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The effects of ibogaine, an alkaloid isolated form the bark of the African shrub, Tabernathe iboga, and noribogaine, a metabolite of ibogaine, on morphine antinociception were determined in male Swiss-Webster mice. Mice were rendered tolerant to morphine by implanting them with a pellet containing 25 mg of morphine base for 3 days. Placebo pellet-implanted mice served as controls. The antinociception of morphine (10 mg/kg, s.c.) was determined alone or in combination with an appropriate dose of ibogaine or noribogaine. Tolerance to morphine developed as a result of morphine pellet implantation as evidenced by decreased antinociceptive response to morphine. Both ibogaine and noribogaine dose-dependently enhanced morphine antinociception in morphine-tolerant but not in morphine-naive mice. It is concluded that ibogaine and noribogaine enhance morphine antinociception in morphine-tolerant mice.

The effects of chronic morphine administration on the kinetics of nitric oxide synthase (NOS) activity were determined in the mouse cerebral cortex and cerebellum. Male Swiss-Webster mice were implanted subcutaneously with morphine pellets each containing 25 mg of morphine base for 3 days. Mice implanted with placebo pellets served as controls. NOS activity was determined by measuring the rate of conversion of [3H]arginine to [3H]citrulline. Morphine pellet implantation increased NOS activity in the cerebral cortex and cerebellum. Analysis of the Eadie-Hofstee plot indicated that the Vmax of NOS in the cortex and cerebellum was 140 and 228 pmol [3H]citrulline formed/min/mg protein and the Km values were 9.3 and 10.1 mumol/l, respectively. Mice implanted with morphine pellets had higher Vmax values in both the cortex and cerebellum, but the Km values did not differ from those of control mice implanted with placebo pellets. It is concluded that chronic treatment with morphine increases NOS activity in the brain without modifying its substrate affinity.

Effects of multiple administrations of cocaine and subsequent cocaine withdrawal on the activity of nitric oxide synthase (NOS) in brain regions and spinal cord of male Swiss-Webster mice were determined. Chronic administration of cocaine resulted in the development of sensitization to its locomotor activity in the mouse. Chronic administration of cocaine was associated with increases in NOS activity in cerebral cortex, cerebellum, midbrain, hypothalamus, hippocampus, amygdala and spinal cord, but NOS activity was unaffected in pons/medulla and corpus striatum. Forty-eight hours after withdrawal from cocaine, NOS activity was increased only in the cerebral cortex. Recent studies have shown that cocaine-induced sensitization to behavioral effects can be inhibited by NOS inhibitors. The present studies provide the first evidence that chronic treatment with cocaine alters NOS activity in brain regions and spinal cord, and are consistent with behavioral studies with cocaine and NOS inhibitors.

Chronic administration of L-arginine (200 mg/kg i.p.) but not of D-arginine (200 mg/kg i.p.) twice a day for 4 days decreased the antinociceptive response to subcutaneously administered morphine-6-beta-D-glucuronide (M6G), a potent metabolite of morphine, in male Swiss-Webster mice as measured by the tail-flick test. However, the antinociceptive response to intracerebroventricularly administered M6G was unaffected by chronic treatment with L-arginine. The decreased antinociceptive response to M6G (s.c.) was reversed by concurrent administration of NG-nitro-L-arginine (5 mg/kg i.p.), an inhibitor of nitric oxide synthase. Acute administration of L-arginine (200 mg/kg i.p.) had no effect on M6G-induced antinociception, but higher doses (400 and 800 mg/kg i.p.) decreased it. Since the antinociceptive response to centrally administered M6G was unaffected by chronic L-arginine treatment, the decreased antinociceptive response of peripherally administered M6G may be related to a decrease of M6G entry into brain structures responsible for antinociceptive action.

