Endogenous opiates: 1983

Reduction of stress-induced analgesia following ethanol exposure in mice

In the present study, we examined the effects of ethanol treatment on the subsequent expression of opioid and nonopioid forms of swim stress-induced analgesia (SSIA). In Experiment 1, mice were injected with ethanol (2.5 g/kg, i.p.) or an equal volume of saline once a day for two days. Animals received no treatment on day 3. On day 4, the animals were tested for opioid (3-min swim in water maintained at 32 degrees C) or nonopioid (3-min swim in water maintained at 20 degrees C) SSIA in the hotplate test (52 degrees C). Mice pretreated with ethanol injections showed a decrease in nonopioid SSIA, but not in opioid SSIA. In Experiment 2, mice were given an ethanol solution (10%) or tap water to drink for 15 days. On day 16, all animals were given tap water to drink. On day 17, the animals were tested for opioid or nonopioid SSIA. Neither form of SSIA was modified in mice that drank the ethanol solution. These results show that ethanol pretreatment can modify nonopioid endogenous analgesic responses in mice. Further, the route of administration influences the effects of ethanol pretreatment on SSIA.

The Tyr-MIF-1 family of peptides

A review of research on the Tyr-MIF-1 family of peptides is presented with emphasis on Tyr-MIF-1 and its structure, passage through the blood-brain barrier, and both opiate antagonist and agonist properties. Family members MIF-1, Tyr-W-MIF-1 and Tyr-K-MIF-1 are also included.

Anatomical localization of immunoreactive oxytocin and beta-endorphin in the bovine neurointermediate lobe

BACKGROUND

Beta-endorphin and oxytocin immunocytochemical localization were examined in the neurointermediate lobe (lobus nervosus and pars intermedia) of the bovine hypophysis in order to describe the anatomical distribution of these two neurointermediate lobe hormones.

METHODS

Twenty-seven bovine hypophyses were collected from slaughterhouse animals (seven mature lactating cows, eleven mature nonlactating cows, three nulliparous heifers, and six steers). Hypophyses were immunostained for oxytocin-containing fibers and beta-endorphin-secreting cells by using the avidin biotin-immunoperoxidase method. The distributions of beta-endorphin-positive cells and oxytocin-positive nerve fibers were plotted on projected outlines of the hypophyses. Immunoreactive staining intensity was graded numerically as weak, moderate, or heavy by three individuals who had no knowledge of the animals' physiological status.

RESULTS

Oxytocin immunoreactivity was confined to the lobus nervosus while beta-endorphin staining was confined to the pars intermedia and the pars distalis. However, oxytocin immunopositive neurosecretory terminals were distributed more heavily in that part of the lobus nervosus bordering the pars intermedia than in the center of the lobe.

CONCLUSIONS

These results were similar to those previously reported for the rat (Swaab et al., 1975; J. Neural Transm., 36:195-215; Deftos and Catherwood, 1980; Life Sci., 27:223-228).

Endogenous methionine enkephalin may play an anticonvulsant role in the seizure-susceptible El mouse

After the intracisternal injection of three protease inhibitors which prevent the degradation of methionine enkephalin (amastatin, Des-Pro2-bradykinin, and phosphoramidon) and a mixture of these protease inhibitors, we investigated the effect on convulsive seizures in the seizure-susceptible El mouse. We also measured the cerebral methionine enkephalin content by high-performance liquid chromatography coupled with radioimmunoassay. Protease inhibitors significantly decreased both the incidence of seizures and the seizure score in El mice in a dose-dependent manner. This anticonvulsant effect was reversed by naloxone (2 mg/kg, sc). The cerebral methionine enkephalin content increased significantly after the administration of protease inhibitors in comparison with saline injection. These findings suggest that it was not protease inhibitors but instead increase of endogenous methionine enkephalin that reduced the incidence of seizures and the seizure score in El mice. Together with our previous data, the present findings support our hypothesis that a deficit in anticonvulsant endogenous methionine enkephalin is involved in the pathogenesis of seizures in the El mouse.

