Application of the PET ligand [11C]ORM-13070 to examine receptor occupancy by the α2C-adrenoceptor antagonist ORM-12741: translational validation of target engagement in rat and human brain

Background

Availability of the α_2C-adrenoceptor (α_2C-AR) positron emission tomography (PET) tracer, [¹¹C]ORM-13070, and the α_2C-AR antagonist ORM-12741 allows probing of the roles of this G-protein coupled receptor subtype in brain function, both in healthy humans and in patients with various brain disorders. This translational study employed [¹¹C]ORM-13070 autoradiography and PET to determine α_2C-AR occupancy by ORM-12741 in rat and human brain, respectively.

Results

ORM-12741 has high affinity (K_i: 0.08 nM) and potent antagonist activity (K_b: 0.04 nM) as well as selectivity (K_i estimates for the human α_2A-AR and α_2B-AR were 8.3 nM and 0.8 nM, respectively) for the human α_2C-AR subtype. [¹¹C]ORM-13070 had highest uptake in the basal ganglia of rat and human brain. Pretreatment with ORM-12741 inhibited [¹¹C]ORM-13070 binding in rat striatum in a time- and dose-dependent manner at 10 and 50 µg/kg (s.c.) with an EC₅₀ estimate of 1.42 ng/mL in rat plasma, corresponding to protein-free drug concentration of 0.23 nM. In the living human brain, time- and dose-related α_2C-AR occupancy was detected with EC₅₀ estimates of 24 ng/mL and 31 ng/mL for the caudate nucleus and putamen, respectively, corresponding to protein-free concentrations in plasma of 0.07 nM and 0.1 nM. Modelling-based maximum α_2C-AR occupancy estimates were 63% and 52% in the caudate nucleus and the putamen, respectively.

Conclusions

ORM-12741 is a selective α_2C-AR antagonist which penetrates the rat and human brain to occupy α_2C-ARs in a manner consistent with its receptor pharmacology.

Trialregistrationnumberanddateofregistration: ClinicalTrial.cov NCT00829907. Registered 11 December 2008. https://clinicaltrials.gov/.

The α2C-adrenoceptor antagonist, ORM-10921, has antipsychotic-like effects in social isolation reared rats and bolsters the response to haloperidol

Early studies suggest that selective α2C-adrenoceptor (AR)-antagonism has anti-psychotic-like and pro-cognitive properties. However, this has not been demonstrated in an animal model of schizophrenia with a neurodevelopmental construct. The beneficial effects of clozapine in refractory schizophrenia and associated cognitive deficits have, among others, been associated with its α2C-AR modulating activity. Altered brain-derived neurotrophic factor (BDNF) has been linked to schizophrenia and cognitive deficits. We investigated whether the α2C-AR antagonist, ORM-10921, could modulate sensorimotor gating and cognitive deficits, as well as alter striatal BDNF levels in the social isolation reared (SIR) model of schizophrenia, comparing its effects to clozapine and the typical antipsychotic, haloperidol, the latter being devoid of α2C-AR-activity. Moreover, the ability of ORM-10921 to augment the effects of haloperidol on the above parameters was also investigated. Animals received subcutaneous injection of either ORM-10921 (0.01mg/kg), clozapine (5mg/kg), haloperidol (0.2mg/kg), haloperidol (0.2mg/kg)+ORM-10921 (0.01mg/kg) or vehicle once daily for 14days, followed by assessment of novel object recognition (NOR), prepulse inhibition (PPI) of startle response and striatal BDNF levels. SIR significantly attenuated NOR memory as well as PPI, and reduced striatal BDNF levels vs. social controls. Clozapine, ORM-10921 and haloperidol+ORM-10921, but not haloperidol alone, significantly improved SIR-associated deficits in PPI and NOR, with ORM-10921 also significantly improving PPI deficits vs. haloperidol-treated SIR animals. Haloperidol+ORM-10921 significantly reversed reduced striatal BDNF levels in SIR rats. α2C-AR-antagonism improves deficits in cognition and sensorimotor gating in a neurodevelopmental animal model of schizophrenia and bolsters the effects of a typical antipsychotic, supporting a therapeutic role for α2C-AR-antagonism in schizophrenia.

Levosimendan alone and in combination with valsartan prevents stroke in Dahl salt-sensitive rats

The effects of levosimendan on cerebrovascular lesions and mortality were investigated in models of primary and secondary stroke. We aimed to determine whether the effects of levosimendan are comparable to and/or cumulative with those of valsartan, and to investigate whether levosimendan-induced vasodilation has a role in its effects on stroke. In a primary stroke Dahl/Rapp rat model, mortality rates were 70% and 5% for vehicle and levosimendan, respectively. Both stroke incidence (85% vs. 10%, P<0.001) and stroke-associated behavioral deficits (7-point neuroscore: 4.59 vs. 5.96, P<0.001) were worse for vehicle compared to levosimendan. In a secondary stroke model in which levosimendan treatment was started after cerebrovascular incidences were already detected, mean survival times were 15 days with vehicle, 20 days with levosimendan (P=0.025, vs. vehicle), 22 days with valsartan (P=0.001, vs. vehicle), and 31 days with levosimendan plus valsartan (P<0.001, vs. vehicle). The respective survivals were 0%, 16%, 20% and 59%, and the respective incidences of severe lesions were 50%, 67%, 50% and 11%. In this rat model, levosimendan increased blood volume of the cerebral vessels, with significant effects in the microvessels of the cortex (∆R=3.5±0.15 vs. 2.7±0.17ml for vehicle; P=0.001) and hemisphere (∆R=3.2±0.23 vs. 2.6±0.14ml for vehicle; P=0.018). Overall, levosimendan significantly reduced stroke-induced mortality and morbidity, both alone and with valsartan, with apparent cumulative effects, an activity in which the vasodilatory effects of levosimendan have a role.

Amphetamine decreases α2C-adrenoceptor binding of [11C]ORM-13070: a PET study in the primate brain

BACKGROUND

The neurotransmitter norepinephrine has been implicated in psychiatric and neurodegenerative disorders. Examination of synaptic norepinephrine concentrations in the living brain may be possible with positron emission tomography (PET), but has been hampered by the lack of suitable radioligands.