The effects of tolerance to l-trans-delta 9-tetrahydrocannabinol (THC) following repeated administration and of subsequent abstinence following drug withdrawal on the cellular immune function were determined in female B6C3F1 mice. Mice were injected with THC (10 mg/kg s.c.) twice daily for 4 days. On day 5, analgesic response to various doses of THC was determined using the tail flick test. Similarly, hypothermic response to THC was also determined. Multiple injections of THC resulted in the development of tolerance to both the analgesic and hypothermic effects of THC. Immune function studies were performed on mice rendered tolerant to or abstinent from THC by these procedures. Neither tolerance nor abstinence subsequent to a 4-day THC administration had any effect on either body weight or thymus weight and cellularity, although both spleen weight and cellularity were decreased in THC-abstinent animals. Likewise, no significant effects on B cell proliferation were observed in either tolerant or abstinent mice. The production of the cytokine interleukin-2 by T helper cells was markedly suppressed in both tolerant and abstinent mice, whereas the production of interleukin-4 was significantly suppressed only in THC-abstinent mice. Significant suppression of tumor cell cytolysis mediated by cytotoxic T cells and natural killer cells was only observed in THC-abstinent mice. These results suggest that THC-mediated modulation of the immune response may result from a differential effect on cellular populations.

The effect of chronic administration of naltrexone, an opioid receptor antagonist, on the activity of the dopamine transporter in brain regions and spinal cord was determined. Male Sprague-Dawley rats were implanted with a pellet containing 10 mg naltrexone for 7 days. Rats serving as controls were implanted with a placebo pellet. Two groups of rats were used. In one, the pellets were left intact, and in the other they were removed 16 h prior to sacrificing. The dopamine transporter was labeled with [3H]GBR 12935. The binding of [3H]GBR 12935 in rats in which naltrexone pellets were left intact was decreased by 63 and 31% in corpus striatum and spinal cord, respectively, when compared to placebo pellet implanted controls. The decrease in binding in the striatum was due to changes in the Bmax value of [3H]GBR 12935; the Kd values did not differ. In hypothalamus, pons-medulla, hippocampus, midbrain, cortex, and amygdala of naltrexone and placebo pellet implanted rats, the binding of [3H]GBR 12935 did not differ. In naltrexone-treated rats from which pellets had been removed, the binding of [3H]GBR 12935 was decreased in hippocampus, amygdala, and spinal cord by 68, 77, and 61%, respectively, in comparison with tissues from the control rats. The results indicate that chronic blockade of opioid receptors results in downregulation of dopamine transporter in selected brain regions and spinal cord.

Two potent inhibitors of nitric oxide synthase (NOS), namely, NG-nitro-L-arginine (NNA) and NG-monomethyl-L-arginine (NMMA) were administered intracerebroventricularly (i.c.v.) in morphine-dependent mice to investigate their effects on abrupt withdrawal and naltrexone-precipitated abstinence signs. Male Swiss-Webster mice were rendered dependent on morphine by subcutaneous implantation of a morphine pellet containing 75 mg of morphine base. Mice implanted with placebo pellets served as controls. NMMA or NNA administered i.c.v. had minimal effects on body weight loss and hypothermia that occur during abrupt withdrawal of morphine. When administered i.c.v., both NNA or NMMA (0.1, 1 and 10 micrograms/mouse) dose-dependently inhibited naltrexone-induced stereotyped jumping behavior in mice. I.c.v. administration of NMMA also attenuated withdrawal induced fecal pellet formation. This effect, however, was not dose-dependent. In conclusion, these results suggest that brain NO plays an important role in the expression of behavioral signs of morphine withdrawal syndrome. In addition, these results support the idea that NOS inhibitors may be potentially useful in the treatment of opioid withdrawal syndrome.

In male Sprague-Dawley rats, acute and chronic effects of dizocilpine (MK-801), a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, were determined on the analgesic and hypothermic actions of U-50,488H, a kappa-opioid receptor agonist. In addition, the in vitro effects of MK-801 on the binding of [3H]ethylketocyclazocine ([3H]EKC) to kappa-opioid receptors in brain and spinal cord of the rat were determined. A single injection of MK-801 given 10 min prior to U-50,488H or given twice a day for 4 days dose-dependently enhanced the analgesic action of U-50,488H. The enhancement of the analgesic response was much greater in rats injected chronically with MK-801 as compared with those injected acutely. Both single and multiple injections of MK-801 failed to affect the hypothermic action of U-50,488H. In vitro, MK-801 inhibited the binding of [3H]EKC to brain and spinal cord membranes with IC50 values of 9.80 +/- 1.7 and 1.37 +/- 0.58 microM, respectively. Chronic administration of MK-801 twice a day for 4 days increased the Bmax value of [3H]EKC binding in the brain, but had no effect on Kd. On the other hand, chronic treatment with MK-801 decreased the Kd of [3H]EKC binding in spinal cord without affecting Bmax. It is concluded that blockade of NMDA receptor enhances the analgesic response to a kappa-opioid receptor agonist and upregulates brain and spinal cord kappa-opioid receptors. Finally, the results suggest that the NMDA receptor may have a role in the regulation of kappa-opioid systems.

