Possible role of cyclic AMP and dopamine in morphine tolerance and physical dependence.

In chronically morphinized rats undergoing naloxone induced withdrawal the cerebellar Cyclic 3′, 5′ adenosine monophosphate (Cyclic AMP) was significantly higher than the controls. The cerebellar dopamine (DA) and norepinephrine (NE) were decreased, elevated or unchanged depending on the duration of morphine treatment. The corpus striatal DA levels during withdrawal were markedly elevated and the striatal cyclic AMP levels were unchanged. The NE levels in the striatal tissue were either elevated or unchanged depending upon the duration of morphine administration. In sharp contrast to the chronically morphinized rats undergoing naloxone induced withdrawal, the rats made morphine dependent over a period of eight weeks showed quite moderate changes in the striatal and cerebellar cyclic AMP and DA levels. Thus alterations in the DA and the cyclic AMP levels in the central nervous system (CNS) may play an important role in the naloxone induced stereotyped morphine withdrawal behavior.     

Effects of U-50,488H and U-50,488H withdrawal on catecholaminergic neurons of the rat hypothalamus

Previous report from our laboratory showed that morphine produces a stimulatory effect of hypothalamic noradrenaline (NA) turnover concurrently with enhanced pituitary-adrenal response after its acute injection and during withdrawal. In the present work we have studied the effects of acute and chronic administration of the kappa agonist U-50,488H as well as the influence of U-50,488H withdrawal on the activity of hypothalamic NA and dopamine (DA) neurons and on the activity of hypothalamic-pituitary-adrenal (HPA) axis. A single dose of U-50,488H (15 mg/kg i.p.) significantly increased hypothalamic NA and decreased DA turnover at the time of an enhanced corticosterone release. Rats rendered tolerant to the kappa agonist by administration of U-50,488H twice a day for 4 days showed no changes in corticosterone secretion. Additionally, a decrease in both hypothalamic MHPG (the cerebral NA metabolite) production and NA turnover was observed, whereas DOPAC concentration and DA turnover were enhanced, which indicate the development of tolerance towards the neuronal and endocrine actions of U-50,488H. After naloxone (3 mg/kg s.c.) administration to U-50,488H-tolerant rats, we found neither behavioural signs of physical dependence nor changes in hypothalamic catecholaminergic neurotransmission. In addition, corticosterone secretion was not altered in U-50,488H withdrawn rats. Present data clearly indicate that tolerance develops towards the NA turnover accelerating and DA turnover decreasing effect of U-50,488H. Importantly and by contrast to mu agonists, present results demonstrate that U-50,488H withdrawal produce no changes in hypothalamic catecholamines turnover or in corticosterone release (an index of the hypothalamus-pituitary-adrenal activity), which indicate the absence of neuroendocrine dependence on the kappa agonist. As has been proposed, this would suggest that the mu and the kappa receptor be regulated through different cellular mechanisms, as kappa agonists have a lower proclivity to induce dependence.     

Depression of Mesolimbic Dopamine Transmission and Sensitization to Morphine During Opiate Abstinence

To investigate the role of mesolimbic dopamine (DA) in the mechanism of drug dependence, extracellular DA was monitored by transcerebral dialysis in the caudal nucleus accumbens under basal conditions and after challenge with morphine (5 mg/kg s.c.) in control rats and in rats made dependent on and then deprived of morphine. Withdrawal from morphine resulted in a marked reduction of extracellular DA concentrations from control values at 1, 2, 3, and 5 days of withdrawal. After 7 days of withdrawal, DA output was less, but still significantly, reduced. Challenge with morphine resulted in stimulation of DA output in controls (maximum, 35%), no effect on the first day of withdrawal, and stimulation similar to controls' on days 2 and 7 of withdrawal. On day 5 and, particularly, on day 3 of withdrawal, morphine-induced stimulation of DA output was markedly potentiated (maximum, 100 and 160%, respectively). Changes in the sensitivity of DA transmission to morphine challenge were associated with changes in the behavioral stimulant effects of morphine, with tolerance on day 1 and marked sensitization on days 3 and 5 but also on day 7, when morphine-induced stimulation of transmission was no longer potentiated. The results indicate that repeated morphine administration induces a state of dependence in DA neurons and a short-lasting tolerance followed by an increased sensitivity to its stimulant effects on DA transmission. These changes might play an important role in the development of opiate addiction and in the maintenance of opiate self-administration in dependent subjects.     

