Measurement of 3-methoxy-4-hydroxyphenylglycol (MHPG) in mouse brain by h.p.l.c. with electrochemical detection, as an index of noradrenaline utilisation and presynaptic alpha 2-adrenoceptor function

Differential encoding of signals and preferences by noradrenaline in the anuran brain

Social preferences enable animals to selectively interact with some individuals over others. One influential idea for the evolution of social preferences is that preferred signals evolve because they elicit greater neural responses from sensory systems. However, in juvenile plains spadefoot toad (Spea bombifrons), a species with condition-dependent mating preferences, responses of the preoptic area, but not of the auditory midbrain, mirror adult social preferences. To examine whether this separation of signal representation from signal valuation generalizes to other anurans, we compared the relative contributions of noradrenergic signalling in the preoptic area and auditory midbrain of S. bombifrons and its close relative Spea multiplicata We manipulated body condition in juvenile toads by controlling diet and used high pressure liquid chromatography to compare call-induced levels of noradrenaline and its metabolite MHPG in the auditory midbrain and preoptic area of the two species. We found that calls from the two species induced different levels of noradrenaline and MHPG in the auditory system, with higher levels measured in both species for the more energetic S. bombifrons call. In contrast, noradrenaline levels in the preoptic area mirrored patterns of social preferences in both S. bombifrons and S. multiplicata That is, noradrenaline levels were higher in response to the preferred calls within each species and were modified by diet in S. bombifrons (with condition-dependent preferences) but not S. multiplicata (with condition-independent preferences). Our results are consistent with a potentially important role for preoptic noradrenaline in the development of social preferences and indicate that it could be a target of selection in the evolution of condition-dependent social preferences.

Silk sericin intake leads to increases in l-serine and l-tyrosine levels in the mouse brain and the simultaneous facilitation of brain noradrenergic turnover

Sericin is a protein component of the silkworm cocoon, and contains a high proportion of L-serine, but it has been mostly disposed of as an industrial waste. However, recent studies have revealed its unique biological functionalities beneficial to human health. This study aimed to evaluate the effect of acute oral intake of sericin on amino acid and neurotransmitter metabolism in the mouse brain. Acute administration of chemically modified sericin (0.26 g/30 g body weight) increased L-serine and L-tyrosine levels in the serum and brain, although the L-tyrosine content in the sericin was less than 3% (w/w). In addition, sericin administration led to a significant facilitation of noradrenergic turnover via enhancement of 3-methoxy-4-hydroxyphenylethyleneglycol, a principal metabolite of noradrenaline, in several of the brain regions examined. These present findings suggest that oral intake of sericin efficiently delivers L-serine and L-tyrosine to the brain, thus stimulating noradrenergic activity in the brain.

Abbreviations: DA: dopamine; 5-HIAA: 5-hydroxyindoleicetic acid; 5-HT: 5-hydroxytryptamine; HVA: homovanillic acid; MHPG: 3-methoxy-4-hydroxyphenylethyleneglycol; 3-MT: 3-methoxytyramine; NA: noradrenaline; NM: normetanephrine; Veh: vehicle

Prenatal metformin treatment improves ovarian function in offspring of obese rats

Maternal obesity causes a wide range of impairment in offspring, such as metabolic and reproductive dysfunctions. We previously demonstrated that female offspring of obese rats have increased serum estradiol levels during early postnatal life, probably because of decreased hepatic cytochrome P450 3A2 levels, which could lead to early onset of puberty and polycystic ovary condition in adulthood. Using metformin during pregnancy and nursing to improve the metabolic status of obese mothers could prevent the sequence of events that lead to an increase in postnatal serum estradiol levels in female offspring and, hence, reproductive dysfunction. We found that metformin prevented an increase in serum estradiol levels at postnatal day 14 in female offspring of obese mothers, which was associated with a restoration of hepatic cytochrome P450 3A2 levels to control values. Treatment using metformin could not prevent advanced puberty, but we observed that the number of antral follicles, follicular cysts and multi-oocyte follicles returned to control values in the female offspring of obese mothers treated with metformin. We also observed an increase in the levels of norepinephrine and the norepinephrine metabolite 3-methoxy-4-hydroxyphenylglycol in the ovaries, indicating increased sympathetic activity in female offspring induced by an obesogenic uterine environment. We found that this effect was prevented by metformin administration. From the results of this study, we concluded that metformin administration to obese mothers during pregnancy and nursing partially prevents ovarian dysfunction in female offspring during adulthood.

