Exploration and motor activity after intraventricular ACTH, morphine and naloxone

Appetitive sexual behavior in male rats: 1. The role of olfaction in level-changing behavior

Level-changing behavior is a form of anticipatory behavior of a male rat, when tested in a bilevel testbox. The male explores the testcage prior to introduction of a female. The female is introduced after 5 min. The number of level changes displayed by the male in this period reflects appetitive aspects of sexual behavior and it was suggested that analysis of this level-changing behavior may function as assessment of sexual motivation. In this study the increase of anticipatory level changes over repeated weekly tests was dependent upon (sexual) olfactory stimulation. The number of anticipatory level changes was reliably reduced by administration of the opioid antagonist naloxone, suggesting that endogenous opioids facilitate this behavior. These results suggest that the increase of anticipatory level changes over repeated tests is a response to olfactory stimuli and reflects appetitive aspects of sexual behavior, which are stimulated by endogenous opioids. These results are in accordance with the concept that analysis of anticipatory level-changing behavior can be used to assess sexual motivation.

Naloxone reduces social locomotor activity in rats

Naloxone, a nonspecific opioid antagonist, has been found to decrease the activity and social behavior of rats tested in pairs but the effects on individual locomotor activity have been equivocal. In the present study, groups of male Long-Evans hooded rats received naloxone (1 or 4 mg/kg, IP) or vehicle alone (isotonic saline) 30 min prior to testing sessions. Individual locomotor activity was measured in two activity boxes (41-cm3) equipped with two infrared photobeams using daily 30-min testing sessions for 5 consecutive days. Following a 1-week washout period (no testing), activity and social attraction (paired distance and contact) were examined in pairs of rats from each group using daily 15-min testing sessions for 4 consecutive days. Locomotor activity and its habituation were not significantly affected by naloxone in rats tested individually. However, both doses of naloxone significantly reduced paired locomotor activity compared to the control group. Measures of social attraction were not significantly affected by naloxone. The present findings suggest that naloxone does not produce nonspecific depressant effects on activity but rather may antagonize opioid release in situational contexts of high arousal (e.g., social activity) with consequent reduction of activity.

Mechanisms of stress: a dynamic overview of hormonal and behavioral homeostasis

Environmental events, both physical and emotional, can produce stress reactions to widely varying degrees. Stress can affect many aspects of physiology, and levels of stress, emotional status, and means of coping with stress can influence health and disease. The stress system consists of brain elements, of which the main components are the corticotropin-releasing hormone (CRH) and locus ceruleus (LC)-norepinephrine (NE)/autonomic systems, as well as their peripheral effectors, the pituitary-adrenal axis and the autonomic system, which function to coordinate the stress response. Activation of the stress system results in behavioral and physical changes which allow the organism to adapt. This system is closely integrated with other central nervous system elements involved in the regulation of behavior and emotion, in addition to the axes responsible for reproduction, growth and immunity. With current trends in stress research which focus on understanding the mechanisms through which the stress-response is adaptive or becomes maladaptive, there is a growing association of stress system dysfunction, characterized by hyperactivity and/or hypoactivity to various pathophysiological states. The purpose of this review is to 1) define the concepts of stress and the stress response from a historical perspective, 2) present a dynamic overview of the biobehavioral mechanisms that participate in the stress response, and 3) examine the consequences of stress on the physiologic and behavioral well-being of the organism by integrating knowledge from apparently disparate fields of science.

A kappa opiate agonist, U50,488H, enhances energy expenditure in rats

The effect of U50,488H (a selective kappa opiate agonist) on oxygen consumption was measured in either resting and free-moving rats. In both states, U50,488H provokes an increase in oxygen consumption. In resting rats, the increase occurs at lower doses than in free-moving rats. The explanation could be that in the free-moving rats the drug results in an increase in energy expenditure, partially compensated by a decrease in activity.

Stress-induced hypokinesia is facilitated by ACTH-(7-10)

Subcutaneous treatment with the neuropeptide ACTH-(4-10) induced hypokinesia in rats subjected to a mild stress induced by placing the animals on a non-functional "hot" plate (21 degrees C) for 30 sec, but not in control animals not exposed to this stress-inducing environment. The lowest effective dose of ACTH-(4-10) was 5 micrograms/kg, administered 50 min before testing. The combination of peptide treatment and the mild stress-inducing procedure mimicked the effect of a short intense stress induced by placing the rats on a hot plate (57 degrees C) for 30 sec, suggesting that this stress-induced hypokinesia is mediated by ACTH neuropeptides. Structure-activity relationship studies revealed that the active core for the ACTH-(4-10)-induced hypokinesia is located in the C-terminal tetrapeptide Phe-Arg-Try-Gly (ACTH-(7-10)). Pretreatment with the opioid antagonist naltrexone did not influence the effect of ACTH-(4-10) indicating that activation of opioid systems is not implicated in this behavioral effect of the peptide.

