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Zolpidem is a novel hypnotic drug which possesses preferential affinity, under in vitro conditions, for the omega 1 (BZD1) subtype of BZD binding sites. In the present study the in vivo interaction of zolpidem with mouse brain BZD binding sites, as labeled by i.v. injection of [3H]Ro 15-1788, has been investigated. Intraperitoneal administration of zolpidem (30 min before sacrifice) decreased in a dose-dependent manner, the retention of [3H]Ro 15-1788 in the cerebral cortex (ED50 = 8.9 mg/kg i.p.); the inhibition by zolpidem was maximal (70%) at 5 to 10 min postinjection and of only 10% 1 hr later. These kinetics are in agreement with its short lasting hypnotic properties. CGS 9896, CL 218,872 and flunitrazepam also prevented the cortical accumulation of [3H]Ro 15-1788 with ED50 values of 12.5, 24 and 0.17 mg/kg i.p., respectively. Zolpidem, like flunitrazepam, diminishes exploratory activity and possesses anticonvulsant and myorelaxant effects in the mouse. However, in contrast to flunitrazepam, the sedative action of zolpidem can be evidenced at a much lower recognition site occupancy (35%) than that needed for myorelaxant or anticonvulsant effects (50-56%). The regional selectivity of zolpidem as an inhibitor of [3H]Ro 15-1788 in vitro and in vivo binding in the mouse brain has been assessed by quantitative autoradiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzodiazepines and other compounds which act at benzodiazepine binding sites have been shown previously to attenuate the acquisition of conditioned fear in rodents when administered before the acquisition session, an effect which may parallel the disruption of human memory produced by anxiolytics and sedatives. Such an action is usually, but not invariably, produced by doses which have direct behavioural depressant effects. The present study was carried out to extend previous work by investigating the effects of the hypnotic benzodiazepine triazolam and the nonbenzodiazepines zolpidem and CL 218,872 on the acquisition of learned fear in mice. All these drugs reduced locomotor activity shortly after injection. They also produced disruptions of the acquisition of learned fear. Triazolam exerted behavioural effects similar to those found previously with other benzodiazepines, the doses which disrupted the acquisition of conditioned fear being similar to, or lower than, the doses which depressed locomotion. In contrast, the results indicated that zolpidem was more potent at reducing locomotion than at interfering with fear conditioning, a result which may reflect the preferential sedative action of zolpidem.

Zopiclone and CGS 9896 are two nonbenzodiazepine compounds which have been shown to displace benzodiazepines from their binding sites. The present study compared the behavioral effects of these two compounds in rats with those of chlordiazepoxide. The three drugs produced dose-related increases in punished drinking as did pentobarbital and meprobamate but not PK 9084, which also acts at benzodiazepine binding sites, or buspirone. Rates of lever pressing suppressed by punishment were also increased by chlordiazepoxide and zopiclone. CGS 9896 exerted a similar although less marked effect. Lever pressing maintained by a differential reinforcement of low rate 18-sec schedule of milk presentation was increased by low doses of chlordiazepoxide and zopiclone and decreased by higher doses leading to dose-related reductions in numbers of reinforcers obtained. CGS 9896 also reduced number of reinforcers but without affecting rate of responding. In rats trained to discriminate a dose of chlordiazepoxide from saline, chlordiazepoxide, zopiclone, pentobarbital and meprobamate produced chlordiazepoxide-appropriate responding. CGS 9896 also produced chlordiazepoxide-appropriate responding at a wide range of doses although the stimulus properties of this compound appeared to be weaker than those of the other active drugs. Chlordiazepoxide and zopiclone produced dose-related increases in food intake in food-deprived rats. CGS 9896 had similar effects at low doses but its effects were less consistent at higher doses. Thus, zopiclone has a behavioral profile very similar to that of chlordiazepoxide. Although many of the effects of CGS 9896 were similar to those of chlordiazepoxide, a number of differences were also observed.