METHODS

We explored the use of the novel α2C-adrenoceptor antagonist PET tracer [(11)C]ORM-13070 for measurement of amphetamine-induced changes in synaptic norepinephrine. The effect of amphetamine on [(11)C]ORM-13070 binding was evaluated ex vivo in rat brain sections and in vivo with PET imaging in monkeys.

RESULTS

Microdialysis experiments confirmed amphetamine-induced elevations in rat striatal norepinephrine and dopamine concentrations. Regional [(11)C]ORM-13070 receptor binding was high in the striatum and low in the cerebellum. After injection of [(11)C]ORM-13070 in rats, mean striatal specific binding ratios, determined using cerebellum as a reference region, were 1.4±0.3 after vehicle pretreatment and 1.2±0.2 after amphetamine administration (0.3mg/kg, subcutaneous). Injection of [(11)C]ORM-13070 in non-human primates resulted in mean striatal binding potential (BP ND) estimates of 0.65±0.12 at baseline. Intravenous administration of amphetamine (0.5 and 1.0mg/kg, i.v.) reduced BP ND values by 31-50%. Amphetamine (0.3mg/kg, subcutaneous) increased extracellular norepinephrine (by 400%) and dopamine (by 270%) in rat striata.

CONCLUSIONS

Together, these results indicate that [(11)C]ORM-13070 may be a useful tool for evaluation of synaptic norepinephrine concentrations in vivo. Future studies are required to further understand a potential contribution of dopamine to the amphetamine-induced effect.

Validation of [(11) C]ORM-13070 as a PET tracer for alpha2c -adrenoceptors in the human brain

This study explored the use of the α2C -adrenoceptor PET tracer [(11) C]ORM-13070 to monitor α2C -AR occupancy in the human brain. The subtype-nonselective α2 -AR antagonist atipamezole was administered to eight healthy volunteer subjects to determine its efficacy and potency (Emax and EC50 ) at inhibiting tracer uptake. We also explored whether the tracer could reveal changes in the synaptic concentrations of endogenous noradrenaline in the brain, in response to several pharmacological and sensory challenge conditions. We assessed occupancy from the bound-to-free ratio measured during 5-30 min post injection. Based on extrapolation of one-site binding, the maximal extent of inhibition of striatal [(11) C]ORM-13070 uptake (Emax ) achievable by atipamezole was 78% (95% CI 69-87%) in the caudate nucleus and 65% (53-77%) in the putamen. The EC50 estimates of atipamezole (1.6 and 2.5 ng/ml, respectively) were in agreement with the drug's affinity to α2C -ARs. These findings represent clear support for the use of [(11) C]ORM-13070 for monitoring drug occupancy of α2C -ARs in the living human brain. Three of the employed noradrenaline challenges were associated with small, approximately 10-16% average reductions in tracer uptake in the dorsal striatum (atomoxetine, ketamine, and the cold pressor test; P < 0.05 for all), but insulin-induced hypoglycemia did not affect tracer uptake. The tracer is suitable for studying central nervous system receptor occupancy by α2C -AR ligands in human subjects. [(11) C]ORM-13070 also holds potential as a tool for in vivo monitoring of synaptic concentrations of noradrenaline, but this remains to be further evaluated in future studies.

Application of cross-species PET imaging to assess neurotransmitter release in brain

RATIONALE

This review attempts to summarize the current status in relation to the use of positron emission tomography (PET) imaging in the assessment of synaptic concentrations of endogenous mediators in the living brain.

OBJECTIVES

Although PET radioligands are now available for more than 40 CNS targets, at the initiation of the Innovative Medicines Initiative (IMI) "Novel Methods leading to New Medications in Depression and Schizophrenia" (NEWMEDS) in 2009, PET radioligands sensitive to an endogenous neurotransmitter were only validated for dopamine. NEWMEDS work-package 5, "Cross-species and neurochemical imaging (PET) methods for drug discovery", commenced with a focus on developing methods enabling assessment of changes in extracellular concentrations of serotonin and noradrenaline in the brain.

RESULTS

Sharing the workload across institutions, we utilized in vitro techniques with cells and tissues, in vivo receptor binding and microdialysis techniques in rodents, and in vivo PET imaging in non-human primates and humans. Here, we discuss these efforts and review other recently published reports on the use of radioligands to assess changes in endogenous levels of dopamine, serotonin, noradrenaline, γ-aminobutyric acid, glutamate, acetylcholine, and opioid peptides. The emphasis is on assessment of the availability of appropriate translational tools (PET radioligands, pharmacological challenge agents) and on studies in non-human primates and human subjects, as well as current challenges and future directions.

CONCLUSIONS

PET imaging directed at investigating changes in endogenous neurochemicals, including the work done in NEWMEDS, have highlighted an opportunity to further extend the capability and application of this technology in drug development.

A PET Tracer for Brain α2C Adrenoceptors, (11)C-ORM-13070: Radiosynthesis and Preclinical Evaluation in Rats and Knockout Mice

We report the development of a PET tracer for α2C adrenoceptor imaging and its preliminary preclinical evaluation. α2C adrenoceptors in the human brain may be involved in various neuropsychiatric disorders, such as depression, schizophrenia, and neurodegenerative diseases. PET tracers are needed for imaging of this receptor system in vivo.

METHODS

High-specific-activity (11)C-ORM-13070 (1-[(S)-1-(2,3-dihydrobenzo[1,4]dioxin-2-yl)methyl]-4-(3-(11)C-methoxymethylpyridin-2-yl)-piperazine) was synthesized by (11)C-methylation of O-desmethyl-ORM-13070 with (11)C-methyl triflate, which was prepared from cyclotron-produced (11)C-methane via (11)C-methyl iodide. Rats and mice were investigated in vivo with PET and ex vivo with autoradiography. The specificity of (11)C-ORM-13070 binding to α2 adrenoceptors was demonstrated in rats pretreated with atipamezole, an α2 adrenoceptor antagonist. The α2C adrenoceptor selectivity of the tracer was determined by comparing tracer binding in wild-type and α2A- and α2AC adrenoceptor knockout (KO) mice. (11)C-ORM-13070 and its radioactive metabolites in rat plasma and brain tissue were analyzed with radio-high-performance liquid chromatography and mass spectroscopy. Human radiation dose estimates were extrapolated from rat biodistribution data.