Is nicotine depression of neonatal motor behavior exerted through ACTH release?

Prenatal exposure to nicotine tartrate (0.25 mg/kg/pregnant female, gestation days 3 through 21.2x daily IP) markedly decreases ambulatory activity and the number of stop and go movements in 15 day old neonatal rats. Postnatal nicotine tartrate administration alone (0.05 mg/kg SC daily from birth) does not affect these movements nor does it further the motor depression induced by prenatal nicotine treatment. Thus the critical period of neural susceptibility to nicotine appears to be during prenatal life. However, when nicotine is given both pre- and postnatally, horizontal movements are increased in the 15 day old animals, an increase that may be due to inhibition of other types of movement. These alterations in motor behavior are correlated with sharp increases in plasma ACTH levels. As our previous studies [1,25] have shown ACTH to affect neonatal motor behavior, it is suggested that nicotine-evoked ACTH release may mediate some of the motor responses attributed to the drug.

Substrate soiled by an unfamiliar conspecific modifies opioid activity in mice placed in novel environments

Naloxone induces behavioural changes in rodents exposed to novel environments, indicating the involvement of endogenous opioid mechanisms in these situations. The present study investigated whether soiled sawdust substrate from the cage of an unfamiliar, isolated, male conspecific modifies the effect of naloxone (0.5 or 12.5 mg/kg) upon behaviour of mice in an open field test situation. There was little difference between the effects of naloxone upon the frequency of acts or postures shown in the soiled and unsoiled environments. Cluster analysis of the activities according to their position and frequency in behavioural sequences, revealed variations in behavioural organisation in these two situations in control animals, and differential responses to naloxone administration. The data are discussed in terms of an involvement in behaviour of opioid mechanisms which can be modified by non-painful, biologically-relevant, aversive stimuli such as unfamiliar, conspecific-soiled substrates.

Stimulation of aggression in male mice by alpha-MSH and its relation to light phase and to saline intake effects

The resident/intruder test was used to examine the social approach and aggressive behaviour of male albino mice. Digging, self-grooming and rearing were also recorded, as was the post-test response to hot-plate exposure. The resident mice were given either a single acute injection of MSH (MSH); 0.9% NaCl to drink (for 48 h prior to testing; SAL); a combination of both treatments (MSH + SAL) or an injection of 0.9% physiological saline (control group; CON). Testing was carried out at the midpoints of the light and dark phases of the 12:12 light cycle. Data on plasma ion levels and hypothalamic cAMP levels were collected after the hot-plate test. MSH stimulated fighting both in the light and dark, and SAL in the light. MSH + SAL reversed the effects of the single treatments in that fighting declined below CON levels in both light and dark. Social contact and other behaviours were much less affected by treatments. Pain responding and plasma ion levels were not changed. Effects on cAMP were largely inconclusive, but intruders had significantly lower levels than the aggressive resident animals.

Behavioral support for an ACTH receptor in the CNS

In this report we present a series of experiments which have led us to support the notion of the presence of an ACTH receptor in the CNS. A short intense heat-stress (hot-plate) applied to the paws of rats will temporarily reduce activity. During the course of experimentation we were able to eliminate a number of logical mediators. Neither adrenalectomy, adrenal-medullectomy, naloxone administration, nor alpha-MSH-(1-12) were able to affect the observed akinesia. Hypophysectomy, however, was able to abolish or mask the behavior and the reduction in activity could be reinstated by the administration of ACTH-(4-10) to hypophysectomised rats. These data support the notion that a short intense stressor can release ACTH and that this ACTH can be responsible for mediating the short term reduction in activity. In addition, the fact that ACTH-(4-10) has only minimal steroidogenic properties and was able to reinstate the behavior led us to speculate that these effects were of central origin. Furthermore, since naloxone was not capable of altering the behavior, the suggestion is that ACTH in this paradigm acted at a receptor site apart from the naloxone sensitive receptor. This site may in fact be an ACTH specific receptor.

What can be learned from the effects of benzodiazepines on exploratory behavior?

