Reserpine pretreatment prevents increases in extracellular striatal dopamine following L-DOPA administration in rats with nigrostriatal denervation

The influence of L-DOPA and reserpine on extracellular dopamine (DA) levels in the striatum of intact and dopaminergic denervated rats was studied using the brain microdialysis technique. In intact rats, reserpine (5 mg/kg s.c.) reduced extracellular DA levels to 4% of basal values. L-DOPA (50 mg/kg i.p.) had no effect on extracellular DA levels in reserpine-pretreated rats. In rats with 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic system, basal levels of extracellular DA were low but markedly increased by L-DOPA (50 mg/kg i.p.). In 6-hydroxydopamine-lesioned rats, pretreatment with reserpine (5 mg/kg s.c.) diminished L-DOPA (50 mg/kg i.p.)-induced increases in extracellular DA levels to 16% of those obtained in denervated animals not pretreated with reserpine (p<0.01). These results suggest that in the intact striatum, extracellular DA stems mainly from vesicular storage sites and that in the striatum with dopaminergic denervation, a large part of the L-DOPA-derived extracellular DA is also derived from a vesicular pool that is released by an exocytosis mechanism.     

Stimulation of the catecholaminergic and serotoninergic neurons in the rat brain by R-(-)-1-(benzofuran-2-yl)-2-propylaminopentane, (-)-BPAP

R-(-)-1-(Benzofuran-2-yl)-2-propylaminopentane HCl, (-)-BPAP, the recently developed selective and much more potent catecholaminergic/serotoninergic enhancer (CAE/SAE) substance than (-)-deprenyl enhances the performance of midbrain neurons, both in vivo and ex vivo, in a characteristic complex manner, presenting one bell shape dose/concentration effect curve in the low nanomolar range and another at higher micromolar range. For example, 4.7 +/- 0.10 nmol/g wet weight noradrenaline was released within 20 min from the quickly removed locus coeruleus of saline treated rats. This amount was increased 30 min after the subcutaneous administration of 0.0005 mg/kg (-)-BPAP to 15.4 +/- 0.55 nmol/g (P < 0.001). However, following the injection of a hundred times higher, 0.05 mg/kg, dose of (-)-BPAP, the amount of noradrenaline (4.3 +/- 0.25 nmol/g) released from the locus coeruleus did not differ from the control value. In ex vivo experiments, when the isolated locus coeruleus was soaked in an organ bath containing (-)-BPAP, the release of noradrenaline was significantly enhanced from 10(-16) M concentration, reached a peak effect at 10(-13) M concentration, but 10(-10) M (-)-BPAP was ineffective. A significant enhancer effect was detected also in the high concentration range from 10(-8) M, the peak effect was reached at 10(-6) M concentration and 10(-5) M (-)-BPAP was ineffective. (-)-BPAP enhanced in the low concentration range the performance of dopaminergic and serotoninergic neurons with a peak effect at 10(-13) and 10(-12) M concentration, respectively. The results with (-)-BPAP, the highly specific artificial enhancer substance, suggest that (i) high and low affinity "enhancer" receptors may exist in the brain, and (ii) that they may be identified with the recently cloned family of the "trace amine" receptors, activated by beta-phenylethylamine and tryptamine, the prototypes of the endogenous enhancer substances.     

1-(Benzofuran-2-yl)-2-(3,3,3-trifluoropropyl)aminopentane HCl, 3-F-BPAP,antagonizes the enhancer effect of (-)-BPAP in the shuttle box and leaves the effect of (-)-deprenyl unchanged

The subcutaneous administration of 1 mg/kg tetrabenazine, once daily for 5 days, which depletes the catecholamine stores in the brain, significantly inhibits in rats the acquisition of a two-way conditioned avoidance reflex in the shuttle box. Enhancer substances, the tryptamine-derived selective and highly potent enhancer, R-(-)-1-(benzofuran-2-yl)-2-propylaminopentane HCl [(-)-BPAP] (0.05-10 mg/kg), the beta-phenylethylamine (PEA)-derived enhancer, (-)-deprenyl (1-5 mg/kg) and the (-)-deprenyl analogue, free of MAO-B inhibitory potency, (-)-1-phenyl-2-propylaminopentane HCl [(-)-PPAP], (1-5 mg/kg), antagonize in a dose-dependent manner the inhibition of learning caused by tetrabenazine. 1-(Benzofuran 2 yl)-2-(3,3,3-trifluoropropyl)aminopentane HCl [3 F BPAP], a newly synthetized analogue of (-)-BPAP with low specific activity, significantly antagonized the enhancer effect of (-)-BPAP but left the effect of (-)-deprenyl and (-)-PPAP unchanged. This is the first proof for a difference in the mechanism of action between a PEA-derived enhancer substance and its tryptamine-derived peer.     