RESULTS

The radiochemical yield, calculated from initial cyclotron-produced (11)C-methane, was 9.6% ± 2.7% (decay-corrected to end of bombardment). The specific activity of the product was 640 ± 390 GBq/μmol (decay-corrected to end of synthesis). The radiochemical purity exceeded 99% in all syntheses. The highest levels of tracer binding were observed in the striatum and olfactory tubercle of rats and control and α2A KO mice-that is, in the brain regions known to contain the highest densities of α2C adrenoceptors. In rats pretreated with atipamezole and in α2AC KO mice, (11)C tracer binding in the striatum and olfactory tubercle was low, similar to that of the frontal cortex and thalamus, regions with low densities of α2C adrenoceptors. Two radioactive metabolites were found in rat plasma, but only one of them was found in the brain; their identity was not revealed. The estimated effective radiation dose was comparable with the average exposure level in PET studies with (11)C tracers.

CONCLUSION

An efficient method for the radiosynthesis of (11)C-ORM-13070 was developed. (11)C-ORM-13070 emerged as a potential novel radiotracer for in vivo imaging of brain α2C adrenoceptors.

Effects of prolonged and maintenance strength training on force production, walking, and balance in aging women and men

To examine effects of 21-week twice/week strength training (ST) period followed by an additional 21-week twice or once/week ST period on force production, walking and balance in aging people. Seventy-two women (58 ± 7 years; W) and 63 (58 ± 6 years) men (M) were randomized for the first 21-week ST period: STW and STM, control (C) CW and CM. Training participants were randomized for the second 21-week ST period: once/week STWx1 and STMx1, twice/week STWx2 and STMx2. LegPress, isometric leg extension rate of force development (RFD), walking time, and balance. First 21-week ST period: leg press, RFD, balance, and walking improved significantly in STW and STM. Second 21-week ST period: leg press first increased in STMx1 and STMx2, and then decreased to the level of 21 weeks in STMx2 and remained unchanged in STWx2 and decreased in STWx1 and STMx1. Walking and balance improved significantly in STWx1 and STWx2. A progressive 21-week ST period twice/week in aging people can lead to large improvements in maximal strength, walking time, and balance in both genders. A further strength training period with the same amount of training may maintain the strength gains, whereas balance and walking may be maintained with less training.

Effect of age on the association between body fat percentage and maximal walking speed

OBJECTIVE

To study the effect of age on the association between body fat percentage and maximal walking speed in older people.

DESIGN AND PARTICIPANTS

Cross-sectional analysis of data collected in the Finnish population-based Health 2000 Survey involving 916 men and 1 222 women aged 55 years and older with complete data on body composition and a walking speed test.

METHODS

Body fat percentage was assessed using bioelectrical impedance analysis and maximal walking speed based on a timed walking test over a distance of 6.1 meters. Linear regression models were used to study the effect of age on association between body fat percentage and maximal walking speed.

RESULTS

The association between body fat percentage quartiles and maximal walking speed differed significantly between persons of different ages (p for age interaction = 0.027). In the age-stratified analyses, the association between body fat percentage and maximal walking speed remained significant among 60-69-year olds and 70-79-year-olds, but disappeared among 55-59-year-olds and 80-year and older after adjustment for potential covariates. Body fat percentage explained 11% of the variation in maximal walking speed among 55-59-year-olds, 21% among 60-69-year-olds, 17% among 70-79-year-olds and 11% among 80-year and older.

CONCLUSION

Association between body fat percentage and maximal walking speed was strongest between the ages of 60 and 79 years. The results suggest that the effects of excess body fatness are especially harmful for physical functioning among adults in their sixties and seventies and they could benefit from interventions.

Muscle mass and strength, body composition and dietary intake in master strength athletes vs untrained men of different ages

AIM

The aim of this study was to compare muscle strength and thickness, body composition and dietary intake between master strength athletes and controls.

METHODS

Cross-sectional comparison between: 1) young control men (25.7+/-3.4 y; n=10); 2) middle-aged master athletes (52.1+/-4.7 y; n=9); 3) middle-aged control men (51.9+/-3.1 y; n=11); 4) older master athletes (71.8+/-3.8 y; n=8); and 5) older control men (70.6+/-3.3 y; n=10). Athletes had been strength trained for 22.8+/-14.9 y. Maximal isometric strength of the leg extensors was measured with a leg dynamometer, body composition by skin folds, muscle thickness of the vastus lateralis with an ultrasound scanner and dietary intake by food diaries for 4 days.

RESULTS

Athletes had more lean body mass than age-matched controls (P<0.001-0.05) and young controls more than older controls (P<0.01). No group differences were observed in the thickness of vastus lateralis. Athletes showed higher absolute strength and strength per vastus lateralis thickness ratio than all control groups (P<0.01-0.001). Body mass adjusted dietary intake did not differ between the strength trained and control men. Dietary intake did not correlate with strength, muscle thickness and lean body mass.

CONCLUSION

The present older men with a long-term history of strength training showed greater muscle strength and strength per muscle thickness ratio than the untrained controls. The data support the usefulness of continuous strength training to preserve muscle strength in older men.

Dietary Intake, Serum Hormones, Muscle Mass and Strength During Strength Training in 49 - 73-Year-Old Men

Effects of dietary intake on serum hormones, muscle cross-sectional area (CSA) and strength during strength training were studied in two groups of men: 1) strength training + nutritional counseling (n = 22, 59.1 +/- 6.1 yrs), and 2) strength training (n = 23, 58.5 +/- 7.1 yrs). Both groups performed strength training twice a week for 21 weeks. Counseling increased carbohydrate (p < 0.01) and fiber intake (p < 0.001) and polyunsaturated/saturated fat-ratio (p < 0.05) and decreased fat intake (p < 0.01). Muscle strength and CSA increased by 16 - 20 % and by 5.4 - 5.9 % in both groups (p < 0.001). Changes in protein content of diet correlated with the changes in the acute postexercise concentrations of total (r = 0.64, p < 0.01) and free testosterone (r = 0.54, p < 0.05) after training in the counseling group. Moreover, changes in the free testosterone responses to heavy-resistance exercise correlated with the increases in the muscle CSA (r = 0.52, p < 0.05) in the counseling group. Serum basal testosterone/sex hormone-binding globulin-ratios correlated with the body mass normalized energy (kJ/kg: r = 0.54, p < 0.001), protein (g/kg: r = 0.42, p < 0.01) and fat (g/kg: r = 0.51, p < 0.01) intake in all participants during the training. The data indicate that protein and fat intake may influence serum testosterone concentrations and that the changes in exercise-induced testosterone responses may contribute to muscle mass development during strength training.