The immunomodulatory potential of the indole alkaloids ibogaine and harmaline was examined in a panel of in vitro immune function assays. These assays were chosen to assess T-cell regulatory and effector function, B-cell function, macrophage function, and natural killer-cell function. The in vitro exposure to either ibogaine or harmaline resulted in a dose-related suppression of all immune functions examined except macrophage function. This suppression was noted at various concentrations in different assays, but was generally only associated with high concentrations (10-100 mumol/l).

Nitric oxide synthase (NOS) activity was determined by the rate of conversion of [3H]arginine to [3H]citrulline in brain regions (midbrain, hypothalamus, cerebellum, hippocampus, corpus striatum, cortex, pons-medulla and amygdala) and spinal cord of male Swiss Webster mice and male Sprague-Dawley rats. In mice, high activity of NOS was found in cerebellum, hypothalamus and midbrain; intermediate activity in pons-medulla, hippocampus, amygdala, corpus striatum and cortex; and low activity in the spinal cord. In rat, highest activity of NOS was observed in cerebellum followed in decreasing order by midbrain, hypothalamus, cortex, striatum, pons-medulla, hippocampus and spinal cord. In all tissues, NOS activity was higher in rat than in mouse. Analysis of the Eadie-Hofstee plot indicated that the Vmax and Km values of the enzyme in cortex and cerebellum of rats were higher than in mouse tissues. These studies show differential distribution of NOS activity in mouse and rat brain regions and spinal cord and higher activity of NOS in rat brain regions and spinal cord compared to mouse tissues.

Both in vivo and in vitro exposure to morphine have been reported to produce a number of immunomodulatory effects in both laboratory animals and humans. The current study was performed to assess the direct in vitro effect of exposure to morphine or morphine metabolites on immune response parameters. Murine B6C3F1 splenic lymphocytes or peritoneal macrophages were cultured in vitro at concentrations of 0.0001-100 mumol/l morphine sulfate, morphine-3-glucuronide, morphine-6-glucuronide, or normorphine. B cell proliferation was significantly suppressed following exposure to all drugs. Production of interleukin (IL)-2, IL-4, and IL-6 was affected only moderately by all drugs except morphine-6-glucuronide, which produced a marked suppression at 100 mumol/l. Both basal and augmented natural killer (NK) cell function were unaffected by any drug except morphine-6-glucuronide, which enhanced NK cell activity at concentrations between 0.0001 and 1.0 mumol/l. In contrast, both morphine-3-glucuronide and morphine-6-glucuronide significantly inhibited cytotoxic T lymphocyte induction at concentrations between 0.0001 and 100 mumol/l, whereas morphine and normorphine were inactive in this assay. In summary, in the absence of direct cellular cytotoxicity, a differential immunomodulation was observed following in vitro exposure to morphine and its metabolites.

The effect of NG-monomethyl-L-arginine (NMMA), an inhibitor of nitric oxide synthase, on the development of tolerance to the analgesic and hypothermic actions of U-50,488H, a highly selective kappa-opiate agonist, was determined in the rat. Male Sprague-Dawley rats were rendered tolerant to the pharmacological actions of U-50,488H by twice daily intraperitoneal injections of the drug (25 mg/kg) for 4 days. To determine the effect of NMMA on tolerance to U-50,488H, NMMA was administered 10 min prior to each injection of U-50,488H. Multiple injections of U-50,488H resulted in the development of tolerance to its analgesic and hypothermic actions. NMMA (2, 4 and 8 mg/kg) inhibited the development of tolerance to the analgesic but not to the hypothermic action of U-50,488H. Multiple injections of U-50,488H resulted in a slower gain in body weight which was not modified by treatment with NMMA. The results indicate that inhibition of nitric oxide synthase can selectively block the tolerance to its analgesic action in the rat.