Catecholamine Concentration in the Developing Rat Brain after γ-Hydroxybutyric Acid

The effect of the GABA receptor agonist γ-hydroxybutyric acid (GHBA) on brain catecholamine concentration was investigated in 1 to 28 day old rats. The infant rats were given GHBA in various doses (375–1500 mg/kg) and the effects on whole brain or regional brain concentration of dopamine (DA) and noradrenaline (NA) were measured. Brain DA concentration increased in a dose-dependent way already from two days of postnatal age. In the regional brain study of the 14- and 28-day-old animals the increase in DA concentration was found to be almost exclusively located in the striatal region. Generally, no changes in NA concentration were found in the whole brain or various brain regions at any of the ages after GHBA. It is concluded that the inhibitory striatal-nigral neurons, utilizing GABA as a transmitter, are functionally developed during early postnatal age.     

Effect of S-adenosyl-L-homocysteine of dopamine catabolism]

1.--The administration of SAH to rats, at physiologically active dose on the sleep, does not change the urinary level of MD and NM. On the other hand, the excretion of DA and NA decreases. 2.--In the brain, SAH does not modify neither the concentration of NA and NM in hypothalamus and thalamus, nor the concentration of DA and MD in corpus striatum. 3.--After intracisternally injection of [14C]DA or [3H]NA, SAH increases the level of [14C]MD and [3H]NM. 4.--Contrary to the studies in vitro, where SAH is an inhibitor of COMT, on the rat it does not seem prevent the methylation of DA and NA.     

Effect of gonadectomy on brain catecholamines during the postnatal period

The effect produced by gonadectomy on dopamine (DA) and noradrenaline (NA) levels in the diencephalon and the rest of the brain of male and female rats during postnatal development has been studied. DA and NA metabolism or biosynthesis seems to be regulated by the ovarian hormones, directly or by means of hypophysary hormones, since both catecholamine levels rise acutely during postnatal development when ovariectomy is performed. In contrast with controls, the NA level is not stable at 45 days, but continues rising to day 60. Orchidectomy also acutely increases the level of diencephalic DA, but in contrast with females, its concentration progressively decreases, being at day 60 the same as in the controls. The reasons that cause this normalization, in the absence of testicular androgens, are unknown. In the same way, the extirpation of the testicles increases the diencephalic concentration of NA, the concentration change is similar to the control one: however, the level is higher. There is also a clear difference from the gonadectomized females, in which the diencephalic NA rises during 45-60 days. Gonadectomy does not significantly alter the level of DA or NA in the rest of the brain.     

Effects of naloxone-precipitated withdrawal after a single dose of morphine on catecholamine concentrations in guinea-pig brain

The effect of naloxone-precipitated withdrawal after acute morphine was studied on the concentrations of noradrenaline (NA), 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and on the metabolite/parent amine ratios MHPG/NA, DOPAC/DA and HVA/DA, in eight regions of the guineapig brain. Guinea-pigs were treated with a single dose of morphine sulphate (15 mg/kg s.c.) or saline (control) and 2h later with naloxone hydrochloride (15 mg/kg s.c.) to precipitate withdrawal. The animals were decapitated at 0.5 h or 1 h after naloxone injections and their brains analysed for monoamine concentrations by HPLC-ECD. At 0.5 h after naloxone-precipitated withdrawal NA and MHPG levels, and the MHPG/NA ratio, were increased in the hypothalamus, and the NA levels were increased in the hypothalamus, medulla/pons and cortex 1 h after naloxone. Naloxoneprecipitated withdrawal also produced increased DA metabolism in the cortex, midbrain and medulla 0.5 h later, and in the cortex, hypothalamus and striatum 1 h later. Hence naloxone-precipitated withdrawal from acute morphine treatment produced a complex pattern of increased synthesis and metabolism of NA and DA which varied over time and with the brain region examined.     