MicroRNA-19b associates with Ago2 in the amygdala following chronic stress and regulates the adrenergic receptor beta 1

Activation of the stress response in the presence of diverse challenges requires numerous adaptive molecular and cellular changes. To identify specific microRNA molecules that are altered following chronic stress, mice were subjected to the chronic social defeat procedure. The amygdala from these mice was collected and a screen for microRNAs that were recruited to the RNA-induced silencing complex and differentially expressed between the stressed and unstressed mice was conducted. One of the microRNAs that were significantly altered was microRNA-19b (miR-19b). Bioinformatics analysis revealed the adrenergic receptor β-1 (Adrb1) as a potential target for this microRNA with multiple conserved seed sites. Consistent with its putative regulation by miR-19b, Adrb1 levels were reduced in the basolateral amygdala (BLA) following chronic stress. In vitro studies using luciferase assays showed a direct effect of miR-19b on Adrb1 levels, which were not evident when miR-19b seed sequences at the Adrb1 transcript were mutated. To assess the role of miR-19b in memory stabilization, previously attributed to BLA-Adrb1, we constructed lentiviruses designed to overexpress or knockdown miR-19b. Interestingly, adult mice injected bilaterally with miR-19b into the BLA showed lower freezing time relative to control in the cue fear conditioning test, and deregulation of noradrenergic circuits, consistent with downregulation of Adrb1 levels. Knockdown of endogenous BLA-miR-19b levels resulted in opposite behavioral and noradrenergic profile with higher freezing time and increase 3-methoxy-4-hydroxyphenylglycol/noradrenaline ratio. These findings suggest a key role for miR-19b in modulating behavioral responses to chronic stress and Adrb1 as an important target of miR-19b in stress-linked brain regions.

Decreased striatal dopamine in group II metabotropic glutamate receptor (mGlu2/mGlu3) double knockout mice

BACKGROUND

Group II metabotropic glutamate receptors (mGlu2 and mGlu3, encoded by Grm2 and Grm3) have been the focus of attention as treatment targets for a number of psychiatric conditions. Double knockout mice lacking mGlu2 and mGlu3 (mGlu2/3-/-) show a subtle behavioural phenotype, being hypoactive under basal conditions and in response to amphetamine, and with a spatial memory deficit that depends on the arousal properties of the task. The neurochemical correlates of this profile are unknown. Here, we measured tissue levels of dopamine, 5-HT, noradrenaline and their metabolites in the striatum and frontal cortex of mGlu2/3-/- double knockout mice, using high performance liquid chromatography. We also measured the same parameters in mGlu2-/- and mGlu3-/- single knockout mice.

RESULTS

mGlu2/3-/-mice had reduced dopamine levels in the striatum but not in frontal cortex, compared to wild-types. In a separate cohort we replicated this deficit and, using tissue punches, found it was more prominent in the nucleus accumbens than in dorsolateral striatum. Noradrenaline, 5-HT and their metabolites were not altered in the striatum of mGlu2/3-/- mice, although the noradrenaline metabolite MHPG was increased in the cortex. In mGlu2-/- and mGlu3-/- single knockout mice we found no difference in any monoamine or metabolite, in either brain region, compared to their wild-type littermates.

CONCLUSIONS

Group II metabotropic glutamate receptors impact upon striatal dopamine. The effect may contribute to the behavioural phenotype of mGlu2/3-/- mice. The lack of dopaminergic alterations in mGlu2-/- and mGlu3-/- single knockout mice reveals a degree of redundancy between the two receptors. The findings support the possibility that interactions between mGlu2/3 and dopamine may be relevant to the pathophysiology and therapy of schizophrenia and other disorders.

Quantification of sibutramine and its two metabolites in human plasma by LC-ESI-MS/MS and its application in a bioequivalence study

Obesity can be considered as a chronic illness of epidemic proportion and its incidents have increased exponentially in recent years. The use of anti-obesity drugs such as sibutramine is somewhat helpful. There is a need to quantify such drugs in biological samples, which is generally quite difficult. In this report, we developed and validated a simple, sensitive and specific liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the quantification of sibutramine (SB) and its two metabolites N-des methyl sibutramine (DSB) and N-di desmethyl sibutramine (DDSB) in human plasma. Zorbax SB-C18 (4.6 mm×75 mm, 3.5 μm, 80 Å) analytical column and 5 mM ammonium formate:acetonitrile (10:90, v/v) mobile phase were used for chromatographic separation of SB, DSB and DDSB. Multiple reaction monitoring (MRM) in the positive mode was used to detect SB, DSB and DDSB at m/z 280.3/124.9, 266.3/125.3 and 252.2/124.9, respectively. Liquid–liquid extraction was used for the extraction of analytes and internal standard from human plasma. This method was validated over a linear concentration range of 10.0–10,000.0 pg/mL for SB, DSB and DDSB with correlation coefficients (r) of ≥0.9997. The drug and the two metabolites were stable in plasma samples. The validated method was successfully applied in a bioequivalence and pharmacokinetic study with human volunteers under fasting condition.

Bupropion SR in adults with ADHD: a short-term, placebo-controlled trial

Increased attention has been given to the alternatives to stimulants in the treatment of attention deficit hyperactivity disorder (ADHD) in both adults and children. This short-term, double-blind trial was designed to evaluate the extended-release form of bupropion in adult subjects meeting DSM-IV and the Utah Diagnostic Criteria for ADHD. Outcome measures were the Clinical Global Impressions-Improvement (CGI-I) and the Wender-Reimherr Adult Attention Deficit Disorder Scale (WRAADDS), which assesses adult ADHD symptoms. Outcome (defined by the CGI-I, average WRAADDS scores, or a 50% improvement on the WRAADDS) favored bupropion SR over placebo, but achieved statistical significance on only one, post hoc measure. Other measures showed trends for improvement with bupropion. Given the small size of this study, these findings deserve further exploration.