Zolpidem is a new, short-acting hypnotic of imidazopyridine structure which binds selectively to a subpopulation of receptors involved in the action of benzodiazepines [omega 1 (BZ1) sites of the gamma-aminobutyric acidA receptors]. The present study investigated whether tolerance and physical dependence develop after repeated treatment with zolpidem as is observed with benzodiazepines. Mice were given zolpidem or the benzodiazepine midazolam (2 x 30 mg/kg, p.o.) for 10 consecutive days. Tolerance to central depressant effects (evaluated by recording spontaneous locomotor activity) and to anticonvulsant effects (measured against pentylenetetrazole-, electroshock- and isoniazid-induced convulsions) was assessed 42 hr after the last administration. A decrease in the latency to isoniazid-induced convulsions was taken as an index of physical dependence and was evaluated 3, 6, 14, 24, 42 and 67 hr after the end of chronic drug treatment. Repeated treatment with midazolam produced tolerance to its sedative and anticonvulsant activities as indicated by shifts of the dose-response curves by a factor of 3 to 5. Fourteen hr after discontinuation of treatment, spontaneous withdrawal was observed and lasted 3 days. When flumazenil was given 3 or 6 hr after the final midazolam injection, precipitated withdrawal was observed. In contrast, after repeated treatment with zolpidem, there was no change in its ability to produce sedative and anticonvulsant effects. Moreover, neither spontaneous nor flumazenil-induced precipitated withdrawal was observed in zolpidem-treated mice.

The levels of noradrenaline, neuropeptide Y, 5-hydroxytryptamine, and substance P were measured and compared between the large arteries of the circle of Willis and the small cerebral vessels of the pia mater in the rat, rabbit, cat, and monkey. In all species, noradrenaline and neuropeptide Y concentrations were greater in the larger arteries than in small pial vessels. Noradrenaline concentrations were reduced following cervical sympathectomy, with the extent of diminution differing greatly in the various the effects of cervical ganglionectomy on neuropeptide Y concentrations were less pronounced. 5-Hydroxytryptamine concentrations in rats, cats, and rabbits were significantly greater in the small pial vessels, although measurable concentrations existed in the circle of Willis. In cats and monkeys, substance P was found in major arteries, but was not detectable at the level of the small pial vessels. The differences in the regional distribution of the various neurotransmitter candidates in the cerebrovascular bed may reflect their physiological significance.

Alpidem in an imidazopyridine derivative which binds selectively to theθ1(BZ1) receptor subtype. It is active in some, but not all, behavioural tests sensitive to benzodiazepine anxiolytics and has clinical anti-anxiety effects. However, in a previous study, it was shown that alpidem did not substitute for chlordiazepoxide in rats trained to discriminate this benzodiazepine. The present experiments were carried out to investigate the discriminative stimulus properties of alpidem in greater detail. In the first experiment rats learned to discriminate a dose of 10 mg/kg alpidem from saline. Acquisition of the discrimination was long and performance unstable. Chlordiazepoxide, clorazepate and zolpidem substituted only partially for alpidem but the effects of the training dose of alpidem were blocked by 10 mg/kg flumazenil. The second experiment established stimulus control more rapidly to a dose of 30 mg/kg alpidem. Alpidem induced dose-related stimulus control, and dose-related and complete substitution for alpidem was produced by zolpidem, abecarnil, CL 218,872, triazolam and suriclone. Partial substitution occurred with chlordiazepoxide, clorazepate and pentobarbital. In most cases, high levels of substitution were produced only by doses which greatly reduced response rates even though the training dose of alpidem produced only modest decreases in rates. Ethanol, buspirone and bretazenil produced very little substitution for alpidem and both flumazenil and bretazenil antagonised the effects of alpidem. In two further experiments alpidem was found to substitute for the stimulus produced by zolpidem (2 mg/kg) but not for that produced by ethanol (1.5 g/kg). In the latter case the benzodiazepines chlordiazepoxide and triazolam did substitute for the ethanol cue. These results confirm that the discriminative stimulus effects of alpidem differ from those produced by benzodiazepines. The effects of alpidem are most similar to those of the other imidazopyridine derivative, zolpidem, and may be related to the selectivity of these drugs of theθ1(BZ1) receptor subtype.

Zolpidem is a non-benzodiazepine hypnotic drug which displaces benzodiazepines from their binding sites in different brain structures. Previous work has demonstrated several differences between zolpidem and benzodiazepines, including differences between the stimulus properties of zolpidem and chlordiazepoxide. In the present study the discriminative stimulus properties of zolpidem were analysed by training rats to discriminate between this drug and saline. It was found that stimulus control developed readily with 2 mg/kg but not with 1 mg/kg zolpidem. The effect was dose-related, had a short duration of action and was antagonised by Ro 15-1788. Furthermore, stimulus control produced by zolpidem was associated with marked reductions in rates of responding. Injections of chlordiazepoxide, triazolam, lorazepam, zopiclone, CL 218,872 and pentobarbital produced dose-related responding on the zolpidem-associated lever but haloperidol did not. However, in general, the doses of those drugs which produced drug-lever responding also reduced response rates. It is possible that the above mentioned differences between the discriminative stimulus produced by zolpidem in rats and those produced by other sedatives may be due to a selective action of zolpidem on a sub-type of benzodiazepine binding site.