Rat brain monoamine and serotonin S2 receptor changes during pregnancy

The concentrations of noradrenaline (NA), dopamine (DA), serotonin (5-HT), and their metabolites were determined in 5 brain areas of non-pregnant, 15 and 20 day pregnant and 4 day post-partum rats. Striatal 5-HT content was significantly lower in 15 and 20 day pregnant rats than in estrous controls. A significant decrease in striatal and frontal cortex 5-hydroxyindole-3-acetic acid (5-HIAA) concentration was observed in 15 day pregnant rats. Significant increases in hypothalamic and hippocampal NA levels were observed at 4 days post-partum. Frontal cortex serotonin S2 receptorKd was reduced in 4 day post-partum rats. There was no significant change in S2 receptorB _max during pregnancy. Levels of progesterone were negatively correlated with striatal DA, homovanillic acid (HVA), 5-HT, and 5-HIAA levels, hypothalamic DA, hippocampal 5-HT, and frontal cortex 5-HIAA values as well as striatal HVA to DA, and HVA to 3,4-dihydroxyphenylacetic acid (DOPAC) ratios and amygdaloid HVA to DOPAC ratios. The limbic neurotransmitter changes might possibly contribute to mood changes which occur during pregnancy and post-partum.     

Role of Corticotropin-Releasing Factor (CRF) Receptor-1 on the Catecholaminergic Response to Morphine Withdrawal in the Nucleus Accumbens (NAc)

Stress induces the release of the peptide corticotropin-releasing factor (CRF) into the ventral tegmental area (VTA), and also increases dopamine (DA) levels in brain regions receiving dense VTA input. Since the role of stress in drug addiction is well established, the present study examined the possible involvement of CRF1 receptor in the interaction between morphine withdrawal and catecholaminergic pathways in the reward system. The effects of naloxone-precipitated morphine withdrawal on signs of withdrawal, hypothalamo-pituitary-adrenocortical (HPA) axis activity, dopamine (DA) and noradrenaline (NA) turnover in the nucleus accumbens (NAc) and activation of VTA dopaminergic neurons, were investigated in rats pretreated with vehicle or CP-154,526 (selective CRF1R antagonist). CP-154,526 attenuated the increases in body weight loss and suppressed some of withdrawal signs. Pretreatment with CRF1 receptor antagonist resulted in no significant modification of the increased NA turnover at NAc or plasma corticosterone levels that were seen during morphine withdrawal. However, blockade of CRF1 receptor significantly reduced morphine withdrawal-induced increases in plasma adrenocorticotropin (ACTH) levels, DA turnover and TH phosphorylation at Ser40 in the NAc. In addition, CP-154,526 reduced the number of TH containing neurons expressing c-Fos in the VTA after naloxone-precipitated morphine withdrawal. Altogether, these results support the idea that VTA dopaminergic neurons are activated in response to naloxone-precipitated morphine withdrawal and suggest that CRF1 receptors are involved in the activation of dopaminergic pathways which project to NAc.     

Influence of fasting and dopamine on the tissue catecholamines diurnal variations

To define the role of catecholamines (CA) in the metabolic adaptation to fasting we examined the effect of exogenous dopamine(DA) on heat production(HP) and CA content in the interscapular brown adipose tissue(IBAT) and adrenals of control-fed and 2-day fasted rats in the morning(M) and in the evening(E). DA stimulates HP in fed rats in the M by 45% but the thermogenic effect of this CA is markedly higher in the E. However, DA had no thermogenic effect in fasted rats. The tissue CA in fed rats fluctuates diurnally: in the IBAT noradrenaline(NA) was much higher in the E while adrenaline(A) in adrenals was lower. DA in fed rats did not change the adrenal A but reduced NA content both in the adrenals and in the IBAT all over the day. Fasting depleted A from adrenals but increased NA content both in the M and in the E. Unlike the adrenals in the IBAT fasting did not affect NA content. In the adrenal gland of fasted rats DA significantly increased the A content to the equal degree during the day, while this CA had no effect on NA content of the IBAT.     

