Monoamine related functional gene variants and relationships to monoamine metabolite concentrations in CSF of healthy volunteers

BACKGROUND: Concentrations of monoamine metabolites in human cerebrospinal fluid (CSF) have been used extensively as indirect estimates of monoamine turnover in the brain. CSF monoamine metabolite concentrations are partly determined by genetic influences. METHODS: We investigated possible relationships between DNA polymorphisms in the serotonin 2C receptor (HTR2C), the serotonin 3A receptor (HTR3A), the dopamine D(4 )receptor (DRD4), and the dopamine β-hydroxylase (DBH) genes and CSF concentrations of 5-hydroxyindolacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy volunteers (n = 90). RESULTS: The HTR3A 178 C/T variant was associated with 5-HIAA levels (p = 0.02). The DBH-1021 heterozygote genotype was associated with 5-HIAA (p = 0.0005) and HVA (p = 0.009) concentrations. Neither the HTR2C Cys23Ser variant, nor the DRD4 -521 C/T variant were significantly associated with any of the monoamine metabolites. CONCLUSIONS: The present results suggest that the HTR3A and DBH genes may participate in the regulation of dopamine and serotonin turnover rates in the central nervous system

Pharmacological Investigations of the Dissociative ‘Legal Highs’ Diphenidine, Methoxphenidine and Analogues

1,2-Diarylethylamines including lanicemine, lefetamine, and remacemide have clinical relevance in a range of therapeutic areas including pain management, epilepsy, neurodegenerative disease and depression. More recently 1,2-diarylethylamines have been sold as ‘legal highs’ in a number of different forms including powders and tablets. These compounds are sold to circumvent governmental legislation regulating psychoactive drugs. Examples include the opioid MT-45 and the dissociative agents diphenidine (DPH) and 2-methoxy-diphenidine (2-MXP). A number of fatal and non-fatal overdoses have been linked to abuse of these compounds. As with many ‘legal highs’, little is known about their pharmacology. To obtain a better understanding, the effects of DPH, 2-MXP and its 3- and 4-MeO- isomers, and 2-Cl-diphenidine (2-Cl-DPH) were investigated using binding studies at 46 central nervous system receptors including the N-methyl-D-aspartate receptor (NMDAR), serotonin, dopamine, norepinephrine, histamine, and sigma receptors as well as the reuptake transporters for serotonin, dopamine and norepinephrine. Reuptake inhibition potencies were measured at serotonin, norepinephrine and dopamine transporters. NMDAR antagonism was established in vitro using NMDAR-induced field excitatory postsynaptic potential (fEPSP) experiments. Finally, DPH and 2-MXP were investigated using tests of pre-pulse inhibition of startle (PPI) in rats to determine whether they reduce sensorimotor gating, an effect observed with known dissociative drugs such as phencyclidine (PCP) and ketamine. The results suggest that these 1,2-diarylethylamines are relatively selective NMDAR antagonists with weak off-target inhibitory effects on dopamine and norepinephrine reuptake. DPH and 2-MXP significantly inhibited PPI. DPH showed greater potency than 2-MXP, acting with a median effective dose (ED50) of 9.5 mg/kg, which is less potent than values reported for other commonly abused dissociative drugs such as PCP and ketamine

Involvement of NMDA receptor complex in the anxiolytic-like effects of chlordiazepoxide in mice

In the present study, we demonstrated that low, ineffective doses of N-methyl-d-aspartic acid (NMDA) receptor antagonists [competitive NMDA antagonist, CGP 37849, at 0.312 mg/kg intraperitoneally (i.p.), antagonist of the glycineB sites, L-701,324, at 2 mg/kg i.p., partial agonist of glycineB sites, d-cycloserine, at 2.5 mg/kg i.p.] administered jointly with an ineffective dose of the benzodiazepine, chlordiazepoxide (CDP, 2.5 mg/kg i.p.), significantly increased the percentage of time spent in the open arms of the elevated plus-maze (index of anxiolytic effect). Furthermore, CDP-induced anxiolytic-like activity (5 mg/kg i.p.) was antagonized by NMDA (75 mg/kg i.p.) and by an agonist of glycineB sites of the NMDA receptor complex, d-serine [100 nmol/mouse intracerebroventricularly (i.c.v.)]. The present study showed a positive interaction between γ-aminobutyric acid (GABA) and glutamate neurotransmission in the anxiolytic-like activity in the elevated plus-maze test in mice and this activity seems to particularly involve the NMDA receptors

Competitive and uncompetitive N -methyl- d -aspartate antagonist discriminations in pigeons: CGS 19755 and phencyclidine

The purpose of the present studies was to examine representative uncompetitive and competitive NMDA antagonists, as well as the glycine/NMDA antagonist, HA 966, in pigeons trained to discriminate either PCP or CGS 19755 from saline. Separate groups of pigeons were trained to discriminate either the uncompetitive, phencyclidine (PCP; 0.32 and 1.0 mg/kg, IM), or the competitive, CGS 19755 ( cis -4-phosphonomethyl-2-piperidine-carboxylic acid; 1.8 mg/kg, IM), NMDA antagonists from saline. Uncompetitive and competitive NMDA antagonists were examined in generalization studies, as were the racemate and the (+) and (−) stereoisomers of HA 966 (3-amino-1-hydroxypyrrolid-2-one). Dizocilpine (MK 801) was fully generalized to PCP but not to CGS 19755. All competitive NMDA antagonists tested were fully generalized to CGS 19755, but not to PCP. The competitive antagonists, however, produced >50% PCP-appropriate responding. The (+) isomer of HA 966 was fully generalized by three of four pigeons discriminating PCP (1.0 mg/kg) or CGS 19755, whereas the racemate and the (−) isomer produced 10% drug-appropriate responding in either discrimination group. The competitive antagonists tended to produce peak drug-appropriate responding at times greater than 60 min after administration, whereas uncompetitive antagonists produced peak drug-appropriate responding at earlier times. HA 966 also had a relatively slow onset of action as compared to PCP. These results suggest that antagonists acting at different modulatory sites of the NMDA receptor complex produce similar, but not identical, discriminative stimuli.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46346/1/213_2005_Article_BF02245248.pd