Effects of Strength Training and Reduced Training on Functional Performance and Metabolic Health Indicators in Middle-Aged Men

Changes in muscular fitness and metabolic health indicators were examined in 22 men (57.9 +/- 6.6 years, BMI 24.5 +/- 2.6 kg/m (2)) and 21 control men (58.2 +/- 6.1 years, BMI 25.4 +/- 2.8 kg/m (2)) during two consecutive 21-week periods: 1) whole body progressive strength training (ST: twice a week), and 2) continued reduced training (CRT: 3 ST sessions/2 weeks, n = 17 + 17). After the 21-week ST period, maximal strength of leg extensors increased in the ST group by 19.6 +/- 7.6 % vs. 2.8 +/- 4.4 % (p < 0.001) and also 10-m walking time and 10-step stair-climbing time shortened by - 17.2 +/- 7.6 % vs. 4.1 +/- 3.9 % (p < 0.01) and by - 8.2 +/- 6.8 % vs. - 3.0 +/- 6.8 % (p < 0.05) compared to the controls. Systolic blood pressure (BP) decreased in the ST group by - 4.4 +/- 6.7 % vs. 1.3 +/- 9.5 % (p < 0.05) compared to the controls after the ST period. Muscle strength as well as walking and stair-climbing times remained the same during the CRT. However, the changes in diastolic BP (- 8.9 +/- 8.7 % vs. - 1.0 +/- 6.6 %, p < 0.05) and fasting blood glucose concentrations (0.1 +/- 0.4 mmol/L vs. 0.3 +/- 0.4 mmol/L, p < 0.05) differed between the ST and control groups after the whole 42-week study period. Strength training has positive health effects in aging men by increasing maximal strength and functional performance and by decreasing resting blood pressure and high-intensity reduced strength training can maintain these health benefits.

Pharmacological characterization and CNS effects of a novel highly selective alpha2C-adrenoceptor antagonist JP-1302

BACKGROUND AND PURPOSE

Pharmacological validation of novel functions for the alpha2A-, alpha2B-, and alpha2C-adrenoceptor (AR) subtypes has been hampered by the limited specificity and subtype-selectivity of available ligands. The current study describes a novel highly selective alpha2C-adrenoceptor antagonist, JP-1302 (acridin-9-yl-[4-(4-methylpiperazin-1-yl)-phenyl]amine).

EXPERIMENTAL APPROACH

Standard in vitro binding and antagonism assays were employed to demonstrate the alpha2C-AR specificity of JP-1302. In addition, JP-1302 was tested in the forced swimming test (FST) and the prepulse-inhibition of startle reflex (PPI) model because mice with genetically altered alpha2C-adrenoceptors have previously been shown to exhibit different reactivity in these tests when compared to wild-type controls.

KEY RESULTS

JP-1302 displayed antagonism potencies (KB values) of 1,500, 2,200 and 16 nM at the human alpha2A-, alpha2B-, and alpha2C-adrenoceptor subtypes, respectively. JP-1302 produced antidepressant and antipsychotic-like effects, i.e. it effectively reduced immobility in the FST and reversed the phencyclidine-induced PPI deficit. Unlike the alpha2-subtype non-selective antagonist atipamezole, JP-1302 was not able to antagonize alpha2-agonist-induced sedation (measured as inhibition of spontaneous locomotor activity), hypothermia, alpha2-agonist-induced mydriasis or inhibition of vas deferens contractions, effects that have been generally attributed to the alpha2A-adrenoceptor subtype. In contrast to JP-1302, atipamezole did not antagonize the PCP-induced prepulse-inhibition deficit.

CONCLUSIONS AND IMPLICATIONS

The results provide further support for the hypothesis that specific antagonism of the alpha2C-adrenoceptor may have therapeutic potential as a novel mechanism for the treatment of neuropsychiatric disorders.

Structure-activity relationship of quinoline derivatives as potent and selective alpha(2C)-adrenoceptor antagonists

Starting from two acridine compounds identified in a high-throughput screening campaign (1 and 2, Table 1), a series of 4-aminoquinolines was synthesized and tested for their properties on the human alpha(2)-adrenoceptor subtypes (alpha(2A), alpha(2B), and alpha(2C)). A number of compounds with good antagonist potencies against the alpha(2C)-adrenoceptor and excellent subtype selectivities over the other two subtypes were discovered. For example, (R)-{4-[4-(3,4-dimethylpiperazin-1-yl)phenylamino]quinolin-3-yl}methanol 6j had an antagonist potency of 8.5 nM against, and a subtype selectivity of more than 200-fold for, the alpha(2C)-adrenoceptor. Investigation of the structure-activity relationship identified a number of structural features, the most critical of which was an absolute need for a substituent in the 3-position of the quinoline ring. The 3-position on the piperazine ring was also found to play an appreciable role, as substitutions in that position exerted a significant and stereospecific beneficial effect on the alpha(2C)-adrenoceptor affinity and potency. Replacing the piperazine ring proved difficult, with 1,4-diazepanes representing the only viable alternative.

Serum, cheek cell and breast milk fatty acid compositions in infants with atopic and non-atopic eczema

BACKGROUND

The major theory implicating diet with allergic diseases is associated with altered food consumption and subsequent changes in fatty acid composition.

OBJECTIVE

To investigate fatty acid compositions among infants with atopic and non-atopic eczema and healthy infants and to evaluate the expediency of non-invasive cheek cell phospholipid fatty acid composition as a marker in patients with eczema.

METHODS

Diagnosis of eczema in infants was confirmed clinically and by positive (atopic eczema, n=6) or negative (non-atopic eczema, n=6) skin prick testing in comparison with controls (n=19). The fatty acid compositions of infant cheek cell and serum phospholipids and breast milk total lipids were analysed by gas chromatography.