Effect of L-DOPA on the Behavioral Activity of Wistar and Spontaneously Hypertensive (SHR) Rats in the Open-Field Test

We studied the effects of i.p. injections of L-DOPA (100 mg/kg) on the behavioral activity of Wistar rats and spontaneously hypertensive rats (SHR) in the open-field test, as well as on the content of catecholamines in the blood plasma of these animals. Prior to the administration of L-DOPA, the total level of locomotor/research activity in SHR was higher, as compared with that in Wistar rats. This was manifested in significantly greater values of the duration of moving of the animals in the center and on the periphery of the field and also in a greater number of rearings on the periphery of this field. At the same time, the episodes of grooming and sitting in Wistar rats were longer. After injections of L-DOPA, interstrain differences increased and became significant for most (9/10) indices of behavioral activity examined in our study. Injections of L-DOPA resulted in significant modifications of the behavioral activity of rats of the above strains, which is evidenced by changes in the number of visits to the peripheral squares of the open field and of rearings in the same field zones. Over repetitive test sessions, interstrain differences between most indices of behavioral activity (except the duration of research activity on the periphery and that of sitting) decreased. Injections of L-DOPA resulted in a significant increase in the content of this agent and dopamine in the blood plasma of rats of both strains; the level of noradrenaline in SHR also increased. The importance of a hereditary factor-determined increase in the activity of catecholaminergic brain systems (first of all, the dopaminergic system) in SHR for the specificity of locomotor behavior of these animals is discussed.     

Activation of 5-HT(1A) but not 5-HT(1B) receptors attenuates an increase in extracellular dopamine derived from exogenously administered L-DOPA in the striatum with nigrostriatal denervation

In order to determine whether L-DOPA-derived extracellular dopamine (DA) in the striatum with dopaminergic denervation is affected by activation of serotonin autoreceptors (5-HT(1A) and 5-HT(1B) receptors), we applied in vivo brain microdialysis technique to 6-hydroxydopamine-lesioned rats and examined the effects of the selective 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and the selective 5-HT(1B) receptor agonist CGS-12066 A on L-DOPA-derived extracellular DA levels. Single L-DOPA injection (50 mg/kg i.p.) caused a rapid increase and a following decrease of extracellular DA, with a peak value at 100 min after L-DOPA injection. Pretreatment with both 0.3 mg/kg and 1 mg/kg 8-OH-DPAT (i.p.) significantly attenuated an increase in L-DOPA-derived extracellular DA and the times of peak DA levels were prolonged to 150 min and 225 min after L-DOPA injection, respectively. These 8-OH-DPAT-induced changes in L-DOPA-derived extracellular DA were antagonized by further pretreatment with WAY-100635, a selective 5-HT(1A) antagonist. In contrast, intrastriatal perfusion with the 5-HT(1B) agonist CGS-12066 A (10 nM and 100 nM) did not induce any changes in L-DOPA-derived extracellular DA. Thus, stimulation of 5-HT(1A) but not 5-HT(1B) receptors attenuated an increase in extracellular DA derived from exogenous L-DOPA. These results support the hypothesis that serotonergic neurons are primarily responsible for the storage and release of DA derived from exogenous L-DOPA in the absence of dopaminergic neurons.     

