupation and the nature of the initiation of the changes resulting in tolerance and dependence. Explorations of the prevention of tolerance and dependence by the concommitant administration to agonist and antagonist or by the prior administration of antagonist or by the subsequent administration of antagonist will be continued. Agents affecting protein synthesis and short-term memory will also be used to investigate the nature of this drug-receptor interaction more fully. The course of non-antagonist-precipitated withdrawal will be studied in both rats and mice using the temperature changes induced by the abrupt cessation of chronic narcotic administration.

There is considerable evidence that opiates and opiate peptides produce their various effects by interacting with mu, delta an/or kappa opioid receptor types. The specificity of these receptor types for mediating specific pharmacological effects, especially euphoria and pain relief are of major importance in understanding the abuse potential and the analgesic action of these agents. In order to compare the roles of these various opiate receptors in mediating various pharmacological actions, the relative potencies of the effects of a variety of opiate ligands and peptides will be determined on four procedures, each modeling a different putative action will be determined. These procedures consist of the determination of (1) the threshold for rewarding intracranial stimulation, a model for drug-induced euphoria, (2) the threshold for detecting stimulation, a model for drug-induced analgesia, (3) the threshold for detection of intracranial stimulation that is neither rewarding or aversive, a model for assessing the effects of drugs on perceptual/attentional function and, (4) the self administration of drugs, a model of the reinforcing effects of abuse substances. All experiments will be carried out in male F-344 rats.

DESCRIPTION (provided by applicant): In recent years a Major thrust in the study of the characteristics of the drug abuser has focused on vulnerability, the possible role that genetics play in this vulnerability, and the molecular underpinnings of the mechanisms of use and relapse into drug use. Intrinsic to the understanding of these problems is the understanding of the mechanisms involved in the action of the abused substances on the brain reward system(s). However, for the most part, researchers have made use of the rat as the animal of choice for study, while most of the experiments on genetic differences make use of mouse as the experimental animal. In trying to investigate the behavior of these genetic mutations investigators have relied mostly on simple unconditioned behavior. The proposed research is designed to adapt for the mouse techniques for measuring the changes in brain-stimulation reward (BSR) that have been successfully used in the rat. The procedures are 1) a discrete trial, rate independent, psychophysical method for measuring the BSR threshold and 2) a parallel procedure that measures the ability of the animal to attend to a stimulus by measuring the detection of non-rewarding stimulation from the same brain site. In addition to measuring the stimulation thresholds, latency of response is also measured. Thus the techniques allow for the determination of not only changes in the reward system but also whether these changes are confounded by motor and attention factors. The proposed experiments will explore differences in response to morphine and cocaine in CB57/B6 and D, and DAT deficient mutant mice. Successful development of these procedures in mice will allow a more specific understanding of the nature of specific phenotypes that may have relationships to the human condition.

DESCRIPTION (provided by applicant): There is evidence that older patients require less morphine for effective analgesic relief than younger patients, suggesting that analgesic potency increases with age. At the same time opiate use in addict populations appear to decline as a function of age, suggesting that the hedonic potency of opiates may decrease with age. The proposed experiments will determine if there are differences in the hedonic effects of morphine, the prototypic opiate, as measured by morphine's effect on the threshold for rewarding electrical intracranial stimulation in young, middle-aged and aged rats. These results will be compared to changes in the analgesic response to morphine as determined by threshold changes in escape from aversive electrical brain stimulation in the three age groups of rats. Because rats quickly become sensitized to morphine-induced stereotypic biting and locomotor behavior and this sensitization may be modeling brain changes associated with relapse in the opiate addict; the development and expression of morphine sensitized behavior will be compared in the three group of subjects. Also, because aging may alter patterns of drug distribution and elimination rates, the pharmacokinetics of morphine will be compared in these different aged groups. To our knowledge, the proposed experiments will be the first to examine the relationship between the analgesic and hedonic effects of opiates and aging. The findings of this study may have implications with regard to both pain management and opiate abuse in the elderly.