RESULTS

The distinction between atopic and non-atopic eczema was manifested in cheek cell phospholipids as linoleic acid (14.69 (13.67-15.53)% of total fatty acids; the median (interquartile range)), the sum of n-6 fatty acids (19.94 (19.06-20.53)%) and the sum of polyunsaturated fatty acids (22.70 (21.31-23.28)%) were higher in infants with atopic eczema compared with non-atopic eczema (12.69 (10.87-13.93); 17.72 (15.63-18.91) and 19.90 (17.64-21.06), respectively; P<0.05) and controls (12.50 (12.16-13.42); 18.19 (17.43-18.70) and 20.32 (19.32-21.03), respectively; P<0.05). Serum phospholipid gamma-linolenic acid was lower in both atopic and non-atopic eczema compared with controls (P<0.05) and additionally eicosapentaenoic acid was higher in atopic eczema compared with controls (P<0.05).

CONCLUSION

These preliminary results suggest differences in fatty acid compositions between the two types of eczema, calling for further evaluation in a larger setting. The two types of eczema may be regulated by different immunological processes, and fatty acids may have a more profound role in the atopic type.

α2A-Adrenoceptors regulate d-amphetamine-induced hyperactivity and behavioural sensitization in mice

Stimulants, such as d-amphetamine, enhance the release of dopamine in the central nervous system (CNS) and induce locomotor activation in mice. When amphetamine is administered repeatedly, the locomotor activation is progressively increased. This behavioural sensitization may be associated with the development of drug craving, addiction and dependence. Also noradrenergic mechanisms participate in the mediation of the effects of psychostimulants. In this study we show that mice lacking the alpha(2)-adrenoceptor subtype A (alpha(2A)-AR knock-out (KO) on C57Bl/6J background) are supersensitive to the acute locomotor effects of d-amphetamine (5 mg/kg) in a novel environment compared to wild-type (WT) control mice. When both genotypes were treated repeatedly with d-amphetamine (2 mg/kg) they developed locomotor hyperactivation (sensitization), but its amplitude was lower in alpha(2A)-AR KO mice. Development of hyperactivation was reduced in both genotypes by pretreatment with the selective alpha(2)-adrenoceptor antagonist, atipamezole (1 mg/kg). Acute atipamezole also attenuated the expression of d-amphetamine-induced behavioural sensitization especially in WT mice. Interestingly, alpha(2A)-AR KO mice failed to exhibit persistent sensitization after 2 weeks of abstinence from repeated d-amphetamine. Rewarding properties of d-amphetamine, measured by conditioned place preference, were similar in both genotypes. These findings indicate that d-amphetamine-induced acute and sensitized locomotor effects are controlled by alpha(2)-adrenoceptors. Drugs antagonizing the alpha(2A)-adrenoceptor subtype may provide a novel approach for reducing drug sensitization and motor complications caused by dopaminergic agents.

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.

Relationship Between Diet and Serum Anabolic Hormone Responses to Heavy-Resistance Exercise in Men

Relationship between dietary intake and serum anabolic hormone concentrations of testosterone (T), free testosterone (FT), and growth hormone were examined at rest as well as after the heavy-resistance exercise (HRE) in 8 strength athletes (SA) and 10 physically active non-athletes (NA). In the first part of the study serum basal anabolic hormone concentrations and dietary intake were examined in the total group of subjects. In the second part of the study a subgroup of 5 SA and 5 NA performed the high volume and high intensity HRE. Dietary intake was registered by dietary diaries for 4 days preceding the loading day. Significant correlations were observed between serum basal T and fat (E%: r = 0.55, p < 0.05, g/kg: r = 0.65, p < 0.01) and protein intake (E%: r = - 0.77, p < 0.001, g/kg: r = - 0.68, p < 0.01) in the total group of subjects. However, when the two groups were examined separately the significant relationships between serum basal T and dietary fat and protein could be noticed in SA only (fat g/kg: SA r = 0.77, p < 0.05; in NA r = 0.44, n.s., protein g/kg: SA r = - 0.84, p < 0.05; in NA r = 0.27, n.s.). Both serum T and FT responses to HRE were correlated with fat (E%: r = 0.85, p < 0.01 and r = 0.73, p < 0.05, g/kg: r = 0.72, p < 0.05 and r = 0.77, p < 0.01) and protein (E%: r = - 0.81, p < 0.01 and r = - 0.69, p < 0.05, g/kg: r = - 0.86, p < 0.01 and r = - 0.65, p < 0.05). The results suggest the possible role of diet leading to alterations in serum T and FT during prolonged strength training, and that diets with insufficient fat and/or excessive protein may compromise the anabolic hormonal environment over a training program.

Comparison of deramciclane to benzodiazepine agonists in behavioural activity of mice and in alcohol drinking of alcohol-preferring rats

Interactions between alcohol and traditional benzodiazepine anxiolytics hamper the treatment of alcoholism-related anxiety disorders. Serotonin 5-HT(2) receptor antagonists, such as deramciclane, are anxiolytic, and considering their pharmacological profile, they might benefit alcoholics with comorbid anxiety. We studied the effects of acute deramciclane (1, 3 and 10 mg/kg i.p.) on alcohol drinking of alcohol-preferring AA rats drinking 10% (vol/vol) ethanol solution in a 4-h limited-access paradigm. Thereafter, a 5-day repeated-treatment experiment was carried out, under corresponding test design, with deramciclane (3 mg/kg i.p.) as a test drug and midazolam (1 mg/kg i.p.) as a benzodiazepine reference compound. Deramciclane had no effect on alcohol consumption in either acute or repeated dosing study. Midazolam increased ethanol drinking, as expected, when administered on successive days. A modified functional observational battery (FOB) procedure was applied to study neurological, behavioural and autonomic effects induced by deramciclane (1-30 mg/kg po) and diazepam (1-30 mg/kg po) in mice at 30 min, 2 h and 4 h after dosing. Deramciclane had a mild dopamine D(2) receptor antagonism-like effect at the highest dose. The effects of diazepam were predictable, myorelaxation-induced motor impairment and anxiolysis-related hyperlocomotion in a novel environment being the characteristic features at the two highest doses. Deramciclane appears to be a safe and well-tolerated drug and we suggest that it might be useful in the treatment of anxiety in alcoholics.

