Increased opioid inhibition of GABA release in nucleus accumbens during morphine withdrawal

The nucleus accumbens is a key component of the reward pathway that plays a role in addiction to many drugs of abuse, including psychostimulants and opioids. The effects of withdrawal from chronic morphine were examined in the nucleus accumbens using brain slices from morphine-treated animals. Recordings were made from interneurons in the shell of nucleus accumbens, and the presynaptic inhibition of GABA-A IPSCs by opioids was examined. In slices from control animals, opioids caused a maximal inhibition of 50%, forskolin increased the IPSC amplitude by less than twofold, and the maximal inhibition by opioids in the presence of forskolin was not changed. During withdrawal, however, forskolin caused approximately a fourfold increase in the amplitude of the IPSC, and the maximal inhibition by opioids was increased to 80%. The results indicate that transmitter release is increased during opioid withdrawal, particularly after the activation of adenylyl cyclase. The cAMP-dependent increase in transmitter release is potently inhibited by opioids, such that the overall effect of opioids is augmented during withdrawal. The induction of an opioid-sensitive cAMP-dependent mechanism that regulates transmitter release may be a critical component of acute opioid withdrawal.     

Activation of coeruleospinal noradrenergic inhibitory controls during withdrawal from morphine in the rat

We previously reported that withdrawal from morphine induces the expression of Fos, a marker of neuronal activity, in spinal cord neurons, particularly in laminae I and II of the superficial dorsal horn, and that the magnitude of Fos expression is increased in rats with a midthoracic spinal transection. We suggested that loss of withdrawal-associated increases in descending inhibitory controls that arise in the brainstem underlie the increased Fos expression after spinal transection. Here, we addressed the origin of the supraspinal inhibition. We injected rats intracerebroventricularly with saline or anti-dopamine-beta-hydroxylase-saporin, a toxin that destroys noradrenergic neurons of the locus coeruleus. Eleven days later, we implanted rats with morphine or placebo pellets, and after 4 d, we precipitated withdrawal with naltrexone. One hour later, the rats were killed, their brains and spinal cords were removed, and transverse sections of the brains and spinal cords were immunoreacted with an antibody to Fos. In placebo-pelleted rats, the toxin injection did not alter behavior and did not induce expression of the Fos protein. However, compared with saline-injected withdrawing rats, the toxin-treated rats that underwent withdrawal demonstrated an intense withdrawal behavior rarely seen in the absence of toxin, namely forepaw fluttering. The rats also had significantly increased Fos-like immunoreactivity in all laminae of the cervical cord and in laminae I and II and the ventral horn of the lumbar cord. No differences were recorded in the sacral cord. We conclude that the effects of spinal transection in rats that withdraw from morphine in part reflect a loss of coeruleospinal noradrenergic inhibitory controls.     

Exposure to uncontrollable stress alters withdrawal from morphine.

Examined the influence of the controllability/uncontrollability of shock as a stressor on the severity of subsequent morphine withdrawal in 2 experiments with 84 male Holtzman rats. In Exp I (36 Ss), Ss that received 2 daily sessions of 80 yoked-inescapable shocks, in contrast to those given 80 escapable shocks or restrained without shock, showed an enhanced series of correlated withdrawal behaviors (i.e., mouthing, teeth chattering, head/body shakes) 24 hrs later when injected with morphine sulfate (5 mg/kg) followed by a naloxone HCl (5 mg/kg) challenge. In Exp II (48 Ss), this finding was replicated with escape-yoked-restrained Ss given saline injections during the pretreatment phase, but the impact that inescapable shock had on later precipitated withdrawal was completely blocked when Ss were administered naltrexone HCl (14 mg/kg) before each shock session. Findings are discussed in terms of the capability of inescapable shock to activate an endogenous opiate system, thereby leading to a sensitization of release or receptor processes that could protentiate later morphine withdrawal. (56 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flavonoids reduce morphine withdrawal in-vitro

Molecular analysis of a bleomycin-induced rearrangement of the aprt gene in CHO cells revealed that it consisted of a nearly perfect three-way exchange among non-homologous sequences, consistent with a mechanism involving cyclically permuted misjoining of the six ends of three double-strand breaks.     

