Abstinent Rats Research Articles

The effect of U-50,488H tolerance-dependence and abstinence on the levels of dynorphin (1–13) in brain regions, spinal cord, pituitary gland and peripheral tissues of the rat

Male Sprague-Dawley rats were rendered tolerant to and physically dependent on U-50,488H, a κ-opiate agonist, by injecting 25 mg/kg of the drug intraperitoneally twice a day for 4 days. Two sets of rats were used. Rats labeled as tolerant-dependent were injected with U-50,488H (25 mg/kg) 1 h before sacrificing on day 5, whereas the abstinent rats were sacrificed on day 5 without the injection of U-50,488H. Of all the tissues examined, the pituitary gland had the highest level of dynorphin (1–13), whereas the heart had the lowest level. The levels of dynorphin (1–13) increased in the hypothalamus, hippocampus and pons/medulla of U-50,488H tolerant-dependent rats, whereas in abstinent rats the levels of dynorphin (1–13) were elevated only in the midbrain. The levels of dynorphin (1–13) in the pituitary gland of U-50,488H tolerant-dependent or abstinent rats were unchanged. In peripheral tissues, the levels of dynorphin (1–13) in the heart of U-50,488H tolerant-dependent rats were increased. In the abstinent rats they were elevated in the adrenals, spleen, and the heart but were decreased in the kidneys. Compared to morphine tolerant-dependent and abstinent rats, significant differences in the levels of dynorphin (1–13) in tissues of 50,488H tolerant-dependent and abstinent rats were observed and may explain many pharmacological differences in the μ- and κ-opiate induced tolerance-dependence and abstinence processes.

Marked inhibition of mesolimbic dopamine release: a common feature of ethanol, morphine, cocaine and amphetamine abstinence in rats

Withdrawal of rats from chronic ethanol, morphine, cocaine and amphetamine resulted in a marked reduction in extracellular dopamine (DA) concentration in the ventral striatum as measured by microdialysis. Following ethanol and naloxone-precipitated morphine withdrawal, the time course of DA reduction paralleled that of the withdrawal symptomatology. On the other hand, following discontinuation of chronic cocaine, DA reduction was delayed by over 24 h but persisted for several days. After amphetamine withdrawal the fall in DA occurred more rapidly but the reduction also persisted for several days. The administration of the NMDA receptor antagonist, MK-801, to rats withdrawn from chronic ethanol, morphine or amphetamine, but not from chronic cocaine, readily reversed the fall in DA output. The reduction in extracellular DA during ethanol withdrawal was also reversed by SL 82.0715, another NMDA receptor antagonist.

The effect of morphine tolerance dependence and abstinence on immunoreactive dynorphin (1–13) levels in discrete brain regions, spinal cord, pituitary gland and peripheral tissues of the rat

The effect of morphine tolerance dependence and protracted abstinence on the levels of dynorphin (1–13) in discrete brain regions, spinal cord, pituitary gland and peripheral tissues was determined in male Sprague-Dawley rats. Of all the tissues examined, the highest level of dynorphin (1–13) was found to be in the pituitary gland. Among the brain regions and spinal cord examined, the levels of dynorphin (1–13) in descending order were: hypothalamus, spinal cord, midbrain, pons and medulla, hippocampus, cortex, amygdala and striatum. The descending order for the levels of dynorphin (1–13) in peripheral tissues was: adrenals, heart and kidneys. In morphine tolerant rats, the levels of dynorphin (1–13) increased in amygdala but were decreased in pons and medulla. In morphine abstinent rats, the levels of dynorphin (1–13) were increased in amygdala, hypothalamus and hippocampus. The levels of dynorphin (1–13) were increased in pituitary but decreased in spinal cord and remained so even during protracted abstinence. The levels of dynorphin (1–13) in the peripheral tissues of morphine tolerant rats were unaffected. However, in the heart and kidneys of morphine abstinent rats, the levels of dynorphin (1–13) were increased significantly. It is concluded that both morphine tolerance and abstinence modify the levels of dynorphin (1–13) in pituitary, central and peripheral tissues. Morphine abstinence differed from non-abstinence process in that there were additional changes (increases) in the levels of dynorphin (1–13) in brain regions (hypothalamus and hippocampus) and peripheral tissues (heart and kidneys) and may contribute to the symptoms of the morphine abstinence syndrome. The lower levels of dynorphin (1–13) in spinal cord may be responsible for the potentiation of morphine effects by κ-opiate agonist in morphine tolerant dependent rodents.