Alpha2A-adrenoceptors are important modulators of the effects of D-amphetamine on startle reactivity and brain monoamines

Amphetamines are commonly used to treat attention-deficit hyperactivity disorder, but are also widely abused. They are employed in schizophrenia-related animal models as they disrupt the prepulse inhibition (PPI) of the acoustic startle response. The behavioral effects of amphetamines have mainly been attributed to changes in dopamine transmission, but they also involve increases in the synaptic concentrations of norepinephrine (NE). alpha2-Adrenoceptors (alpha2-ARs) regulate the excitability and transmitter release of brain monoaminergic neurons mainly as inhibitory presynaptic auto- and heteroreceptors. Modulation of acoustic startle and its PPI by the alpha2A-AR subtype was investigated with mice lacking the alpha2A-AR (alpha2A-KO) and their wild-type (WT) controls, without drugs and after administration of the alpha2-AR agonist dexmedetomidine or the antagonist atipamezole. The interaction of D-amphetamine (D-amph) and the alpha2-AR-noradrenergic neuronal system in modulating startle reactivity and in regulating brain monoamine metabolism was assessed as the behavioral and neurochemical responses to D-amph alone, or to the combination of D-amph and dexmedetomidine or atipamezole. alpha2A-KO mice were supersensitive to both neurochemical and behavioral effects of D-amph. Brain NE stores of alpha2A-KO mice were depleted by D-amph, revealing the alpha2A-AR as essential in modulating the actions of D-amph. Also, increased startle responses and more pronounced disruption of PPI were noted in D-amph-treated alpha2A-KO mice. alpha2A-AR also appeared to be responsible for the startle-modulating effects of alpha2-AR drugs, since the startle attenuation after the alpha2-AR agonist dexmedetomidine was absent in alpha2A-KO mice, and the alpha2-AR antagonist atipamezole had opposite effects on the startle reflex in alpha2A-KO and WT mice.

Pharmacological evidence for the role of central alpha 1B-adrenoceptors in the motor activity and spontaneous movement of mice

Central alpha 1-noradrenergic neurotransmission has been shown to be an important complement of dopaminergic transmission in the control of motor activity but the identity of the responsible alpha 1 receptor subtype has not yet been identified. This was investigated in the present experiment by measuring the effects of intraventricular administration of a series of alpha 1 antagonists varying in affinities for the three known receptor subtypes--1a, 1b and 1d--on active behavior in mice in response to a cage change. It was found that the potency of the drugs to block both gross and small movements correlated highly with published affinities for the cloned 1b receptor but not for those of either the cloned 1a or 1d receptors. It is concluded that central alpha 1B receptors are critically involved in the mediation of the (nor)adrenergic influence on active behavior, a finding which has implications for basic and clinical research in both movement and mood disorders.

Hyperinsulinemia increases norepinephrine metabolism in the ventromedial hypothalamus of rats

Numerous studies have implicated increased ventromedial hypothalamic (VMH) norepinephrine (NE) activity as a contributing factor to the obese, hyperinsulinemic, glucose intolerant condition. However, factors contributing to the increased VMH NE activity remain unknown. This study therefore investigated in normal rats the effect of a hyperinsulinemic-euglycemic clamp on VMH monoamine turnover and utilization via simultaneous VMH microdialysis to establish a role for hyperinsulinemia in the stimulation of VMH NE activity. Within 20 min of initiation of the hyperinsulinemic-euglycemic clamp, VMH extracellular methoxyhydroxy phenylglycol (metabolite of NE) level increased by 54% and remained approximately at this level for the 100 min duration of the clamp relative to control values (p<0.05). Hyperinsulinemia did not affect VMH dopamine or serotonin metabolism. Subsequent establishment of a hyperinsulinemic-hypoglycemic camp did not alter the VMH monoamine metabolism profile relative to the hyperinsulinemic-euglycemic clamp. Infusion of saline (as control) in a separate group of rats over the entire clamp period induced no changes in any monoamine metabolic profile relative to baseline. Hyperinsulinemia can feedback to stimulate VMH NE activity and, as a result, may contribute to the initiation and/or perpetuation of the obese, hyperinsulinemic, glucose-intolerant state.