两种吗啡依赖大鼠模型脑内单胺神经递质水平的比较

目的通过对吗啡诱导的躯体依赖与精神依赖两种大鼠模型脑内单胺类递质水平的比较,探讨其在吗啡依赖形成中的作用。方法采用剂量递增法复制吗啡依赖大鼠模型,然后用纳洛酮催促,引起躯体戒断症状。连续给予吗啡（5mg／kg,ip）6d,引起大鼠产生显著的条件性位置偏爱效应。脑组织去甲肾上腺素（NE）、5-羟色胺（5-HT）和多巴胺（DA）含量采用荧光分光光度法测定。结果吗啡依赖大鼠催促戒断后脑内NE和5-HT水平明显升高,DA水平下降。吗啡在引起大鼠明显位置偏爱的同时,使大鼠脑内DA和5-HT水平显著升高,NE无明显改变。结论吗啡依赖的形成和戒断与脑内单胺神经递质有密切关系,吗啡依赖的躯体戒断症状与NE升高有关,而吗啡诱导的精神依赖则与脑内DA水平升高有关。     

The stimulatory roles of catecholamines and acetylcholine in the regulation of gonadotropin release in ovariectomized estrogen-primed rats.

Injections of 2 mg of progesterone into ovariectomized estrogen-primed rats significantly increased serum LH and FSH concentrations 3, 5 and 8 hr later. Receptor blockers of noradrenaline (NA), dopamine (DA) or acetylcholine (ACH), phenoxybenzamine (20 mg/kg body weight), pimozide (1mg/kg body weight) or atropine (700 mg/kg body weight), respectively, prevented the progesterone-induced gonadotropin release. On the other hand, none of them blocked the gonadotropin release following unilateral electrochemical stimulation (100 microA for 60 sec) of the medial preoptic area which occurred 0.5 and 1.5 hr later, although pimozide or atropine reduced serum LH concentrations at 4.0 hr after stimulation. Furthermore, the sites of action of NA, DA and ACH with respect to LH release were examined by intracerebral implantation in ovariectomized estrogen-primed rats DA or ACH, when implanted unilaterally into the medial preoptic urea, induced a significant increase in serum LH 5 hr later, whereas NA decreased LH levels. Implantations of NA or ACH into the bed nucleus of the stria terminalis or the medial amygdala increased serum LH although the effect of NA into the latter was not statistically significant. Only implantations of NA among the three substances into the lateral septum induced LH release. These results suggest that all of NA, DA and ACH play stimulatory roles in the regulation of gonadotropin secretion, and that there are regional differences of their effectivenesses in releasing LH within the limbic-preoptic area.     

Increasing synaptic noradrenaline, serotonin and histamine enhances in vivo binding of phosphodiesterase-4 inhibitor (R)-[11C]rolipram in rat brain, lung and heart

Phosphodiesterase-4 (PDE4) is one of the main enzymes that specifically terminate the action of cAMP, thereby contributing to intracellular signaling following stimulation of various G protein-coupled receptors. PDE4 expression and activity are modulated by agents affecting cAMP levels. The selective PDE4 inhibitor (R)-rolipram labeled with C-11 was tested in vivo in rats to analyze changes in PDE4 levels following drug treatments that increase synaptic noradrenaline (NA), serotonin (5HT), histamine (HA) and dopamine (DA) levels. We hypothesized that increasing synaptic neurotransmitter levels and subsequent cAMP-mediated signaling would significantly enhance (R)-[(11)C]rolipram retention and specific binding to PDE4 in vivo. Pre-treatments were performed 3 h prior to tracer injection, and rats were sacrificed 45 min later. Biodistribution studies revealed a dose-dependent increase in (R)-[(11)C]rolipram uptake following administration of the monoamine oxidase (MAO) inhibitor tranylcypromine, NA and 5HT reuptake inhibitors (desipramine [DMI], maprotiline; and fluoxetine, sertraline, respectively), and the HA H(3) receptor antagonist (thioperamide), but not with DA transporter blockers GBR 12909, cocaine or DA D(1) agonist SKF81297. Significant increases in rat brain and heart reflect changes in PDE4 specific binding (total-non-specific binding [coinjection with saturating dose of (R)-rolipram]). These results demonstrate that acute treatments elevating synaptic NA, 5HT and HA, but not DA levels, significantly enhance (R)-[(11)C]rolipram binding. Use of (R)-[(11)C]rolipram and positron emission tomography as an index of PDE4 activity could provide insight into understanding disease states with altered NA, 5HT and HA concentrations.     

