Huda Akil

Immunocytochemical localization of methionine enkephalin: Preliminary observations

Abstract Antiserum directed against methionine enkephalin (metenkephalin) was used to determine its anatomical distribution in rat brain. Cross reactivity of that antiserum was not detectable against leucine enkephalin (leu-enkephalin), β-lipotropin (β-LPH), β-endorphin or assorted peptide fragments of met-enkephalin; alpha-endorphin was 370 times less active than met-enkephalin. The localization of met-enkephalin was carried out in the presence of excess leu-enkephalin and yet could be blocked with equal amounts of met-enkephalin. Met-enkephalin was detected in several structures in the spinal cord, medulla, pons, mesencephalon, diencephalon and telencephalon. No met-enkephalin was detected in cerebellum or cerebral cortex.

Binding of 3H-β-endorphin to rat brain membranes: Characterization of opiate properties and interaction with ACTH

The binding of tritiated beta-endorphin (3H-beta-EP) to brain homogenates is described. This has been difficult to achieve due to the lack of availability of 3H-beta-EP and to technical difficulties associated with high non-specific binding of beta-EP. We now report that 3H-beta-EP binding is saturable, stereospecific, has high affinity and is inhibited by sodium. Its dissociation rate is ten-fold longer than that of naloxone. Its regional distribution exhibits interesting differences from naloxone and enkephalin binding. ACTH1-24 appears to displace it more effectively than it displaces 3H-naloxone. The results are discussed in terms of multiple transmitter systems and the multiple opiate receptor hypothesis.

Enkephalin-like material in normal human CSF: Measurement and levels

Abstract An opioid material in normal human lumbar CSF has been partially characterized and quantified. This material resembles methionine-enkephalin in its behavior in two chromatographic systems. It interacts with the opiate receptor assay and with a methionine-enkephalin radioimmunoassay. Mean human values are 3.12–3.25 pmoles of methionine-enkaphalin equivalents but the median is 1.7–1.9 pmoles. While this material resembles enkephalin, it cannot be identified as such with our current techniques.

Neuroanatomical and Neurochemical Substrates of Drug-Seeking Behavior: Overview and Future Directions

The focus of this volume, Molecular and Cellular Aspects of the Drug Addictions, addresses but one perspective of an admittedly complex biological, psychological, and social phenomenon: the administration of drugs for nonmedical reasons. It is readily acknowledged that, in the human, “drug abuse” and “addiction” involve interactions between biological, psychological, and social dimensions. However, it is also readily apparent from both human and animal research that much can be discussed concerning the biological dimension; drugs are self-administered because of their effects on biological systems in the brain. Moreover, research is leading us steadily closer to the specific neurochemical, neuroanatomical, molecular, and cellular actions that are important in the self-administration of drugs.

Naloxone blocks amphetamine-induced rearing: Potential interaction between catecholamines and endorphins

Abstract 1. 1. The effect of 10 mg/kg of naloxone on amphetamine- (1.5 mg/kg) induced behavior was evaluated. 2. 2. Naloxone did not alter amphetamine-induced hyperactivity or stereotypy, but did selectively block rearing behavior. 3. 3. This effect raises two interesting issues: a) It suggests that the first phase of amphetamine-induced behavior in rats (hypermotility) might be considered as having two subcomponents modulated by different mechanisms; b) It adds support to an already growing literature on possible catecholamine-endorphin interactions.

Naloxone administration in chronic hallucinating schizophrenic patients

The recent discovery of the endogenous opiate peptides has been followed by a massive research effort aimed at defining the role of these substances in both normal and abnormal physiology. A part of this research has focused on the possible role of the opiate peptides in psychiatric disorders. Controversial evidence has recently been presented suggesting a role for endogenous opiate systems in mood and psychoses. Terenius et al. (1976) reported that some opiate peptide fractions were elevated in unmedicated schizophrenic and manic patients. These concentrations decreased when the schizophrenic patients were medicated and when the manic patients became depressed (Terenius et al. 1976). Gunne et al. (1977) then attempted to reverse the theorized opiate peptide contribution to schizophrenia by administering the opiate antagonist naloxone (0.4 mg, i.v.). They reported decreased auditory hallucinations in four of six schizophrenic patients tested. This study was single blind, did not use standard rating scales or explicit subject selection criteria (Gunne et al. 1977). Yet, the report of decrease or loss of auditory hallucinations was intriguing. Several groups then attemptedto replicate this study without much success. Volavka et al. (1977) used the same dose of naloxone (0.4 mg) in carefully selected subjects, observed them for several hours and observed no effect on schizophrenic symptoms. Davis et al. (1977) gave between 0.4 and 10 mg of naloxone i.v. (usually, 0.4 mg) to patients from several diagnostic categories. These patients were studied for 1 hour and while they may have had improved cognition, no change in hallucinations was reported. Most recently Janowsky et al. (1977) have infused 1.2 mg of naloxone to a general population of schizophrenic subjects and observed no important changes over an hour.