Zolpidem [N,N,6-trimethyl-2-(4-methylphenyl)imidazo[1,2-a]pyridine-3-acetamide hemitartrate] is reported to be a rapid onset, short duration hypnotic that interacts at the benzodiazepine recognition site. The present report establishes the neuropsychopharmacological profile of zolpidem and compares it with those of benzodiazepine hypnotics. Although in mice the effects of zolpidem are qualitatively similar to those of midazolam, triazolam and flunitrazepam, sedation with zolpidem occurs at doses 10 and 20 times lower than those inducing anticonvulsant and myorelaxant effects, respectively. In contrast, the benzodiazepines studied induce sedation at doses causing myorelaxation and which are 2 to 6 times superior to those antagonizing pentetrazole-induced convulsions. In the rat, zolpidem induces sleep (as indicated behaviorally and electrocorticographically) and displays anticonflict activity in a punished drinking paradigm, as do the benzodiazepines. However, whereas benzodiazepine hypnotics induce EEG sleep patterns in curarized rats at doses similar or inferior to those active in the conflict test (in freely moving animals), the hypnotic effect of zolpidem is seen at doses 10 times lower than those producing an anticonflict effect. Moreover, a qualitative difference between the effects of zolpidem and benzodiazepines is observed in electrocorticographic recordings obtained in curarized rats: electrocorticographic hypersynchronization induced by zolpidem is dominated by the energy increase within the 2 to 4 Hz band whereas the benzodiazepines increase predominantly energy levels within the 12 to 14 Hz band. Studies of the sleep-wakefulness cycle in the rat and the cat revealed that hypnotic doses of zolpidem do not alter the pattern of physiological sleep, although elevated doses of the drug decrease paradoxical sleep and increase slow wave sleep. In rats trained to discriminate chlordiazepoxide, zolpidem fails to generalize with the chlordiazepoxide-associated lever indicating that the compound and benzodiazepines do not share the same discriminative stimulus properties. Nevertheless, the anticonvulsant, hypnotic, myorelaxant and anticonflict effects of zolpidem are antagonized by benzodiazepine receptor antagonist Ro 15-1788 and CGS 8216 indicating an involvement of the benzodiazepine recognition site in the action of this drug. The highly selective sedative effect of zolpidem (as compared to myorelaxant and anticonvulsant effects) suggests that it may possess a specificity for certain subtypes of benzodiazepine receptors.

The effects of the anti-ischemic agents ifenprodil and its derivative SL 82.0715 ((+/-)-alpha-(4-chlorophenyl)-4-[(4-fluorophenyl) methyl]-1-piperidineethanol] have been analyzed in a number of models indicative of N-methyl-D-aspartate (NMDA) antagonistic potential in vitro and in vivo. Ifenprodil and SL 82.0715 potently and noncompetitively antagonize the stimulatory effects of NMDA on cyclic GMP production in immature rat cerebellar slices (IC50 values, 0.4 and 10 microM, respectively), as well as the NMDA-evoked [3H]acetylcholine release in adult rat striatal slices (IC50 values, 1.6 and 6.6 microM, respectively). Ifenprodil is 10 times more potent than (+/-)3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) but less active than the reference noncompetitive NMDA channel blockers [MK 801, ((+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine ], phencyclidine and 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP)] in these models. Ifenprodil and SL 82.0715 partially displace (maximal displacement 40-50% at 10 microM) the NMDA receptor ligand [3H]CPP from its binding site to rat brain membranes (IC50 values, 0.1 and 0.3 microM, respectively) in a noncompetitive manner; in the micromolar range the two agents also partially displace the NMDA channel ligand [3H]TCP from its binding site to rat brain membranes, and noncompetitively antagonize the L-glutamate-induced increase in [3H]TCP binding. Ifenprodil (0.01-1 microM) partially antagonizes the depolarizing effects of NMDA on the immature rat hemisected spinal cord in vitro. In mouse cultured spinal cord neurons, ifenprodil dose-dependently antagonizes the depolarizing effects of micropressure applied NMDA. Inhibition of the effects of NMDA in this model by ifenprodil and SL 82.0715 is noncompetitive. In vivo and after systemic i.p. administration, ifenprodil and SL 82.0715 antagonize the stimulatory effects of intrastriatally dialyzed NMDA on striatal dopamine release in rats (ID50 values, 0.9 and 0.3 mg/kg, respectively), and block the harmaline-evoked increase in cerebellar cyclic GMP production in mice (ID50 values, 3 and 4 mg/kg, respectively). These results indicate that ifenprodil is a noncompetitive NMDA antagonist which has a mechanism of action distinct from either the reference competitive NMDA receptor antagonists (CPP and 2-amino-5-phosphonovalerate) or the noncompetitive NMDA channel blockers (phencyclidine, TCP and MK 801). The potent NMDA antagonistic effects of the ifenprodil class of compounds are likely to be related to the demonstrated anti-ischemic potential of these compounds.

