Hemendra N. Bhargava

Rapid induction and quantitation of morphine dependence in the rat by pellet implantation

Four schedules of subcutaneous morphine pellet implantation were developed to render rats rapidly physically dependent on morphine. The schedules included implantation of four morphine pellets over a 3-day period (schedule 1), six morphine pellets over a 3-day period (schedule 2), six pellets over a 7-day period (schedule 3), and ten pellets over a 10-day period (schedule 4). Each morphine pellet contained 75 mg of morphine base. The degree of morphine dependence was quantitated by determining the median effective dose (ED50) of naloxone required to induce the stereotyped jumping response. Hypothermia and weight loss, during abrupt and naloxone-induced withdrawal, were also measured. Rats on schedule 4 exhibited a high degree of dependence on morphine as evidenced by an extremely low naloxone ED50 for the precipitated withdrawal jumping response, whereas schedules 1 and 2 produced a low degree of dependence as shown by high naloxone ED50s. Further evidence for a high degree of physical dependence on morphine is schedule 4 rats was indicated by their greater loss in body weight and greater hypothermic response after abrupt and after naloxone precipitated withdrawal compared with these responses in the rats in the other three schedules. A correlation was found to exist between naloxone ED50 for the jumping response, body weight loss, and hypothermia observed during naloxone-induced withdrawal in morphine-dependent rats. These studies suggest that the implantation of four morphine pellets in the rat produces a mild degree of dependence and that caution should be exercised when making generalized conclusions about the biochemical correlations involved when four or less number of pellets, each containing 75 mg of morphine base, are used to induce morphine dependence in the rat.

Cyclo (leucylglcine) inhibits the development of morphine induced analgesic tolerance and dopamine receptor supersensitivity in rats

Abstract Intraperitoneal administration of cyclo (leucylglycine) (2 and 4 mg/kg of body weight) prior to and during chronic morphinization in male Sprague-Dawley rats inhibited the development of tolerance to the analgesic effect of morphine. Rats were rendered tolerant to morphine by subcutaneous implantation of four morphine pellets, each containing 75 mg of morphine free base, over a 3-day period. The development of tolerance was evidenced by decreased response to morphine and inhibition of tolerance by the greater analgesic response. Cyclo (leucylglycine) also antagonized the decrease in motor activity (sedation) during morphine withdrawal. Dopamine receptor sensitivity was enhanced in morphine tolerant rats as measured by apomorphine (2 mg/kg) induced increases in spontaneous motor activity. Cyclo (leucylglycine) administration also blocked dopamine receptor supersensitivity induced by chronic morphinization. It is concluded that development of tolerance to opiates may be associated with enhanced dopamine receptor sensitivity since both the phenomena were blocked by cyclo (leucylglycine).

The effects of thyrotropin releasing hormone and histidyl-proline diketopiperazine on delta-9-tetrahydrocannabinol-induced hypothermia

Abstract The effects of central and peripheral administration of thyrotropin releasing hormone (TRH) and its postulated metabolite, histidyl-proline diketopiperazine (HPD) on △9-tetrahydrocannabinol (THC) induced hypothermia in mice were investigated. Intraperitoneal administration of THC produced hypothermia. The peak response was observed between 1 and 2 hours and the hypothermia lasted for 5 to 6 hours. Intracerebral or intraperitoneal administration of TRH prior to THC injection antagonized the hypothermic response of the latter. Similar effects were produced by histidyl-proline diketopiperazine given intracerebrally. However, HPD was completely ineffective when given intraperitoneally. The antagonism of THC-induced hypothermia by TRH may be mediated by its conversion to HPD in the central nervous system.

Development of narcotic tolerance and physical dependence: Effects of Pro-Leu-Gly-NH2 and cyclo (Leu-Gly)