Differences in the binding of [ 3H][D-Ser 2,Thr 6]leucine-enkephalin and [ 3H][D-Pen 2,D-Pen 5]enkephalin to brain membranes of morphine tolerant-dependent rats

The effect of morphine tolerance-dependence and abstinence on the characteristics of δ-opialc receptors was determined in male Sprague-Dawlcy rats. Two ligands used lor characterizing the receptors were [ 3H][D-Ser 2,Thr 6]leucine-enkephalin ([ 3H]DSTLE) and [ 3H][D-Pen 2,D-Pen 5]enkephalin ([ 3H]DPDPE). Rats were implanted s.c. under light other anesthesia with six morphine pallets (each containing 75 mg of morphine free base). Rats which served as controls were implanted similarly with placebo pellets. Two scis of rats were used. In one group of rats. the pellets were left intact (tolerant-dependent) at the time of sacrificing and in the other the pellets had been removed 18 h earlier (abstiment). The spinal cord and brain regions (amygdala, hippocampus, hypothalamus, corpus striatum, mid-brain, pons and medulla and cortex) were dissected for binding studies. The binding of [ 3h]dstle to membranes of cerebral cortex of morphinc-tolcrant-dependent rats was decreased in comparison to control rats. and was due to a decrease in B max, rather than K d value. The binding of [ 3H]DSTLE to other brain regions or spinal cord of morphinc-tolerant-depcndent and abstinent rats did not differ from their respective controls. On the other hand, the binding of [ 3H]DPDPE was unaffected in any brain region or the spinal cord of morphine-tolerant-depcndent and abstinent rats when compared to their controls. The decrease in binding of [ 3H]DSTLE to cortical membranes of morpihine-tolerant-dcpendent rats amounted to 15%. Since DSTLE also binds to μ-opiate receptors, which have earlier been shown to be decreased in cortex of inorptline-toleranl-dependent rats, and the hinding of a more selective δ-opiate ligand [ 3H]DPDPE was unaffected, it is concluded that central δ-opiate receptors do not play a role in the development of morphine-induced tolerance-dependence or abstinence processes in the rat.

β-endorphin and methionine-enkephalin levels in discrete brain regions, spinal cord, pituitary gland and plasma of morphine tolerant-dependent and abstinent rats

The effect of morphine tolerance-dependence, protracted and naloxone-precipitated abstinence on the levels of β-endorphin and methionine-enkephalin in discrete brain regions, spinal cord, pituitary gland and plasma was determined in the male Sprague-Dawley rats. Among the brain regions examined, the levels of β-endorphin in descending order were: hypothalamus, amygdala, midbrain, hippocampus, corpus striatum, pons and medulla and cortex. The levels of β-endorphin in midbrain, hypothalamus, and pituitary of morphine tolerant-dependent rats were decreased significantly. During protracted withdrawal β-endorphin levels were decreased in amygdala, spinal cord and pituitary. During naloxone-precipitated abstinence β-endorphin levels were increased in corpus striatum, midbrain and cortex. In addition, in naloxone-precipitated abstinence β-endorphin levels were decreased in pituitary gland and hippocampus but increased in plasma. The levels of methionine-enkephalin in brain regions in decreasing order were: corpus striatum, pons and medulla, amygdala, hypothalamus, midbrain, hippocampus and cortex. The levels of methionine-enkephalin in pons and medulla, amygdala, hippocampus and pituitary gland were decreased in morphine tolerant-dependent rats. During protracted abstinence from morphine, methionine-enkephalin levels in spinal cord, amygdala, pons and medulla, midbrain, cortex, corpus striatum and pituitary gland were decreased. The levels of methionine-enkephalin in hypothalamus and corpus striatum of naloxone-precipitated abstinent rats were increased but were decreased in amygdala and pituitary gland. These results suggest that during morphine tolerance-dependence and during protracted abstinence β-endorphin and methionine-enkephalin levels in discrete brain regions and pituitary gland are decreased. During precipitated abstinence β-endorphin levels are increased in brain regions (except hippocampus) and plasma but decreased in pituitary, whereas methionine-enkephalin levels in amygdala and pituitary gland are decreased except in corpus striatum and hypothalamus where they are increased. The pituitary levels of β-endorphin where reduced in all three conditions. However, the levels after withdrawal were not significantly different from those in tolerant—dependent animals.