Chronic nicotine causes functional upregulation of ionotropic glutamate receptors mediating hippocampal noradrenaline and striatal dopamine release

It has been proposed that (-)-nicotine can activate release-stimulating presynaptic nicotinic acetylcholine receptors (nAChRs) on glutamatergic nerve terminals to release glutamate, which in turn stimulates the release of noradrenaline (NA) and dopamine (DA) via presynaptic ionotropic glutamate receptors on catecholaminergic terminals. The objective of this study was to compare the function of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazide-4-propionic acid (AMPA) glutamate receptors in synaptosomes of rat hippocampus and striatum following acute and chronic (-)-nicotine administration. In hippocampal synaptosomes, prelabeled with [3H]NA, both the NMDA- and AMPA-evoked releases were higher in (-)-nicotine-treated (10 days) than in (-)-nicotine-treated (1 day) or vehicle-treated (1 or 10 days) rats. In striatal synaptosomes prelabeled with [3H]DA, the NMDA-evoked, but not the AMPA-evoked, release of [3H]DA was higher in (-)-nicotine-treated (10 days) than in nicotine-treated (1 day) or vehicle-treated (1 or 10 days) animals. Chronic (-)-nicotine did not affect catecholamine uptake, basal release and release evoked by high-K+ depolarization. Thus, chronic exposure to nicotine enhances the function of ionotropic glutamate receptors mediating noradrenaline release in the hippocampus and dopamine release in the striatum.     

Tissue catecholamine concentrations in spontaneously hypertensive rats

Tissue concentrations of noradrenaline (NA), dopamine (DA) and adrenaline (A) were compared in spontaneously hypertensive (SHR) and normotensive (NCR) rats, aged 1, 3, 8, 14 and 24 weeks The organs analyzed included the brain, subdivided into prosencephalon and rhombencephalon, heart, adrenal glands and kidney. Brain catecholamines were significantly lower in SHR than in NCR, and the difference appeared already at the age of 3 weeks. Concomitant increase was found in the adrenal NA and A concentrations of the SHR. Concentration of NA in the heart decreased in the SHR following onset of hypertension. It is concluded that the diminished NA, DA and A concentrations in the brain as well as the augmented adrenal NA and A levels in the SHR may be causally related to the development of hypertension, while the heart NA level reflects the secondary, hypertension -- related changes.     

Increased Noradrenaline Levels in the Rostral Pons can be Reversed by M1 Antagonist in a Rat Model of Post-traumatic Stress Disorder

The dysregulation of hypothalamic–pituitary–adrenal axis and noradrenergic, serotonergic and glutamatergic systems are thought to be involved in the pathophysiology of post-traumatic stress disorder. The effect of selective M1 muscarinic receptor antagonist, pirenzepine on anxiety indices was investigated by using elevated plus maze, following exposure to trauma reminder. Upon receiving the approval of ethics committee, Sprague–Dawley rats were exposed to dirty cat litter (trauma) for 10 min and 1 week later, the rats confronted to a trauma reminder (clean litter). The rats also received intraperitoneal pirenzepine (1 or 2 mg/kg/day) or saline for 8 days. Noradrenaline (NA) concentration in the rostral pons was analyzed by HPLC with electrochemical detection. The anxiety indices of the rats subjected to the trauma reminder were increased when compared to control rats (p < 0.05). Pirenzepine treatment in traumatized rats displayed similar anxiety indices of non-traumatized rats treated with physiological saline. Although freezing time was prolonged with pirenzepine in traumatized groups the change was not found statistically significant. The NA level was 1.5 ± 0.1 pg/mg in non-traumatized rats and increased to 2.4 ± 0.2 pg/mg in traumatized rats. Bonferroni post hoc test revealed that the NA content of the rostral pons of the traumatized rats treated with physiological saline was significantly higher than the content of other groups (p < 0.01). We conclude that NA content in the rostral pons increases in respect to confrontation to a trauma reminder which can be reversed by M1 antagonist pirenzepine indicating the roles of M1 receptors.     