Alpha2-adrenergic drug effects on brain monoamines, locomotion, and body temperature are largely abolished in mice lacking the alpha2A-adrenoceptor subtype

alpha(2)-ARs regulate brain monoaminergic function by inhibiting neuronal firing and release of monoamine neurotransmitters, noradrenaline (NA), serotonin (5-HT) and dopamine (DA). Both alpha(2A)- and alpha(2C)-AR inhibit monoamine release in vitro in brain slices, but the in vivo roles of individual alpha(2)-AR subtypes in modulating monoamine metabolism have not been characterised. Metabolism of brain monoamine neurotransmitters, locomotor activity and body temperature were investigated in mice with targeted inactivation of the gene encoding alpha(2A)-AR (alpha(2A)-knockout, alpha(2A)-KO) and wild-type (WT) mice after treatment with the alpha(2)-AR agonist dexmedetomidine and the antagonist atipamezole. Dexmedetomidine caused profound hypothermia (up to 14.7 degrees C mean reduction in rectal temperature) and locomotor inhibition in WT mice, and inhibited the turnover of NA, 5-HT and DA, but increased NA turnover in alpha(2A)-KO mice. alpha(2)-AR agonist-induced hypothermia and locomotor inhibition were attenuated, but not totally abolished, in alpha(2A)-KO mice. These results suggest that alpha(2A)-ARs are principally responsible for the alpha(2)-AR mediated inhibition of brain monoamine metabolism, but other alpha(2)-ARs, possibly alpha(2C)-ARs, are also involved, especially in the striatum. However, secondary effects of the physiological alterations caused by drug administration, especially hypothermia, may have contributed to the observed neurochemical changes in WT mice.

The alpha2-adrenoceptor antagonist atipamezole reduces the development and expression of d-amphetamine-induced behavioural sensitization

The possible effect of atipamezole, a potent and specific alpha(2)-adrenoceptor antagonist, on the development and expression of d-amphetamine-induced behavioural sensitization was evaluated in mice. Male (C57Bl/6J) mice were given daily doses of d-amphetamine (2 mg/kg). In addition, groups of mice received injections of atipamezole (0.3 or 1 mg/kg) 20 min before d-amphetamine or vehicle administration. Idazoxan (1 mg/kg) was used in some experiments to extend the results to other alpha(2)-adrenoceptor antagonists. Challenge doses of d-amphetamine were administered to the mice on days 7-9 to evaluate the effects of alpha(2)-adrenoceptor antagonists on the d-amphetamine sensitization, evidenced by increased locomotor activation. Mice treated repeatedly with d-amphetamine developed strong locomotor sensitization that was reduced by pretreatment with alpha(2)-adrenoceptor antagonists. Acute atipamezole at both doses attenuated the expression of d-amphetamine-induced sensitization. Atipamezole at 1 mg/kg alone had no effect on locomotor activity, but the lower dose (0.3 mg/kg) increased locomotor activity after repeated administration. These results indicate that alpha(2)-adrenoceptor antagonists modulate the actions of d-amphetamine in a manner not explicable by their enhancing actions on noradrenaline and dopamine release, and may thus provide a novel approach to the treatment of motor complications caused by dopaminergic agents, such as dyskinesias, and perhaps also drug dependence.

Behavioral and neurochemical characterization of alpha(2A)-adrenergic receptor knockout mice

Genetic manipulation of mice now provides new tools to evaluate the biological functions of the alpha(2)-adrenergic receptor (alpha(2)-AR) subtypes (alpha(2A), alpha(2B), and alpha(2C)). To investigate the role of the alpha(2A)-AR in the modulation of mouse primary behavioral characteristics and brain neurochemistry, mice with targeted inactivation of the gene for the alpha(2A)-AR were compared with wild-type C57BL/6 control animals. First, a comprehensive behavioral screen was employed to provide a detailed characterization of basic neurologic functions. Thereafter, the mice were analyzed in three models of anxiety, i.e. the elevated-plus maze test, the marble burying test and the open field test. The diurnal activity pattern of the mice was assessed in a 24-h locomotor activity test. Furthermore, receptor autoradiography of the brain was performed using the subtype-non-selective alpha(2)-AR antagonist radioligand [(3)H]RS-79948-197. Lack of the alpha(2A)-AR was associated with alterations in autonomic functions, including increased heart rate and piloerection. The mutant mice also exhibited impaired motor coordination skills, increased anxiety-like behavior and an abnormal diurnal activity pattern. In addition, neurochemical analysis of monoamine neurotransmitters revealed a considerable increase in brain norepinephrine turnover in mice lacking alpha(2A)-AR. Our results provide further support for the crucial role of the alpha(2A)-AR in modulating brain noradrenergic neurotransmission and many aspects of mouse behavior and physiology.

Spatial working memory improvement by an alpha2-adrenoceptor agonist dexmedetomidine is not mediated through alpha2C-adrenoceptor

1. Aged alpha2C-adrenoceptor knockout and wild type mice were used to investigate whether alpha2C-adrenoceptors are involved in mediating the beneficial effects of alpha2-adrenoceptor agonist, dexmedetomidine, on spatial working memory. 2. A win-stay task in the radial arm maze was used to dissociate the effects of dexmedetomidine on working vs. reference memory. In addition, the animals were tested in simple response habit learning in the T-maze. 3. Knockout mice made more working memory errors after the change of the baited arm in radial arm maze, but after training reached again as accurate level of performance as wild type controls. Dexmedetomidine 5 and 10 microg/kg alleviated the increase in spatial working memory errors after the change of the baited arm in knockout mice. Knockout and wild type mice performed equally well in T-maze, and dexmedetomidine had no effect on this simple response learning. 4. The present results indicate that alpha2-adrenoceptor agonists have a selective effect on spatial working memory not only in monkeys but also in mice. Further, this study confirms our earlier finding that the presence of alpha2C-adrenoceptors is not necessary for the spatial working memory enhancing effect of alpha2-adrenoceptor agonists.

