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Nisoxetine, 3-(o-methoxyphenoxy)-3-phenyl-N-methyl-propyl-amine, is a new inhibitor of norepinephrine uptake. Nisoxetine antagonized 6-hydroxydopamine-induced depletion of norepinephrine in mouse heart with an ED50 of 0.9 mg/kg but had no effect on p-chloroamphetamine-induced depletion of serotonin in mouse brain at doses up to 32 mg/kg. Using the antagonism of these depleting agents to estimate inhibition of uptake into noradrenergic and serotoninergic neurons, we compared nisoxetine to several known amine uptake inhibitors. The order of effectiveness in antagonizing 6-hydroxydopamine action was protriptyline greater than desmethylimipramine greater than EXP 561 greater than nisoxetine greater than nortriptyline greater than chlorpheniramine greater than desmethylchlorimipramine greater than imipramine greater than doxepin greater than amitriptyline greater than chlorimipramine, with fluoxetine and its N-demethylated metabolite (103947) having no effect. In blocking p-chloroamphetamine, the order of effectiveness was EXP 561 greater than fluoxetine greater than 103947 greater than chlorpheniramine greater than chlorimipramine, with desmethylchlorimipramine, protriptyline, and nortriptyline having marginal effects and nisoxetine and the other drugs no effect at the highest dose tested, 32 mg/kg. Nisoxetine is thus one of the more potent and specific inhibitors of norepinephrine uptake, differing remarkably from fluoxetine to which it is related structurally.

Administration of morphine sulfate (1--4 mg/kg i.v.) to cats produces changes in body temperature, with hyperthermia appearing with larger doses. Since the central neurotransmitters dopamine and serotonin have been implicated in thermoregulation, studies were done to determine whether morphine's action could be mediated via these transmitters. Temperature responses were measured in freely moving cats by means of rectal thermometer probes. Either pimozide, 0.5 mg/kg i.p., a specific DA receptor blocker, or fluoxetine HCl, 10 mg/kg i.p., a specific inhibitor of 5-HT uptake, was administered 2--3 h prior to morphine injection. Temperatures were monitored for 3.5 h after morphine administration. Both agents were found to enhance the hyperthermic response to morphine with the maximum morphine effect occurring in most cases by 2 h. The results indicate that a balance in the ratio of 5-HT : DA may be involved in cat thermoregulation and that the hyperthermic response in the cat to morphine may be effected by shifting this 5-HT : DA ratio.

Fluoxetine (Li-ly 110140) caused a 63 percent inhibition of [3H]serotonin uptake into platelets obtained from normal volunteers to whom the drug was administered daily for 7 days. This dose had no effect on the usual pressor response produced by injections of norepinephrine or tyramine.

Electrical self-stimulation (SS) in the median raphé of the rat but not in the locus coeruleus resulted in a dramatic rise of body temperature. This hyperthermia was facilitated by pretreatment with a inhibitor of serotonin uptake. The functional significance of the hyperthermia elicited by stimulation of the media raphé was discussed on the basis of the relationship between SS and primary reinforcers.

The ability of L-5-hydroxytryptophan (L-5HTP), a serotonin precursor, to elevate plasma levels of corticosterone in rats was confirmed. Pretreatment of the rats with 3-(p-trifluoromethylphenoxy)-N-methyl-3-phenyl-propylamine hydrochloride (Lilly 110140) markedly enhanced the elevation of corticosterone levels by L-5HTP. Since Lilly 110140 is a specific inhibitor of serotonin uptake, these results support the hypothesis that L-5HTP elevates corticosterone by enhancing neurotransmission through a serotoninergic pathway influencing ACTH release.

An uptake system on the serotonin neuronal membrane apparently functions to inactivate serotonin that has been released into the synaptic cleft. Various inhibitors of this active transport system on serotonin neurons are known, and some are specific in the sense that they do not inhibit the active uptake system on norepinephrine neurons. The most widely studied specific inhibitor of the serotonin neuron pump is fluoxetine, 3-(p-trifluoromethylphenoxy-N-methyl-3-phenyl propylamine (Lilly 110140). When fluoxetine or other effective but less specific serotonin uptake inhibitors are given, a rapid decrease in serotonin turnover occurs and the rate of firing of single neural units in the serotonin rich raphe area of brain is reduced. This decrease in serotonin turnover and release may be a compensatroy mechanism in response to an enhanced action of serotonin on synaptic receptors. Through the use of fluoxetine and other serotonin uptake inhibitors, the role of serotonin neurons in various brain functions--behavior, sleep, regulation of pituitary hormone release, thermoregulation, pain responsiveness, and so on--can be studied.