The involvement of noradrenergic transmission in the morphine-induced locomotor hyperactivity in mice withdrawn from repeated morphine treatment

1. Our previous studies suggest that in addition to the cerebral dopaminergic systems the noradrenergic ones have a crucial role in the morphine-induced behavioural sensitization in mice. Therefore the effects of alpha2-adrenoceptor antagonist, idazoxan (1 and 3 mg kg(-1), i.p.) on morphine-induced locomotor hyperactivity as well as on morphine-induced changes in cerebral noradrenaline (NA) and striatal dopamine (DA) metabolism were studied in mice withdrawn for 3 days from 5 day repeated morphine treatment. The concentrations of NA, free 3-methoxy-4-hydroxyphenylethylene glycol (MOPEG), DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxytyramine (3-MT) were determined. 2. Acute morphine (10 mg kg(-1), s.c.) increased locomotor activity in control and in morphine-withdrawn mice; idazoxan alone did not alter the activity. Idazoxan pretreatment did not alter the locomotor hyperactivity induced by acute morphine in control mice but potentiated it in morphine-withdrawn mice. 3. Acute morphine elevated MOPEG less but increased DOPAC and HVA more clearly in morphine-withdrawn mice than in controls, and decreased 3-MT only in controls. Idazoxan alone did not alter the NA or DA metabolite concentrations in control mice, but elevated MOPEG as well as DOPAC in morphine-withdrawn mice. 4. In control mice idazoxan enhanced acute morphine's elevating effect on MOPEG. In withdrawn mice idazoxan counteracted the tolerance so that acute morphine elevated MOPEG in these mice to about similar level as in controls. 5. Idazoxan pretreatment abolished the HVA increasing effect of acute morphine both in control and withdrawn mice. In control mice idazoxan enhanced morphine's elevating effect on DOPAC and abolished morphine's decreasing effect on 3-MT. Idazoxan did not alter morphine's effects on DOPAC or 3-MT concentrations in withdrawn mice. 6. Our results show that in morphine-withdrawn mice idazoxan pretreatment reveals the morphine-induced locomotor sensitization. This most probably occurs by overcoming the tolerance towards the acute morphine-induced increase of cerebral NA turnover and release. It is suggested that in mice the cerebral noradrenergic in addition to the dopaminergic systems are major determinants of the behavioural sensitization to morphine.

Nicotinic acetylcholine receptor (nACh-R) agonist-induced changes in brain monoamine turnover in mice

The aim of the present study was to evaluate the effects of nicotinic acetylcholine receptor (nACh-R) agonists such as (-)-nicotine and related compounds on brain monoamine turnover. A single administration of (-)-nicotine (0.04, 0.2, 1.0, and 5.0 mg/kg SC) increased both noradrenaline (NA) and dopamine (DA) turnover in a dose-dependent manner, and the maximum effects were achieved 30 min after treatment with (-)-nicotine (1.0 mg/kg). The effect of (-)-nicotine on serotonin (5-HT) turnover was complicated; 5-HT turnover was increased at a low dose of (-)-nicotine (0.04 mg/kg) but decreased at a high dose (1.0 mg/kg). The (-)-nicotine (1.0 mg/kg)-induced changes in monoamine turnover were blocked by pretreatment with the centrally acting nACh-R channel blocker mecamylamine (2.0 mg/kg i.p.) but not by hexamethonium (2.0 mg/kg i.p.). These findings indicate that systemically administered (-)-nicotine can enhance brain NA and DA turnover and affect 5-HT turnover, both of which are mediated by central nACh-R. The changes in the monoamine turnover induced by (+/-)-anabasine were similar to those induced by (-)-nicotine, while (-)-lobeline and (-)-cytisine had little effect, and 1,1-dimethyl-4-phenyl-piperazinium (DMPP) increased NA and 5-HT turnover but not DA turnover at all doses tested. (S)-3-Methyl-5-(l-methyl-2- pyrrolidinyl)isoxazole (ABT-418), a selective neuronal nACh-R agonist, increased NA, DA and 5-HT turnover, but had a weaker effect on DA turnover than NA and 5-HT turnover. In addition, 9-amino-1,2,3,4-tetrahydroacridine (THA), an acetylcholine esterase inhibitor, also increased monoamine turnover in the brain. Pretreatment with mecamylamine completely blocked the THA-induced increase in NA and 5-HT turnover, but not in DA turnover, suggesting that the nACh-R system is involved in the THA-induced increase in brain NA and 5-HT turnover. On the other hand, (-)-cytisine, a partial agonist for the beta 2 subunit containing nACh-R, completely inhibited the nACh-R agonist- and THA-induced increases in NA turnover, but not in DA turnover, and normalized the changes in 5-HT turnover. In conclusion, the subtypes of nACh-Rs mediating DA turnover may be different from those mediating NA and 5-HT turnover in the CNS.