DESCRIPTION (provided by applicant): In the alcoholic, even after the cessation of drinking, there may be residual effects that last for months and possibly years. The abstinent alcoholic, for a variety of reasons, will have a craving for alcohol long after the last drink. Although there is evidence that chronic ethanol administration in rodents can cause neuroanatomical damage with concomitant cognitive deficits, there has been only a slight suggestion that there may be post-withdrawal changes in functional local cerebral metabolic glucose utilization. Although craving is generally believed to be cue manifested the only animal experimental models of cue induced intracerebral changes have been confined to the study of the measurement of neurotransmitter changes 24 hours after the last of a number of repeated ethanol doses. The specific aims of the research is to test the hypothesis that there are protracted changes in basal cerebral metabolism resulting from oral self- administration of alcohol and that these effects are enhanced by the presence of alcohol cues. The proposed experiments will use the quantitative 2-deoxy-D-[I- 14C]glucose (2-DG) autoradiographic method to determine the local cerebral metabolic rates of glucose a number of weeks after the cessation of daily oral self-administration of ethanol in the Wistar rat. These effects will be studied in the presence and absence of cues associated with the ingestion of the ethanol. The 2-DG analysis will focus on those interconnected regions of the limbic system that have been shown to be altered by chronic oral ethanol self- administration. Positive findings will allow for future research directed toward the understanding of the mechanisms involved in these protracted effects and the developments of possible pharmacological interventions that will interfere with these actions.

DESCRIPTION (provided by applicant): The major objective of the proposed research is to study the interaction of the brain reward system with the brain pain system and the effects of morphine on this interaction. The intracerebral implanting of two stimulating electrodes, one in a reward site and one in a nociceptive site allows the determination of the brain stimulation escape threshold (BSE) in the presence of rewarding brain stimulation as well as the determination of the brain stimulation reward threshold (BSR) in the presence of nociceptive stimulation. This interaction should help us understand how events that produce pleasure may alter the perception of pain and the corollary, how events that cause pain may alter the perception of pleasure. A dramatic example of the environment causing an impact on the modulation of pain was the report of the WWII establishment of a beachhead at Anzio in Italy. Many of the wounded refused morphine (75%) and it was reported that many were euphoric. The wound meant they would be evacuated and thus escape alive from one of the highest casualty battles of the war. The brain stimulation reward procedure allows a direct activation of that area of the brain that subserves usual pleasurable events, e.g., food, sex, drugs and most likely euphoria. Measurement of the BSE threshold in the presence of rewarding brain stimulation allows a study of the direct effect of the brain reward centers on the perception of pain. The reciprocal question, does pain change the sensitivity of a brain reward site? Out-patients in pain, who are not in a controlled environment and are using prescription opiates, may be a greater risk for addiction than the person without pain exposed to the same opiates. Thus, the pain itself may increase the rewarding value of morphine facilitating opiate addiction. The specific experiments will be carried out in rats in which two electrodes are surgically implanted in each animal, one in a reward site (the medial forebrain bundle) and the other in a pain site (mesencephalic reticular formation). In addition to determining the effect of rewarding brain stimulation on the perception of pain caused by stimulating a brain pain pathway, experiments will be conducted on the effect of rewarding brain stimulation on two types of peripheral pain stimulation. These involve a reflexive tail withdrawal to a heat stimulus (spinal) and instrumental escape from nociceptive foot shock (supra spinal). In all of the experiments thresholds will be determined using a modification of the classic method of limits. PUBLIC HEALTH RELEVANCE: The proposed experiments are designed to determine if activation of those parts of the brain that are related to pleasure will alter the perception of pain and whether such activation will enhance the analgesic effects of morphine. A second aspect of the research will determine if the presence of pain contributes to the development of addiction by making the effect of morphine more pleasurable. It is possible that such findings will contribute to the development of better analgesics that are less addicting.