3-(p-Trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine (Lilly 110140), when injected into rats at i.p. doses of 1 to 10 mg/kg, prevented the lowering of brain serotonin by 4-chloroamphetamine. The duration of 110140 action was very long, significant antagonism of 4-chloroamphetamine action being apparent still at 48 hours after a single dose of 10 mg/kg of 110140. The N,N-dimethyl tertiary amine derivative was as effective as 110140 itself in antagonizing serotonin depletion by 4-chloroamphetamine, but other structurally related compounds has less activity or were inactive. Likewise, six tricyclic antidepressant drugs injected at 10 mg/kg i.p. did not antagonize the action of 4-chloroamphetamine. When injected into rats whose brain serotonin levels had already been depleted by 3-hour pretreatment with 4-chloroamphetamine, 110140 terminated the action of 4-chloroamphetamine and permitted serotonin levels to return to normal. Lilly 110140 did not antagonize the depletion of brain serotonin or norepinephrine by reserpine, which implies that reserpine does not require the membrane pump for entry into the neuron. The depletion of brain serotonin, but not norepinephrine, by alpha-ethyl-3-hydroxy-4-methylphenethylamine (H75/12) was blocked by 110140. In contrast to chlorimipramine, 110140 did not antagonize the depletion of norepinephrine levels in heart and spleen by 6-hydroxydopamine. The data suggest that 110140 is a specific drug for inhibiting uptake into serotoninergic neurons in the brain.

The effects of fenfluramine and other sanorectic drugs on the consumption of both protein and total calories by rats given simultaneous access to two isocaloric diets containing 5 or 45 percent casein were examined. Anorectic doses of fenfluramine failed to decrease protein intake but increased the proportion of total dietary calories represented by protein. In contrast, anorectic doses of d-amphetamine decreased protein and calorie consumption proportionately. Subanorectic doses of fenfluramine also increased the proportion of caloric intake represented by protein among animals given prior treatment with the serotonin precursor tryptophan. Fluoxetine, a drug that blocks reuptake of serotonin, similarly spared protein consumption while reducing caloric intake. These observations indicate that two distinct brain mechanisms, sensitive to different drugs, underlie the elective consumption of protein and calories.

The importance of neuronal uptake processes in rat arteries and veins was compared using nisoxetine and fluoxetine, selective inhibitors for neuronal uptake of norepinephrine and serotonin, respectively. Nisoxetine (10(-7) - 10(-5) M) increased the sensitivity to exogenous norepinephrine in the portal and mesenteric veins (10-fold) and in the mesenteric artery (2.5-fold). Responses to field stimulation were also increased afternisoxetine in all three vessels. After nisoxetine, aortic responses to norepinephrine were unaltered and in all tissues, serotonin-induced contractions were reduced. Fluoxetine did not potentiate responses to norepinephrine or to field stimulation except in the mesenteric vein where sensitivity to norepinephrine was increased and the relaxation rate after field stimulation was prolonged. Although serotonin has been detected in blood vessels, fluoxetine did not increase vascular responses to serotonin. These studies suggest that rat mesenteric veins have a highly sensitive neuronal uptake mechanism of norepinephrine. Furthermore, these data provide indirect evidence against a functionally important serotonergic uptake process in rat blood vessels and suggest that neuronal uptake of serotonin does not exert a major role in terminating the vascular action of this biogenic amine.

The 5-hydroxytryptamine (5-HT, serotonin) specific presynaptic reuptake inhibitor Lilly 110140 (fluoxetine hydroxhloride) was injected systemically in rats trained to bar-press for rewarding stimulation to the caudal portion of the medial forebrain bundle. Rates of self stimulation were reduced in proportion to drug dosage, and these reductions were partially reversible by methysergide. These findings are consistent with previous reports suggesting an inhibitory role for 5-HT in self stimulation.

Nisoxetine, a potent and specific inhibitor of norepinephrine uptake, suppressed REM sleep in cats. Oral doses as small as 0.1 mg/kg were effective during the first 2 1/2 hours of a recording session; 0.25 mg/kg, for 5 hours. The amount of slow wave sleep increased in cats that received 0.1-1.0 mg/kg of nisoxetine. These changes in sleep pattern resemble those reported after treatment with somewhat higher doses of tricylic antidepressants.