8-OH-DPAT-induced mydriasis in mice: a pharmacological characterisation

8-Hydroxy(di-n-propylamino)tetralin (8-OH-DPAT; 0.1-50 mg/kg i.p.) evoked a dose-dependent mydriatic response in conscious mice (ED50 = 5.8 mg/kg i.p.) which was maximal after 10 min. 8-OH-DPAT (2 mg/kg i.p.)-induced mydriasis was attenuated by the alpha 2-adrenoceptor antagonists, idazoxan (1 and 3 mg/kg i.p.) and yohimbine (1 and 3 mg/kg i.p.), by the 5-HT1 receptor antagonists, pindolol (10 mg/kg i.p.) and quipazine (2 mg/kg i.p.), and by the selective 5-HT1A receptor antagonist, (-)-N-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-1-yl]-2-phenyl propionamide ((-)-WAY 100135; 1-10 mg/kg s.c.). These data argue that both central alpha 2-adrenoceptors and 5-HT1A receptors are involved in the mediation of mydriasis induced by 8-OH-DPAT. The synaptic location of these receptors was determined using either N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4; 100 mg/kg i.p.) or 5,7-dihydroxytryptamine (5,7-DHT; 75 micrograms i.c.v.)+p-chlorophenylalanine (PCPA; 200 mg/kg i.p.); these lesioning procedures respectively produced highly significant losses of whole brain noradrenaline (72% depletion) and 5-HT (78% depletion). The former abolished 8-OH-DPAT (5 mg/kg i.p. (ED50)) mydriasis, whereas the latter was without effect. 8-OH-DPAT (0.5-5 mg/kg i.p.) also dose-dependently increased the noradrenaline metabolite, 3-methoxy-4-hydroxy-phenylglycol (MHPG), in mouse whole brain minus cerebellum. Taken together these results show that 8-OH-DPAT initially stimulates 5-HT1A receptors, and it is likely that this is followed by release of noradrenaline onto postsynaptic alpha 2-adrenoceptors, the latter effect being responsible for the mydriatic response.

Regional differences in cerebral noradrenaline turnover in mice withdrawn from repeated morphine treatment and tolerance to the effects of acute morphine

The effects of morphine withdrawal and challenge doses (10 or 30 mg/kg) on the alpha-methyl-p-tyrosine (alpha MT)-induced noradrenaline (NA) depletion as well as on the free 3-methoxy-4-hydroxyphenylethylene glycol (MOPEG) concentration were studied in various brain areas of NMRI mice. Morphine was given subcutaneously 3 times daily for 5 days followed by 1 or 3 days' withdrawal. In morphine withdrawn mice the alpha MT-induced NA depletion and the free MOPEG concentrations were differentially altered. At 1-day withdrawal the alpha MT-induced NA depletion was retarded and the NA concentration was elevated in the forebrain area indicating reduced release of NA. Simultaneously, however, the free MOPEG concentration was significantly elevated in the forebrain area and in the lower brain stem suggesting enhanced NA turnover. No withdrawal-induced changes were found in the hypothalamic NA turnover. Acute morphine elevated the free MOPEG concentration and accelerated the alpha MT-induced NA depletion in all brain areas of control mice but not in mice withdrawn for 1 day from repeated morphine treatment. At 3 days' withdrawal, however, the 30 mg/kg morphine dose slightly accelerated the NA depletion in the forebrain area. These results show that morphine withdrawal differentially alters the alpha MT-induced NA depletion and the free MOPEG concentration in various mouse brain areas. These effects are relatively modest suggesting that in mice the noradrenergic mechanisms play a minor role in morphine withdrawal syndrome. However, in all brain areas of the morphine-withdrawn mice tolerance was found towards the NA turnover and release accelerating effect of acute morphine.

Evidence that RU 24969-induced locomotor activity in C57/B1/6 mice is specifically mediated by the 5-HT1B receptor

1. The behavioural effects of the 5-HT1B receptor agonists, RU 24969 and CGS 12066B, have been investigated in C57/B1/6 mice. 2. RU 24969 (1-30 mg kg-1) produced intense and prolonged hyperlocomotion and other behavioural changes. 3. CGS 12066B caused similar effects, but they were much less pronounced, inconsistent and transient irrespective of whether this drug was given i.p. (1-15 mg kg-1) or i.c.v. (0.2-40 micrograms). However, CGS 12066B (7.5 and 15 mg kg-1) caused a dose-related inhibition of RU 24969 (7.5 mg kg-1)-induced hyperlocomotion indicating that the former is a 5-HT1B partial agonist. 4. RU 24969 (7.5 mg kg-1 i.p.)-induced hyperlocomotion was inhibited by the (-)-, but not (+)-isomers of pindolol (4 mg kg-1) and propranolol (20 mg kg-1) but not by metoprolol (10 mg kg-1) or ICI 118,551 (5 mg kg-1), consistent with an involvement of 5-HT1A or 5-HT1B receptors. 5. The response was not altered by the selective 5-HT1A receptor antagonist, WAY 100135 (5 mg kg-1, s.c.), the 5-HT2A/5-HT2C receptor antagonist, ritanserin (0.1 mg kg-1), the selective 5-HT3 receptor antagonist, ondansetron (1 mg kg-1) or the non-selective 5-HT receptor antagonists methysergide (3 mg kg-1) and metergoline (3 mg kg-1). 6. Although spiroxatrine (0.1 mg kg-1) and ketanserin (1 mg kg-1) inhibited RU 24969-induced hyperlocomotion, these effects were probably due to antagonism of dopamine D2 receptors and alpha 1-adrenoceptors respectively. 7. Taken together, these results indicate that RU 24969-induced hyperlocomotion results specifically from activation of central 5-HTIB receptors.8. Lesioning of 5-HT neurones with 5,7-dihydroxytryptamine (75 microg, i.c.v.) or depletion with pchlorophenylalanine(200 mg kg-1, i.p. for 14 days) had no effect on RU 24969-induced hyperlocomotiondemonstrating that the 5-HTIB receptors involved are postsynaptic and that they do not show super sensitivity.9. The involvement of other monoamine neurotransmitter systems in RU 24969-induced hyperlocomotionwas also examined. The response was inhibited by the al-adrenoceptor antagonist, prazosin(1 mg kg-1), the dopamine DI receptor antagonist, SCH 23390 (0.05 mg kg-1) and the dopamine D2 receptor antagonist, BRL 34778 (0.03 mg kg-1), but not by the M2-adrenoceptor antagonist, idazoxan(1 mg kg-1). Lesioning noradrenergic neurones with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine(100 mg kg-1) markedly attenuated this behaviour. These results show that the hyperlocomotion is expressed via noradrenergic and dopaminergic neurones acting on alpha 1-adrenoceptors, DI and D2 receptors.10. RU 24969 decreased brain concentrations of 5-hydroxyindoleacetic acid whilst simultaneously increasing 5-HT, consistent with the reduction of 5-HT neuronal activity by activation of 5-HTlA and 5-HTIB autoreceptors. RU 24969 increased brain 3-methoxy-4-hydroxyphenylglycol, but not noradrenaline, concentrations which supports the involvement of noradrenergic neurones in the expression of hyperlocomotion. RU 24969 did not alter dopamine, dihydroxyphenylacetic acid or homovanillic acid concentrations in the nucleus accumbens suggesting that the dopaminergic neurones terminating there are not directly involved.

