Clinical efficacy of gamma-hydroxybutyric acid in treatment of opiate withdrawal

This paper describes the role of gamma-hydroxybutyric acid (GHB) in the treatment of opiate withdrawal syndrome. In the two patients described, after having abruptly withdrawn from long-term methadone treatment, GHB was orally administered (each dose given every 4–6 h) for 8–9 days. The GHB showed both a high efficacy (some mild and transient symptoms attributable to opiate withdrawal were observed, but only in the first days of therapy) and a good tolerability (no clinical phenomena interpreted as GHB side effects were found). These results could be of interest in improving the pharmacological treatment of drug addiction.     

Methadone maintenance treatment: An update

Available data (this review includes old major articles and recent articles) show that, although results are heterogenous, methadone maintenance treatments (MMTs) have a real efficiency not only to reduce illicit opiate abuse (50–80% of patients under MMT did not use heroin in the preceding month) but also to reduce criminality, HIV risks and mortality, and to improve social rehabilitation, without inducing other alternative substance abuse. A minority of patients (perhaps 5–20%) stay on MMT on a very long-term basis (more than 10 years). Efficiency of MMTs are rather poorly related to patients' variables, with the exception of a moderately deleterious effect of a low age at onset of opiate dependance, a precocious or high involvement in criminality and an abuse of non-opiate drugs. On the other hand, variables related to treatment play a more important role in explaining heterogeneity of results. Optimal daily dose, high quality of medical and psycho-social services, clear orientation towards social rehabilitation and treatment retention (to allow a sufficient duration of treatment) and slow detoxification regimen of well-stabilized patients are all factors contributing to better results.     

Role of μ1-opiate receptors in supraspinal opiate analgesia: a microinjection study

Microinjection of opiates into either the periaqueductual gray, locus coeruleus, nucleus raphe magnus, or nucleus reticularis gigantocellularis elicits a profound naloxone-sensitive analgesia. μ-Opioid receptors have been implicated in supraspinal analgesia and studies from our laboratory have demonstrated the importance of the μ₁-receptor subtype. In an effort to examine the receptor subtypes responsible for opioid analgesia in specific brain regions, we examined dose-response relationships and naloxonazine sensitivity of morphine and two enkephalin derivatives in the above 4 brain regions. Both morphine and [ -Ser², Leu⁵]enkephalin-Thr⁶ (DSLET) were effective analgesics in all regions examined. The poor affinity of DSLET for μ₂-receptors and of morphine for δ-receptors, combined with their similar, high affinity for μ₁-receptors, implied a μ₁-mechanism of action. The μ₁-selective antagonist naloxonazine effectively blocked the analgesic responses of both compounds in all regions. [ -Pen², -Pen⁵]enkephalin (DPDPE), a potent δ-ligand which does not interact with μ₁-receptors, did not elicit analgesia in either the periaqueductal gray or locus coeruleus at any dose tested. These results suggest that opiates and opioid peptides produce analgesia in these 4 brain regions through μ₁-receptors. The inactivity of DPDPE argues against a role for δ-receptors and the similar analgesic potencies of morphine and DSLET makes a significant role for μ₂-receptors unlikely.     

Opiate ([3H]-naloxone) binding to hypothalamic and cerebral cortical slices of mouse brain

We have characterized the binding of [3H]-naloxone to thick (400 microns) slices of hypothalamus and cerebral cortex from mouse brain. Binding is reversible, saturable, stereospecific, thermolabile, readily displaceable by opiates and sensitive to phenoxybenzamine and phentolamine. Values for KD and Bmax are very close to published figures obtained in brain homogenates. Metabolic inhibitors (ouabain and azide) have no effect on specific binding. The assay is rapid, simple and involves minimal tissue preparation.     

Opiate binding to brain slices and ontogenesis of hypothalamic [3H]naloxone binding sites

We have developed a radioligand binding assay based on the use of hypothalamic slices and have examined the ontogenesis of [³H]naloxone binding sites in male and female rats. [³H]NAL binding is reversible, saturable, stereospecific, of high affinity, readily displaceable by morphine and is sensitive to phenoxybenzamine. These characteristics suggest that [³H]NAL readily binds to opiate receptors in brain slices. With this assay we have demonstrated that: (a) there is an age-related increase in opiate binding sites in rat hypothalamus, (b) there are sex differences in the binding affinity of the sites and (c) the values of B_max are approximately 2–5-fold higher than the levels previously reported from assays with brain homogenates.     