Effects were determined of chronic administration and withdrawal of a highly selective kappa-opioid receptor agonist, U-50,488H, on methionine-enkephalin levels in central and peripheral tissues of male Sprague-Dawley rats. Rats were rendered tolerant to and physically dependent on U-50,488H by twice daily injections of 25 mg/kg of this compound for 5 days. Rats deemed abstinent were injected with this drug for 4 days and sacrificed on 5th day. Methionine-enkephalin concentration increased in the hippocampus of U-50,488H-tolerant-dependent rats, whereas in abstinent rats, its level was elevated only in the hypothalamus. Levels of methionine-enkephalin in the pituitary gland of U-50,488H-tolerant-dependent or abstinent rats were unchanged. Among peripheral tissues, methionine-enkephalin concentration decreased in the adrenal gland of U-50,488H-tolerant-dependent rats. In the U-50,488H-abstinent rats, methionine-enkephalin concentration was elevated in the heart. In tissues of morphine- and U-50,488H-tolerant-dependent and abstinent rats methionine-enkephalin concentrations were affected differentially, suggesting inherent differences in mu- and kappa-opiate-mediated tolerance-dependence and abstinence processes.

The effect of dizocilpine (MK-801), an N-methyl-D-aspartate receptor antagonist, on the development of tolerance to the analgesic and hyperthermic effects of morphine was determined in the rat. Tolerance to morphine in male Sprague-Dawley rats was induced by implanting subcutaneously 6 morphine pellets during a 7-day period. Two schedules of intraperitoneal injections of MK-801 were used. In one, the drug was injected once a day, and in the other it was injected twice a day. The doses of MK-801 were 0.03, 0.1 and 0.3 mg/kg. In the treatment once a day, MK-801 blocked the development of tolerance to the analgesic effect of morphine, but there was no dose-dependent effect. In the treatment twice a day, MK-801 produced a dose-dependent inhibition of tolerance to the analgesic effect of morphine. Higher doses of MK-801 produced high mortality. MK-801 given once a day or twice a day failed to affect the tolerance to the hyperthermic effect of morphine. In both schedules of MK-801 treatment, the highest dose of MK-801 resulted in high mortality. It is concluded that MK-801 is selective in blocking the tolerance to the analgesic effect of morphine in the rat.

Previously it was demonstrated that intravenously administered morphine produced greater analgesic but lower hyperthermic responses to morphine in 24-week-old rats in comparison to 8-week-old rats. The differential pharmacological responses to morphine could not solely be attributed to the pharmacokinetic parameters, namely area under the serum morphine concentration-time curve, serum levels of morphine extrapolated to zero time, half-life, mean residence time, apparent volume of distribution at the steady state, terminal rate constant and total body clearance of morphine in serum. In order to determine whether the differences in pharmacological responses to morphine in rats from two age groups are related to differential distribution of morphine in the central nervous system, in the present study, the time course of the distribution of morphine in brain regions (hypothalamus, hippocampus, cortex, pons and medulla, amygdala, midbrain and corpus striatum), spinal cord and serum following intravenous injection of 10 mg/kg dose to 8- and 24-week-old male Sprague-Dawley rats was determined. Morphine injected intravenously produced a greater analgesic but less intense hyperthermic effect in 24-week-old rats in comparison to 8-week-old rats. In most of the brain regions and spinal cord, with few exceptions, the concentration of morphine was found to be greater in 24-week-old rats than in 8-week-old rats. Similarly, the ratio of the concentration of morphine in brain region or spinal cord to serum was significantly higher in rats from the older age group. The studies demonstrate that the altered pharmacological responses to intravenously administered morphine to rats of differing ages may be related to the higher concentration of morphine in the central nervous system of older rats, which in turn may be related to the differences in the blood-brain barrier to morphine in the two age groups.

Effects of naltrexone administered intravenously on the pharmacological actions and kinetics of morphine in serum following intravenous administration of morphine were determined in male Sprague-Dawley rats. A 10 mg/kg dose of morphine produced an analgesic response as measured by the tail flick test. Morphine also produced a hyperthermic effect. Naltrexone dose (0.625-2.5 mg/kg)-dependently antagonized the analgesic and hyperthermic effects of morphine. The effect of naltrexone (0.625 and 2.5 mg/kg) on the pharmacokinetic parameters area under the serum morphine concentration time curve (AUC0-->infinity), serum levels of morphine extrapolated to zero time (Cmax), half-life (t1/2), mean residence time (MRT), total body clearance (Clt), and volume of distribution at steady state (Vss) of morphine in serum was determined. Naltrexone (0.625 mg/kg) significantly increased AUC0-->infinity, Cmax, t1/2 MRT, but decreased the Vss, elimination rate constant (k) and Clt. The higher dose of naltrexone (2.5 mg/kg) produced an increase in the Cmax value of morphine in the serum, but the other pharmacokinetic parameters were unaffected. Since increased morphine concentrations in serum produced by naltrexone cannot explain its antagonistic effects on analgesia and hyperthermia, it is concluded that naltrexone produces its effects by blocking opiate receptors at the appropriate sites. The increases in serum morphine levels by naltrexone may be related to displacement of morphine from protein binding sites and inhibition of morphine metabolism by glucuronyl transferase. This study for the first time demonstrates that in the rat, when morphine and naltrexone are given concurrently, although serum levels of morphine increase, pharmacological effects of morphine are antagonized.(ABSTRACT TRUNCATED AT 250 WORDS)