Endorphins do not affect behavioral stress responses in mice

Effects of endorphins on behavioral stress responses were investigated in mice. For this purpose, we used environment-induced conditioned suppression of motility and forced swimming-induced immobility. The cerebral ventricular administration of alpha-endorphin (2.5-10 nmol), beta-endorphin (0.38-1.5 nmol), or gamma-endorphin (2.5-10 nmol) failed to affect either the environment-induced conditioned suppression of motility or the forced swimming-induced immobility. We have indicated previously that enkephalins attenuate both stress responses and, in contrast, dynorphin potentiates them. These findings indicate that the endorphinergic systems are not responsible for behavioral stress responses and that the role played by endorphins in the present stressful situations may be different from that of enkephalin and dynorphin.

Stress-induced changes in brain Met-enkephalin, Leu-enkephalin and dynorphin concentrations

Methionine-enkephalin (Met-enkephalin), leucine-enkephalin (Leu-enkephalin) and dynorphin A (1-17) (dynorphin A) concentrations in discrete brain areas were determined in the mice showing behavioral changes induced by stress using radioimmunoassay (RIA). In the present experiment, we used environment-induced conditioned suppression of motility and forced swimming-induced immobility. In the environment-induced conditioned suppression of motility, Met-enkephalin concentration in the striatum and hypothalamus significantly decreased. Leu-enkephalin concentration in the hypothalamus also decreased. Dynorphin A concentration in the striatum decreased, but significantly increased in the hypothalamus and pituitary. In the forced swimming-induced immobility, Met-enkephalin concentration in the striatum significantly decreased. Leu-enkephalin concentration in the hypothalamus and pituitary significantly decreased. Dynorphin A concentration in the pituitary decreased, but significantly increased in the hypothalamus. Our results indicated that the concentrations of Met-enkephalin, Leu-enkephalin and dynorphin A in the discrete brain areas changed in two different stressful situations. These findings suggested that these peptides might modulate the behavioral changes induced by stressors.

"Paradoxical" effects of morphine on antipredator defense reactions in wild and laboratory rats

In a Fear/Defense Test Battery, measuring defensive reactions to a present, approaching and contacting predator, the highest dose of morphine tested (7.5 mg/kg) reliably reduced vocalization to dorsal contact, to vibrissae stimulation, and to an anesthetized conspecific in laboratory-bred wild R. norvegicus. Except for a dose-dependent reduction in flinch/jump reactions to dorsal contact (taps), other defensive behaviors (flight, freezing, etc.) were not reliably altered by morphine treatment (0, 1.0, 2.5, 7.5 mg/kg). Vocalization responses to vibrissae stimulation in wild-trapped R. rattus were reliably increased following naloxone (1.0 and 10.0 mg/kg) administration, lending support for opiate receptor involvement in the mediation of defensive vocalization. In the Anxiety/Defense Test Battery, measuring defensive reactions to situations associated with a predator (cat) or with cat odor, laboratory rats showed no decrease in defensive behavior with morphine (0, 1.0, 5.0 mg/kg). In direct contrast to the above findings, the effects of morphine treatment in this test battery suggested a generalized increase in defensiveness to noncontacting and nonpainful threat stimuli. These effects included a decrease in time spent near the cat compartment, with a complementary increase in time spent at maximum distance, a decrease in transits between these sections, an increase in crouching, and a decrease in grooming and rearing. This pattern of results suggests that morphine may have two opposing effects on defensive behavior, a generalized enhancement, together with a more specific reduction of responses to tactile or painful stimulation. A very widespread pattern of reliable sex or sex x drug effects in the Anxiety/Defense Test Battery was in good agreement with previous reports of sex differences in these tests, with females generally more defensive than males. Consonant with previous findings, no reliable sex differences were found with the Fear/Defense Test Battery, although several values approached an acceptable level of statistical significance.

Naloxone: lack of effect of a very low dose on fluid intake and activity in rats

Opiate antagonists, such as naloxone, have been employed to indicate the possible involvement of endogenous opioids in a variety of behaviours including the pathogenesis of schizophrenia. This paper describes two experiments which were performed to determine the effects of naloxone on fluid intake and activity in rats. In experiment 1, the administration of 1mg/kg naloxone significantly (p<0.001) reduced water intake. 10mg/kg naloxone considerably reduced water intake, although this result was not significant. This influence was transient, since water intake was restored to control levels at the end of the 4 hours test period, and not dose related. A low dose of naloxone 0.01mg/kg produced no effect. In experiment 2, doses of 1 and 10mg/kg did not influence locomotor activity, rearing or grooming in the open field. These results suggest that naloxone may exert a primary antidipsogenic action that does not depend upon any suppression of concomitant activity. Furthermore, mechanisms controlling water intake and activity appear to be dissociated. A speculative role for the endogenous opioid system is discussed.