The effect of morphine on responses of ventrolateral orbital cortex (VLO) neurons to colorectal distension in the rat

In 49 halothane-anesthetized rats, we characterized the responses of single neurons in the ventrolateral orbital cortex (VLO) to a noxious visceral stimulus (colorectal balloon distension, CRD), and studied the effects of intravenous morphine on these responses using standard extracellular microelectrode recording techniques. One hundred and four neurons were isolated on the basis of spontaneous activity. Fifty-seven (55%) responded to CRD, of which 32% had excitatory and 68% had inhibitory responses. Neurons showed tendencies toward graded responses to graded CRD pressures (20–100 mmHg), with maximum excitation or inhibition occurring at 80 or 100 mmHg, respectively. Responses to noxious (pinch, heat) and innocuous (brush, tap) cutaneous stimuli were studied in 80 of the VLO neurons isolated. Thirty-three (41%) of these neurons (21 CRD-responsive and 12 CRD-nonresponsive) had cutaneous receptive fields, of which 79% were large and bilateral, 18% were small and bilateral, 3% were small and ipsilateral. Ninety-four percent of these neurons responded only to noxious cutaneous stimulation, 6% responded to both noxious and innocuous stimulation. No neurons responded solely to innocuous stimulation. Cumulative doses of morphine (0.0625, 0.125 and 0.25 mg/kg i.v.) produced statistically significant dose-dependent attenuation of neuronal responses to CRD. Naloxone (0.4 mg/kg i.v.) reversed the effects of morphine. Morphine and naloxone had no significant effects on spontaneous activity. These data support the involvement of VLO neurons in visceral nociception.     

Opiate binding to brain slices and ontogenesis of hypothalamic [H]naloxone binding sites

We have developed a radioligand binding assay based on the use of hypothalamic slices and have examined the ontogenesis of [³H]naloxone binding sites in male and female rats. [³H]NAL binding is reversible, saturable, stereospecific, of high affinity, readily displaceable by morphine and is sensitive to phenoxybenzamine. These characteristics suggest that [³H]NAL readily binds to opiate receptors in brain slices. With this assay we have demonstrated that: (a) there is an age-related increase in opiate binding sites in rat hypothalamus, (b) there are sex differences in the binding affinity of the sites and (c) the values of B_max are approximately 2–5-fold higher than the levels previously reported from assays with brain homogenates.     

Opiate receptor subtype binding in gerbil hippocampus is altered by forebrain ischemia

A role for endogenous opioids in trauma-induced brain injury has been supported by pharmacological studies. The present series of experiments were initiated to extend these observations by measuring opiate receptor subtype binding in gerbil hippocampus following 7 days recovery from a 10 min ischemic insult. Quantitative in vitro autoradiography was utilized to measure mu [( 3H]DAGO), kappa [( 3H]bremazocine + 10 microM morphiceptin + 100 nM DSLET), delta [( 3H]DSLET + 10 microM morphiceptin) and lambda [( 3H]naloxone + 300 nM diprenorphine) binding. While ischemic tissue samples at the level of the dorsal hippocampus showed complete loss of CA1 pyramidal cells, we observed no significant alterations in mu or delta binding suggesting a non-pyramidal cell localization of these receptors. Kappa binding decreased significantly to 88% of control in the CA1 and CA3 regions while lambda binding in the stratum lucidum (CA3) increased to 165% of control. Our results show that opiate receptor subtypes are differentially affected by an ischemic insult.     

Effect of opiate receptor blockade on pain sensitivity in the rat

Blockade of opiate receptors by naloxone (2 mg/kg) was found to produce a significant increase in pain sensitivity as measured by the tail-flick test. This finding supports the view that endogenous opiate systems may play a role in the modulation of pain sensitivity. Naloxone, however, was found to have no effect on pain responsiveness as measured by tail-pinch. These findings, together with additional reports, suggest that endogenous opiate systems may exert differential actions on different sensory modalities.     

The opiate receptor: a single 110 kDa recognition molecule appears to be conserved in Tetrahymena, leech, and rat

We compared the molecular nature of the rat brain opiate receptor with that of the invertebrate leech, Haemopis marmorata, and the protozoan, Tetrahymena, in order to examine the issue of apparent receptor heterogeneity with respect to biochemical structure. A binding study with rat brain membrane verified that [¹²⁵I]β-endorphin ([¹²⁵I]βE), a broad specificity ligand, is displaced by the antagonist (-)-naloxone, but not the inactive stereoisomer (+)-naloxone; agonists considered prototypes for μ, δ, and κ opiate receptors all displayed stereospecific binding displacement. For SDS-PAGE analysis of the opiate receptor [¹²⁵I]β-endorphin was covalently affixed to its recognition molecule with the cross-linking reagent DSS. Primary reaction products occur at 110, 58/55, and 29 kDa. Cross-linking products of all 3 molecular weights are effectively reversed by opiate ligands, regardless of their μ, δ, or κ specificities. Peptide mapping studies in SDS gels, using limited proteolysis, showed that the 110 kDa band can be digested into 58 and 29 kDa fragments and the 58 kDa band into a 29 kDa fragment. Additional smaller molecular weight fragments were generated from the 110, 58/55, and 29 kDa bands which shared their molecular weights. Two possible explanations for the extensive homology between the three major cross-linking products are: (1) the 110 kDa species is the opiate receptor, and the 58 and 29 kDa species are proteolytic fragments; and (2) one of the lower molecular weight species is the opiate receptor, and adjacent receptors are aggregated into the 110 kDa complex through cross-linking. An evolutionary conservation of the opiate receptor is suggested by the presence of the same 3 major cross-linking products in Tetrahymena, leech, and rat.     