Spinal amino acid release and precipitated withdrawal in rats chronically infused with spinal morphine

Glutamate receptors are implicated in the genesis of opioid tolerance and dependence. Factors governing release of amino acids in systems chronically exposed to opiates, however, remain undefined. Using rats, each prepared with a spinal loop dialysis catheter and with a chronic lumbar intrathecal infusion catheter connected to a subcutaneous minipump, the release of amino acids before and during antagonist-precipitated withdrawal in unanesthetized rats was examined. Spinal infusion of morphine (20 nmol/micro l/hr) for 4 d had little effect on resting release of amino acids. In morphine-infused, but not saline-infused, rats naloxone (2 mg/kg, i.p.) evoked an immediate increase in the release of L-glutamate (299 +/- 143%) and taurine (306 +/- 113%) but not other amino acids. The magnitude and time course of the release of these amino acids significantly correlated with behavioral indices of withdrawal intensity. Acute intrathecal pretreatment immediately before naloxone with clonidine (20 microg; alpha2 agonist), MK-801 (3 microg; noncompetitive NMDA antagonist), or aminophosphonopentanoic acid (AP-5; 3 microg; competitive NMDA antagonist) suppressed naloxone-induced increases in spinal L-glutamate and taurine release and behavioral signs of withdrawal in spinal morphine-infused rats. Results point to a correlated increase in spinal L-glutamate release, which contributes to genesis of the opioid withdrawal syndrome. Agents such as clonidine that suppress opioid withdrawal may owe their action to an inhibition of excitatory amino acid release. The effects of MK-801 and AP-5 suggest a glutamate-evoked glutamate release.     

Brain injury and morphine withdrawal.

"A review of the literature indicates lack of agreement as to the presence or absence of opiate withdrawal symptoms following surgically imposed brain damage. The controversy is resolved when recourse is made to the temporal factor, i.e., the time at which withdrawal is carried out relative to the time an operation is performed. It is suggested that the withdrawal phenomenon is as complex as addiction itself, and that both are related to many peculiar effects that accrue to cerebral tissue destruction." 26 references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of morphine withdrawal in the rat.

The present studies examined behavioral changes during precipitated morphine withdrawal in 7- to 42-day-old rat pups. One group of rats was injected with morphine sulfate (10.0 mg/kg) twice daily for 6.5 days. Another group of 7-day-old rats received a lower dose of morphine (3.0 mg/kg). Controls were saline injected or untreated litters (7-day-old pups only). On Day 7, a target pup was injected with saline or naltrexone (0.3–20.0 mg/kg). Preweaning pups were observed in a warm chamber with the litter. Forty-two-day-old rats were tested individually. Morphine-treated pups tested with naltrexone showed significant alterations in behavior that varied at different ages. For example, rolling, stretching, and head and paw moves were observed at the younger ages, whereas burrowing, diarrhea, jumps, teeth chatter, and wet dog shakes occurred in the older rats. These data indicate that morphine-abstinent rats demonstrate withdrawal signs that are within the developmental repertoire of the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential acetylcholine and GABA release from cultured chick retina cells

In the present work we investigated the mechanisms controlling the release of acetylcholine (ACh) and of gamma-aminobutyric acid (GABA) from cultures of amacrine-like neurons, containing a subpopulation of cells which are simultaneously GABAergic and cholinergic. We found that 81.2 +/- 2.8% of the cells present in the culture were stained immunocytochemically with an antibody against choline acetyltransferase, and 38.5 +/- 4.8% of the cells were stained with an antibody against GABA. Most of the cells containing GABA (87.0 +/- 2.9%) were cholinergic. The release of acetylcholine and GABA was mostly Ca2+-dependent, although a significant release of [3H]GABA occurred by reversal of its transporter. Potassium evoked the Ca2+-dependent release of [3H]GABA and [3H]acetylcholine, with EC50 of 31.0 +/- 1.0 mm and 21.6 +/- 1.1 mm, respectively. The Ca2+-dependent release of [3H]acetylcholine was significantly inhibited by 1 micrometer tetrodotoxin and by low (30 nm) omega-conotoxin GVIA (omega-CgTx GVIA) concentrations, or by high (300 nm) nitrendipine (Nit) concentrations. On the contrary, the release of [14C]GABA was reduced by 30 nm nitrendipine, or by 500 nm omega-CgTx GVIA, but not by this toxin at 30 nm. The release of either transmitters was unaffected by 200 nm omega-Agatoxin IVA (omega-Aga IVA), a toxin that blocks P/Q-type voltage-sensitive Ca2+ channels (VSCC). The results show that Ca2+-influx through omega-CgTx GVIA-sensitive N-type VSCC and through Nit-sensitive L-type VSCC induce the release of ACh and GABA. However, the significant differences observed regarding the Ca2+ channels involved in the release of each neurotransmitter suggest that in amacrine-like neurons containing simultaneously GABA and acetylcholine the two neurotransmitters may be released in distinct regions of the cells, endowed with different populations of VSCC.     

Focal brain stimulation attenuates morphine withdrawal behaviors.