Stimulation of presynaptic dopamine autoreceptors by 4-(2-di-n-propylaminoethyl) indole (DPAI)

The dopaminergic activity of 4-(2-di-n-propylaminoethyl)indole (DPAI) was investigated. In animal models for postsynaptic dopaminergic activity DPAI showed only very weak or no effects. In rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal tract, very weak contralateral turning behavior was induced in 4/6 rats. DPAI did not induce stereotyped behavior but caused a pronounced reduction in locomotor activity. In male rats pretreated with reserpine, DPAI lowered serum prolactin levels. Levels of homovanillic acid (HVA) were monitored in the striatum of the chloral hydrate anesthetized rat by means of in vivo voltammetry. DPAI administration reduced the faradaic peak corresponding to HVA. In rats pretreated with the decarboxylase inhibitor, NSD-1015, DPAI blocked the accumulation of dopa in response to gamma-butyrolactone. The results of this study indicate that DPAI possesses a high degree of selectivity for presynaptic dopamine autoreceptors, and little or no effect on postsynaptic dopamine receptors.     

Central antidopaminergic properties of 2-bromolisuride, an analogue of the ergot dopamine agonist lisuride

2-Bromolisuride (2-Br-LIS), a derivative of the ergot dopamine (DA) agonist lisuride, was investigated in rodents in comparison with the DA antagonist haloperidol with regard to its influence on DA related behaviour, cerebral DA metabolism and prolactin (PRL) secretion. 2-Br-LIS produced catalepsy in mice (ED50 3.3 mg/kg i.p.), antagonized apomorphine-induced stereotypies in mice (ED50 0.4 mg/kg i.p.), antagonized DA agonist-induced stereotypies in rats (0.1-1.56 mg/kg i.p.), inhibited locomotor activity in rats (0.025-6.25 mg/kg i.p.), antagonized the hyperactivity produced by various DA agonists in rats (0.025-6.25 mg/kg i.p.) and inhibited the apomorphine-induced hypothermia in mice (0.05-0.78 mg/kg i.p.). 2-Br-LIS (0.03-10 mg/kg i.p.) stimulated DA biosynthesis and DOPAC formation in the striatum and DA rich limbic system of rats, but had no effect on serotonin turnover. In striatum and limbic forebrain of gamma-butyrolactone-pretreated rats 2-Br-LIS reversed the apomorphine-induced inhibition of DOPA accumulation. 2-Br-LIS (0.03 - 3 mg/kg) enhanced PRL secretion in intact male rats. These findings indicate DA antagonistic properties of 2-Br-LIS presumably due to blockade of central pre- and postsynaptic DA receptors being of approximately the same order of potency as haloperidol. 2-Br-LIS is the first ergot compound with definite antidopaminergic properties suggesting its potential usefulness as a neuroleptic.     

Measurement of spontaneous motor activity by using the vibrator response method in rats

To investigate the usefulness of spontaneous motor activity (SMA) measurement using the vibrator response method, the acute effects of drugs on SMA were observed in Sprague-Dawley male rats. There were no significant differences between four devices. Methamphetamine (0.3-1 mg/kg, i.p.) and 1-2 mg/kg (s.c.) of apomorphine increased the SMA, but 0.05-0.2 mg/kg (s.c.) of apomorphine decreased the SMA. Apomorphine at 1-2 mg/kg (s.c.) significantly increased the SMA when the vibrator response method was used as compared with the Animex method. These results suggest that the vibrator response apparatus is useful for the measurement of SMA in rats.     

Effects of novel 5-HT1A receptor antagonists on measures of postsynaptic 5-HT1A receptor activation in vivo

The effects of two putative 5-HT_1A antagonists, 4-(2′-methoxyphenyl)-1-[2′-[N-(2″-pyridinyl)-p-iodobenzamido]ethyl]piperazine (p-MPPI) and 4-(2′-methoxyphenyl)-1-[2′-[N-(2″-pyridinyl)-p-flourobenzamido]ethyl]piperazine (p-MPPF), were examined in vivo in two tests of postsynaptic 5-HT_1A receptor activation, hypothermia and reciprocal forepaw treading, in the rat. Both p-MPPI (10 mg/Kg, I.p.) and p-MPPF (10 mg/Kg, I.p.) antagonized the hypothermia induced by the 5-HT_1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (0.5 mg/Kg, S.c.). Neither p-MPPI nor p-MPPF administered alone at a dose of 10 mg/kg (i.p.) induced hypothermia. Similarly, both p-MPPI (10 mg/Kg, I.p.) and p-MPPF (2.5 mg/Kg, I.p.) completely antagonized 8-OH-DPAT (2 mg/Kg, S.c.)-induced forepaw treading in rats pretreated with reserpine (1 mg/Kg, S.c., 18–24 hours prior to the experiment). p-MPPI and p-MPPF, at doses of 10 mg/kg (i.p.) did not induce forepaw treading in reserpine pretreated animals. The results of the present study demonstrate that p-MPPI and p-MPPF act as 5-HT_1A receptor antagonists in these measures of postsynaptic 5-HT_1A a receptor activation.     