Fengabine (SL 79.229) is a novel benzylidene derivative with clinically proven antidepressant action. Fengabine is active in behavioral models for antidepressant drug action, reversing the passive avoidance deficit in olfactory bulbectomized rats, antagonizing the escape deficit in the learned helplessness model and decreasing paradoxical sleep in the rat. In contrast to tricyclic antidepressants, fengabine antagonizes 5-hydroxytryptophan-induced head twitches and only weakly reverses reserpine-induced ptosis. Fengabine inhibits neither monoamine uptake nor monoamine oxidase. A GABAergic mechanism of fengabine is indicated as bicuculline reverses its action in the olfactory bulbectomy and learned helplessness models. The wide-spectrum anticonvulsant action of fengabine is consistent with a GABA-mimetic action and is in contrast to the proconvulsant effect of most classical antidepressants.

The effects of fengabine (a novel benzylidene derivative possessing clinically demonstrated antidepressant action) on neurochemical parameters related to norepinephrine, serotonin and gamma-aminobutyric acid (GABA) neurons have been investigated in the rat and mouse brain. When given acutely, fengabine (50-1000 mg/kg i.p.) does not alter norepinephrine uptake but accelerates the turnover rate of norepinephrine in the rat brain as demonstrated by the enhancement of: the alpha-methyl-p-tyrosine-induced disappearance of norepinephrine in the hypothalamus; 3,4-dihydroxyphenylacetic acid levels in noradrenergic cell body areas; the pargyline-induced accumulation of normetanephrine in the hypothalamus; and 3,4-dihydroxyphenylethyleneglycol levels in the hypothalamus, septum and spinal cord. No tolerance to the effect of fengabine on the latter biochemical parameter was observed after repeated treatment for 2 weeks at doses of 100 or 200 mg/kg i.p., b.i.d. Fengabine (100 or 200 mg/kg i.p., b.i.d.), given for 14 days, causes a desensitization of isoprenaline-stimulated adenylate cyclase in septal and cortical slices of the rat but fails to modify cortical beta, alpha-1 or alpha-2 adrenoceptor binding sites. Fengabine (up to 400 mg/kg i.p.) has no effect on rat cerebral serotonin uptake, synthesis or metabolism. Moreover, when given subacutely (100 or 200 mg/kg i.p., b.i.d. for 2 weeks), it fails to alter rat cortical serotonine receptors or [3H]imipramine binding sites. Fengabine (up to 50-100 microM) is also inactive in vitro on [3H] GABA binding to GABAA or GABAB receptors in the rat brain or on GABA transaminase activity in the mouse brain.(ABSTRACT TRUNCATED AT 250 WORDS)

In rats, a single injection of antipsychotic drugs produced a transitory change in the kinetic state of tyrosine hydroxylase (TH) in striatum and nucleus accumbens. The affinity of TH for 2-amino-4-hydoxy-6,7-dimethyl-5,6,7,8-tetrahydropterine (DMPH4) and the Vmax with respect ot tyrosine were increased. The relative potencies of anti-psychotics to change the kinetics of TH in striatum and nucleus accumbens when injected into rats were measured in the presence of 0.4 mM DMPH4. The doses of methiothepin, pimozide and halopridol which increased the affinity for DMPH4 of striatal TH were lower than those required to produce a similar change in nucleus accumbens. In contrast, thioridazine and clozapine were more effective in nucleus accumbens than in striatum. Chlorpromazine was equally active in these two tissues. Haloperidol increased the turnover rate of dopamine in striatum with doses that are relatively smaller than those required in the nucleus accumbens. Clozapine was more active in increasing turnover rate of dopamine in nucleus accumbens; the activity of chlorpromazine in these two tissues was equal. These results suggest that antipsychotics with high incidence of extrapyramidal side effects affect the nigrostriatal dopaminergic pathway selectively.