Binding characteristics of [3H]SCH 23390 in spinal cord and discrete brain regions of kappa-opiate tolerant-dependent and abstinent rats.

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.

Spinal cord thyrotropin releasing hormone receptors of morphine tolerant-dependent and abstinent rats

The effect of chronic administration of morphine and its withdrawal on the binding of 3H-[3-MeHis 2]thyrotropin releasing hormone ( 3H-MeTRH) to membranes of the spinal cord of the rat was determined. Male Sprague-Dawley rats were implanted with either 6 placebo or 6 morphine pellets (each containing 75-mg morphine base) during a 7-day period. Two sets of animals were used. In one, the pellets were left intact at the time of sacrificing (tolerant-dependent) and in the other, the pellets were removed 16 hours prior to sacrificing (abstinent rats). In placebo-pellet-implanted rats, 3H-MeTRH bound to the spinal cord membranes at a single high affinity binding site with a B max of 21.3±1.6 fmol/mg protein, and an apparent dissociation constant K d of 4.7±0.8 nM. In morphine tolerant-dependent or abstinent rats, the binding constants of 3H-MeTRH to spinal cord membranes were unaffected. Previous studies from this laboratory indicate that TRH can inhibit morphine tolerance-dependence and abstinence processes without modifying brain TRH receptors. Together with the present results, it appears that the inhibitory effect of TRH on morphine tolerance-dependence and abstinence is probably not mediated via central TRH receptors but may be due to its interaction with other neurotransmitter systems.

Down-regulation of hypothalamic 5-HT 1A receptors in morphine-abstinent rats

The effects of morphine tolerance-dependence and abstinence on 5-HT 1A receptors in brain regions and spinal cord of the rat were determined. Tolerance to and physical dependence on morphine was induced in male Sprague-Dawley rats by implanting six morphine pellets (each containing 75 mg of morphine free base) during a seven day period. Two groups of rats were used for binding studies. In one group the pellets were left intact (tolerant-dependent) and in the other they were removed (abstinent). Rats were killed, and spinal cords and brains were excised. Brain was dissected into seven regions (amygdala, hippocampus, hypothalamus, striatum, midbrain, pons + medulla and cortex). 5-HT 1A receptors were characterized by using [ 3H]8-hydroxy-di-n-propylaminotetralin ([ 3H]DPAT) as the ligand and unlabelled 5-HT to determine the non-specific binding. In morphine and placebo tolerant-dependent rats the binding of [ 3H]DPAT to 5-HT 1A receptors in brain regions and spinal cord did not differ. The B max value of [ 3H]DPAT in the hypothalamus of morphine abstinent rats was decreased by 61.9%. No change in B max value was observed in other brain regions and spinal cord. The K d values were unaffected. Subcutaneous administration of DPAT produced hypothermia in rats from which pellets had been removed. The intensity of DPAT-induced hypothermic response was greater in morphine abstinent rats as compared to placebo abstinent rats. Since DPAT is believed to have a major action on the presynaptic 5-HT neurons, it is concluded that in morphine abstinent rats 5-HT 1A receptors are down-regulated in hypothalamus, but in morphine tolerant-dependent rats they are unaffected.

The binding of 3H-(3-MeHis 2) thyrotropin releasing hormone to brain and pituitary membranes of morphine tolerant-dependent and abstinent rats

The effect of chronic administration of morphine and subsequent withdrawal on brain and pituitary receptors for thyrotropin releasing hormone (TRH) was investigated in Sprague-Dawley rats. The rats were implanted subcutaneously with four morphine pellets (each containing 75 mg of morphine free base) during a 3-day period. Placebo pellets, which contained all the excipients of morphine pellets except the morphine, were implanted in rats which served as controls. Both tolerance and physical dependence on morphine have been shown to develop as a result of this procedure. TRH receptors were labeled with 3H-(3-MeHis 2) TRH (MeTRH). 3H-MeTRH bound to brain membranes at a single high affinity site with B max (receptor density) value of 24.6±2.2 fmol/mg protein and K d (apparent dissociation constant) value of 3.7±0.4 nM. The binding of 3H-MeTRH to five regions of the brain namely, hypothalamus, cortex, striatum, midbrain and pons + medulla, as well as pituitary was also investigated. The binding of 3H-MeTRH to pituitary membranes was increased during the development of tolerance, whereas the binding to membranes prepared from different brain regions was unaffected. Serum concentration of triiodothyronine (T 3) and thyroxine (T 4) were found to be lower in chronic morphine-treated rats when compared to placebo-treated rats, however, serum TSH level remained unaltered. Twenty-four hours after the removal of morphine pellets (natural withdrawal), the binding of 3H-MeTRH to pons + medulla membranes was greater than in placebo control group. Naloxone-precipitated withdrawal produced results which were qualitatively similar to those obtained in rats from which pellets had been removed. The results suggest that the development of tolerance to morphine may be associated with changes in the pituitary-thyroid axis.