The purpose of this review is to assess the value of using tests of exploratory behavior to study the actions of benzodiazepines. The methods of measuring exploration and the factors influencing it are briefly described. The effects of benzodiazepines on exploratory behavior of rats and mice are reviewed; and the dangers of interpreting the results of such tests in terms of any of the clinical effects of the benzodiazepines is stressed. Finally, the interactions between benzodiazepines and other drugs acting at the GABA-benzodiazepine receptor complex are described. The results of these experiments caution against global classification of compounds as benzodiazepine "antagonists."

ACTH peptides as organizers of neuronal patterns in development: maturation of the rat neuromuscular junction as seen by scanning electron microscopy

SEM was used to visualize the normal postnatal development of the neonatal rat neuromuscular junction (nmj). Maturational changes evoked by ACTH/MSH 4-10 (10 micrograms/kg/day IP) or ACTH/MSH 4-9 (Org 2766) (0.01 microgram/kg/day IP) were compared to controls and to pups treated with nicotine during prenatal and postnatal life, or only during the gestation period. Pregnant females received 0.25 mg/kg 2X daily IP; neonates 0.05 mg/kg/day SC. The Desaki and Uehara and Fahim et al. methods revealed the nmj on the extensor digitorum muscle to be covered by a delicate drapery of postjunctional folds that surround the immature endplate region. By the second week of postnatal life, these folds become more complex and cover a larger area. Upon maturation the folds descend and invaginate into the muscle fiber. Peptide treatment with either ACTH/MSH 4-10 or ACTH/MSH 4-9 accelerates maturation of the endplate as demonstrated by the increased convolutions of the folds. Similar effects follow nicotine administration. The observed changes in morphology of the developing nmj subjected to nicotine may be mediated through nicotine-evoked ACTH release.

The influence of persistent crowding on the age changes of behavioral parameters and survival characteristics of rats

One hundred fifty-six male Sprague-Dawley rats were submitted to crowding (12 rats/Makrolon-IV cage) from an age of 5 months onwards. An equal number from the same age cohort served as a control (6 rats/Makrolon-IV cage). As part of an age-test program, behavioral parameters (spontaneous motor activity, reactive motor activity and maze-learning ability) were measured at various ages between 8 and 30 months. The rats were sacrificed for additional measurements after the behavioral tests. Survival curves and age-specific mortality rates were calculated for those rats which died spontaneously in the course of the study. Control rats showed a significant decrease in spontaneous motor activity after an age of 18 months. Reactive motor activity of the controls revealed a fall in the number of large movements between 9 and 15 months, whereas the number of small movements increased up to an age of 30 months. Crowding conditions increased significantly both spontaneous and reactive activity. Maze-learning ability declined significantly with age in the controls whereas crowded rats revealed a tendency to better performance which seemed to be submitted to a seasonal rhythm. Crowded rats showed an improved survival characteristic, beginning at an age of 700 days. Mortality curves turned out to be distinct and parallel by straight line regression. It has been concluded that the positive effects of crowding on behavioral parameters and survival could be attributed to a decrease in vulnerability rather than to a lowered rate of aging.

Behavioral activity of a short chain ACTH analog

The behavioral activity of ACTH1-17 analog (beta-Ala1, Lys17) ACTH1-17-4 -amino-n-butilamide (Ala1-Lys17-ACTH1-17) has been studied in the rat. Acquisition of shuttle-box active avoidance behavior was facilitated by Ala1-Lys17-ACTH1-17 administered both subcutaneously (SC) and intracerebroventricularly (ICV), and this effect was suppressed by peripheral administration of haloperidol or naltrexone. Extinction of pole jumping active avoidance behavior was delayed by SC administration of the peptide in a dose-dependent manner. Retention of a step-through passive avoidance behavior was facilitated SC or ICV injection of Ala1-Lys17-ACTH1-17. Adrenalectomy failed to modify the effects of the peptide on the retention of passive avoidance behavior. Furthermore, ICV injection of graded doses of Ala1-Lys17-ACTH1-17 induced excessive grooming, and this effect was totally prevented by intraperitoneal (IP) injection of haloperidol or naltrexone SC administration of Ala1-Lys17-ACTH1-17 induced a slight but significant increase in negative responses in a test for behavioral responsiveness to electrical footshock. This effect was totally prevented by IP injection of naltrexone. It is concluded that Ala-Lys17-ACTH1-17 shares some of the behavioral effects of ACTH4-10 and some ACTH1-24, but it seems to be more potent than the latter peptides. Both dopamine and opioid transmission seem to be involved in the behavioral activity of Ala1-Lys17-ACTH1-17.