Administration of Pro-Leu-Gly-NH2 (MIF) and cyclo (Leu-Gly) blocked the development of tolerance to and physical dependence on morphine, induced by the pellet implanation procedure in mice. Inhibition of tolerance development by peptides was evidenced by the presence of an analgesic response (increase in jump threshold) as determined by measuring the jump threshold to an increasing electric current, after a challenge dose of morphine (40 mg/kg). The same dose of morphine did not alter the jump threshold in morphine tolerant mice which were injected with saline prior to pellet implantation. The inhibition of the development of physical dependence on morphine by these peptides was evidenced by the antagonism of the hypothermic response which occurs during abrupt or naloxone-induced withdrawal. The naloxone-induced withdrawal jumping response was unaffected by these peptides. Dose-response experiments indicated that cyclo (leu-Gly) was much more potent than MIF in these tests. These peptides, when given after the development of tolerance and dependence, did not modify either the analgesic response to morphine or the symptoms of abrupt and naloxone-precipitated withdrawal. The inhibition of development of analgesic tolerance and physical dependence was not associated with changes in brain morphine concentration. The data indicate that these peptides do not interfere withe the morphine-morphine receptor complex formation but alter a subsequent step in the genesis of some aspects of tolerance and dependence processes.

Inhibition of naloxone-induced withdrawal in morphine dependent mice by l-trans-Δ9-tetrahydrocannabinol

The effects of various doses of 1-trans-delta9-tetrahydrocannabinol (delta9-THC) on naloxone-induced withdrawal were studied in mice rendered dependent on morphine by the pellet implantation procedure. When administered i.p., 30 min prior to naloxone, delta9-THC, inhibited the naloxone-induced withdrawal jumping response. Two other signs of morphine withdrawal (defecation and rearing behavior) were also suppressed by deltapTHC. It is suggested that delta9-THC or some of its derivatives may have potential use in narcotic detoxification.

Effects of methionine-enkephalin and morphine on spontaneous locomotor activity: Antagonism by naloxone

Abstract Methionine-enkephalin (MEK), a postulated endogenous ligand for the opiate receptors, when administered intracerebroventricularly (ICV) in a dose of 1.75 μmoles/kg) of morphine sulfate had no effect on motor activity. Higher doses (7.0 μmoles/kg) of both MEK and morphine produced profound depression in motor activity; the decrease was significant from 6 to 30 min after their administration. Subcutaneous administration of naloxone (1 mg/kg) did not alter the motor activity. However, administration of naloxone (1 mg/kg) 2 min prior to MEK (7.0 μmole//kg) administration completely blocked the effect of the latter for 15 min while antagonizing the effect of 7.0 μmoles/kg of morphine for 10 min. At 30 min after 7.0 μmoles/kg of either MEK or morphine administration, the motor activity in these groups was identical with that of the naloxone treated group. Methionine-enkephalin in doses of 0.2 and 0.4 μmole/kg had no effect on motor activity for 1 hr observation period. A significant increase in motor activity was recorded 45 and 60 min after 0.2 μmole/kg of morphine sulfate, whereas 0.4 μmole/kg dose of morphine showed significant increase in motor activity only at 60 min after its administration. Furthermore, 0.2 μmole/kg of morphine produced a greater increase in motor activity compared with 0.4 μmole/kg dose at 45 and 60 min after administration. It is concluded that morphine and MEK produce differential effects on mouse spontaneous motor activity with respect to time and dose and that naloxone can inhibit the effects of MEK more effectively than that of morphine on motor activity.

Effect of some cannabinoids on naloxone-precipitated abstinence in morphine-dependent mice

Mice were rendered morphine-dependent by the subcutaneous implantation of a pellet containing 75 mg of morphine base; 72 h after the implantation, the animals were injected intraperitoneally either with vehicle or with various doses of Δ9-tetrahydrocannabinol, Δ8-tetrahydrocannabinol, cannabidiol, cannabinol, or 11-hydroxy-Δ8-tetrahydrocannabinol. Thirty minutes after injection of the cannabinoids, the antagonist, naloxone HCl, was administered to induce the stereotyped withdrawal jumping syndrome. The dose of naloxone needed to induce withdrawal jumping in 50% of the animals (ED50) was determined for each dose of the cannabinoids. All of the cannabinoids inhibited the naloxone-precipitated morphine abstinence as evidenced by an increase in the naloxone ED50. Two additional signs of morphine abstinence, defecation and rearing behavior, were also suppressed by the cannabinoids. The relative effectiveness of the cannabinoids in inhibiting morphine abstinence appeared to be in the following order: Δ9-tetrahydrocannabinol > Δ8-tetrahydrocannabinol > 11-hydroxy-Δ8-tetrahydrocannabinol > cannabidiol > cannabinol.These data suggest that cannabinoids may be useful in facilitating narcotic detoxification.