Rapid and simultaneous assay of monoamine neurotransmitters and their metabolites in discrete brain areas of mice by HPLC with Coulometric detection

For simultaneous assay of the three monoamine neurotransmitters, norepinephrine, dopamine, and serotonin, and four respective metabolites in brain tissue, a rapid and simple method using high-performance liquid chromatography with coulometric detection is described. Because the present method permits the determination of these target substrates within 10 min or less in one chromatographic run, 150 samples can be analyzed using an autosampler and an integrator in a 24-h period. Within-run coefficients of variation for the target substrates in the standard solution and the whole brain sample were less than 3% and 2% (n = 40), respectively. The quantitative detection limits were 0.01-0.1 pmol. The present procedure was applied to measure the target substrates in several discrete brain areas in mice.

?2 Autoreceptor-mediated modulation of tyrosine hydroxylase activity in noradrenergic regions of the rat brain in vivo

The physiological importance of brain alpha 2-adrenoceptors in controlling the activity of tyrosine hydroxylase in noradrenergic regions was investigated using the accumulation of 3,4-dihydroxyphenylalanine (DOPA) after decarboxylase inhibition as a measure of the rate of tyrosine hydroxylation (and synthesis of noradrenaline) in vivo. In the hypothalamus and cerebral cortex, clonidine (0.025-1 mg/kg, i.p.) decreased (18%-43%) and idazoxan (0.1-80 mg/kg, i.p.) increased (20%-73%) the synthesis of DOPA in a dose-dependent manner. Moreover, pretreatment with idazoxan (0.1 mg/kg) antagonized the effect of clonidine (0.1 mg/kg) in the hypothalamus. After treatment with reserpine (5 mg/kg, s.c., 18 h before decapitation) and depletion of noradrenaline, clonidine (0.5 mg/kg) continued to decrease (50%-55%) but idazoxan (20 mg/kg) failed to increase the synthesis of DOPA, which suggested the involvement of an alpha-auto-receptor mechanism. Acute treatments of rats (not exposed to reserpine) with a wide variety of adrenoceptor agonists such as guanfacine 6, B-HT920, xylazine, bromoxidine (1 mg/kg) and antagonists such as yohimbine, phentolamine, prazosin (10 or 20 mg/kg) resulted in significant decreases (15%-55%) or increases (21%-99%) in the synthesis of DOPA in both brain regions. However, other agonists (oxymetazoline, azepexole, tramazoline, methoxamine) and antagonists (tolazoline, dihydroergotamine, phenoxybenzamine, propranolol) did not modify the synthesis of DOPA. In the hypothalamus and cerebral cortex the effects of the drugs were consistent with the selectivity of alpha-adrenoceptor agonists and antagonists (except prazosin) for an alpha 2-adrenoceptor. The results also suggest that the alpha 2-autoreceptor that modulates the synthesis of noradrenaline in the rat brain appears to belong to the prazosin-sensitive alpha 2B-subtype.

