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In membranes from rat brain striatum, opiate agonists stimulated low-K GTPase. Half-maximal enhancement of enzyme activity was obtained with 0. 09m microM morphine and 3.8 microM levorphanol. This order of potency corresponded to that of the affinities of these compounds in binding to opiate receptor. The effect was inhibited by the antagonist naloxone. As shown by the use of the enantiomers levorphanol and dextrorphan, only the pharmacologically active stereoisomer stimulated GTPase. In membranes isolated from morphine-dependent rats, the activity of GTPase was reduced 20-40% relative to that in control rats. After the precipitation of morphine abstinence by naloxone, brain GTPase activity was intermediate between the respective values for naive and dependent animals.

Ribonuclease has been studied in the whole brain homogenate of mice after a single dose of morphine (10 mg/kg), during the development of tolerance and dependence, during the course of withdrawal and naloxone administration. The enzyme increased dose dependently following the administration of morphine. Withdrawal caused a sudden fall in the enzyme with partial recovery by the 6th day of abstinence. Naloxone injections in normal, tolerant, dependent and deprived animals caused a reduction in the enzyme level. The morphine-induced increase in enzyme activity is suggested to be in direct correlation with a reduction in protein synthesis which can be ascribed to a disturbance of the translation processes.

Fluctuations in the content and distribution of adenosine triphosphatase in the brain of mice during the period of morphine tolerance-dependence development as well as normal and and naloxone induced withdrawal have been studied. The histochemical investigation revealed the enzyme activity in the neurons, neuroglia and blood vessels. In the control animals the nucleus caudatus putamen, globus pallidus, hippocampus, nuclei of amygdala, nuclei hypothalami, substantia grisea centralis, griseum pontis, nucleus trapezoideus, nucleus prepositus hypoglossi, nucleus parabrachialis, nucleus vestibularis, nucleus nervi hypoglossi, nucleus dorsalis nervi vagi, nucleus olivaris and nucleus centralis superior are found to be very rich in ATPase. However, morphine treatment inhibited the enzyme in all the above nuclei and it was linear with the increase in dose and the duration of the treatment. Cytophotometric studies reveal that the differences in the enzymatic activity varies from nuclei to nuclei. Surprisingly enough, normal withdrawal as well as naloxone induced withdrawal significantly elevated the enzyme levels. All above findings have been confirmed biochemically. The study gives a firm support of the earlier finding that morphine inhibits ATPase. In addition to this, the present work also reveals a direct antagonistic effect of naloxone on the content of the enzyme in the morphine treated animals. This suggests that the observed inhibition of the enzyme is narcotic specific. The role of ATPase in the Na+, K+ transport is discussed with respect to morphine action. In the light of the present investigation, the effect of morphine on the neurotransmitter release, and the cause and effect there upon has been analyzed. It has been suggested that ATPase might be the enzyme responsible for the observed pharmacological responses of the neurons to the application of the drug by affecting the Na+, K+ flux and neurotransmitter release.

The effect of acute methadone withdrawal was studied on PGE1-sensitive platelet adenylate cyclase of 8 former heroin addicts who had been stabilized with methadone. During acute methadone withdrawal there was a significant increase in PGE1-sensitive platelet adenylate cyclase activity, which correlated with the severity of withdrawal symptoms. This suggests that PGE1-sensitive adenylate cyclase and cyclic adenosine monophosphate (cyclic AMP) are involved in the human addictive process.

In rats rendered tolerant to the dependent on morphine, striatal cyclic AMP metabolism was significantly enhanced as reflected by elevated cyclic AMP levels and adenylate cyclase activity. Following withdrawal from morphine treatment, whereas the activity of straital adenylate cyclase was significantly reduced when compared to morphine-dependent rats, the drop in cyclic AMP was not significant. Although addition of dopamine (40 muM) stimulated equally well the striatal adenylate cyclase from control or morphine-dependent animals, the activity of dopamine-stimulated enzyme was blocked in animals undergoing withdrawal. The crude synaptosomal fraction of the whole brain obtained from morphine-dependent rats exhibited an even more pronounced increase in cyclic AMP which was accompanied by elevated adenylate cyclase and protein kinase activity. Naloxone administration suppressed this rise in cyclic AMP and reversed the morphine-stimulated increases in adenylate cyclase and protein kinase. Following the withdrawal of morphine treatment, alterations in cyclic AMP metabolism were similar to those noted for the morphine-naloxone group.