The opioid system in neurologic and psychiatric disorders and in their experimental models

Evidence from experimental and clinical studies suggests the involvement of the endogenous opioid system in several neurologic and psychiatric disorders (Alzheimer's, Huntington's and Parkinson's diseases, drug-induced movement disorders, Gilles de la Tourette syndrome, stroke, ischemia, brain and spinal cord injury, epilepsy, schizophrenia and affective disorders). However, its involvement is rather a secondary one, perhaps being a severe consequence of a primary, nonopioid disturbance. Thus, treatment of an opioidergic manifestation of a disorder of nonopioidergic origin is necessarily symptomatic and targets only the restoration of the opioid system; such treatment may be beneficial in ameliorating the clinical symptoms of the disorder.

Effects of [D-Ala2] Met-enkephalinamide, a Met-enkephalin analog, on delayed response by squirrel monkeys

Squirrel monkeys were tested on an indirect spatial delayed response task after subcutaneous injections of either physiological saline, 100, or 500 microgram/kg [D-Ala2] methionine enkephalinamide (DAME). During Experiment 1 monkeys completed two-choice delayed response problems with 0-, 6-, 12- and 18- sec delays; DAME significantly enhanced performance at 18-sec delays but not for the shorter delay. During Experiment 2, monkeys performed a nine-choice spatial delayed response task with 0-, 4- and 8-sec delays. In Experiment 2, low but not high doses of DAME impaired performance. Memory functions represented by a bias-free performance measure paralleled percentage correct in both experiments. Therefore, DAME effect, in enhancing and in impairing performance, were not attributable to changes in the relative number of systematic spatial errors (positional win-shift; lose-stay, position perseveration, and position preference).

Electron microscopic localization of enkephalin-like immunoreactivity in the human adrenal medulla

Enkephalin-like immunoreactivity in human adrenomedullary cells was studied at the light and electron microscopic levels. Enkephalin immunostaining was associated with chromaffin granules and, in a few cells, with the rough endoplasmic reticulum as well. The relative number of stained granules varied from cell to cell, and a correlation with a particular granular population was not noted. Both large and small granules were labelled. It is concluded that in the human the ability to store enkephalin immunoreactive peptides is a general property of chromaffin granules and, furthermore, is not correlated with specific granular subpopulations or the particular type of catecholamine stored within the cell.

Ingestive responses to mu and delta opioid receptor agonists in the domestic fowl

1. Four experiments were conducted using the highly specific mu and delta opioid receptor agonists morphiceptin (B-casomorphin 1-4, amide) or [Met5]-enkephalin, respectively, to evaluate the effect of mu and delta opioid receptor agonists on ingestive behaviour in the domestic fowl. 2. Intracerebroventricular (ICV) administration of 0.625, 1.25, 2.5 and 5.0 micrograms of morphiceptin significantly stimulated drinking, while having no effect on feeding. Intramuscular injection of 0.5, 1.5 and 3.0 mg morphiceptin/kg body weight induced a significant increase in feeding, whereas drinking was not altered. 3. ICV administration of 0.625, 1.25, 2.5 and 5.0 micrograms [Met5]-enkephalin, as well as intramuscular injection of 0.5, 1.5 and 3.0 mg [Met5]-enkephalin significantly stimulated feeding while having no effect on drinking. 4. These results suggest that, in the central nervous system, mu opioid receptor agonists stimulate drinking and delta receptor agonists stimulate feeding. At sites outside the blood-brain barrier, both mu and delta opioid receptor agonists stimulate feeding.

Neuroendocrine profile in bulimia nervosa

The neuroendocrinology of bulimia nervosa has only recently been investigated, with initial research suggesting some biological overlap with both anorexia nervosa (AN) and depression. Similarities among AN, depression, and bulimia include a nonsuppressed Dexamethasone Suppression Test and an abnormal growth hormone (GH) response to thyrotropin-releasing hormone (TRH). Bulimics and anorectics both tend to have a delayed thyrotropin (TSH) response to TRH and elevated basal GH levels. Bulimics, however, have a normal GH response to clonidine, a nonblunted TSH response to TRH, low basal prolactin (PRL) levels, and may have an exaggerated PRL response to TRH. Unpublished data suggest bulimics may have a gonadotropin profile distinct from either AN or depression, as well as a variety of other endocrinopathies. Although many of these abnormalities may reflect malnutrition despite normal weight, other factors that are as yet unidentified are likely to be contributing to the neuroendocrine abnormalities seen in bulimia.