The binding of 3H-D-Pen2-D-Pen5-enkephalin (DPDPE), a highly selective delta-opiate receptor agonist, to membranes of discrete brain regions and spinal cord of 10-week-old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were amygdala, hippocampus, hypothalamus, pons and medulla, corpus striatum, midbrain and cortex. 3H-DPDPE bound to membranes of brain regions and spinal cord at a single high affinity site with apparent dissociation constant value of 4 nmol/l, except in cortex where the values were higher. The highest density of 3H-DPDPE binding sites were in hypothalamus and lowest in pons and medulla. The receptor density (Bmax value) and apparent dissociation constant (Kd value) of 3H-DPDPE to bind to delta-opiate receptors on the membranes of hippocampus, hypothalamus, corpus striatum, midbrain, cortex, pons and medulla and spinal cord of WKY and SHR rats did not differ. The Bmax value of 3H-DPDPE in amygdala of SHR rats was higher than in WKY rats, but the Kd values in the two strains did not differ. It is concluded that SHR rats have a higher density of delta-opiate receptors, labeled with 3H-DPDPE, in amygdala in comparison with WKY rats. Whether such a difference in the density of delta-opiate receptors is related to the elevated blood pressure of SHR rats is not clear.

The decay characteristics of tolerance and physical dependence on morphine induced by a pellet implantation procedure were determined in male Sprague-Dawley rats. Rats were implanted subcutaneously with 6 morphine pellets during a 7-day period. The pellets were removed, and at various times thereafter tolerance to the analgesic and hyperthermic effects of morphine was measured by determining the response in rats implanted with morphine and placebo pellets. Similarly, the physical dependence was assessed by monitoring withdrawal signs following an injection of naloxone. A high degree of tolerance developed to the analgesic and hyperthermic effects of morphine. Similarly, a high degree of physical dependence also developed as evidenced by a high incidence of jumping response, teeth chattering and production of fecal boli induced by injections of naloxone. In addition, loss of body weight and body temperature also occurred. The analgesic and hyperthermic response to morphine recovered very gradually. There was no significant difference in the analgesic and hyperthermic responses to morphine on day 4 after the pellet removal in rats implanted with morphine and placebo pellets. The decay of tolerance was linear with time for the analgesic effect (r = 0.98) and for the hyperthermic effect (r = 0.93). The change in symptoms of physical dependence on morphine with time depended on the specific symptom monitored. The average number of jumps and teeth chattering decreased with time in a linear fashion with r values of 0.98 and 0.99, respectively. However, the number of fecal boli and wet dog shakes increased linearly with time (r = 0.97). The recovery of loss of body weight was also linear with time. Thus, it is clear that fecal boli and wet dog shakes, which increase in number as the dependence decays, are signs of a low degree of dependence. The results suggest that different central or peripheral mechanisms may be operating in different withdrawal symptoms. These studies may prove to be useful when studying the mechanisms involved in the induction and reversibility of tolerance and dependence processes, and in long-term effects of opiates at a time when the tolerance and physical dependence is no longer evident.

The analgesic and thermic responses to morphine (5 and 10 mg/kg) injected intravenously to 8- and 24-week-old male Sprague-Dawley rats were determined. Greater analgesic and lower hyperthermic responses to morphine in 24-week-old rats in comparison to 8-week-old rats were observed. The pharmacokinetic parameters of morphine administered intravenously were also determined. Cmax for 5 and 10 mg/kg doses of morphine were smaller in 24-week-old rats in comparison to 8-week-old rats; however, AUC0----infinity was smaller only for 5 mg/kg dose. For 10 mg/kg dose, mean residence time (MRT) and the apparent steady state volume of distribution (Vss) for the older rats were higher than for the younger ones, but for 5 mg/kg dose the values did not differ. The enhanced responses to morphine in older age group of rats for 5 mg/kg dose cannot be explained solely on the basis of pharmacokinetics. However, for 10 mg/kg dose of morphine, the greater responses in 24-week-old rats could probably be related to increases in MRT and Vss. Factors other than serum kinetics, like kinetics of morphine in the brain as well as the brain opiate receptors, may also be involved in the differential effects of morphine in rats of different ages.