A pharmacological analysis elucidating why,in contrast to (-)-deprenyl (selegiline), alpha-tocopherol was ineffective in the DATATOP study

The Parkinson Study Group who conducted the Deprenyl and Tocopherol Antioxidative Therapy of Parkinsonism (DATATOP) trial designed their study in the belief that the MAO inhibitor (-)-deprenyl (selegiline), the antioxidant alpha-tocopherol, and the combination of the two compounds will slow the clinical progression of the disease to the extent that MAO activity and the formation of oxygen radicals contribute to the pathogenesis of nigral degeneration. In fact, (-)-deprenyl only delayed the onset of disability associated with early, otherwise untreated Parkinson's disease, however, in contrast to the expectation of the authors, alpha-tocopherol proved to be ineffective in the DATATOP study. Enhancer substances, (-)-deprenyl, (-)-1-phenyl-2-propylaminopentane [(-)-PPAP] the (-)-deprenyl analogue free of MAO inhibitory potency, and R-(-)1-(benzofuran-2-yl)-2-propylaminopentane [(-)-BPAP] the presently known most potent enhancer substance, are peculiar stimulants. They enhance the impulse propagation mediated release of the catecholamines in the brain. Due to their enhancer effect, the amount of catecholamines released from selected discrete brain areas (striatum, substantia nigra, tuberculum olfactorium, locus coeruleus) is significantly higher in rats treated with an enhancer substance than in saline treated rats. We compared the effect of (-)-deprenyl 0.025 and 0.25 mg/kg, (-)-PPAP 0.1 mg/kg, (-)-BPAP 0.0001 mg/kg, and alpha-tocopherol 25 and 50 mg/kg, in this test. The doses of (-)-deprenyl and alpha-tocopherol were selected to be in compliance with the dose given in the DATATOP study. Compared to saline treated rats, the enhancer substances significantly increased the amount of dopamine released from the striatum, substantia nigra and tuberculum olfactorium and the amount of norepinephrine released from the locus coeruleus; alpha-tocopherol was ineffective. The results indicate that alpha-tocopherol was ineffective, because, unlike (-)-deprenyl it dose not enhance the activity of the nigrostriatal dopaminergic neurons.     

Evidence for O-dealkylation of 7-pentoxyresorufin by cytochrome P450 2B1/2B2 isoenzymes in brain

O-dealkylation of 7-pentoxyresorufin (PR) was studied in rat brain to characterise the functional activity specific for cytochrome P450 2B1/2B2 isoenzymes in brain microsomes. Brain microsomes catalyzed the O-dealkylation of PR in the presence of NADPH. Pretreatment with phenobarbital (PB; 80 mg/kg body wt, i.p.× 5 days) resulted in 3-4 fold induction of pentoxyresorufin-O-dealkylase (PROD) activity while 3-methylcholanthrene (MC; 30 mg/kg body wt, i.p. × 5 days) did not produce any significant increase in enzyme activity. Kinetic studies revealed that the rate of velocity (Vmax) for the O-dealkylation of PR was significantly increased to 2.9 times higher in brain microsomes isolated from PB pretreated rats. In vitro studies using metyrapone, an inhibitor of P450 2B1/2B2 catalyzed reactions and antibody for hepatic PB inducible P450s (P450 2B1/2B2) significantly inhibited the activity of PROD in cerebral microsomes prepared from PB pretreated animals. These studies suggest that PB inducible isoenzymes of P450, i.e. P450 2B1/2B2 specifically catalyze the O-dealkylation of PR in brain microsomes.     