Methionine-enkephalin immunoreactivity in the gonads and nervous system of two insect species: Locusta migratoria and Sarcophaga bullata

Methionine(met)-enkephalin immunoreactivity as visualized by the peroxidase-antiperoxidase procedure, is present in spermatogonia, spermatocytes, spermatids, and young ovarian follicles of Locusta (panoistic type) and Sarcophaga (polytrophic type). Follicle cells and mature spermatozoa are always immunonegative as are locust vitellogenic follicles. In oocytes and in trophocytes, the met-enkephalin-like material first appears around the nucleus and is then dispersed throughout the cytoplasm. Later, it is present only in the periphery. In the ovary of both insects, no immunoreactivity is found with antisera against adrenocorticotrophic hormone, melanophore stimulating hormone, beta-endorphin, corticotropin releasing factor, or leucine-enkephalin. All these antisera yield a positive reaction when applied to the central nervous system as does the met-enkephalin antiserum. This study indicates that the met-enkephalin-like peptide may play a role in reproductive physiology.

Chromatographic identification of Met- and Leu-enkephalin in the human fetal spinal cord

Using the indirect immunofluorescence method, enkephalin-like immunoreactivity was visualized on human fetus spinal cord sections (gestational age from 17 to 25 weeks). Immunolabeled varicose fibers and terminal-like structures were seen through the whole length fetal spinal cord principally in the dorsal gray, in the intermediate gray and in the lateral funiculus. A few enkephalin-like immunoreactive cells were sometimes detected in the intermediate gray. Finally, some immunolabeled fibers were also visible in the ventral spinal cord especially proximate to the motor nuclei areas at the sacral level. Fetal spinal cord tissue extracts from the cervical thoracic and lumbosacral region were chromatographically analyzed using high pressure liquid chromatography in combination with the radioimmunoassay. This biochemical analysis indicates that authentic pentapeptides Met- and Leu-enkephalin may account for a large part (more than 90%) of the enkephalin-like immunoreactivity detected in the fetal spinal cord investigated. Taken together our results suggest that the biosynthetic processing of Met- and Leu-enkephalin in this tissue might be functional early before birth.

The function of lateral hypothalamic catecholamine and endorphin systems in the control of motor performance

Morphine (1 or 10 micrograms in 1 microliter) or beta-endorphin (1 microgram in 1 microliter) were injected bilaterally into the posterior lateral hypothalamus of Sprague-Dawley rats to determine what effect they may have on motor performance. Severe reductions in open field performance and motor reflex control were observed after the injection of 1 microgram of beta-endorphin or morphine into this area. The injection of 10 micrograms of morphine into the same area was less effective in causing motor impairment. The central (32.7 micrograms in 1 microliter) and peripheral (2 mg/kg) injection of naloxone did not prevent the motor impairment observed after the injection of beta-endorphin or morphine. Pretreatment with 6-hydroxydopamine into the lateral hypothalamus in a multistage regime did not prevent the motor impairment observed after beta-endorphin or morphine injection. These results indicate that lateral hypothalamic participation in the control of motor function may not involve the ascending nigrostriatal and mesocortical dopamine systems and that endogenous opiate systems may function independently to influence motor performance.

Inhibitory action of opioid peptides on ouabain-sensitive Na+-K+ and Ca2+-dependent ATPase activities in bovine cardiac sarcolemma

The present study demonstrates that morphine (10(-6) and 10(-5) M), methionine-enkephalin or leucine-enkephalin (10(-10), 10(-8), and 10(-6) M) were able to inhibit significantly, in a dose-dependent manner, both the sarcolemmal Ca2+-dependent ATPase and the ouabain-sensitive Na+-K+ ATPase activities. The inhibitory action of these opioids on the two ATPases was not antagonized by preincubation with naloxone (10(-6) M). Naloxone alone (10(-8), 10(-6) and 10(-5) M) did not affect both the sarcolemmal Ca2+-dependent ATPase and the ouabain-sensitive Na+-K+ ATPase activities. Heat-denatured methionine-enkephalin (10(-6) M) or leucine-enkephalin (10(-6) M) also unaffected both the ATPases. The possibility is also discussed that opioid peptides may regulate myocardial contractility by modulating the movement of ions across the heart sarcolemma.