The catecholamine-stimulated adenosine triphosphatase (ATP-ase) activities in mouse brain synaptosomes were inhibited by morphine both in vitro and in vivo. Morphine up to 10(-3) M had no effect on basal ATPase activities but at 10(-4) M significantly inhibited dopamine-sensitive ATPase activities in vitro. The morphine effect was antagonized by an opiate antagonist, naloxone. The catecholamine-sensitive ATPase activities were also inhibited by acute administration of morphine. The inhibition was dose-dependent. However, naloxone partially antagonized the morphine inhibition of depamine-sensitive ATPase activity but not norepinephrine-sensitive ATPase activity. A significant decrease in the sensitivity of synaptosomal ATPase to catecholamines was observed in mice rendered tolerant by morphine pellet implantation. The Na+,K+-ATPase was more affected by morphine as compared to Mg++-ATPase activity. The dopamine-sensitive Na+,K+-ATPase activity was restored by 50% in precipitated withdrawal mouse brain synaptosomes. Norepinephrine-sensitive ATPase activity was also restored partially in precipitated withdrawal animals. These results suggest that in mouse brain synaptosomes morphine may be interacting with ATPase at or near the catecholamine-active sites.

The possible role of succinic dehydrogenase (SD) in producing physical dependence to morphine by affecting tissue respiration was investigated in Swiss albino mice during the development of morphine tolerance through a period of addiction and naloxone withdrawal therapy. Tolerance and physical dependence were induced by injecting the mice with morphine sulfate subcutaneously at 8-hour intervals, increasing the dose from 10 mg/kg BW every 24 h for 15 days. The animals were considered to be addicted when they were able to tolerate an otherwise lethal dose of 150 mg/kg 3 times a day. Results indicated that succinic dehydrogenase was inhibited throughout the 15-day period of morphine administration and that this effect was greatest in tolerant animals. Increasing the dose and duration of treatment did not cause further decreases in enzyme activity; instead, after 15 days levels of enzyme activity increased in addicted animals compared with tolerant mice. Furthermore, morphine abstinence for 2 days, markedly increased the levels of SD activity, while 6 days of abstinence had little effect. Naloxone withdrawal at each stage was associated with increased SD activity, but the increase was significant only in tolerant mice.

Changes in succinic dehydrogenase (SDH), during morphine dependence development, normal and antagonists (naloxone and naltrexone) precipitated withdrawals, have been analysed in the spinal cord and medulla oblongata of mice. The study reveals the following highlights. 1. There is a progressive inhibition of SDH upto six days of morphine treatment. However, the physically dependent animals demonstrate a significant recovery of the enzyme suggesting that steady-state level of the enzyme is achieved. 2. Antagonists application to morphine treated animals significantly reverted the enzyme, but the control level is achieved only with naloxone in single dose treated animals. 3. The abstinence of drug for two days not only recovered but also significantly raised the enzyme level both in spinal cord and in medulla oblongata. The antagonists treatment to these animals are insignificant. 4. A further withdrawal of the drug recovered the enzyme towards the control level, and on 15th day SDH is completely recovered. The antagonist treatments in withdrawal groups demonstrated insignificant changes. Overall data clearly show that enzymatic changes are morphine mediated, and at least 15 days of drug abstinence is needed for a complete recovery of the enzyme (Acta neurol. belg., 1988, 88, 281-289).

Acute administration of morphine induced significant increases of gamma-amino-butyric acid (GABA) content and L-glutamate decarboxylase (GAD) activity at the dorsal parts of the dorsal horn and surroundings of the central canal in the rat spinal cord, in which GABA inhibitory interneurons may play significant roles. In the thalamus, morphine also induced significant increases of GABA content and GAD activity in the vicinity of the ventrolateral part of the ventral nucleus (VM), entopeduncular nucleus (EP), nucleus reuniens thalami (RE), nucleus parafascicularis thalami (PF) and interpeduncular nucleus (IP), respectively. The most significant increase of GABA was observed in the VM and PF, which are known to receive neuronal inputs from secondary neurons involved in the perception of pain. In spite of well-known involvement of periaqueductal gray matter (PVG) in the occurrence of morphine analgesia, GABA content in this area did not change following acute administration of morphine. The above mentioned increases of GABA in the spinal cord and thalamus were antagonized by the pretreatment with levallorphan, a narcotic antagonist, and were not observed when an analgesic dose of sodium salicylate or pentazocine was administered. On the other hand, acute administration of morphine failed to alter the microdistribution of taurine (2-aminoethanesulfonic acid) in the rat spinal cord and thalamus, in which significant increases of GABA content were observed. Contrary to the results obtained in acutely morphine-treated rats, animals rendered dependent by the implantation of a morphine pellet showed significant increases of taurine content in the spinal cord, whereas no change in GABA contents was detected in both spinal cord and thalamus. The present results suggest that morphine analgesia may involve mechanisms intensifying the inputs of GABA inhibitory neurons at the levels of the spinal cord and thalamus, where the primary and secondary neurons involved in the perception of pain are terminated respectively. Possible involvement of alterations in spinal taurine contents in the occurrence of morphine dependence are also suggested.