Brain and spinal cord 5-HT 2 receptors of morphine-tolerant-dependent and -abstinent rats

The effects of morphine tolerance-dependence and abstinence on 5-HT 2 receptors in brain and spinal cord of the rat were determined. Tolerance to and physical dependence on morphine was induced in male Sprague-Dawley rats by implanting six morphine pellets (each containing 75 mg of morphine free base) during a seven day period. Two groups of rats were used for binding studies. In one group the pellets were left intact and in the other they were removed. The rats were killed and spinal cords and brains were excised and dissected into six regions (amygdala, hippocampus, hypothalamus, striatum, midbrain and pons + medulla). 5-HT 2 receptors were characterized by using [ 3H]spiperone as the ligand and unlabelled ketanserin to determine the non-specific binding. In morphine and placebo abstinent rats the binding of [ 3H]spiperone to 5-HT 2 receptors in brain regions and spinal cord did not differ. The B max values of [ 3H]spiperone to bind to membranes prepared from non-abstinent morphine-dependent rats were increased in amygdala (78.0%), midbrain (65.0%) and pons + medulla (92.0%). The K d values were unaffected. It is concluded that in morphine-tolerant-dependent rats 5-HT 2 receptors are up-regulated in amygdala, midbrain and pons + medulla, but in morphine-abstinent rats they are unaffected.

Methionine-enkephalin and β-endorphin levels in spleen and thymus gland of morphine tolerant-dependent and abstinent rats

The effect of chronic administration of morphine and abrupt and naloxone-precipitated withdrawal on the levels of β-endorphin and methionine-enkephalin in spleen, adrenals and thymus glands of Sprague-Dawley rats was determined. Rats were made tolerant to and dependent on morphine by subcutaneous implantation of 6 morphine pellets (75 mg morphine in each) during a 7-day period. The tolerant-dependent (with pellets intact) and abstinent (pellets removed 18 hours earlier) rats were sacrificed. In another group, rats with pellets intact were injected with naloxone and sacrificed 10 min later (precipitated abstinence). The weights of the tissues under any of the above treatments did not change nor did the levels of methionine-enkephalin and β-endorphin in adrenals. The level of β-endorphin was elevated in the spleen and thymus of morphine tolerant-dependent rats, while the levels of methionine-enkephalin in rats undergoing abrupt or naloxone-precipitated abstinence were significantly higher than in their respective placebo controls. The levels of methionine-enkephalin in the thymus gland of rats with placebo and morphine pellets left intact did not differ. It is concluded that in morphine tolerant-dependent rats the levels of β-endorphin in spleen and thymus are elevated. During abrupt and naloxone-precipitated abstinence, the levels of methionine-enkephalin in the thymus gland are significantly elevated possibly due to an inhibition of their release. Since these opioid peptides have been implicated in immunomodulation, and alterations were seen in organs controlling immune function, the present results may be helpful in explaining altered immune function in morphine dependent and abstinent states.

Renal sympathetic nerve activity during morphine abstinence in sino‐aortic baroreceptor‐denervated rats