Effects of naloxone on the mechanical activity of isolated rat hearts perfused with morphine or opioid peptides

In isolated rat hearts, the infusion for 10 min of 10(-10), 10(-8) or 10(-6) M (-)naloxone affected the cardiac function by markedly increasing the coronary pressure and by reducing both the heart rate and the developed tension. A lower dose of (-)naloxone (10(-11) M) or a dose of 10(-6) M (+)naloxone, did not modify the cardiac function. Morphine (10(-6) or 10(-5) M) and 10(-10), 10(-8) or 10(-6) M methionine-enkephalin or leucine-enkephalin, both significantly reduced the coronary pressure of the isolated rat hearts, during the first 4-6 min of perfusion, but the coronary pressure progressively increased above the control value in the last 4 min of perfusion. Each opioid also influenced the mechanical activity of the isolated rat heart, by significantly lowering both the heart rate and the developed tension. (-)Naloxone, at all the doses tested, was only able to antagonise the hypotensive effect induced by the opioids on the coronary pressure and was ineffective in counteracting the negative inotropic and chronotropic effects produced by each opioid. The perfusion in the presence of (+)naloxone (even at a dose of 10(-6) M) did not affect the opioid-induced changes on both the coronary pressure and the mechanical performance of the isolated heart.

The effects of opioid antagonists on ingestive behavior in the domestic fowl

The effects of opioid antagonists on food and water intake in commercial stocks of chickens were investigated. Four experiments were conducted to examine the effects of naloxone (N-allylnoroxymorphone) and naltrexone (N-cyclopropylnoroxymorphone) in broiler and Single-Comb White Leghorn cockerels. Birds were injected intramuscularly with either naloxone HCl or naltrexone HCl at doses from 2.5 to 10 mg/kg. Food and water were offered ad lib 15 min post-injection. In broilers, naloxone dose-dependently attenuated food and water consumption for 300 min, while in Leghorns naloxone attenuated food and water intake for 240 and 300 min, respectively. Naltrexone dose-dependently reduced food and water consumption for 300 min in both broilers and Leghorns. Neither naloxone nor naltrexone significantly altered food or water intake at 24 hr. A fifth experiment was conducted to verify the specificity of opioid antagonism for water intake. Broiler cockerels received an intraperitoneal injection of either isotonic saline (0.15 M NaCl) or hypertonic saline (2.5 M NaCl) followed by an intramuscular injection of either isotonic saline or naloxone HCl (5 mg/kg). Food was withheld for the entire experiment while water was offered ad lib 15 min following the second injection. Naloxone significantly attenuated drinking in normally hydrated and osmotically challenged birds for 150 min. The results suggest a role for endogenous opioid peptides in the regulation of food and water intake in meat and egg-laying stocks of chickens.

Analgesic properties of valproic acid might be related to activation of pro-enkephalin system in rat brain

Recent in vivo and in vitro studies have shown the involvement of gamma-aminobutyric acid (GABA) in analgesia. We investigated if the analgesia induced by an acute valproic acid (VPA) administration might be related to the activation of the enkephalinergic system. VPA administration (i.p.) induces 30 min after treatment a significant and dose-dependent increase of Leu-enkephalin and Met-enkephalin in the striatum, hypothalamus, cortex and brainstem. In the hypophysis no modification was observed for these two neuropeptides. The Met-enkephalin-Arg-Gly-Leu levels are affected by VPA administration in a more complex pattern. Such results suggest the implication of an enkephalinergic system in GABAergic analgesia.

Binaltorphimine and nor-binaltorphimine, potent and selective kappa-opioid receptor antagonists

The opioid antagonist activities of two bivalent ligands, BNI and nor-BNI, have been evaluated in smooth muscle preparations and in mice. Both ligands are highly potent and selective as kappa opioid receptor antagonists, with relatively feeble blocking activity at mu and delta opioid receptors. BNI and nor-BNI represent the first highly selective kappa opioid receptor antagonists and should be of great utility as molecular probes for identifying the interaction of agonist ligands with kappa opioid receptors in vitro and in vivo.