Effect of corticosterone on noradrenergic nuclei in the pons-medulla and [3H]NA release from terminals in hippocampal slices

The aim of the present study was to investigate possible membrane and genomic effects of corticosterone on the noradrenergic system of the rat brain. Corticosterone effects were studied in vivo by treating rats s.c. with 10 mg/kg corticosterone for 7 or 14 days. In the first two experiments corticosterone significantly decreased the noradrenaline (NA) and dopamine (DA) levels in the pons-medulla, an area which contains the A1-A7 noradrenergic cell groups, while the NA and DA levels in the dorsal hippocampus remained unchanged. In a third experiment where the locus coeruleus (LC) and the A1 and A2 nuclei (A1,A2) were analysed separately, NA levels were unchanged but total MHPG levels and the total MHPG/NA ratio were decreased in the A1,A2 area. Chronic corticosterone treatment (14 days) did not alter the alpha 2-adrenoceptor-mediated modulation of [3H]NA release from dorsal hippocampal slices. Neither the spontaneous outflow nor the electrically stimulated release of [3H]NA from dorsal hippocampal slices of untreated rats was affected by exposure of the slices to corticosterone (10(-7) M - 10(-4) M) in the superfusion buffer. Thus, chronic corticosterone treatment of rats altered the noradrenergic system of the pons-medulla, but did not change the alpha 2-adrenoceptor-mediated modulation of NA release in the dorsal hippocampus, a major terminal area of the LC neurons. Corticosterone also did not appear to have a direct membrane effect on the NA terminals in the dorsal hippocampus of the rat.

A comparison of various antidepressant drugs demonstrates rapid desensitisation of alpha 2-adrenoceptors exclusively by sibutramine hydrochloride

The functional status of presynaptic and postsynaptic alpha 2-adrenoceptors in murine brain was respectively monitored using the hypoactivity (sedation) and mydriasis (pupil dilatation) responses to clonidine (0.1 mg/kg IP). Both responses were attenuated 24 h after 3 days of injection of sibutramine hydrochloride (3 mg/kg IP). To ascertain whether this property was exclusive to sibutramine, the following antidepressant drugs were also tested for their ability to down-regulate alpha 2-adrenoceptors rapidly: amitriptyline, doxepin, nomifensine, desipramine, amoxapine, fluoxetine, zimeldine, tranylcypromine and mianserin. When given for 3 or 5 days at the low dose of 3 mg/kg IP, none of the other antidepressants reduced clonidine-induced hypoactivity or mydriasis. Furthermore, increasing the dose of amitriptyline, doxepin, nomifensine, desipramine, amoxapine and tranylcypromine to 10 mg/kg IP did not enable these antidepressants to attenuate the alpha 2-adrenoceptor-mediated responses after 3 days of treatment. An electroconvulsive shock (ECS; 200 V, 2 s) given once daily attenuated clonidine-induced mydriasis, but not hypoactivity, when administered for 3 days and both responses when administered for 5 days. In conclusion, this comparative study using antidepressant treatments with differing pharmacological modes of action demonstrated that sibutramine was the only drug which rapidly down-regulated pre- and postsynaptic alpha 2-adrenoceptors. ECS down-regulated postsynaptic alpha 2-adrenoceptors when given for 3 days, but required 5 days to desensitise both alpha 2-adrenoceptor populations.

Extracellular brain cortical levels of noradrenaline in ischemia: effects of desipramine and postischemic administration of idazoxan

Using microdialysis, extracellular noradrenaline (NA) levels in the rat cerebral cortex were studied under isoflurane/N2O anaesthesia before, during and for 6 hours following 10 min of forebrain ischemia in a 2-vessel occlusion model. A microdialysis probe was introduced into the parietal cortex and dorsal hippocampus in anaesthetized rats and continuously perfused with Krebs-Ringer-bicarbonate buffer with or without the NA uptake inhibitor desipramine (DMI, 5 microM). Twenty min fractions were collected and the extracellular NA levels were measured in the dialysates using HPLC with electrochemical detection. The basal NA concentration in the dialysate was 10.5 +/- 1.8 (mean +/- SEM) pg/20 min fraction and increased to 39.3 +/- 4.8 pg/20 min fraction after local administration of DMI. During ischemia, NA increased to 38 times the basal level without DMI, and 6 times with DMI included during two hours' perfusion prior to ischemia. After recirculation NA levels returned to, or even transiently decreased below, preischemic values. With DMI present in the dialysis buffer, administration of idazoxan immediately following ischemia delayed the return to preischemic NA levels in the recirculation phase. In the absence of DMI, no effect of idazoxan on postischemic levels of NA was found. Local administration of DMI increases basal extracellular NA levels and reduces the ischemia-induced NA release. The latter effect may be a due to inhibition of the NA uptake system working in a reversed mode, or as a result of decreased synthesis of NA due to activation of presynaptic alpha 2-receptors by the increased synaptic NA levels. Postischemic treatment with the alpha 2-adrenoceptor antagonist idazoxan in combination with DMI prolongs the period of elevated extracellular NA levels, which may be of importance for the protective properties of idazoxan against ischemic cell injury.