Influence of thyrotropin releasing hormone and histidyl-proline diketopiperazine on spontaneous locomotor activity and analgesia induced by Δ9-tetrahydrocannabinol in the mouse☆

The influence of thyrotropin releasing hormone (TRH) and its postulated metabolite histidyl-proline diketopiperazine (HPD) on sedation and analgesia produced by delta 9-tetrahydrocannabinol (THC) was investigated in mice. Intracerebral administration of HPD (10 microgram) by itself decreased motor activity, whereas, TRH (10 microgram) was without any effect. THC (10 and 20 mg/kg) given i.p. decreased the motor activity and this effect was antagonised by prior treatment with TRH or HPD. Administration of THC produced analgesia as evidenced by delay in the tail-flick reaction time to a thermal stimulus. Pretreatment with TRH or HPD also antagonized the THC-induced analgesia. THC-induced analgesia was not modified by s.c. pretreatment with naloxone, an opiate antagonist. TRH or HPD pretreatment had no effect on the distribution of total radioactivity representing THC and its metabolites in brain and plasma. These studies indicate that TRH and HPD can antagonize THC-induced sedation and analgesia and that HPD may be an active metabolite of TRH. These effects were observed without altering the distribution of the drug and metabolite in brain and plasma, and therefore their effect may involve their direct actions on the central nervous system. Finally THC induced analgesia does not seem to involve opiate receptors and their involvement in the mechanism by which TRH or HPD antagonize THC-induced analgesia is unlikely.

THE EFFECT OF MELANOTROPHIN RELEASE INHIBITING FACTOR (MIF) AND CYCLO (LEU-GLY) ON THE TOLERANCE TO MORPHINE-INDUCED ANTINOCICEPTION IN THE RAT: A DOSE-RESPONSE STUDY

1 The effects of melanotrophin release inhibiting factor (MIF) and its cyclic analogue cyclo (Leu‐Gly) on tolerance to the analgesic effect of morphine were studied in male Sprague‐Dawley rats. 2 Tolerance to morphine was induced by implantation of four morphine pellets (each containing 75 mg of morphine free base) during a 3 day period. 3 Daily subcutaneous administration of MIF and cyclo (Leu‐Gly) before and during the morphine pellet implantation inhibited the development of tolerance to morphine analgesia. The minimum daily dose of the peptides required to produce a significant effect was 0.5 mg/kg. 4 The effects of single injections of MIF and cyclo (Leu‐Gly) on morphine tolerance revealed that the minimum doses of cyclo (Leu‐Gly) and MIF to inhibit morphine tolerance were 4 and 8 mg/kg, respectively. 5 Chronic treatment with morphine resulted in an enhanced hypothermic response to a dopamine agonist, apomorphine. The enhancement of this response was blocked by both MIF and cyclo (Leu‐Gly) in doses that inhibited morphine tolerance. 6 It is concluded that MIF and cyclo (Leu‐Gly) block the development of analgesic tolerance as well as dopamine receptor hypersensitivity induced by chronic morphine treatment and the two phenomena may be interrelated.

The effects of thyrotropin-releasing hormone on the central nervous system responses to chronic morphine administration

The effects of thyrotropin-releasing hormone (TRH) on abrupt and naloxone-precipitated abstinece symptoms were determined in male Swiss-Webster mice rendered dependent on morphine by SC implantation of morphine pellets. Intracerebral (IC) administration of TRH inhibited the hypothermic response observed during abrupt (removal of morphine pellets) and naloxone (0.1 mg/kg SC) precipitated withdrawal. IC injection of TRH also inhibited the naloxoneprecipitated withdrawal jumping response as evidenced by increases in the dose of naloxone required to elicit the response. The effects of TRH on the development of morphine dependence were also investigated. A single SC injection of TRH (4–16 mg/kg) did not modify development of morphine dependence. Administration of TRH prior to and during morphine pellet implantation inhibited the development of dependence as evidenced by inhibition in the development of abrupt and naloxone-induced withdrawal hypothermia. Even though the hypothermic response was blocked, multiple SC administration of TRH failed to modify naloxone-induced stereotyped jumping response. These studies indicate that TRH administration can modify central nervous system responses to chronic morphine treatment and that separate sites may initiate withdrawal jumping behavior and affect temperature regulation during abrupt and antagonist-induced abstinence.