A new immunization procedure for obtention of anti-leucine-enkephalin antibodies. Part II. Effects of olfactory bulb removal on pro-enkephalin related peptides in rat brain

Bilateral Olfactory Bulb Removal (OBR) induced both complex behavioral alterations and a decrease of many neurotransmitter levels. We studied brain levels of the pro-enkephalin related peptides 45 days after OBR. Opioid levels were studied using three different highly specific antisera exhibiting very high affinities in radioimmunoassays in striatum, hypothalamus, hypophysis, brain stem and cortex. Methionine enkephalin levels increase significantly in striatum (42%), hypophysis (94%) and hypothalamus (25%) and non-significantly in the other areas. Leucine-enkephalin levels tended to increase in all dissected structures but a significant increase only occurred in striatum (42%). Octapeptide levels (Methionine-enkephalin-Arg-Gly-Leu) significantly increase in striatum (22%) and decrease in hypophysis (97%) and in brain stem (76%). All these results are partially consistent with the decrease of opiate binding described previously after OBR and suggest a complex imbalance in neurotransmitters after such a sensorial deprivation. It is suggested that the modifications of enkephalinergic neurotransmission might be related to the stressful state induced by OBR.

Central nervous system effects of peptides, 1980-1985: a cross-listing of peptides and their central actions from the first six years of the journal Peptides

A tabular synopsis is presented for articles concerned with the effects of peptides on the central nervous system that appeared in the journal Peptides from 1980-1985. A table arranged alphabetically by peptide and one arranged by effects, both listing routes of injection, species, direction of change, and qualifying notes, provides easy cross-referencing of peptides and their effects. Over 80 peptides and over 135 effects are listed. The list of peptides includes, but is not limited to: ACTH, angiotensin, bombesin, bradykinin, calcitonin, casomorphin, CCK, ceruletide, CGRP, CRF, dermorphin, DSIP, dynorphin, endorphins, enkephalins, GRF, gastrin, LHRH, litorin, metkephamid, MIF-l, motilin, MSH, NPY, NT, oxytocin, ranatensin, sauvagine, substances P and K, somatostatin, TRH, VIP, vasopressin, and vasotocin. The list of effects includes, but is not limited to: aggression, alcohol, analgesia, attention, avoidance, behavior, cardiovascular regulation, catalepsy, conditioned behavior, convulsions, dopamine binding and metabolism, discrimination, drinking, EEG, exploration, feeding, fever, gastric secretion, GI motility, grooming, learning, locomotor behavior, mating, memory, neuronal activity, open field, operant behavior, rearing, respiration, satiety, scratching, seizure, sleep, stereotypy, temperature, thermoregulation and tolerance.

Morphine distribution following infusion into lateral ventricle during hibernation and euthermia

The intracerebral pattern of diffusion of 3H-morphine was studied autoradiographically following continuous infusion (4, 9, and 18 hr; 1 microliter/hr) into the lateral ventricle during hibernation and euthermia (i.e., not hibernating) in ground squirrels (Citellus lateralis). Morphine diffusion into the parenchyma during both states was extensive, resulting in increased autoradiographic optical density of 34 structures examined. The zone of radiolabeled tissue was primarily ipsilateral, and it expanded with increasing duration of infusion. Diffusion into contralateral regions was more evident in hibernation, although the total area of radiolabeled tissue was not significantly greater than that of euthermic animals. The average optical densities of autoradiographs from hibernating brains were significantly greater than those from euthermic animals, suggesting greater accumulation of labeled material during hibernation. These data suggest that neuroactive compounds released into the ventricular space can achieve widespread distribution within the brain during hibernation (in which all physiological parameters are profoundly depressed) as well as during euthermia. Thus, the apparent lack of development of physical dependence to morphine during hibernation is not due to a restricted distribution of morphine in the hibernating brain.

Plasma immunoreactive beta-endorphin in bulimics

The plasma beta-endorphin response to glucose ingestion was compared in 8 bulimics and 8 controls. The bulimics demonstrated a sustained elevation of plasma beta-endorphin unrelated to glucose ingestion throughout the 5-hour study period. It is hypothesized that such an elevation of beta-endorphin is the result of stress and that it may play an important role in the perpetuation of the binge-vomiting cycle.