Endogenous opiates: Through 1978

The discovery of receptors in the brain for opiates and the structure of the endogenous peptides for these receptors has led to an explosion of interest in this field. The present review is the first of an annual series. It summarizes many of the highlights of research with opiate peptides published with a date of 1978 or earlier.     

Heroin neuroteratogenicity: delayed-onset deficits in catecholaminergic synaptic activity

Prenatal heroin exposure evokes neurochemical and behavioral deficits that, in part, reflect disruption of septohippocampal cholinergic function. In earlier studies, we found that cholinergic synaptic defects involve primary changes in cell signaling proteins that are shared by other transmitter systems. In the current study, we determined whether heroin also targets noradrenergic and dopaminergic inputs that operate through the same signaling cascades. Mice exposed to prenatal heroin showed significant deficits in norepinephrine and dopamine levels and much more pronounced effects on neurotransmitter turnover, an index of synaptic activity. Adverse effects were not present in the immediate postnatal period but rather emerged just before weaning and worsened subsequently. By young adulthood, the most highly-affected regions (hippocampus, cerebral cortex) displayed almost complete inactivation of noradrenergic and dopaminergic tonic activity. These effects arise after prior deficits in cell signaling are discernible, suggesting that the presynaptic effects are secondary to actions on signal transduction cascades shared by numerous neurotransmitter inputs and targeted by other neuroteratogens. These results may explain why apparently unrelated developmental neurotoxicants may ultimately produce a common set of neurochemical and behavioral anomalies.     

Kappa-Opioid and NMDA glutamate receptors are differentially targeted within rat medial prefrontal cortex

Activation of kappa-opioid receptors (KOR) in the medial prefrontal cortex (mPFC) modulates excitatory transmission, which may involve interactions with N-methyl-D-aspartate (NMDA) glutamate receptors. We investigated possible anatomical correlates of this modulation by using dual labeling electron microscopy to examine the cellular distributions of antibodies raised against KOR and the R1 subunit of the NMDA receptor (NR1). KOR immunoreactivity primarily was localized to plasma and vesicular membranes of axons and axon terminals that were morphologically heterogeneous. A small proportion of KOR immunoreactivity was associated with cytosolic compartments of dendrites and membranes of glial processes. NR1 labeling was mainly postsynaptic, associated most often with membranes of cytoplasmic organelles in cell bodies and large dendrites and plasmalemmal surfaces of distal dendrites. The remaining NR1-labeled profiles were axonal profiles and glial processes. Of all cellular associations between labeled profiles, the majority were KOR-labeled axons that contacted NR1-immunoreactive dendrites or cell bodies. Occasionally the two antigens were colocalized in axon terminals that formed either asymmetric synapses or displayed varicose morphology. KOR and NR1 also were colocalized within dendrites, and rarely were observed in the same cell bodies. Occasionally glial processes coursing adjacent to axo-spinous appositions expressed both KOR and NR1 immunoreactivity. These results indicate that ligand activation of KOR or NMDA receptors differentially modulates excitatory transmission in the mPFC through pre- and postsynaptic mechanisms, respectively. The data also suggest more minor roles for colocalized KOR and NMDA receptors in shared regulation of presynaptic transmitter release, postsynaptic responsivity, and glial function.     

Hibernation: An opioid-dependent state?

Hibernation reduces substantially the heart rate of hamsters as well as the respiratory rate, the body temperature and the arousal level. The heart rate is reversed dramatically by the injection of low doses of Naloxone and in some cases the hamster arouses prematurely from hibernation. The effect is not due to the pain of the injection because saline injections do not produce such changes. The effect requires a pre-existing state of hibernation because Naloxone has no cardioacceleratory or arousal effect in non-hibernating hamsters that have had their heart rate and body temperature decreased substantially during hypothermia. These results suggest that endogenous opioids may comtribute specifically to the state of hibernation. Moreover, a physiological role may exist for an anti-opioid system in the promotion of arousal from hibernation.     