Social and exploratory behaviour in the rat after septal administration of ORG 2766 and ACTH4-10

The time spent in active social interaction by pairs of male rats in a dimly-lit, familiar test arena, was decreased significantly after intraseptal injection of ACTH4-10 (250-500 ng). In contrast, the time spent in active social interaction was increased significantly after intraseptal injection of the tri-substituted ACTH4-9 analogue ORG 2766 (250-500 pg). Neither ACTH4-10 (250 ng) nor ORG 2766 (250 pg) affected exploration or locomotor activity measured in a holeboard, after intraseptal injection. Intraseptally administered ACTH4-10 (250 ng) increased aggression measured in a colony intruder model, but ORG 2766 (250 pg) was without effect.

Chlordiazepoxide-induced ataxia, muscle relaxation and sedation in the rat: effects of muscimol, picrotoxin and naloxone

Chlordiazepoxide-induced ataxia was potentiated by muscimol (0.5 mg/kg) and antagonised by picrotoxin (2 and 4 mg/kg) and by naloxone (2 and 4 mg/kg). The muscle-relaxant effects of chlordiazepoxide were not significantly altered by any of these three drugs and nor was the chlordiazepoxide-induced decrease in exploratory head-dipping. However, the sedative effects of chlordiazepoxide, measured by a reduction in spontaneous motor activity, were antagonised by picrotoxin.

Endogenous opiates: 1981

This paper is the fourth of an annual series reviewing the research concerning the endogenous opiate peptides. This installment covers only work published during 1981 and attempts to provide a comprehensive, but not exhaustive, survey of the area. Previous papers in the series have dealt with research done before 1981. Topics concerning endogenous opiates reviewed here include a delineation of their receptors, their distribution, their precursors and degradation, behavioral effects resulting from their administration, their possible involvement in physiological responses, and their interactions with other peptides and hormones. Due to the burgeoning literature in this field, the comprehensive nature of this review in the future will be limited to considerations of behavioral phenomena related to the endogenous opiates.

Behavioural responses to novelty in two inbred mouse strains after intrahippocampal naloxone and morphine

Male C57BL/6 and DBA/2 mice were injected intrahippocampally with either naloxone (0.5 microgram) or morphine (1.0 microgram), or saline vehicle alone and, after 15 min, some 12 behavioural components carried out in a novel environment were recorded for 20 min. Naloxone reduced exploratory rearing responses, wall-leaning and object-sniffing in strain C57BL/6 and augmented these behaviours in strain DBA/2, while morphine depressed the scores in both. In conjunction with previously obtained evidence that the mouse hippocampus contains a genotype-dependent cholinergic mechanism which regulates responses to novelty, these findings support the hypothesis that hippocampal opioid peptides modulate the cholinergic control of exploration in mice, possibly indirectly through GABAergic pathways. In contrast, locomotor activity, defaecation and tail elevation remained practically unaffected by the two drugs, and grooming showed another kind of genotype-treatment interaction, that is to say, after morphine.

Peptide influences on the development and regeneration of motor performance

ACTH 1-39 (0.2 U IP daily for up to 18 days) has a beneficial effect on the functional reorganization of regenerating motor units of the extensor digitorum longus (EDL) in the adrenalectomized adult rat following crushing of the peroneal nerve. Motor unit activity (maximum twitch tension amplitude/mean increment in twitch tension as voltage is increased by 0.1 V gradations) and nerve-muscle efficiency (tetanic tension from indirect stimulation/tetanic tension from direct stimulation of EDL) were enhanced by ACTH 1-39. Other electrophysiological and contractile parameters were unaffected by the peptide. Spontaneous motor activity in cold stressed 13 day old rats was prolonged by Org 2766, a substituted analogue of ACTH/MSH 4-9, (0.1 microgram/kg daily) but unaffected by the same dosage of ACTH/MSH 4-10. The responsiveness of developing and regenerating motor systems to neuropeptides indicates a plasticity of neuronal connections, which depends on peptide sequence, dosage and the physiological state of the animal (normal, depressed, regenerating or developing, at rest or stressed).

Contrasting effects of Org 2766 and alpha-MSH on social and exploratory behavior in the rat

Intraperitoneal injection of Org 2766 (0.01-0.4 microgram/kg) produced a dose-related increase in the number of social contacts and in the time spent in active social interaction by pairs of male rats tested in arenas with which they were familiar, but had little effect when the rats were tested in unfamiliar arenas. The increased social interaction was not accompanied by any change in motor activity. In contrast, alpha-MSH (20-200 microgram/kg) decreased the time spent in active social dose-related. Both peptides reduced exploratory head-dipping only at high doses (4-8 microgram/kg for Org 2766 and 200 microgram/kg for alpha-MSH); this change was not accompanied by a reduction in motor activity.