29 male Long-Evans hooded rats were stereotaxically implanted with a bipolar stimulating electrode in the periaqueductal gray and also received a subcutaneous surgical implantation of a 72-mg morphine or a placebo pellet. 72 hrs following pellet implantation, naloxone-precipitated withdrawal was induced. Opiate withdrawal behaviors (OWBs) were observed and quantified. Ss then received focal brain stimulation for 30 min, after which they were again observed for OWBs. Data suggest that focal brain stimulation attenuates OWBs, specifically the recessive behaviors associated with autonomic changes. Findings are consistent with those of other studies, from which it is speculated that more than 1 system is involved in the mediation of opioid dependence and analgesia. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Narp regulates long-term aversive effects of morphine withdrawal.

Although long-lasting effects of drug withdrawal are thought to play a key role in motivating continued drug use, the mechanisms mediating this type of drug-induced plasticity are unclear. Because Narp is an immediate early gene product that is secreted at synaptic sites and binds to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, it has been implicated in mediating enduring forms of synaptic plasticity. In previous studies, the authors found that Narp is selectively induced by morphine withdrawal in the extended amygdala, a group of limbic nuclei that mediate aversive behavioral responses. Accordingly, in this study, the authors evaluate whether long-term aversive effects of morphine withdrawal are altered in Narp knockout (KO) mice. The authors found that acute physical signs of morphine withdrawal are unaffected by Narp deletion. However, Narp KO mice acquire and sustain more aversive responses to the environment conditioned with morphine withdrawal than do wild type (WT) controls. Paradoxically, Narp KO mice undergo accelerated extinction of this heightened aversive response. Taken together, these studies suggest that Narp modulates both acquisition and extinction of aversive responses to morphine withdrawal and, therefore, may regulate plasticity processes underlying drug addiction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reversal of akinesia and release of festination by morphine or GABA applied focally to the nucleus reticularis tegmenti pontis.

In 22 male Long-Evans hooded rats, focal application of 5 μg of morphine sulfate to the nucleus reticularis tegmenti pontis (NRTP) reversed the akinesia induced by ip haloperidol (5 mg/kg) or morphine (40 mg/kg) and released festinating forward locomotion. GABA (200 μg) applied to this nucleus also reversed such akinesia. Intraventricular naloxone (10 μg) or picrotoxin (0.1 μg) blocked the effects of such focally applied drugs. Thus, morphine and GABA appear to act physiologically on the cells of the NRTP. Results suggest that systemic morphine, in addition to producing immobility, simultaneously facilitates a readiness for locomotion by inactivating a final common inhibitory system in the region of the NRTP. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased release of kaliuretic peptide during immersion-induced central hypervolemia in cirrhotic humans

Kaliuretic peptide is a recently discovered potent stimulator of potassium and water excretion. Its role in modulating renal water handling in cirrhotic patients has not been defined. The responses of circulating kaliuretic peptide and atrial natriuretic factor in 8 cirrhotic subjects to water immersion were significantly greater (p < 0.05) than those of 7 healthy volunteers. With cessation of immersion, atrial natriuretic factor decreased within 30 min to preimmersion values, whereas kaliuretic peptide remained significantly elevated > 1 h, suggesting a slower clearance for kaliuretic peptide. The peak diuretic response to immersion corresponded in a temporal fashion to the peak circulating concentration of kaliuretic peptide, suggesting a possible physiological role of kaliuretic peptide in modulating volume homeostasis in cirrhotic humans.     

Alterations in brain endogenous histamine levels in rats after chronic morphine treatment and morphine withdrawal

Chronic but not acute treatment with morphine resulted in a significant decrease in the histamine concentration in the rat hypothalamus while a slight decrease was noted in the brain stem and cortex. Naloxone precipitated morphine withdrawal caused a significant decrease in histamine concentration in all three brain regions investigated. Withdrawal of morphine resulted in a further significant decrease in histamine level in the hypothalamus, brain stem and cortex. Substitution of morphine by methadone induced changes similar to these seen in rats chronically treated with morphine alone. The present data suggest that in addition to the other biogenic amines histamine may be involved in the pharmacological effects of morphine.     

Muscarinic M1 receptor mediated inhibition of GABA release from rat cerebral cortex

Presynaptic modulation of [3H]GABA release was examined using rat cerebral cortical slices. In vitro addition of carbachol, a muscarinic receptor agonist, resulted in a significant suppression of the release of [3H]GABA evoked by high potassium (50 mM) stimulation in a dose dependent manner, while noradrenaline, isoproterenol, dopamine, 5-hydroxytryptamine, histamine and glutamic acid had no significant effect on the evoked release of [3H]GABA. This suppressive effect of carbachol was antagonized invariably by atropine. Furthermore, it was found that the suppressive action of carbachol could be antagonized by pirenzepine, a selective M1 muscarinic receptor antagonist, but not by AF-DX 116 and 4-DAMP, M2 and M3 receptor antagonists, respectively. These results suggest that the release of GABA from cerebral cortical GABA neurons may be modulated by presynaptic M1 muscarinic receptor.     