Evaluation of the α2C-adrenoceptor as a neuropsychiatric drug target

The functional characterization of the three distinct alpha2-adrenoceptor (Q2-AR) subtypes was for long hampered by the inavailability of subtype-selective pharmacological probes. Recent studies with gene-targeted mice have revealed that the alpha2A-AR has a major role in the mediation of many prominent effects of subtype non-selective alpha2-AR agonists, i.e. sedation, analgesia, hypothermia, sympatho-inhibition, and reduction of blood pressure. We have now employed several neuropsychopharmacological test models to investigate the effects mediated by the alpha2C-AR subtype and this receptor's potential as a CNS drug target. The studies employed two genetically engineered mouse strains, having either a targeted inactivation of the alpha2C-AR gene (alpha2C-KO) or over-expressing the alpha2C-AR (alpha2C-OE). Lack of alpha2C-AR expression was associated with increased amphetamine-induced locomotor activity, startle reactivity, aggression, and activity in the forced swimming test; prepulse inhibition of the startle reflex was attenuated. Opposite changes were observed in the alpha2C-OE mice. The results suggest that the alpha2C-AR subtype has a distinct inhibitory role in the processing of sensory information and in the control of motor and emotion-related activities in the CNS. It is therefore possible that alpha2C-AR-selective drugs may have therapeutic value in the treatment of various neuropsychiatric disorders.

Alpha2C-adrenoceptor overexpression disrupts execution of spatial and non-spatial search patterns

We investigated the role of alpha2C-adrenoceptors in the modulation of spatial and non-spatial navigation behaviour. Alpha2C-adrenoceptor overexpressing mice developed an ineffective thigmotaxic search pattern characterized by swimming close to the pool walls during both spatial and non-spatial water maze training. A subtype-non-selective alpha2-adrenoceptor antagonist, atipamezole (1000 microg/kg, s.c.), fully reversed this impairment in their search strategy. Withdrawal of atipamezole at the end of spatial training resulted in an immediate disruption of the search pattern in alpha2C-adrenoceptor overexpressing mice. The swimming pattern of alpha2C-adrenoceptor overexpressing mice during a five day free swimming period was normal, when no cognitive component was required. Diazepam (0.3 and 1.0 mg/kg, i.p.), neither improved the accuracy in finding the platform nor decreased thigmotaxis. These results suggest that alpha2C-adrenoceptors may modulate the execution of complex navigation patterns.

Overexpression of alpha2C-adrenoceptors impairs water maze navigation

We investigated the role of overexpression of alpha2C-adrenoceptors in water maze navigation in mice transgenically manipulated to have a threefold overexpression of the alpha2C-adrenoreceptors. Alpha2C-adrenoreceptors overexpressing mice swam more in the peripheral annulus of the pool and did not find the hidden escape platform as well as the wild type control mice. A subtype-nonselective alpha2-adrenoreceptor antagonist, atipamezole (ATI, 1000 microg/kg, s.c.), fully reversed the deficit in platform finding and search strategy in overexpressing mice. Noradrenaline depletion (-95%) induced by N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) did not impair platform finding of wild type or overexpressing mice. The DSP-4 lesion slightly increased swimming in the peripheral annulus in wild type mice, but not in overexpressing mice. The DSP-4 lesion produced a dissociable effect on the action of atipamezole to improve platform finding and search strategy in overexpressing mice: atipamezole did not alleviate the platform finding deficit in DSP-4 lesioned overexpressing mice, but normalized their abnormal search strategy. These results suggest that the abnormal search pattern and deficit in the accuracy of platform finding are mediated by constitutive activity of overexpressed alpha2C-adrenoreceptors.

Genetic alteration of the alpha2-adrenoceptor subtype c in mice affects the development of behavioral despair and stress-induced increases in plasma corticosterone levels

alpha2-Adrenoceptors (alpha2-AR) modulate many central nervous system functions, such as regulation of sympathetic tone, vigilance, attention, and reactivity to environmental stressors. Three alpha2-AR subtypes (alpha2A, alpha2B, and alpha2C) with distinct tissue-distribution patterns are known to exist, but the functional significance of each subtype is not clear. Since specific, alpha2-AR subtype-selective pharmacological probes are not available, mice with genetically altered alpha2C-AR expression were studied in order to investigate the possible involvement of the alpha2C-AR in physiological and behavioral responses to acute and repeated stress. A modified version of Porsolt's forced swimming test was used to assess the possible effects of altered alpha2C-AR expression on the development of behavioral despair. alpha2C-Overexpression increased and the lack of alpha2C-AR (alpha2C-KO) decreased the immobility of mice in the forced swimming test, ie alpha2C-AR expression appeared to promote the development of behavioral despair. In addition, alpha2C-KO was associated with attenuated elevation of plasma corticosterone after different stressors, and overexpression of alpha2C-ARs was linked with increased corticosterone levels after repeated stress. Moreover, the brain dopamine and serotonin balance, but not norepinephrine turnover, was dependent on alpha2C-AR expression, and the expression of c-fos and junB mRNA was increased in alpha2C-KO mice. Since alpha2C-KO produced stress-protective effects, and alpha2C-AR overexpression seemed to promote the development of changes related to depression, it is suggested that a yet-to-be developed subtype-selective alpha2C-AR antagonist might have therapeutic value in the treatment of stress-related neuropsychiatric disorders.

Role of alpha2C-adrenoceptor subtype in spatial working memory as revealed by mice with targeted disruption of the alpha2C-adrenoceptor gene

The role of the alpha2C-adrenoceptor subtype in mediating the beneficial effect of alpha2-adrenoceptor agonists on spatial working memory was studied in adult mice with targeted inactivation of the alpha2C-receptor gene (KO) and their wild-type controls (WT). A delayed alternation task was run in a T-maze with mixed delays varying from 20 s to 120 s. Dexmedetomidine, a specific but subtype nonselective alpha2-adrenoceptor agonist, dose-dependently decreased the total number of errors. The effect was strongest at the dose of 5 microg/kg (s.c.), and was observed similarly in KO and WT mice. KO mice performed inferior to WT mice due to a higher number of perseverative errors. Dexmedetomidine slowed initiation of the motor response in the start phase at lower doses in WT mice than in KO mice but no such difference was observed in the return phase of the task, suggesting involvement of alpha2C-adrenoceptors in the cognitive aspect of response preparation or in response sequence initiation. According to these findings, enhancement of spatial working memory is best achieved with alpha2-adrenoceptor agonists which have neither agonistic nor antagonistic effects at the alpha2C-adrenoceptor subtype.

