Morphine-induced effects on the hypothalamic stimulation-evoked emotional/behavioral reactions and peculiarities of abstinent syndrome in adult and old rats

Abstract

Experiments were carried out on adult young (6-to-9-month-old) and old (28-to-B0-month-old) rats. The effects of a single i.p. injection of morphine on self-stimulation of the lateral hypothalamic region and on active avoidance responses evoked by stimulation of the ventromedial hypothalamic nucleus were studied. In a separate series of the experiments we studied age-related specificities of the abolition syndrome after a course of intraventricular injections of morphine. In mo~t old rats single injections of morphine resulted in intensification of self-stimulation, while in most adult rats such injections suppressed this reaction. In old animals Injections of morphine resulted in more pronounced increases In the threshold and latency of the active avoidance responses, as compared with similar changeS in adult rats. Natural abolition of a 15-day-long course of injections of morphine resulted in the development of a characteristic abstinent syndrome that was more intensively manifested In old rats. Our results show that "hedonic" and anti-aversive effects of morphine increase with aging; this phenomenon probably facilitates the development of morphine dependence in old organisms. INTRODUC~ONNow it has been shown [I ] that the influence of morphine on the hypothalamic mechanisms of emotional reinforcement plays an important role in the development of morphine dependence. In this case, "hedonic" and anti-aversive effects of morphine are regarded as main reinforcing factors. Structures involved in formation of positive emotional reinforcement are localized in the lateral hypothalamic region (LHR), while a system of negative emotional reinforcement is usually related to the ventromedial nucleus (VMN) of the hypothalamus [2]. tt was shown that in the course of aging, the functional state of the LHR and VMN neuronal systems undergoes considerable modifications [3,4]. A significant age dependence of the effects of morphine on t Institute of Gerontology, Academy of Medical Sciences of Ukraine, Klev, Ukraine.electrical activity in the LHR and VMR was demonstrated [5]. It can be supposed that age-related changes in the functions of the emotiogenic hypothalamic zones represent an important factor that determines the specificity of the effects of morphine and, respectively, specificity of the process of development of drug dependence at different age periods. Our present study is aimed at elucidating the specificities of the effects of morphine on the reinfo/'cing functions of the LHR and VMN structures and of the specific features of the development of morphine dependence in adult and old rats. 92 METHODSExperiments were carried out on adult young and old male Wistar rats (6-to-9-and 28-to-30-month-old animals, respectively).Effects of Morphine on the Functions of the LHR and VMN. The effects of morphine on the functions of 0090-29"/719712902-00925t800 9 199"/ Plenum Publir.hmS Coeporauoa

Effect of morphine on the concentration of monoamines in the emotiogenic zones of the hypothalamus in adult and old rats

“…These structures are the components of the systems of positive and negative emotional reinforcement, respectively. We showed earlier [2,3 ] that single injections of morphine evoke in old animals rather more intensive shifts in the electrophysiological manifestations and parameters of emotional/behavioral reactions to LHZ and VMN stimul Institute of Gerontology, National Academy of Medical Sciences of Ukraine, Kiev, Ukraine.…”