Preclinical studies with nisoxetine (Compound 94939) (3-[o-Methoxyphenoxy]-N-methyl-3-phenylpropylamine HCl) had shown it to have antidepressant properties and to be almost devoid of anticholinergic activity and depressant effects on cardiac conduction (in contrast to the commonly used tricyclic antidepressants from which nisoxetine significantly differs in structure). Placebo and nisoxetine (10-20 mg b.d. for 7 days) were administered to normal volunteers in a single-bind crossover study. Adverse side effects were minimal. There were no significant changes in heart rate or blood pressure seen when no other drugs were given. The effect of nisoxetine on uptake of biogenic amines was utilized to study its mechanism of action. The transient rise in blood pressure seen after an intravenous bolus of tyramine decreased by one-half to two-thirds while the rise in blood pressure upon continuous noradrenaline infusion was enhanced some two-to eight-fold. Both effects occurred after on dose and were greater with larger doses and chronic administration. In vitro, nisoxetine inhibits 5-HT uptake into platelets. However, platelets harvested from subjects receiving chronic nisoxetine administration did accumulate 5-HT. Plasma concentration of nisoxetine in these individuals was shown to be lower than that needed to block 5-HT uptake. We concluded that nisoxetine, in safe doses, specifically increased the sensitivity of noradrenaline and decreased tyramine responsiveness, presumably by blocking uptake at the axonal membrane. In contrast, in these clinical doses it had virtually no effect on 5-HT uptake into platelets.

Fluoxetine prevents the loss of 5-hydroxytryptamine (5HT) uptake in synaptosomes of cerebral cortex after intraperitoneally administered p-chloroamphetamine (p-CA) with an ED50 of 3.8 mg/kg i.p. in rats. However, at 50 mg/kg, it does not prevent the loss of norepinephrine (NE) uptake in synaptosomes of hypothalamus after intraventricularly administered 6-hydroxydopamine (6-OHDA). Nisoxetine, on the other hand, centrally protects NE uptake from the neurotoxic effect of 6-OHDA with an ED50 value of 5 mg/kg i.p. At 50 mg/kg, it gives only 35% protection of 5HT uptake from the neurotoxic effect of p-CA. In comparison with the ED50 values of tricyclic antidepressants, both fluoxetine and nisoxetine are more potent and selective blockers of neurotoxicity resulting from the central actions of p-CA and 6-OHDA, respectively, in vivo.

The uptake of 14C-5-HT by rat blood platelets was examined in vitro in experimental conditions which allowed measurement of the initial velocity and excluded other passive processes across the cell membrane. In these conditions, the effect of two non tricyclic antidepressant drugs (Lilly 110140 and trazodone) was investigated. Lilly 110140 was as active as chlorimipramine and several times more active than imipramine as an inhibitor of 14C-5-HT uptake. Like chlorimipramine, Lilly 110140 appeared to be either a non-competitive or an uncompetitive inhibitor, according to the concentration of drug used. Trazodone also inhibited 14C-5-HT uptake by platelets but to a lesser extent than chlorimipramine, imipramine or Lilly 110140. m-Chlorophenylpiperazine, a possible metabolite of trazodone, was about 3 times more potent an inhibitor than the parent molecule. Both compounds acted non-competitively. Compared with published data on the effect of Lilly 110140 and trazodone on brain 5-HT, the present results support the suggestion that rat platelets are a useful pharmacological model of serotoninergic nerve endings.

A convenient GLC method was developed to assay the chemically related CNS agents dl-3-(p-trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine (Ia) and dl-3-(0-methoxy-phenoxy)-N-methyl-3-phenylpropylamine (Ib). Subsequently, this GLC method was used to monitor the stability of Ia and Ib in acidic and basic media. These CNS agents were stable in basic solution but labile under acid conditions, and the degradations of both compounds approximated pseudo-first-order kinetics. Products formed during the acid hydrolysis of Ia and Ib were identified and were shown not to interfere in the GLC assays of the parent ethers.