D-amphetamine and L-5-hydroxytryptophan-induced behaviours in mice with genetically-altered expression of the alpha2C-adrenergic receptor subtype

Three human and mouse genes encoding alpha2-adrenoceptor subtypes (alpha2A, alpha2B, and alpha2C) have been cloned. The alpha2C-adrenoceptor is the most abundant alpha2-adrenoceptor subtype in the striatum and modulates metabolism of both dopamine and serotonin. To investigate the possible involvement of the alpha2C-adrenoceptor subtype in behaviours regulated by dopamine and serotonin, two strains of genetically-engineered mice were examined. One had a targeted inactivation of the alpha2C-adrenoceptor gene, and the other had tissue-specific over-expression of alpha2C-adrenoceptors. The locomotor activity of the mice was evaluated after stimulation with D-amphetamine, and the behavioural serotonin syndrome and head twitches were investigated after L-5-hydroxytryptophan treatment. In addition, the effects of D-amphetamine and L-5-hydroxytryptophan were studied after pretreatment with dexmedetomidine, a subtype-nonselective alpha2-adrenoceptor agonist. The lack of alpha2C-adrenoceptor expression increased and the over-expression of alpha2C-adrenoceptors decreased the response to D-amphetamine stimulation. The effect of alpha2C-adrenoceptor gene inactivation was more prominent in D-amphetamine-treated males than in females. Dexmedetomidine inhibited D-amphetamine-induced hyperlocomotion and the L-5-hydroxytryptophan-induced serotonin syndrome, but the inhibition was attenuated in mice lacking alpha2C-adrenoceptors. However, the head twitches induced by L-5-hydroxytryptophan were effectively inhibited by dexmedetomidine in all studied mice, which suggests that alpha2A-adrenoceptors mediate the inhibition of the head twitch response. The results lend further support to the proposed existence of functionally distinct alpha2-adrenoceptor subtypes that can serve as new and specific therapeutic targets in various neuropsychiatric diseases.

Alpha2C-adrenoceptor-overexpressing mice are impaired in executing nonspatial and spatial escape strategies

Drugs acting via alpha2-adrenoceptors modulate cognitive functions mediated via frontostriatothalamic feedback loops. The alpha2C-adrenoceptor subtype is expressed in the basal ganglia, hippocampus, and neocortex, areas that are involved in memory and other cognitive functions. alpha2C-Overexpressing (OE) mice were impaired in spatial or nonspatial water maze (WM) tests, and alpha2 antagonist treatment fully reversed the WM escape defect in OE mice. However, alpha2C-overexpression did not influence open field and passive avoidance behaviors or cortical EEG arousal or the actions of alpha2 agonist or antagonist drugs on these functions. Our results suggest that alpha2C-adrenoceptors can modulate navigation to a hidden or visible escape platform, whereas many other actions of alpha2-adrenergic agents, such as sedation, are not mediated via alpha2C-adrenoceptors. Therefore, alpha2-agonists lacking alpha2C-AR affinity or alpha2C-AR subtype-selective alpha2 antagonists could modulate functioning of frontostriatothalamic feedback loops more effectively than the current subtype-nonselective drugs.

Adrenergic alpha2C-receptors modulate the acoustic startle reflex, prepulse inhibition, and aggression in mice

Studies on animal models of stress, anxiety, aggression, and sensorimotor gating have linked specific monoamine neurotransmitter abnormalities to the cognitive and behavioral disturbances associated with many affective neuropsychiatric disorders. Although alpha2-adrenoceptors (alpha2-ARs) have been suggested to have a modulatory role in these disorders, the specific roles of each alpha2-AR subtype (alpha2A, alpha2B, and alpha2C) are largely unknown. The restricted availability of relevant animal models and the lack of subtype-selective alpha2-AR drugs have precluded detailed studies in this area. Therefore, transgenic mice were used to study the possible role of the alpha2C-AR subtype in two well established behavioral paradigms: prepulse inhibition (PPI) of the startle reflex and isolation-induced aggression. The alpha2C-AR-altered mice appear grossly normal, but subtle changes have been observed in their brain dopamine (DA) and serotonin (5-HT) metabolism. In this study, the mice with targeted inactivation of the gene encoding alpha2C-ARs (alpha2C-KO) had enhanced startle responses, diminished PPI, and shortened attack latency in the isolation-aggression test, whereas tissue-specific overexpression of alpha2C-ARs (alpha2C-OE) was associated with opposite effects. Correlation analyses suggested that both the magnitude of the startle response and its relative PPI (PPI%) were modulated by the mutations. In addition, the differences in PPI, observed between drug-naive alpha2C-OE mice and their wild-type controls, were abolished by treatment with a subtype nonselective alpha2-agonist and antagonist. Thus, drugs acting via alpha2C-ARs might have therapeutic value in disorders associated with enhanced startle responses and sensorimotor gating deficits, such as schizophrenia, attention deficit disorder, post-traumatic stress disorder, and drug withdrawal.

Genetic alteration of alpha 2C-adrenoceptor expression in mice: influence on locomotor, hypothermic, and neurochemical effects of dexmedetomidine, a subtype-nonselective alpha 2-adrenoceptor agonist

alpha 2-Adrenergic receptors (alpha 2-ARs) regulate many physiological functions and are targets for clinically important antihypertensive and anesthetic agents. Three human and mouse genes encoding alpha 2-AR subtypes (alpha 2A, alpha 2B, and alpha 2C) have been cloned. We investigated the involvement of the alpha 2C-AR in alpha 2-adrenergic pharmacology by applying molecular genetic techniques to alter the expression of alpha 2C-AR in mice. The effects of dexmedetomidine, a subtype-nonselective alpha 2-AR agonist, on monoamine turnover in brain and on locomotor activity were similar in mice with targeted inactivation of the alpha 2C-AR gene and in their controls, but the hypothermic effect of the alpha 2-AR agonist was significantly attenuated by the receptor gene inactivation. Correspondingly, another strain of transgenic mice with 3-fold overexpression of alpha 2C-AR in striatum and other brain regions expressing alpha 2C-AR showed normal reductions in brain monoamine metabolism and locomotor activity after dexmedetomidine, but their hypothermic response to the alpha 2C-AR agonists was significantly accentuated. The hypothermic effect of alpha 2-AR agonists thus seems to be mediated in part by alpha 2C-AR. Some small but statistically significant differences between the strains were also noted in brain dopamine metabolism. Lack of alpha 2C-AR expression was linked with reduced levels of homovanillic acid in brain, and mice with increased alpha 2C-AR expression had elevated concentrations of the dopamine metabolite compared with their controls.