The effect of the alpha adrenoceptor blocking agent yohimbine on cerebral dopamine metabolism has been investigated in the rat. Yohimbine (1 to 10 mg/kg i.p.) increased in both striatum and limbic areas 1) homovanillic acid and dihydroxyphenylacetic acid levels, 2) tyrosine hydroxylase activity measured in vitro, 3) the in vivo accumulation of dihydroxyphenylalanine after NSD 1015 and 4) the rate of dopamine disappearance after alpha-methyl-p-tyrosine. The inability of clonidine to prevent the yohimbine-induced enhancement of striatal homovanillic acid levels in doses that antagonize the yohimbine-induced increase in noradrenaline turnover as well as the failure of other alpha adrenoceptor blocking agents (tolazoline, phentolamine and prazosin) to increase dopamine metabolism suggest that alpha adrenoceptors are not involved in the yohimbine-induced alteration of dopamine metabolism. Similarly to neuroleptic agents, yohimbine reduced striatal acetylcholine concentrations and counteracted the dopamine (10(-5) M)-induced inhibition of the potassium-evoked release of [3H]acetylcholine from slices of caudate nucleus. Yohimbine failed to further enhance striatal homovanillic acid levels in animals pretreated with a supramaximal dose of haloperidol. Moreover, in rats treated with haloperidol for 10 days, the effect of yohimbine on striatal homovanillic acid and acetylcholine levels was markedly reduced. It is concluded that yohimbine possesses postsynaptic dopamine receptor blocking properties in addition to its ability to inhibit alpha adrenergic receptors. The failure of yohimbine to affect dopamine-sensitive adenylate cyclase activity in striatal homogenates suggests an action of the compound on the D2 receptor.

6,7-Dihydroxy-2-dimethylaminotetralin (TL-99), N-n-propyl-3-(3-hydroxyphenylpiperidine [(+/-)-3-PPP], N-n-propylnorapomorphine and pergolide were evaluated for activity on a number of biochemical parameters that are presumed to indicate an agonist effect at dopamine (DA) autoreceptors (antagonism of the gamma-hydroxybutyrate-induced increase in dopa formation), at postsynaptic DA receptors (elevation of acetylcholine levels) or at both types of DA receptors (diminution of DA synthesis and homovanillic acid levels) in rat striatum. All four agents decreased striatal dopa accumulation (in the presence and in the absence of gamma-hydroxybutyrate). N-propylnorapomorphine, pergolide and TL-99 also reduced homovanillic acid levels and increased acetylcholine concentrations in striatum whereas (+/-)-3-PPP was inactive. The compounds were all more potent in diminishing dopa accumulation caused by gamma-hydroxybutyrate treatment than in increasing acetylcholine levels [(+/-)-3-PPP showing the highest dissociation] indicating a preferential agonist activity at DA autoreceptors. The relative selectivity of the compounds for DA autoreceptors and postsynaptic DA receptors was evaluated further by studying the antagonism by these drugs of the activation of striatal dopa formation (index of both DA autoreceptor and postsynaptic DA receptor stimulation) and tyrosine hydroxylase (index of postsynaptic DA receptor stimulation only) induced by haloperidol or reserpine. The DA agonists were all more potent in antagonizing the neuroleptic-induced increase in DA synthesis than in counteracting the drug-induced activation of tyrosine hydroxylase, with (+/-)-3PPP exhibiting the highest dissociation. The present results indicate that the DA agonists studied possess some selectivity for striatal DA autoreceptors, (+/-)-3-PPP being the most selective in this respect.

Gamma-hydroxybutyric acid (GHBA) in doses that increased the striatal dopamine (DA) content of rat brain failed to increase the affinity of striatal tyrosine hydroxylase (TH) for its pterdine cofactor or to change the sensitivity of the enzyme to the inhibition by DA. Haloperidol (1 mg/kg) decreased the apparent Kmof striatal TH for the pteridine cofactor. However, when GHBA was injected before haloperidol it prevented the decrease in the apparent Kmof TH, in a dose related manner. In vitro GHBA (10-4 M) neither changed the stimulation of the striatal adenylyl cyclase by DA nor its inhibition by haloperidol.

