Introduction to symposium on endorphins and behavioural processes; review of literature on endorphins and exercise

Dynamic training and circulating neuropeptides in rheumatoid arthritis: a two-year follow-up study

Previous research has suggested that a short-term (6 week) high-intensity and a subsequent long-term (1 year) low-intensity dynamic training programme in 8 patients with rheumatoid arthritis (RA) increased circulating levels of beta-endorphin (beta-EP) during the high-intensity training and of corticotropin-releasing factor (CRF) and beta-lipotropin (beta-LPH) levels during the low-intensity training, without an increase of pain experience. The present follow-up study of the patients, using the data obtained after an additional 1-year period of no standardized training as reference values, indicated that CRF levels decreased significantly (P less than 0.01) in relation to those obtained 1 year earlier. For beta-LPH and beta-EP, no corresponding decreases were noted. No significant difference concerning experience of pain over time was found. High-performance liquid chromatography demonstrated a complex elution pattern with low basal concentration of beta-LPH, which increased after 60 min of training.

Effects of hyperbaric simulation of scuba diving pressure on plasma beta-endorphin

In contrast to our previous studies on the submersion of scuba divers in a state of neutral buoyancy, neither plasma beta-endorphin-like immunoreactivity (beta-EIR) nor affective feelings were significantly changes in scuba divers by mimicking diving pressures of 2 feet (0.6 m) and 50 feet (15.2 m) for 20 min in a hyperbaric chamber. It is concluded that the submersion-induced increase in plasma beta-EIR and accompanying changes in affect reported previously are not due solely to changes in pressure.

Electric muscle stimulation in the spontaneously hypertensive rat induces a post-stimulatory reduction in activity: role of different opioid receptors

We have previously shown that prolonged low-frequency muscle stimulation, inducing contractions of the gastrocnemius muscle, in conscious spontaneously hypertensive rats leads to an opioid-mediated post-stimulatory reduction in blood pressure and analgesia. In the present study we investigated whether muscle stimulation would also induce a post-stimulatory reduction in behavioural activity in the spontaneously hypertensive rats. Selective opioid receptor antagonists were used to analyse the involvement of endogenous opioids. Muscle stimulation, lasting 60 min, induced a post-stimulatory sedation that outlasted the stimulation for hours. Sniffing, locomotor activity and total behavioural activity were significantly reduced. The post-stimulatory reduction in activity was reversed back to control levels by a high dose of naloxone (15 mg kg-1 i.v.). The selective mu-receptor antagonist beta-funaltrexamine, given intracerebroventricularly before stimulation, did not influence the development of the post-stimulatory drop in activity. The delta-receptor antagonist ICI 154,129 had no effect at all on the already developed sedation, whereas MR 2266 BS, a kappa-receptor antagonist (3 mg kg-1 i.v.), completely reversed the drop in activity. These results show that muscle stimulation gives rise to an opioid-mediated post-stimulatory reduction in activity in spontaneously hypertensive rats. The results also indicate the involvement of the opioid kappa-receptor in the behavioural response.

Dynamic training and circulating levels of corticotropin-releasing factor, beta-lipotropin and beta-endorphin in rheumatoid arthritis

The study aimed at evaluating the effects of a dynamic training program on circulating levels of corticotropin-releasing factor (CRF), beta-lipotropin (beta-LPH), and beta-endorphin (beta-EP) in 8 patients (5 females and 3 males, aged 39-65 years) with classical/definite rheumatoid arthritis (RA). Blood samples were collected immediately before, in the middle of, and after a 6-week high-intensity training period as well as after a subsequent 1-year period of low-intensity training. In addition, baseline data were obtained 3 weeks before the start of the training program. Use of multivariate analyses of variance, and of analyses of variance of contrast variables, indicated a short-term effect of the high-intensity training program for beta-EP with increased levels (P less than 0.05) between the 3rd and the 6th weeks, no significant differences being obtained for CRF or beta-LPH here. Corresponding analyses with regard to the combined high and low-intensity training program revealed CRF (P less than 0.01), and beta-LPH (P less than 0.01) levels to increase over time, no long-term effect being found for beta-EP. Despite the intensity of the dynamic training program, no change was found in pain experience as measured on a visual analogue scale.

Effects of temporary withdrawal from regular running

Forty regular male runners were divided into two similar groups and studied for six weeks. One group continued normal running, but the other stopped running for the middle two weeks of the study. Questionnaires were completed at the end of each week. Symptoms of depression were greater in the withdrawn than in the control group at the end of the second week of withdrawal. Somatic symptoms, anxiety, insomnia and feelings of being under strain were greater in the withdrawn group after both the first and second weeks of withdrawal. The groups did not differ in the final two weeks, when running had been resumed. These effects strengthen the view that stopping regular physical exercise produces a 'withdrawal syndrome', and that exercise might therefore be regarded as addictive. The increase in depression may reflect a more gradual loss of the antidepressive effect of exercise training.

Ventricular arrhythmia precipitated by flumazenil

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Open-field behavior is not related to treadmill performance in exercising rats

We examined the association between open-field behavior and treadmill performance in 39 adult male Sprague-Dawley rats. Three daily, five-minute trials were conducted in an open field of 49 19 cm squares. The objectivity of the open-field test was established by intraclass correlations (R) for observer agreement on total squares traversed (R = .99) and a subjective behavioral rating scale for anxiety (R = .92). As expected, total squares were inversely correlated (r = -.86) with the subjective anxiety ratings. An independent observer also rated animals on treadmill performance across six daily, five-minute trials of level running at 15 m/min. Performance ratings were objective (rs = .89) and reproducible (R = .91). A volitional endurance run at 30 m/min on level grade was also conducted on a subsequent day. Extreme groups of low anxious (N = 7) and high anxious (N = 7) animals were then identified from convergent responses on total square traversals and the subjective behavioral ratings that were reproducible (R = .72 to .78) of trials two and three of the open-field test. Repeated measures ANOVA showed no group differences (p greater than 0.10) on mean treadmill performance across trials. Endurance was also the same for each group (p greater than 0.05). Our findings indicate that the open-field test is objective and reliable, and it does not reveal a selection bias effect on treadmill performance or endurance. Thus, open-field behavior can be used as a dependent or subject-matching variable in studies of adult male Sprague-Dawley rats when motor-driven treadmill running is a behavioral intervention or outcome measure.

Beta-endorphin and ACTH in plasma: effects of physical and psychological stress

The effects of the expectancy of an official race (22000 m) and the performance of this last event on plasma levels of beta-Endorphin (B-End) and ACTH have been assessed. In a group of nine athletes, samples were obtained first in basal conditions; second in the day of the run before the warming up period and third after running. B-End immunoactivity was increased from 15.7 +/- 2.0 pg/ml to 23.4 +/- 2.5 pg/ml before the run and up to 30.6 +/- 2.9 pg/ml after the trial. ACTH levels were increased from 8.4 +/- 1.2 pg/ml to 17.9 +/- 2.3 pg/ml before running and up to 36.2 +/- 3.9 pg/ml after running. The results suggest that psychological and physical stress act synergically to increase the levels of B-End and ACTH during the practice of physical exercise.

Endogenous opiates: 1985

This paper is the eighth installment of our annual review of research involving the endogenous opiate peptides. It is restricted to the non-analgesic and behavioral studies of the opiate peptides published in 1985. The specific topics this year include stress, tolerance and dependence, eating, drinking and alcohol consumption, gastrointestinal and renal activity, mental illness, learning and memory, cardiovascular responses, respiration and thermoregulation, seizures and neurological disorders, activity, and some other selected topics.