This study was undertaken to investigate the influence of the arterial baroreceptors on the response of renal sympathetic nerve activity (rSNA) during naloxone‐precipitated morphine abstinence in rats. In chronically baroreceptor‐denervated, morphine‐dependent rats, rSNA, mean arterial pressure (MAP) and heart rate (HR) were studied before and after repeated i.v. bolus doses of naloxone (0.005–5 mg kg−1), during chloralose anaesthesia or in the conscious state.In the anaesthetized animals, naloxone doses of 0.05–5 mg kg−1 caused a pronounced inhibition of rSNA, reaching a level 61 % below pre‐naloxone activity. This was accompanied by increases in MAP and HR. In the conscious rats, the lower doses of naloxone elicited an initial state of increased somatomotor activity. This was paralleled by slight increases in rSNA and MAP. After 4–5 min, the behavioural excitation faded and was replaced by lethargy. The rats exhibited still signs of withdrawal in the form of piloerection, chromodacryorrhoea and defaecations. Concomitantly, rSNA returned towards the pre‐naloxone level, while MAP showed a sustained increase. The higher naloxone doses exacerbated the hypertension without any further changes in rSNA or in behaviour.We conclude that the influence of the baroreceptors is of minor significance for the inhibition of rSNA during naloxone‐precipitated abstinence in anaesthetized rats. In conscious, intact rats, however, the baroreceptors seem to contribute to rSNA inhibition since no significance decrease of rSNA occurred in baroreceptor‐denervated rats in the present study. This is in contrast to our previous finding of a marked inhibition of rSNA in rats with intact baroreceptors.

The Role of GABA in morphine abstinence in rats

GABA mimetics such as baclofen, aminooxyacetic acid (AOAA) and diazepam decreased naloxone-precipitated abstinence wet dog shakes in morphine dependent rats. The GABA antagonists bicuculline and picrotoxin were not effective in small doses. The inhibition of wet dog shakes by baclofen, AOAA and diazepam was not reversed by bicuculline. This suggests that baclofen, AOAA and diazepam may inhibit morphine wet dog shakes not by direct GABA receptor stimulation. Inhibition by baclofen of wet dog shakes was reversed by 5-hydroxytryptophan (5-HTP) suggesting that the inhibiting effects of GABA mimetics are mediated by serotoninergic neurons.

Taurine inhibits wet-dog shakes and hippocampal seizures induced by opioid peptides in rats.

Wet dog shakes (WDS) are paroxysmal shudders of head, neck and trunk. This behavior has been observed when dipping animals into cold water (41), application of xylene to the für (39) and tactile stimulation around ears (1). Pharmacological studies revealed that WDS can be produced by administration of thyrotropin-releasing hormone (9,24,29,41,42), 5-Hydroxytryptamine (3,12), or kainic acid (5,25). WDS are also known as a classical sign of morphine abstinence in rats (40,43). In 1976, Bloom et al. first reported that this shaking behavior was elicited by acute administration of β-endorphln into the lateral ventricle in rats. Similar observations were made in rats with enkephalin (15). In addition, it was found that epileptic discharges were provoked by the intraventricular (icv) injection of opioid peptides and WDS always accompanied the onset of seizure discharges (15,16,37). These findings suggest that there may be an association between electrical seizure activities and WDS.KeywordsSeizure ActivityOpioid PeptideAminobutyric AcidIntraventricular InjectionSeizure DischargeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Effect of long-term nicotine treatment on [ 3H] nicotine binding sites in the rats brain

Male rats were receiving nicotine (base), 50 mg/kg in their drinking fluid for 9 and 41 weeks, respectively. A markedly reduced intake of fluid was observed during both regimes of nicotine treatment. At withdrawal of nicotine after 9 weeks of treatment the intake of water was immediately increased up to control level while in rats with 41 weeks of exposure the intake of drinking fluid increased to 65% over the control level still 14 days after withdrawal of nicotine. Tolerance to nicotine was measured after 7 days of abstinence in rats treated for 9 weeks. No significant change in cholineacetyltransferase (ChAT) activity or number of muscarinic binding sites in brain was observed after 9 or 41 weeks of nicotine treatment. Twenty-four hours after withdrawal from the 41 weeks nicotine treatment there was a significant increase of 46% in the number of [ 3H] nicotine binding sites in the hippocampus while the number of binding sites was decreased by 44% in the cortex and unchanged in the midbrain. On day 14th of abstinence these changes had disappeared. Following 9 weeks of nicotine treatment no change in [ 3H] nicotine binding was observed after 24 h or 7 days of abstinence.

Three different types of α-interferons alter naloxone-induced abstinence in morphine-addicted rats

The opiate abstinence syndrome represents a fundamental feature of the addictive process, with the degree of addiction being directly correlated to the intensity of withdraw. Therefore, the discovery of substance capable of attenuating withdrawal sings may provide insights into the dynamics of opiate addiction. The present study demonstrates that three different types of α-interferons modify the behavioral signs associated with naloxone-induced abstinence in rats addicted to morphine. These observations suggest that opiate addiction may, in part, be due to an immune response in that immunomodulators (interferon) are capable of altering the naloxone-induced abstinence syndrome in morphine-dependent rats.