Effects of reserpine on dopamine metabolite in the nucleus accumbens and locomotor activity in freely moving rats

The effect of reserpine (2 mg/kg i.p.) on both locomotor activity and the turnover of dopamine metabolite in the rat nucleus accumbens was estimated by using an activity monitor (Animex) and by in vivo brain microdialysis. Three to five hours after reserpine administration locomotor activity was reduced and there was a concomitant increase in the level of the dopamine metabolite, homovamillic acid. These findings suggest that depletion of dopamine from the nucleus accumbens may result in decreased locomotor activity. The data support the notion that dopamine in this tissue contributes to the control of locomotion.     

Chronic pretreatment with methylphenidate induces cross-sensitization with amphetamine

Consequence of the long-term use of psychostimulants as treatment for attention deficit/hyperactivity disorder (ADHD) is unknown, particularly whether treatment with psychostimulants at an early age increases an individual's potential for cross-sensitization to other stimulants exposed at a later age. Cross-sensitization occurs when pretreatment with one stimulant leads to greater sensitivity to another stimulant. The aims of this study were to investigate whether chronic treatment with methylphenidate (MPD; Ritalin) in both juvenile and adult rats induced cross-sensitization to amphetamine at a later time and whether this cross-sensitization to amphetamine was age-dependent. Male Sprague-Dawley rats were randomly divided into four treatment groups: (1) group treated intraperitoneally (i.p.) with saline as juveniles and adults, (2) group treated with 0.6 mg/kg amphetamine, i.p., as juveniles and adults, (3) group treated with 2.5 mg/kg MPD, i.p., as juveniles and adults, and (4) group treated with saline, i.p., as juveniles and 2.5 mg/kg MPD, i.p., as adults. All of the animals received an amphetamine (0.6 mg/kg, i.p.) challenge on the last experimental day. We examined the effects of chronic MPD treatment in juvenile and adult rats on their locomotor response to an acute amphetamine exposure. Three different locomotor indices were studied using an automated activity monitoring system. Changes in the locomotor responses to amphetamine of these animals were compared to those of control rats that were pretreated with saline as juveniles and as adults. It was found that prior chronic treatment with MPD produced cross-sensitization to the locomotor response to amphetamine as observed in the horizontal activity and total distance traveled. It also appears that this cross-sensitization to amphetamine may not be dependent on the age of the subjects, i.e., whether subjects were juvenile or adult rats when they received drugs, but rather it depended on the behavioral index examined.     

Interaction of the tachykinin NK3 receptor agonist senktide with behavioral effects of cocaine in marmosets (Callithrix penicillata)

Brain neuropeptide transmitters of the tachykinin family are involved in the organization of many behaviors. However, little is known about their contribution to the behavioral effects of drugs of abuse. Recently, antagonism of the tachykinin NK3-receptor (NK3-R), one of the three tachykinin receptors in the brain, was shown to attenuate the acute and chronic behavioral effects of cocaine in rats and the acute effects in non-human primates. In order to expand these findings we investigated the effects of the NK3-R agonist, succinyl-[Asp6, Me-Phe8]SP(6-11) (senktide), on the acute behavioral effects of cocaine in marmoset monkeys (Callithrix penicillata) using a figure-eight maze procedure. Animals were pretreated with senktide (0, 0.1, 0.2, 0.4 mg/kg, s.c.), and received either a treatment with cocaine (10 mg/kg) or saline (i.p.). Cocaine increased locomotor activity and the duration of aerial scanning behavior, but reduced exploratory activity, bodycare activity, the frequency of aerial scanning, and terrestrial glance behavior. Senktide blocked the effects of cocaine on locomotor activity, but enhanced the cocaine effects on exploratory activity, aerial scanning frequency, and terrestrial glance behavior. Senktide alone did not significantly influence monkey behavior in this study. These data expand previous findings suggesting a complex role of the NK3-R in the acute behavioral effects of cocaine in non-human primates.     