Rats were trained to discriminate a dose of the NMDA antagonist MK-801 from saline using a standard, two-lever, operant procedure. The acquisition of this discrimination was rapid, rats reaching criterion performance in a mean of 32 sessions. The discriminative stimulus produced by MK-801 generalized to phencyclidine and (+)N-allylnormetazocine but only low levels of generalization were seen with (-)N-allylnormetazocine and with the anti- ischaemic drug ifenprodil and its derivative SL 82.0715. The MK-801 stimulus was partially antagonized by haloperidol. The results show that MK-801 can produce a discriminative stimulus which is shared by other non-competitive NMDA antagonists which have similar behavioural effects in other procedures. However, ifenprodil and SL 82.0715, which have also been shown to antagonize the effects of NMDA, do not produce similar behavioural effects or discriminative stimuli presumably because they act through a different site.

Ifenprodil and SL 82.0715 are noncompetitive N-methyl-D-aspartate (NMDA) antagonists whose inhibitory actions are not explained by antagonistic effects at any of the three commonly recognized sites within the NMDA receptor complex (recognition, channel and modulatory glycine sites). We presently show that ifenprodil and SL 82.0715 antagonize the effects of NMDA via a selective action at the recently described polyamine modulatory site. Spermine and spermidine (0.5-100 microM) increase the binding of [3H]1-[1-(2-thienyl)cyclohexyl] piperidine to washed rat forebrain membranes in the presence of glutamate (10 microM). This effect is antagonized by ifenprodil and SL 82.0715 (0.1-10 microM) at concentrations which do not displace [3H]1-(2-thienyl)cyclohexyl] piperidine in the absence of added polyamine. Spermine and spermidine (up to 100 microM) do not significantly alter the binding of [3H]glycine but increase the binding of the NMDA recognition site ligand [3H](+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid. Ifenprodil and SL 82.0715 (0.1-10 microM) antagonize this effect; ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-10-imine maleate) or 7-chlorokynurenate (100 microM) are ineffective. In immature rat cerebellar slices, spermine and spermidine (10-1000 microM) potentiate the maximal effects of NMDA (80-160 microM) on cyclic GMP production. Spermine (100-1000 microM) reverses the antagonistic effects of ifenprodil (0.15-50 microM) but not of ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-10-imine acid or kynurenate on the NMDA receptor-mediated increase in cyclic GMP levels. Ifenprodil (0.01-1 microM) potently but only partially antagonizes the depolarizing effects of NMDA (10 microM) on the immature rat spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Summary We studied the relationship between changes of 3′,5′-cyclic adenosine monophosphate (cAMP) and tyrosine hydroxylase (TH) activity in adrenal medulla of rats exposed to cold stress. Exposure of rats to 4° C produced a ten-fold increase of the cAMP content of adrenal medulla in about 30 min. This increase persisted for about one hour; the levels of cAMP returned to control value within 120 min in spite of the continued exposure to 4° C. In rats with monolaterally denervated (splanchnicotomized) adrenal, the exposure to 4° C produced only insignificant changes of cAMP concentration. During the exposure to 4° C we also observed an increase (about two times) of catecholamine turnover rate as measured by 3H-dopamine efflux from adrenal glands. This increased efflux persisted for 6 h of exposure to cold suggesting that the efflux of 3H-dopamine can increase without a simultaneous increase of cAMP concentrations. Exposure of rats to 4° C for two hour also increases (about two times) the TH activity as measured 24 h later. Exposure of the animals to 4° C for a time period longer than two hour (4 or 24 h) failed to produce further increases of TH activity. These results support the concept that the increase of cAMP concentrations in adrenal medulla may play a central role in initiating the chain of biochemical events modulating the synthesis of TH.

The electrically evoked, calcium-dependent release of 3H-acetylcholine from slices of rat striatum was inhibited in a concentration-dependent manner by (+)-amphetamine (0.2–20 µM). This inhibitory effect of (+)-amphetamine was unaffected by depletion of the endogenous stores, of dopamine by pretreatment with rescrpine (5 mg/kg, 24h). However, the combined treatment of reserpine with a-methyl-p-tyrosine (300 mg/kg) or NSD 1015 (100 mg/kg) reduced significantly these inhibitory effects of (+)-amphetamine. Similar results were obtained after chronic 6-hydroxydopamine lesions of the corpus striatum. The inhibition of 3H-acetylcholine release by (+)-amphetamine in rats pretreated with reserpine was potentiated in the presence of 10 µM pargyline. These results support the view that the inhibitory effects of (+)-amphetamine on the electrically-evoked release of 3H-acetylcholine are mediated by dopamine released from a special pool of newly synthetized transmitter rather than through a direct action on an amphetamine recognition site or receptor.