The noradrenergic neurotoxins DSP4 and Xylamine bind to opiate receptors

DSP4 and xylamine compete with [3H]-naloxone for opiate binding sites with IC50 values of approximately 1 microM. This effect can be blocked by excess naloxone but not by the noradrenaline uptake inhibitors cocaine or desipramine. Other drugs containing the 2-chloroalkylamine structure--phenoxybenzamine, dibenamine, chloroethyl clonidine, the cholinotoxin AF-64 and 2-dimethylaminoethyl chloride--were similarly tested. Phenoxybenzamine and dibenamine were also able to compete with [3H]-naloxone for binding at the opiate receptor. Experiments in vivo demonstrated that DSP4, like other opiates, can rapidly reduce LH secretion in the rat. This effect is prevented by naloxone but not by desipramine. These data suggest the use of caution in interpreting the results of experiments in which DSP4 and xylamine are used as "specific" noradrenergic uptake inhibitors or as neurotoxins.     

Opiate modulation of separation-induced distress in non-human primates

Infant rhesus monkeys respond to separation from their mothers with a dramatic increase in vocalizations and activation of autonomic and pituitary-adrenal systems. Using the mother-infant separation paradigm in rhesus monkeys, we focused on the role of opiate systems in modulating the behavioral and neuroendocrine consequences of a brief, naturally occurring stressor. In the first experiment, morphine 0.1 mg/kg significantly decreased separation-induced vocalizations without affecting activity levels. In the second experiment, naloxone 1.0 mg/kg increased distress vocalizations but lower doses had no effect. In the third experiment we blocked the effect of morphine 0.1 mg/kg with naloxone 0.1 mg/kg, a dose of naloxone that had no intrinsic effects of its own. This suggests that the reduction of separation-induced vocalizations by morphine is mediated by opiate receptors. The last experiment demonstrated that separation-induced increases in pituitary-adrenal hormones can also be modulated by opiate agonists and antagonists. These findings are consistent with work in non-primate species and support the hypothesis that opiate receptors are specifically involved in mediating separation-induced vocalizations and pituitary-adrenal activation in primates.     

Beta-endorphin enhances the replication of neurotropic human immunodeficiency virus in fetal perivascular microglia

The effect of an endogenous opiate, β-endorphin, on the replication of HIV was investigated in brain perivascular microglia. Beta-endorphin enhanced the synthesis of p-24 antigen and transactivation of HIV promoter. Dialysed culture supernatants of endorphin-treated microglia re-activated latent HIV infection. These culture supernatants showed elevated levels of interleukin-1β, IL-6 and tumor necrosis factor α. Sub-optimal concentration of β-endorphin potentiated GP-120-induced synthesis of these cytokines. Nalaxone reversed β-endorphin-induced, but not GP-120-induced, cytokine production and enhanced HIV replication. These results suggest that endogenous opiates may contribute to the progression of AIDS dementia complex.     

Morphine alters preproenkephalin gene expression

Rats made tolerant/dependent to morphine by s.c. implantation of drug pellets displayed a significant decrease in striatal preproenkephalin mRNA that persisted during the period of withdrawal. Levels of Met-enkephalin were normal at the end of treatment, but reduced after withdrawal. The direction and time-course of these alterations are consistent with roles for altered neuronal gene expression in the phenomena of opiate tolerance and dependence.     

Recent developments in opiate research and their implications for psychiatry

Summary Considerable progress in opiate research has been made during the last few years regarding the identification and localization of opiate receptors in vitro and in vivo, the analysis of drug-receptor interactions and the characterization of an endogenous ligand of the opiate receptor. There is little evidence that effects induced by chronic exposure to opiates — development of tolerance and dependence — are due to changes in opiate receptor mechanisms; it is supposed that the adaptive changes occur mainly in the chain of events triggered by the drug-receptor interaction. Such changes may be directly or indirectly related to the metabolism of neurotransmitters and/or cyclic nucleotides. The obvious links between physical and psychic equivalents of opiate dependence are discussed. Present data points to the significance of brain stem and limbic structures in both these processes, monoamines probably playing an important role. Relations between psychic manifestations of opiate addiction and mental disorders are pointed out.Herrn Professor Dr. med. Gerd Peters zu seinem 70. Geburtstag gewidmet.     

Chronic exposure to morphine attenuates expression of interleukin-1β in the rat hippocampus

The cytokine, interleukin-1β (IL-1β), can modulate both immune and neuroendocrine events. Alteration of IL-1β expression by exogenous factors, such as morphine, may affect the neuro-endocrine-immune axis. Brain sections from male rats implanted with either morphine or placebo pellets were stained for IL-1β immunoreactivity. The results showed pronounced attenuation of IL-1β immunoreactivity in the dentate gyrus and the CAl-CA3 fields of the hippocampus in morphine-implanted rats compared to placebo controls. It has been suggested that the hippocampus is involved in the regulation of hypothalamic activity. Attenuation of IL-1β expression in the hippocampus by chronic exposure to morphine may be one of the mechanisms underlying the neuro-endocrine-immune modulatory effects of opiate addiction.