The influence of intracerebroventricular administration of (+/-) propranolol and (+/-) verapamil on experimental myocardial ischemia and necrosis in rats

In albino rats, infarctoid myocardial lesions were produced by intraperitoneal (i.p.) administration of isoproterenol (75 mg/kg, during 3 days). In other groups, the descending anterior left coronary artery was ligated. In both experimental settings, the intracerebroventricular (i.c.v.) administration of (+/-) propranolol (100-200-300 microg/animal/day, during 7 days) or (+/-) verapamil (40-80-160 microg/animal/day, during 7 days) afforded a significant protection (with the exception of the lowest dose) on the investigated parameters: arrhythmias, ischemic zone (in coronary ligated rats), lactate dehydrogenase and aspartate aminotransferase activity of the serum, focal necrosis (in isoproterenol treated rats). This protective activity is lower than that afforded by i.p. administered (+/-) propranolol (5 mg/kg, during seven days) or (+/-) verapamil (5 mg/kg, during seven days). From these data it may be concluded that (+/-) propranolol and (+/-) verapamil have a protective action on the experimental myocardial ischemia and necrosis in rats, not only when the drugs come in direct contact with the heart, but also acting upon the central nervous system.     

Modulation of luteinizing hormone(LH) release by clonidine and opioid peptides in castrated male rats

The effect of clonidine, a central alpha-adrenergic agonist, on the suppression of LH release induced by beta-endorphin or FK33-824, an endogenous opioid peptide or its synthetic analog, was investigated in castrated male rats, with or without pretreatment with reserpine. Pulsatile LH secretion was inhibited by intravenous injection of FK33-824 (400 micrograms/kg), or intraventricular injection of beta-endorphin (5 micrograms). Without pretreatment with reserpine, intraperitoneal administration of clonidine (1 mg/kg) failed to reverse the inhibition of LH release induced by these peptides. However, with pretreatment with reserpine (10 mg/kg), clonidine abolished the inhibitory effect on LH secretion induced by these peptides in castrated male rats. These data indicate that, unlike the results in ovariectomized, steroid-primed rats, pretreatment with reserpine allows the alpha-adrenergic system to act more peripherally than the opioid neuronal system in a neuronal network-regulating LH release in castrated male rats.     

The role of dopamine and serotonin in the prolongation of post-decapitation convulsions in mice.

L-DOPA (320 mg/kg, i.p.) increased the duration of the clonic phase of post-decapitation convulsions (PDC) by 60% in mice pretreated with the peripheral decarboxylase inhibitor, Ro 4-4602 (50 mg/kg, i.p.). Assays of brains at the time of decapitation showed a 300% increase in dopamine (DM), an 80% reduction in serotonin (5-HT) and no change in norepinephrine (NE) levels. The effect of L-DOPA on PDC was not blocked by haloperidol (0.5 – 5.0 mg/kg), a blocker of DM receptors, nor by diethyldithiocarbamate (400 mg/kg) an inhibitor of NE synthesis. Parachlorophenylalanine (300 mg/kg × 3 days) produced an 80% reduction in 5-HT and a prolongation of PDC similar to that observed after L-DOPA. Prolongation of PDC was also seen after the 5-HT antagonists methysergide (5 mg/kg) and cinanserin (10 mg/kg), but not after cyproheptadine (10 mg/kg). The 5-HT precursor, 5-hydroxytryptophan (100 mg/kg), produced no change in PDC when used alone but inhibited L-DOPA's prolongation of PDC. The results suggest that L-DOPA acts by depleting 5-HT in bulbospinal pathways and thus enhancing reflex activity in the spinal cord.     

The discovery of 4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazolo-[1 ,5-a]-pyrimidine: a corticotropin-releasing factor (hCRF1) antagonist