Automated recording of home cage activity and temperature of individual rats housed in social groups: The Rodent Big Brother project

Measuring the activity and temperature of rats is commonly required in biomedical research. Conventional approaches necessitate single housing, which affects their behavior and wellbeing. We have used a subcutaneous radiofrequency identification (RFID) transponder to measure ambulatory activity and temperature of individual rats when group-housed in conventional, rack-mounted home cages. The transponder location and temperature is detected by a matrix of antennae in a baseplate under the cage. An infrared high-definition camera acquires side-view video of the cage and also enables automated detection of vertical activity. Validation studies showed that baseplate-derived ambulatory activity correlated well with manual tracking and with side-view whole-cage video pixel movement. This technology enables individual behavioral and temperature data to be acquired continuously from group-housed rats in their familiar, home cage environment. We demonstrate its ability to reliably detect naturally occurring behavioral effects, extending beyond the capabilities of routine observational tests and conventional monitoring equipment. It has numerous potential applications including safety pharmacology, toxicology, circadian biology, disease models and drug discovery

Evidence that the anxiolytic-like effects of chlordiazepoxide on the elevated plus maze are confounded by increases in locomotor activity.

In exploratory animal models of anxiety, such as the elevated plus maze, the anxiogenic- and anxiolytic-like effects of drugs may be confounded by changes in locomotor activity. In the present experiments, the sensitivity of several measures of anxiety and locomotor activity in the elevated plus maze were assessed. Both chlordiazepoxide hydrochloride (CDP, 7.5 mg/kg) and d-amphetamine sulphate (AMP, 0.75, 1.5 mg/kg) increased the percent time on the open arms and doses of 7.5 mg/kg and 1.5 mg/kg CDP and AMP, respectively, increased the number of entries into the open arms. The increase in these measures might suggest that both compounds induced an anxiolytic-like effect. Although FG 7142 (30.0 mg/kg) did not decrease the number of entries to the open arms, it did decrease the time on the open arms, which might suggest that it had anxiogenic-like effects. Similarly, buspirone reduced both the number of entries into the open arms and the time spent on the open arms. However, all the compounds significantly affected locomotor activity. CDP (3.0 and 7.5 mg/kg) increased the total number of arm entries, the distance travelled on the open arms and the mean speed of the animals on the open, and in the closed arms. Moreover, the distance travelled by the animals in the closed arms was increased by 1.0 mg/kg CDP, a dose that had no measurable effects on the indices of anxiety.(ABSTRACT TRUNCATED AT 250 WORDS

One-trial tolerance to the effects of chlordiazepoxide on the elevated plus maze may be due to locomotor habituation, not repeated drug exposure.

The phenomenon of "one-trial tolerance" to the effects of chlordiazepoxide hydrochloride (CDP) in the elevated plus maze was re-examined. Unlike previous experiments, pre-exposure to the maze resulted in habituation and a consequential reduction in time spent on the open arms. The habituation effect was measured by recording the actual distance travelled by the rats in the maze and this was found to be significantly reduced by pre-exposure. Pre-exposure to the maze in the presence of CDP resulted in a reduced response to its "anxiolytic-like" effects (increasing time on the open arms compared to vehicle control rats). However, although the time spent on the open arms was reduced by pre-exposure, CDP significantly increased the time spent on the open arms by rats pre-exposed under a non-drugged state. These results suggest that rats do not become tolerant to the effects of CDP, but rather the reduced response to CDP after pre-exposure is due to habituation of exploratory behaviour

The behavioural effects of MK-801: a comparison with antagonists acting non-competitively and competitively at the NMDA receptor.

The selective non-competitive NMDA receptor antagonist, MK-801, potently blocked convulsions induced in the mouse by N-methyl-DL-aspartic acid (NMDLA) with an i.v. ED50 dose of 0.2 mg/kg. Similar doses of MK-801 were also effective in blocking seizures induced by pentylenetetrazol (PTZ), electroshock and by sound in audiogenic seizure-prone animals. Other less selective non-competitive NMDA receptor antagonists including phencyclidine (PCP), thienylcyclohexylpiperidine (TCP), (+)-N-allylnormetazocine [+)-NANM, (+)-SKF 10,047) and ketamine also blocked NMDLA-induced seizures with a rank order of potency of MK-801 greater than PCP greater than TCP = (+)-NANM greater than ketamine. The competitive NMDA receptor antagonist, 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) blocked NMDLA-induced seizures with an ED50 of 4.5 mg/kg, 22- and 560-fold more potently than the competitive antagonists, 2-DL-amino-7-phosphonoheptanoic acid (2-APH) and 2-DL-amino-5-phosphonovaleric acid (2-APV), respectively. MK-801 was the most potent of the non-competitive antagonists to induce a motor syndrome including head weaving, body rolling, increased locomotion and ataxia, characteristic of the behavioural response to PCP in the mouse. The syndrome was also present following injection of the competitive NMDA receptor antagonists, although they were generally less potent (probably a reflection of poor brain penetration) and less efficacious than the non-competitive antagonists. For all compounds except CPP, the anticonvulsant ED50 dose was close to the minimum effective dose to induce motor stimulation: CPP was 5- to 10-fold more potent as an anticonvulsant.(ABSTRACT TRUNCATED AT 250 WORDS