Effects of antidepressant drugs and electroconvulsive shock on pre- and postsynaptic alpha 2-adrenoceptor function in the brain: rapid down-regulation by sibutramine hydrochloride

Clonidine (0.1 mg/kg IP)-induced hypoactivity and mydriasis responses were respectively used as functional indices of pre- and postsynaptic alpha 2-adrenoceptors in mouse brain. A single injection of various antidepressant drugs had no effect on either response when measured 24 h later. However, 14 days' treatment with sibutramine HCl (3 mg/kg IP), dothiepin (50 mg/kg IP), amitriptyline (10 mg/kg IP), desipramine (10 mg/kg IP) or tranylcypromine (10 mg/kg IP) markedly attenuated both clonidine-induced hypoactivity and mydriasis. Repeated administration of zimeldine (10 mg/kg IP), mianserin (10 mg/kg IP) or clenbuterol (5 mg/kg IP) had no effect on either response. Subchronic treatment with sibutramine HCl (3 mg/kg IP; 3 days) also attenuated pre- and postsynaptic alpha 2-adrenoceptor function. Five ECS (200 V, 2 s) spread over 10 days, but not a single shock, reduced the hypoactivity and mydriasis responses to clonidine. Together, the results indicate that pre- and postsynaptic alpha 2-adrenoceptor function is attenuated by repeated treatment with those antidepressants which acutely increase synaptic levels of noradrenaline. These adrenergic receptor populations are also desensitized by ECS, although this effect is probably mediated via a different mechanism. Finally, the rapid down-regulation observed with sibutramine HCl is not confined to beta-adrenoceptors alone, because pre- and postsynaptic alpha 2-adrenoceptor function is also attenuated by 3 days of treatment with this novel antidepressant drug.

Clonidine produces mydriasis in conscious mice by activating central alpha 2-adrenoceptors

Intraperitoneal (i.p.) injection of the alpha 2-adrenoceptor agonist clonidine (1-3000 micrograms/kg) produced dose-dependent pupil dilatation in conscious C57/Bl/6 mice with an ED50 of 54 micrograms/kg (95% confidence limits 40-74 micrograms/kg). This response was rapid in onset and of approximately 30 min duration. The alpha 2-adrenoceptor antagonists idazoxan (1 or 3 mg/kg i.p.) and yohimbine (1 or 3 mg/kg i.p.) both produced dose-related miosis, but the alpha 1- and beta-adrenoceptor antagonists prazosin (1 or 3 mg/kg i.p.) and pindolol (1 or 3 mg/kg i.p.) were without effect. These doses of idazoxan and yohimbine potently reversed the mydriasis induced by clonidine (100 micrograms/kg i.p.), while prazosin and pindolol were again ineffective. Clonidine-induced mydriasis was also unaltered by the 5-HT antagonists, methysergide (2.5 mg/kg i.p.) and ketanserin (0.1 mg/kg i.p.) or 0.1 mg/kg i.p. of the dopamine antagonists, haloperidol, SCH 23390 and BRL 34778. A dose of 0.25 microgram clonidine, which was ineffective when administered i.p., produced marked mydriasis after intracerebroventricular (i.c.v.) injection. In addition, the mydriasis produced by i.p. injection of clonidine (100 micrograms/kg) was abolished by i.c.v. dosing of 2.5 micrograms idazoxan or yohimbine, but again not by prazosin or pindolol. Together, these data provide strong evidence to indicate that clonidine-induced mydriasis is exclusively mediated via central alpha 2-adrenoceptors and that this response provides a useful model for studying the function of these receptors.

Clonidine-induced hypoactivity and mydriasis in mice are respectively mediated via pre- and postsynaptic alpha 2-adrenoceptors in the brain

Since brain alpha 2-adrenoceptors occur both pre- and postsynaptically, experiments were carried out to determine the synaptic locations of those receptors mediating clonidine-induced hypoactivity and mydriasis. Intraperitoneal (i.p.) injection of clonidine (1-3000 micrograms/kg) to mice dose dependently induced these two responses and also decreased brain concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG). The ED50 values were: 120 micrograms/kg for hypoactivity (95% confidence limits 103-140 micrograms/kg), 54 micrograms/kg for mydriasis (95% confidence limits 40-74 micrograms/kg) and 18 micrograms/kg for MHPG reduction (95% confidence limits 8-36 micrograms/kg) suggesting that these responses could all be presynaptically mediated. However, methamphetamine which increases noradrenaline turnover was found to dose dependently produce mydriasis, but not hypoactivity, after peripheral (0.1-5 mg/kg i.p.) or central (0.5-10 micrograms i.c.v.) injection. The mydriasis produced by methamphetamine (0.5 mg/kg i.p.) was abolished by i.c.v. injection of 1 micrograms idazoxan or yohimbine, but not 2.5 micrograms prazosin or pindolol, showing this effect was mediated by central alpha 2-adrenoceptors. Methamphetamine (1-10 micrograms i.c.v.) potentiated the mydriasis induced by clonidine (50 micrograms/kg i.p.) suggesting this was a postsynaptic alpha 2-adrenoceptor response. By contrast, methamphetamine (1-10 micrograms i.c.v.) dose dependently reversed clonidine (100 micrograms/kg i.p.) hypoactivity indicating this response was mediated by presynaptic alpha 2-adrenoceptors. These hypotheses were confirmed by destruction of noradrenergic neurones using DSP-4 (100 mg/kg i.p. x 2). This treatment prevented the mydriasis response to methamphetamine (0.5 mg/kg i.p.), but not clonidine (100 micrograms/kg i.p.) and markedly attenuated clonidine (100 micrograms/kg i.p.) hypoactivity.