Immunohistochemical and biochemical studies of the enkephalins, β-endorphin, and related peptides

There are several hypotheses concerning the relationships between the various endorphins and enkephalins (Hughes et al., 1975; Li and Chung, 1976; Guillemin et al., 1976; Bradbury et al., 1976). Such hypotheses include the possibility that β-endorphin or a similar pituitary peptide is primarily a precursor of met-enkephalin (Cox et al., 1975), that met-enkephalin and other peptides such as α and γ-endorphin are breakdown products of β-endorphin (Austen et al., 1977), or that the enkephalins and β-endorphin constitute two distinct endogenous opioid systems (Watson et al., 1977a, b, c; Akil et al., 1978; Bloom et al., 1977b). Furthermore, because of the history of their discovery, the enkephalins have been primarily associated with the brain (Hughes et al., 1975; Simantov and Snyder, 1976), while α, β, and γ-endorphin have been primarily linked to the intermediate and anterior lobes of the pituitary (Cox et al., 1975; Guillemin et al., 1976; Li and Chung, 1976; Bloom et al., 1977a; Bradbury et al., 1976; Graf et al., 1976; Teschemacher, 1975), and particularly to β-lipotropin (β-LPH) their putative prohormone (Moon et al., 1973; Pelletier et al., 1977). Elucidation of the relationships between these endogenous opioid peptides is a crucial first step towards a better understanding of their biosynthetic and degradative pathways, and as a prerequisite for the study of their physiological functions.

ENKEPHALINASE: PRELIMINARY CHARACTERIZATION AND COMPARISON WITH ANGIOTENSIN CONVERTING ENZYME

Of two brain enzymes which cleave enkephalin, an endopeptidase (enkephalinase) is apparently specific for the endogenous enkephalinergic system. This enzyme is different from angiotensin converting enzyme (ACE). The insensitivity of enkephalinase to chloride and lack of activity in certain buffers was in contrast to ACE. A powerful nonapeptide inhibitor of ACE was relatively impotent as an enkephalinase inhibitor.

MULTIPLE OPIATE BINDING SITES IN RAT BRAIN: DIFFERENTIAL DISPLACEMENT OF 3H-NALOXONE BINDING BY DIFFERENT OPIATE LIGANDS

The ability of ethylketocyclazocine methane sulfonate (EKC) and SKF 10,047 (SKF) to displace 3H-naloxone binding was examined in a washed membrane preparation of rat brain. Scatchard analysis of 3H-naloxone binding yields a curvilinear plot which can be resolved into high and low affinity components. Both EKC and SKF displace high affinity naloxone binding but at concentrations up to 10 μM are unble to displace low affinity binding. The low affinity binding is displacable by morphine and naltrexone.

THE EFFECT OF ACUTE ADMINISTRATION OF MORPHINE AND OPIATE ANTAGONISTS ON THE INDOLE CONTENT OF THE RAT PINEAL GLAND

Summary Several groups have suggested the possible opiate regulation of the pineal gland. To investigate this hypothesis, we have studied the effect of acute administration of morphine and opiate antagonists on the indole content of the rat pineal gland. Experiments were performed at night to correspond with peak pineal melatonin concentrations. Male rats were given intraperitoneal injections of either 10 mg/kg morphine sulfate or saline followed by either 8 mg/kg naltrexone, 4 mg/kg naloxone or saline. Animals were sacrificed 45 minutes after morphine administration and pineal indole contents were assayed by high pressure liquid chromatography (HPLC) or radioimmunoassay (RIA). Results indicate that morphine increases pineal melatonin content while the concommittant administration of naltrexone or naloxone totally blocks this effect. Paradoxically, antagonists alone also tend to increase pineal melatonin. A parallel dimunition in pineal serotonin content was observed in both conditions. Tryptophan, while not affected by the administration of morphine, was significantly depressed in pineal glands of animals treated with naltrexone alone. These observations suggest a possible role for the regulation of pineal responsiveness by endogenous opiate peptides.