Structure activity relationship studies led to the discovery of 4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazo lo-[1,5-a]-pyrimidine 11-31 (DMP904), whose pharmacological profile strongly supports the hypothesis that hCRF1 antagonists may be potent anxiolytic drugs. Compound 11-31 (hCRF1 Ki = 1.0+/-0.2 nM (n = 8)) was a potent antagonist of hCRF1-coupled adenylate cyclase activity in HEK293 cells (IC50= 10.0+/-0.01 nM versus 10 nM r/hCRF, n = 8); alpha-helical CRF(9-41) had weaker potency (IC50 = 286+/-63 nM, n = 3). Analogue 11-31 had good oral activity in the rat situational anxiety test; the minimum effective dose for 11-31 was 0.3 mg/kg (po). Maximal efficacy (approximately 57% reduction in latency time in the dark compartment) was observed at this dose. Chlordiazepoxide caused a 72% reduction in latency at 20 mg/kg (po). The literature compound 1 (CP154526-1, 30 mg/kg (po)) was inactive in this test. Compound 11-31 did not inhibit open-field locomotor activity at 10, 30, and 100 mg/kg (po) in rats. In beagle dogs, this compound (5 mg/kg, iv, po) afforded good plasma levels. The key iv pharmacokinetic parameters were t1/2, CL and Vd,ss values equal to 46.4+/-7.6 h. 0.49+/-0.08 L/kg/h and 23.0+/-4.2 L/kg, respectively. After oral dosing, the mean Cmax, Tmax t1/2 and bioavailability values were equal to 1260+/-290 nM, 0.75+/-0.25 h. 45.1+/-10.2 h and 33.1%, respectively. The overall rat behavioral profile of this compound suggests that it may be an anxiolytic drug with a low motor side effect liability.     

Effect of (-)-para-fluoro-deprenyl on survival and copulation in male rats.

Six-month old male rats were treated with 0.25 mg/kg, s.c., (-)p-fluoro-deprenyl (n = 40) or salt solution (n = 20) three times a week for 25 months. Three of the 20 saline-treated and 15 of the 40 drug-treated males survived (p = 0.05). Sexual activity of the survivors was tested at the end of the experiment. Three of the (-)p-fluoro-deprenyl-treated 31-month-old males proved to be sexually fully active, though, Wistar rats lose their ability to ejaculate by completing their second year of life. Non-copulator, 13 month old male rats were treated instead of the usually used 0.25 mg/kg dose with 0.01 mg/kg, s.c., (-)deprenyl (n = 9), (-)p-fluoro-deprenyl (n = 9) and salt solution (n = 9), three times a week, for 82 weeks and mating activity was tested weekly. The lifespan of the non-copulators was very short: 102 weeks for saline (n = 9), 106 weeks for (-)deprenyl (n = 8) and 104 weeks for (-)p-fluoro-deprenyl (n = 7). Survival was lightly changed by this very small dose treatment, one (-)deprenyl-treated male and two (-)p-fluoro-deprenyl-treated rats remained alive. The copulatory activity, however, was substantially improved.     

Differential effects of (R)-, (R, S)- and (S)-8-hydroxy-2-(di-n-propylamino)tetralin on hippocampal serotonin release and induction of hypothermia in awake rats

The effects of (R)- and (S)-optical isomers of 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and of the racemate (R,S)-8-OH-DPAT on serotonin (5-HT) release in the ventral hippocampus of awake rats and on induction of the whole-body hypothermia were studied. Extracellular 5-HT levels were determined by a newly developed high-sensitive HPLC method based on derivatization with benzylamine and fluorescence detection. The basal levels of 5-HT in 20 min microdialysates from rats perfused with Ringer solution or with Ringer solution containing 1 microM citalopram were 6.3 +/- 1.3 fmol/20 microl and 36.1 +/- 4.2 fmol/20 microl (n=20), respectively. The reduction of hippocampal 5-HT levels induced by subcutaneous (s.c.) administration of (R,S)-8-OH-DPAT (0.3 mg/kg) was significantly attenuated by the presence of 5-HT reuptake inhibitor citalopram in Ringer solution only at its peak value at 40 min (maximal reduction to 60% compared to 46% of control values in Ringer-perfused rats), whereas the overall effects were comparable at both experimental conditions. Injection of (R)-8-OH-DPAT (0.3 mg/kg s.c.) caused further reduction of 5-HT levels, to 49% and 41%, respectively, whereas (S)-8-OH-DPAT (0.3 mg/kg s.c.) caused maximal reduction of 5-HT levels only to 74% of controls in both perfusion groups. Similar pattern and time-courses were observed in rats with hypothermia induced by injection of 8-OH-DPAT enantiomers, where (R,S), (R)-forms were about two-times more potent than the (S)-isomer. It is concluded that the acute systemic dose of (R)-, (S)- and (R,S)-8-OH-DPAT enantiomers exerted enantiomer-specific effects on 5-HT(1A) receptor-mediated function both at the presynaptic and postsynaptic sites as revealed by monitoring hippocampal 5-HT levels and body temperature.