Evidence That Intermittent,Excessive Sugar Intake Causes Endogenous Opioid Dependence

Objective: The goal was to determine whether withdrawal from sugar can cause signs of opioid dependence. Because palatable food stimulates neural systems that are implicated in drug addiction, it was hypothesized that intermittent, excessive sugar intake might create dependency, as indicated by withdrawal signs. Research Methods and Procedures: Male rats were food‐deprived for 12 hours daily, including 4 hours in the early dark, and then offered highly palatable 25% glucose in addition to chow for the next 12 hours. Withdrawal was induced by naloxone or food deprivation. Withdrawal signs were measured by observation, ultrasonic recordings, elevated plus maze tests, and in vivo microdialysis. Results: Naloxone (20 mg/kg intraperitoneally) caused somatic signs, such as teeth chattering, forepaw tremor, and head shakes. Food deprivation for 24 hours caused spontaneous withdrawal signs, such as teeth chattering. Naloxone (3 mg/kg subcutaneously) caused reduced time on the exposed arm of an elevated plus maze, where again significant teeth chattering was recorded. The plus maze anxiety effect was replicated with four control groups for comparison. Accumbens microdialysis revealed that naloxone (10 and 20 mg/kg intraperitoneally) decreased extracellular dopamine (DA), while dose‐dependently increasing acetylcholine (ACh). The naloxone‐induced DA/ACh imbalance was replicated with 10% sucrose and 3 mg/kg naloxone subcutaneously. Discussion: Repeated, excessive intake of sugar created a state in which an opioid antagonist caused behavioral and neurochemical signs of opioid withdrawal. The indices of anxiety and DA/ACh imbalance were qualitatively similar to withdrawal from morphine or nicotine, suggesting that the rats had become sugar‐dependent.     

Influence of thyroidectomy on brain catecholamines during the postnatal period

The influence of early thyroidectomy (Tx) on changes in dopamine (DA) and noradrenaline (NA) during the postnatal period (30, 45 and 60 days old) was studied in the diencephalon and the rest of the brain of male and female rats. Thyroidectomy interfered with the normal growth of the animals, decreased brain weight and markedly influenced the developmental pattern of both DA and NA in the diencephalon. When compared with control values, the DA concentration, in 45- and 60-day-old Tx male rats, was 29 and 43% lower, respectively, and 21 and 43% lower, respectively, in Tx females. Diencephalic NA levels in Tx rats were also lower than those observed in controls, 15% inferior in 45- and 60-day-old males; 27 and 22% lower, respectively, in females. Thyroidectomy does not significantly alter the level of either amine in the rest of the brain.     

Different alterations in the development of the noradrenergic innervation of the cerebellum and the brain stem produced by neonatal 6-hydroxydopa.

The administration of 6-hydroxydopa (6-OH-DOPA) to rats during their pre- or postnatal development, produced long-term modifications in the distribution of noradrenaline (NA) within the brain. In the cerebellum, the concentration of NA was increased in adult rats exposed to the drug between the day 16 of gestation and the day of birth. When injected 3 days after birth, the drug did not modify NA levels while treatment at 20 days produced a marked depletion of cerebellar NA. The concentration of NA in the brain stem showed a different pattern of response to 6-OH-DOPA. Prenatal administration elevated NA in this region and, in contrast to the response of the cerebellum, injections in the inmediate postnatal period also elevated the transmitter content. Treatment at 20 days after birth resulted in a marked depletion of NA levels in the adult brain stem. These results demonstrate the existence of temporal differences in the responses to neonatal 6-OH-DOPA in two structures innervated by noradrenergic pathways originated in neurons of the nucleus locus coeruleus.     

Long term effect of lithium on brain regional catecholamine metabolism

Administration of LiCl (2-4 mmol/kg/day, po) to adult male albino rats for 7 consecutive days increased the catabolism of dopamine (DA) in striatum (ST) and noradrenaline (NA) in hypothalamus (H). Extension of the period of treatment with LiCl (2-4 mmol/kg/day, po) to 14 consecutive days increased catabolism of DA in CX (cerebral cortex) and PM (pons-medulla) and NA in H, and decreased metabolism of DA in ST and NA in PM. Further prolongation of treatment with LiCl (2 or 4 mmol/kg/day, po) for 21 consecutive days greatly affected DA and NA metabolism in the respective brain regions. These results, thus suggest that LiCl produces region specific differential action depending on its dosage and duration of treatment in catecholaminergic activity in rat brain.