The effect of delta- and kappa-opiate receptor agonists on the binding of 3H-(3-MeHis2) thyrotropin-releasing hormone (3H-MeTRH) to membranes of the spinal cord and amygdala of male Sprague-Dawley rats was determined in an effort to further understand interactions between opiates and TRH receptors. The agonists used were D-Ala2-MePhe4-Gly-ol5-enkephalin (DAMGO, mu-receptor), cyclic D-penicillamine2-D-penicillamine5-enkephalin (DPDPE, delta-receptor), cyclic D-penicillamine2-L-penicillamine5-enkephalin (DPLPE, delta-receptor), D-Ala2-D-Leu5-enkephalin (delta-receptor), U-50,488H and U-69,593 (kappa-receptor). 3H-MeTRH bound to amygdala and spinal cord membranes at a single site with Bmax values of 35.7 +/- 5.4 and 15.8 +/- 2.6 fmol/mg protein, and Kd values of 6.3 +/- 1.1 and 5.2 +/- 0.7 nmol/l, respectively. The competition experiments were carried out at a concentration of 2 nmol/l 3H-MeTRH. The concentration of opiate ranged from 10(-9) to 10(-4) mol/l. DAMGO, DPDPE and DPLPE had no effect on the binding of 3H-MeTRH to amygdala or spinal cord membranes. The two highly selective kappa-agonists differed in their interaction with TRH receptors. Whereas U-69,593 did not modify the binding of 3H-MeTRH, U-50,488H significantly inhibited the binding of 3H-MeTRH to both spinal cord and amygdala membranes. U-50,488H has been found to be 10 times more potent than U-69,593 at the central kappa-opiate receptors and may explain their differential action at the TRH receptors. It is concluded that mu- and delta-opiate agonists do not interact with brain and spinal cord TRH receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of chronic administration of U-50,488H, a highly selective kappa-opiate receptor agonist, and its subsequent withdrawal were determined. The binding characteristics of [3H]SCH 23390 to dopamine D1 receptors were investigated on membranes of rat spinal cord and in discrete brain regions. Male Sprague-Dawley rats received U-50,488H (25 mg/kg) intraperitoneally twice a day for 4 days. Animals serving as controls received only vehicle. Two different treatment schedules were used. In one, rats were injected with U-40,588H on day 5 and were sacrificed 1 h later (tolerant-dependent rats). In another, the rats were sacrificed 16 h after the last injection of U-50,488H (abstinent rats). Chronic administration of U-50,488H resulted in the development of tolerance to its analgesic effect, as demonstrated by the decreased response to a challenge dose of U-50,488H compared to vehicle-injected rats. The binding characteristics (Bmax and Kd values) of [3H]SCH 23390 were unaffected in spinal cord and other regions of brain of tolerant-dependent rats. In U-50,488H-abstinent rats, Bmax values of [3H]SCH 23390 were increased in hypothalamic and striatal membranes, but Kd values were unaffected. These results suggest that, in U-50,488H-abstinent rats, dopamine D1 receptors are up-regulated in hypothalamus and striatum.