Fluoxetine, a drug that inhibits serotonin inactivation by reuptake from the synaptic cleft and thereby enhances serotonin nerve function, was used to study the possible role of serotonin neurons in the activation of the pituitary-adrenal system of rats by swim stress or insulin-induced hypoglycemia. Fluoxetine pretreatment enhanced the elevation of plasma corticosterone produced by injection of L-5-hydroxytryptophan but did not significantly alter the elevation of plasma corticosterone by swim stress or by insulin-induced hypoglycemia, even when the stimulus was shown to be submaximal. The results suggest that serotonin neural pathways postulated to stimulate ACTH secretion are not involved in the activation of adrenocortical function by these stimuli.

Fluoxetine hydrochloride (Lilly 110140: 3-p-trifluoromethylphenoxy-3-phenyl-N-methyl-propylamine hydrochloride) inhibited the metabolism of hexobarbital and ethinamate in rodents and prolonged the hypnotic effects of these drugs.

Pretreatment of rats with an agent that inhibits uptake into serotoninergic neurons [Lilly 110140: 3-(p-trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine hydrochloride] prevented the depletion of brain serotonin by 4-chloroamphetamine, presumably by preventing the entry of 4-chloroamphetamine into the serotonin neuron. When the uptake inhibitor was given after 4-chloroamphetamine, the lowering of both serotonin and tryptophan hydroxylase levels in brain was reversed. Serotonin levels returned to normal after 110140 administration to 4-chloroamphetamine-treated rats at a rate similar to the calculated rate of serotonin turnover in rats treated with 110140 alone. Progressively less reversibility of the 4-chloroamphetamine effect occurred when 110140 was injected at 8, 16 and 24 hr after 4-chloroamphetamine, and no reversibility was observed when 110140 was injected at 32 or 48 hr after 4-chloroamphetamine. These findings indicate that the depletion of brain serotonin by 4-chloroamphetamine is initially reversible but that there is a gradual transition into an irreversible effect between 24 and 48 hr after 4-chloroamphetamine injection. Apparently the prolonged presence of 4-chloroamphetamine inside the serotonin neuron produced by continual reuptake of 4-chloroamphetamine is required for the semi-permanent depletion of brain serotonin stores.

Rats treated with Lilly 110140, a specific inhibitor of serotonin re-uptake in brain, are less sensitive to electroshock. Lilly 110140 antagonizes the hyperalgesia following injections of p-chlorophenylalanine and potentiates morphine analgesia. Naloxone blocks the analgesia following morphine, but has no effect on Lilly 110140-induced analgesia. Brain serotonin neurons may, at least in part, mediate analgesia.

Profound hypothermia (6 degrees C) was induced in cold exposed golden hamsters (Mesocricetus auratus) by a combination of drugs that potentiate brain serotonergic activity (fluoxetine and pargyline) and inhibit noradrenergic activity (alpha-methyl-p-tyrosine). Individual drugs and combinations of 2 were ineffective.

3-(p-Trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine (Lilly 110140) competitively inhibited the uptake of serotonin (5-HT), norepinephrine (NE) and dopamine into synaptosomes of rat brain with Ki values of 5.5 x 10-minus8, 9.5 x 10-minus6 and 1.3 x 10-minus5 M, respectively. Aiming for a more effective inhibitor of 5-HT uptake, we found the trifluoromethyl group in the phenoxy ring was most favorable at the para-position and was better than other substituting groups including fluoro, chloro, methyl and methoxy groups. The N-demethylated (primary amine) and the N.N-diemthylated (tertiary amine) derivatives inhibited the uptake of monoamines with the same effectiveness as Lilly 110140 (a secondary amine). The uptake of 5-HT into synaptosomes was significantly inhibited 15 minutes after an intraperitoneal administration of Lilly 110140. The inhibition persisted for a 24-hour period. NE uptake in vitro maintained a normal rate during the entire time course. Lilly 110140 likewise had no effect on the in vitro and in vivo accumulation of 3-H-tryptophan in the brain. The effect of Lilly 110140 and the tricyclic drug, chlorimipramine, was compared. Although chlorimipramine inhibited the uptake of 5-HT into synaptosomes with same effectiveness as Lilly 110140 in vitro, it reduced the uptake of both 5-HT and NE in vivo. Chlorimipramine exerted its greatest inhibition on the two uptake processes in the 1st hour and none by the 4th hour. Unlike the tricyclic drugs, imipramine, chlorimipramine, desipramine and chlordesipramine, Lilly 110140 and its primary amine derivative did not block the in vivo uptake of NE into rat heart. The present study suggests that Lilly 110140 is a potent and selective inhibitor for uptake of 5-HT into synaptosomes of rat brain.