Abstinence symptoms during withdrawal from chronic marijuana use.

Although marijuana is the most commonly used illicit drug in the United States, it is not established whether withdrawal from chronic use results in a clinically significant abstinence syndrome. The present study was conducted to characterize symptoms associated with marijuana withdrawal following chronic use during a supervised 28-day abstinence period. Three groups of participants were studied: (a) current chronic marijuana users, (b) former chronic marijuana users who had not used marijuana for at least 6 months prior to the study, and (c) marijuana nonusers. Current users experienced significant increases in anxiety, irritability, physical tension, and physical symptoms and decreases in mood and appetite during marijuana withdrawal. These symptoms were most pronounced during the initial 10 days of abstinence, but some were present for the entire 28-day withdrawal period. These findings support the notion of a marijuana withdrawal syndrome in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of dopamine in withdrawal jumping in morphine dependent rats

The role of dopamine (DA) in precipitated withdrawal jumping was studied in morphine dependent rats. Pretreatment with various dopaminergic agonists induced a dose-dependent increase in naloxone induced jumping. Pimocide totally blocked the facilitatory effect of piribedil while naloxone induced jumping was not dose-dependently decreased. Biochemical measurements revealed that during precipitated withdrawal the level of DA was elevated and the accumulation of 3,4-dihydroxy-phenylacetic acid (DOPAC) and homovanillic acid (HVA) after probenecid as well as the level of 3-methoxytyramine in the striatum was reduced. Unilateral inactivation of the caudate by local injection of KCl induced contralateral circling during withdrawal. Additional systemic haloperidol pretreatment did not change the direction of circling while additional apomorphine pretreatment changed the direction to ipsilateral and increased the circling rate highly. These latter as well as the biochemical findings strongly suggest an inhibition of striatal DA-mechanisms during withdrawal. The apparent contradiction of these findings to the above finding showing a facilitatroy role of DA-agonists on jumping is discussed.     

Attenuation of morphine withdrawal symptoms by subtype-selective metabotropic glutamate receptor antagonists

1. We have previously shown that chronic antagonism of group I metabotropic glutamate receptors (mGluRs), in the brain, attenuates the precipitated morphine withdrawal syndrome in rats. In the present investigation we assessed the effects of chronic antagonism of group II and III mGluRs on the severity of withdrawal symptoms in rats treated chronically with subcutaneous (s.c.) morphine. 2. Concurrently with s.c. morphine we infused intracerebroventricularly (i.c.v.) one of a series of phenylglycine derivatives selective for specific mGluR subtypes. Group II mGluRs (mGluR2,3), which are negatively coupled to adenosine 3':5'-cyclic monophosphate (cyclic AMP) production, were selectively antagonized with 2s, 1's, 2's-2-methyl-2-(2'-carboxycyclopropyl) glycine (MCCG). Group III mGluRs (mGluR4,6,7 and 8), which are also negatively linked to cyclic AMP production, were selectively antagonized with alpha-methyl-L-amino-4-phosphonobutanoate (MAP4). The effects of MCCG and MAP4 were compared with alpha-methyl-4-carboxyphenylglycine (MCPG), which non-selectively antagonizes group II mGluRs, as well as group I mGluRs (mGluR1,5) which are positively coupled to phosphatidylinositol (PI) hydrolysis. 3. Chronic i.c.v. administration of both MCCG and MAP4 significantly decreased the time spent in withdrawal, MCPG and MCCG reduced the frequency of jumps and wet dog shakes and attenuated the severity of agitation. 4. Acute i.c.v. injection of mGluR antagonists just before the precipitation of withdrawal failed to decrease the severity of abstinence symptoms. Rather, acute i.c.v. injection of MCCG significantly increased the time spent in withdrawal. 5. Our results suggest that the development of opioid dependence is affected by mGluR-mediated PI hydrolysis and mGluR-regulated cyclic AMP production.     

The effect of excitatory aminoacids on GABA release from mediobasal hypothalamus of female rats

A possible sex difference in the mean sagittal area of the anterior commissure (AC) was investigated in normal, newborn-castrated, and perinatally-androgenized rats. A second experiment included castrated adult rats from each sex exposed to testosterone twelve days before sacrifice. In normal rats, as well as in those exposed to testosterone as adults, no quantitative difference was found in the AC. However, perinatal exposure to testosterone induced a 20-25% increase in the mean area of the AC of rats from each sex. It is proposed that gonadal sex steroids may have a reciprocal influence upon the structure of central olfactory pathways, due to the influences of the main olfactory system upon gonadotropin secretion.