Design and interpretation of opiate antagonist trials in dementia

In view of the reports of possible beneficial effects of naloxone in dementia, rationales and strategies for studying endogenous opiate systems are reviewed. Important considerations in the design and interpretation of clinical investigations using naloxone are also reviewed. The nature and distribution of endogenous opiate systems are summarized from an historical perspective. Endogenous opiate systems are distributed throughout the central nervous system and play important roles in a variety of brain functions, including memory and learning. In view of this, several rationales are evident for studying endogenous opiate systems in dementia, since it is a syndrome in which structures known to contain opiate systems are disturbed, functions modulated by opiate systems are disturbed, and other neurotransmitter systems (functionally linked to endogenous opiate systems) are disturbed. Different strategies for studying endogenous opiate systems are reviewed, including examination of body fluids and pharmacologic challenge studies. Naloxone hydrochloride, a competitive opiate receptor antagonist, is a commonly used pharmacologic agent. The design of a multidose naloxone study of 12 dementia patients is discussed, with reference to the pharmacokinetics, pharmacodynamics, and specificity of naloxone as well as to the nature of the dependent measures selected for this study. No cognitive benefit was observed in this study. Behavioral arousal was observed at naloxone doses, with more evident psychomotor retardation at higher doses. These findings are contrasted with the results of naloxone challenges in other studies. The varying effects of naloxone within and across populations can be conceptualized in terms of the basic and clinical considerations previously discussed. The importance of dose-finding studies is stressed for this and other drug trials.

Central and peripheral involvement of mu receptors in gastric secretory effects of opioids in the dog

The effects of dermorphin and morphine on gastric acid secretion were studied in conscious dogs with both gastric fistulas (GF) and Heidenhain pouches (HP). Under basal conditions dermorphin and morphine, infused systemically at graded doses, produced a significant increase in acid secretion from both GF and HP. This increase was significantly inhibited by naloxone, naltrexone methylbromide and N-methyl-levallorphan methanesulphonate. Dermorphin did not modify the acid output stimulated by 2-deoxy-D-glucose from GF, while morphine significantly inhibited it; on the contrary acid secretion from HP was increased in this test by both dermorphin and morphine. Acid secretion from GF stimulated by pentagastrin was unaffected by morphine and significantly enhanced by dermorphin. Under these conditions a significant increase in acid secretion from HP was recorded with dermorphin and morphine. Naloxone and N-methyl-levallorphan methanesulphonate, given during pentagastrin-stimulated secretion, significantly inhibited acid output 'per se' from GF and HP and prevented the stimulatory effect of dermorphin and morphine. Bethanechol-induced secretion from GF and HP was significantly increased by both dermorphin and morphine. The present results demonstrate that opioids have simultaneous yet opposite effects on acid secretion in the dog and that mu receptors are involved in both the excitatory and inhibitory effects. Excitatory effects do not seem to be mediated via a vagal pathway (peripheral ?), in contrast to the inhibitory effects (central ?). The inhibitory effects of opiate antagonists on pentagastrin-stimulated secretion suggest a physiological role of peripheral opioid receptors in gastric acid secretion.

Aging and the blood-brain barrier: changes in the carrier-mediated transport of peptides in rats

Age-related changes in the brain's saturable, specific, carrier-mediated transport system for the small, N-tyrosinated peptides Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and methionine-enkephalin (Met-Enk) were studied in Fischer 344 rats aged 4 and 26 months. These studies showed statistically significant differences between the two age groups for both the Tmax (transport maximum) [3.22 +/- 0.013 nmol/min/g (young rats, mean +/- S.E.M.) vs 2.41 +/- 0.009 nmol/min/g (age rats)] and T50 (the amount required to achieve 50% of that maximum) [84.9 +/- 1.0 nmol/g (young) vs 65.1 +/- 0.60 nmol/g (aged)]. The T50:Tmax ratio was nearly equal to the two groups: 26.4 (young) vs 26.9 (aged), consistent with the uncompetitive type of inhibition indicative of alterations in the substrate-carrier complex. In addition, blood concentrations of Tyr-MIF-1-like immunoactivity were nearly doubled in aged rats (3.24 +/- 0.373 vs 1.67 +/- 0.0904 pM/ml), while blood concentrations of Met-Enk-like immunoactivity and brain concentrations of immunoactive Tyr-MIF-1 and Met-Enk showed no statistically significant difference between age groups. Thus, a carrier-mediated system responsible for the transport of peptides across the blood-brain barrier undergoes changes with aging.