The effect of melanotropin release inhibiting factor (Pro-Leu-Gly-NH2, MIF) was determined on changes induced by two neuroleptics, haloperidol and centbutindole, in cerebral cortical 5-hydroxytryptamine (5-HT) receptors. Male Sprague-Dawley rats were injected daily i.p. with vehicle, haloperidol (1.0 mg/kg) or centbutindole (0.5 mg/kg), respectively, for 21 days. On day 22, these 3 groups were further divided into 2 subgroups and injected with either vehicle or MIF (2.0 mg/kg, i.p.) daily for 3 days. 3H-5-HT was used to study 5-HT1 receptors, and 3H-spiroperidol to label 5-HT2 receptors in the cerebral cortex. Chronic administration of haloperidol significantly increased (39.7%) the maximal binding capacity (Bmax) of 3H-5-HT binding to 5-HT1 receptors. Dissociation constant (Kd) values did not change. Centbutindole had no effect on 5-HT1 receptors. MIF had no effect on 5-HT1 receptors, nor did it alter haloperidol-induced increases in the Bmax of 3H-5-HT binding to 5-HT1 receptors. Chronic administration of centbutindole significantly increased (61.1%) the Bmax of 3H-spiroperidol binding to 5-HT2 receptors. No change occurred in the Kd values. Chronic treatment with haloperidol had no effect on 5-HT2 receptor characteristics. MIF had no effect on 5-HT2 receptors or on the increase in 5-HT2 receptor density induced by centbutindole. The behavioral syndrome induced by 5-hydroxytryptophan (5-HTP) (50, 100 and 200 mg/kg, i.p.) was also measured in rats treated chronically with haloperidol or centbutindole. Haloperidol had no effect on the 5-HTP syndrome, whereas centbutindole stimulated by 24-45% the intensity of the syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of chronic administration of methimazole (0.05% w/v) in drinking water for 32 days to male Sprague-Dawley rats on the binding of opioid ligands, 3H-Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO, mu-receptors), 3H-Tyr-D-Ser-Gly-Phe-Leu-Thr (DSTLE, delta-receptors) and 3H-ethylketocyclazocine (EKC, kappa-receptors) to membranes of brain regions was determined. Chronic administration of methimazole to rats decreased their rate of body weight gain, colonic temperature, systolic blood pressure and heart rate in comparison to vehicle-treated rats. Administration of methimazole also decreased the serum concentration of triiodothyronine (total T3) and T4 when compared to vehicle-treated rats. The binding of 3H-DAGO to membranes of amygdala, pons and medulla, striatum, midbrain and cortex of methimazole-treated rats was greater than vehicle-treated rats, however, the binding to membranes of hypothalamus in the two treatment groups did not differ. The binding of 3H-DSTLE in amygdala and hypothalamus of methimazole-treated rats did not differ but it was significantly greater in pons and medulla, midbrain, cortex and striatum of methimazole-treated rats than vehicle-treated rats. The binding of 3H-EKC to membranes of pons and medulla was lower and of striatum and cortex of methimazole-treated rats was significantly greater than vehicle-treated rats, but the binding to membranes of amygdala, hypothalamus, and midbrain of the two treatment groups did not differ. The results indicate that brain, mu-, delta- and kappa-opioid receptors are differentially altered in hypothyroidism.

The effect of hypothyroidism on the thyrotropin-releasing hormone (TRH) receptors in several brain regions and pituitary of rats was determined. TRH receptors were labeled with 3H-(3-MeHis2)TRH (3H-MeTRH). Hypothyroidism was induced in male Sprague-Dawley rats by administering methimazole (0.05% w/v) in drinking water for 32 days. Rats serving as controls were given water without the methimazole. The development of a hypothyroid state was evidenced by significant decreases in colonic temperature, systolic blood pressure, heart rate and serum concentration of triiodothyronine (total T3), thyroxine and T3 uptake (T3U) as compared to control rats. The rate of gain in body weight of methimazole-treated rats was significantly lower than that of control rats. Binding of 3H-MeTRH at 2 nM concentration to membranes prepared from brain regions (striatum, hypothalamus, cortex, midbrain and pons plus medulla) of methimazole-treated and control rats did not differ. However, binding of 3H-MeTRH to pituitary membranes of methimazole-treated rats was significantly lower as compared to the pituitary of control rats. The results indicate that, in the rat, development of hypothyroidism is associated with down-regulation of pituitary TRH receptors but brain receptors remain unaffected.

Previous studies from this laboratory had indicated that in spontaneously hypertensive (SHR) rats the development of hypertension paralleled increases in brain receptors for thyrotropin-releasing hormone (TRH). The increase appeared to be confined to hypothalamus and striatum. The present studies were undertaken to determine the binding characteristics of TRH receptors in the peripheral tissues of SHR and normotensive Wistar-Kyoto (WKY) rats. TRH receptors were labeled with 3H-MeTRH. The binding of 3H-MeTRH to membranes prepared from spinal cord, heart, lung, kidney and adrenal gland of SHR and WKY rats was determined. In WKY rats, the binding of 3H-MeTRH to various tissue membranes was in the following order: spinal cord greater than kidney greater than lung greater than heart = adrenals. The binding of 3H-MeTRH to spinal cord membranes of SHR rats was significantly higher in comparison to WKY rat tissues, whereas the binding of 3H-MeTRH in kidney, heart, lung and adrenals of the two strains of rats did not differ. The increase in the binding of 3H-MeTRH to spinal cord of SHR rats was due to increases in the Bmax values and not in the Kd values. The results suggest that in addition to the brain, TRH receptors in the spinal cord of SHR rats are also up-regulated and may also play an important role in the regulation of blood pressure.