Morphine and clonidine oral self-administration: A study in morphine dependent or abstinent rats

1. The ability of morphine and of clonidine to support self-administration has been evaluated in morphine dependent or abstinent rats, using an orally reinforced operant technique (F.R. 20). 2. It was found that: — Morphine drinking can function as a reinforcer of an operant response both in dependent and abstinent rats. — The bitter taste of morphine becomes a secondary reinforcer for rats usually working for the alkaloid. — Clonidine supports oral self-administration in morphine abstinent, but not in morphine dependent rats. 3. The data are in line with clinical findings and give a further evidence that oral self administration in rats can be an useful model for the analysis of drug dependence.

Disposition of ethanol and its effect on rectal temperature in morphine-dependent, morphine-abstinent and morphine-naive rats.

Rats were treated chronically with twice daily injections of morphine hydrochloride in gradually increasing doses from 20 to 200 mg/kg for 22 consecutive days. Rats in a control group were injected with 0.9% NaCl. At 1 hour after the last injection of morphine (dependent state) and at 3 and 16 days after abrupt withdrawal (abstinent state) the animals were injected intraperitoneally with 2.0 g/kg ethanol. Blood ethanol concentrations (tail blood) and rectal temperatures were determined at 30-60 min. intervals for up to 7 hours. The absorption of ethanol was slower in rats treated with morphine and the time taken to reach the end of the blood concentration curve was increased. This implies a slower turnover of ethanol in morphine-dependent and abstinent rats. At 16 days after withdrawal, the blood ethanol profiles were the same as in control rats not exposed to morphine. Injection of morphine (200 mg/kg) intolerant animals caused a pronounced hyperthermia which lasted for about 4 hours. Ethanol treatment rapidly counteracted the rise in body temperature. Morphine abstinent rats showed a hypothermic response to ethanol. The altered disposition of ethanol in acute withdrawal may result from physiological disturbances such as impaired fluid balance, dehydration, altered peripheral blood flow and poor nutritional status. There was no evidence for a faster rate of ethanol metabolism in the hypermetabolic state associated with morphine tolerance and dependence.

Macromolecular changes in brain stem of morphinized rats

Incorporation of [3H]valine into trichloroacetic acid-(TCA)-precipitable, water-soluble or membrane-bound material of whole brain and brain-stem did not differ significantly in morphine-intoxicated, morphine abstinent and control rats. The animals were intoxicated with morphine (final dose 340 mg/kg b.w.) for 15 days, using an ingestion method with no impairment of the caloric intake compared to controls. Abstinent rats were withdrawn from morphine for 2 days after 13 days of intoxication. Measurements of [3H]valine or [14C]valine incorporated into soluble or membrane-bound brain stem proteins failed to demonstrate any significant changes in specific protein bands from morphinized rats. Separation was achieved by polyacrylamide gel electrophoresis with or without sodium-dodecyl sulphate (SDS) or by isoelectric focusing. After immunoabsorption chromatography to remove those proteins antigenically similar to serum proteins, an increase in the staining intensity and in incorporation of [3H]valine into two protein bands (with isoelectric points (Ip:s) 5.75 and 7.7) was seen in brain stem from long-term morphine-intoxicated rats. The results show that macromolecular interactions are involved in long-term morphine actions.

Evidence that 5-hydroxytryptamine in the forebrain is involved in naloxone-precipitated jumping in morphine-dependent rats.

A withdrawal syndrome was precipitated by naloxone in morphine-dependent rats injected with 5,7-dihydroxytryptamine (5,7-DHT) in the ventromedial tegmentum (VMT) at the level of the nucleus interpeduncularis. 5,7-DHT, which markedly depleted 5-hydroxytryptamine (5-HT) in the forebrain but not in the brainstem, significantly reduced jumping in abstinent rats with no significant effect on other withdrawal signs. The effect of morphine 10 mg kg-1 on responses on the hot plate was unchanged in 5,7-DHT-treated rats. The findings suggest that 5-HT in the forebrain is selectively involved in the jumping of morphine-abstinent rats.