Intraperitoneal administration of L-tyrosine (used as methyl ester HCl) produced dose-dependent analgesia in male Sprague-Dawley rats as measured by the tail-flick test. The maximal analgesic response was obtained with 200 mg/kg dose of tyrosine. Administration of morphine also produced a dose-dependent analgesic response. Tyrosine in doses of 50 mg/kg or higher potentiated morphine-induced analgesia. The analgesic response of tyrosine (200 mg/kg) was antagonized by naloxone (1 mg/kg), an opiate antagonist. Subcutaneous administration of methyl naltrexone bromide (MRZ 2663 BR, 1 and 10 mg/kg) had no effect on tyrosine-induced analgesia. Intracerebroventricular injection of MRZ 2663 BR (1 and 10 micrograms/rat) effectively blocked tyrosine-induced analgesia. It is concluded that tyrosine-induced analgesia and its potentiation of analgesic response to morphine may be mediated via either the opiate receptors or activation of endogenous opioidergic systems of central origin.

The effect of chronic administration of morphine to Sprague-Dawley rats on the binding of dopamine receptor agonist, 3H-N-n-propylnorapomorphine (3H-NPA) to striatal membranes was determined. For chronic administration of morphine, rats were implanted subcutaneously with four morphine pellets (each containing 75 mg of morphine free base) during a 3-day period. Placebo pellet-implanted rats served as controls. Two experimental protocols were followed. In one, the rats were sacrificed 70 h after the implantation of first pellet and in the other, the pellets were removed and the animals were sacrificed 24 h later, and the binding of 3H-NPA was determined. Rats receiving morphine showed no difference in the total number of binding sites (Bmax value) but there was a decrease in the apparent dissociation constant (Kd value) compared with placebo controls. Moreover, such a decrease in Kd in morphine-treated rats persisted even 24 h after removal of morphine pellets. The effect of prolyl-leucyl-glycinamide (MIF; 2 mg/kg), which has been shown to inhibit the development of tolerance to and dependence on morphine, on the changes in the binding of 3H-NPA induced by the implantation of morphine pellets was also determined. MIF antagonized the decreases in Kd values induced by the administration of morphine. However, when administered chronically by itself, MIF had no effect on either the Bmax or Kd values of 3H-NPA. It is concluded that the chronic administration of morphine is associated with enhanced activity of dopamine receptors in the central nervous system as revealed by lowering of the Kd value of the agonist, NPA.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of repeated administration of U-50,488H, a kappa-opioid receptor agonist, on the development of tolerance to its analgesic effect and on the 5-HT1 and 5-HT2 receptors in the cerebral cortex and spinal cord of the rat were determined. Male Sprague-Dawley rats were injected twice daily with U-50,488H, (25 mg/kg, i.p.) or its vehicle for 4 days. The assessment of tolerance to the analgesic effect and biochemical determinations were made on day 5. Repeated administration of U-50,488H resulted in the development of tolerance to its analgesic effect. The 5-HT1 and 5-HT2 receptors were characterized by using 3H-5-hydroxytryptamine (3H-5-HT) and 3H-spiperone as the ligands and unlabeled 5-hydroxytryptamine (5-HT) and ketanserin, respectively, to determine the nonspecific binding. In the spinal cord 3H-5-HT bound to 5-HT1 receptors at a single high-affinity site with a Bmax value of 41.3 +/- 9.6 fmol/mg protein and a Kd value of 22.6 +/- 7.0 nmol/l. 3H-Spiperone bound to 5-HT2 receptors in the spinal cord with a Bmax value of 16.1 +/- 3.8 fmol/mg protein and a Kd value of 0.36 +/- 0.15 nmol/l. Repeated administration of U-50,488H to rats did not affect spinal cord 5-HT1 and 5-HT2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)