Effects of intracerebroventricularly injected glucagon-like peptide-1 on cardiovascular parameters; role of central cholinergic system and vasopressin

We aimed to investigate the effects of intracerebroventricularly (i.c.v.) injected glucagon-like peptide-1 (GLP-1) on blood pressure and heart rate, and whether central cholinergic system and vasopressinergic system play roles in these effects. Male Wistar albino rats were used throughout the experiments. Blood pressures and heart rates were observed before and for 30 min following drug injections. i.c.v. GLP-1 (100, 500 and 1000 ng/10 microl) caused a dose-dependent increase in both blood pressure and heart rate. Nicotinic receptor antagonist mecamylamine (25 microg/10 microl, i.c.v.) and muscarinic receptor antagonist atropine (5 microg/10 microl, i.c.v.) prevented the stimulating effect of GLP-1 on blood pressure. The effect of GLP-1 on heart rate was blocked only by mecamylamine. The V1 receptor antagonist of vasopressin (B-mercapto B, B-cyclopentamethylenepropionyl, O-Me-Tyr,Arg)-vasopressin (10 microg/kg), that was applied intraarterially, only prevented the effect of GLP-1 on blood pressure, but did not show any effect on heart rate. Our data indicate that i.c.v. GLP-1 increases blood pressure and heart rate, and stimulation of central nicotinic and partially muscarinic receptors and vasopressinergic system play a role in the effects of i.c.v. GLP-1 on blood pressure. The effect of GLP-1 on heart rate may be partially due to stimulation of central nicotinic receptors.     

Regulation of Histamine Turnover via Muscarinic and Nicotinic Receptors in the Brain

To clarify the regulation of central histaminergic (HAergic) activity by cholinergic receptors, the effects of drugs that stimulate the cholinergic system on brain histamine (HA) turnover were examined, in vivo, in mice and rats. The HA turnover was estimated from the accumulation of tele-methylhistamine (t-MH) during the 90-min period after administration of pargyline (65 mg/kg, i.p.). In the whole brain of mice, oxotremorine, at doses higher than 0.05 mg/kg, s.c., significantly inhibited the HA turnover, this effect being completely antagonized by atropine but not by methylatropine. A large dose of nicotine (10 mg/kg, s.c.) also significantly inhibited the HA turnover. This inhibitory effect was antagonized by mecamylamine but not by atropine or hexamethonium. A cholinesterase inhibitor, physostigmine, at doses higher than 0.1 mg/kg, s.c., significantly inhibited the HA turnover. This effect was antagonized by atropine but not at all by mecamylamine. None of these cholinergic antagonists used affected the steady-state t-MH level or HA turnover by themselves. In the rat brain, physostigmine (0.1 and 0.3 mg/kg, s.c.) also decreased the HA turnover. This inhibitory effect of physostigmine was especially marked in the striatum and cerebral cortex where muscarinic receptors are present in high density. Oxotremorine (0.2 mg/kg, s.c.) and nicotine (1 mg/kg, s.c.) also decreased the HA turnover in the rat brain. However, these effects showed no marked regional differences. These results suggest that the stimulation of central muscarinic receptors potently inhibits the HAergic activity in the brain and that strong stimulation of central nicotinic receptors can also induce a similar effect.     

Uptake of Exogenous Aspartate into Circumventricular Organs but Not Other Regions of Adult Mouse Brain

Abstract: Adult mice were treated intraperitoneally with aspartate (Asp) at one of several doses (0.47–3.75 mmol/kg) and 30 min later given a subcutaneous Asp injection at the same dose. This treatment regimen resulted in steady state blood Asp elevations, a given dose producing the same degree of elevation at both 30 and 60 min. The lowest and highest doses, respectively, produced fourfold and 55-fold elevations of serum Asp. In selected circumventricular organ (CVO) regions of brain which lack blood brain barriers, tissue Asp levels rose 1.5 and 3 times above control values following the lowest and highest doses, respectively, whereas tissue Asp remained unchanged in non-CVO brain regions. Thus, even very moderate Asp dosing causes marked increases in CVO Asp. In order to analyze the pattern of Asp uptake into CVO, Asp was assayed in numerous subdivisions of each CVO, and maps were constructed which reflected microregional concentration differences. The pattern of Asp distribution suggests that Asp enters brain via fenestrated capillaries serving certain portions of CVO and then spreads into adjacent brain tissue. In separate experiments, we administered a single high dose of Asp (15 mmol/kg) to both adult and infant mice and measured Asp in serum and select brain regions 60 min later. Asp concentrations in serum and CVO (but not other brain regions) rose markedly at both ages but the increases were greater in serum and therefore also in CVO of infants. This may explain in part the observation that a given dose of Asp destroys a larger number of CVO neurons in infant than in adult mice. Our findings support a growing body of evidence that CVO are an important communication link between blood and brain.     

Nicotine enhances delayed matching-to-sample performance by primates

The non-human primate provides an excellent model for studies of learning and memory, and one particular test, the delayed matching-to-sample task, is performed in a similar manner by both humans and non-human primates. Five young adult macaques were employed in this study, displaying variable capacities for retention in the task. Baseline performance was very consistent and three levels of performance difficulties (95-100%, 80-85% and 65-75% correct choices) were employed by including several delay intervals (0-60 sec) in each session. A reproducible enhancement in performance by nicotine in macaques performing a delayed matching-to-sample task was demonstrated. Nicotine enhanced performance with an average increase of 10% at the longest retention delay interval. This beneficial effect of nicotine was abolished in animals pretreated with a low dose (0.5 mg/kg) of mecamylamine to block central nicotinic receptors. Selective blockade of peripheral nicotinic receptors with hexamethonium was without effect on the nicotine response. A high dose (2 mg/kg) of mecamylamine itself induced a marked inhibition of performance, while an equivalent dose of hexamethonium was without effect. These experiments point to the possibility that central nicotinic receptors may be exploited pharmacologically to enhance memory performance. In this respect it is interesting that nicotine was most effective at enhancing performance when recall was more difficult, that is, on the longer retention interval delays. This could signify that nicotine might be particularly effective in the most impaired individuals. Lastly, it is encouraging that the mecamylamine induced decrease in cognitive performance might provide a new model of memory impairment from which to study the pathogenesis and develop new pharmacological strategies for the dementias.     

Receptor subtypes mediating depressor responses to microinjections of nicotine into medial NTS of the rat

Microinjections (50 nl) of nicotine (0.01-10 microM) into the nucleus of the solitary tract (NTS) of adult, urethan-anesthetized, artificially ventilated, male Wistar rats, elicited decreases in blood pressure and heart rate. Prior microinjections of alpha-bungarotoxin (alpha-BT) and alpha-conotoxin ImI (specific toxins for nicotinic receptors containing alpha7 subunits) elicited a 20-38% reduction in nicotine responses. Similarly, prior microinjections of hexamethonium, mecamylamine, and alpha-conotoxin AuIB (specific blockers or toxin for nicotinic receptors containing alpha3beta4 subunits) elicited a 47-79% reduction in nicotine responses. Nicotine responses were completely blocked by prior sequential microinjections of alpha-BT and mecamylamine into the NTS. Complete blockade of excitatory amino acid receptors (EAARs) in the NTS did not attenuate the responses to nicotine. It was concluded that 1) the predominant type of nicotinic receptor in the NTS contains alpha3beta4 subunits, 2) a smaller proportion contains alpha7 subunits, 3) the presynaptic nicotinic receptors in the NTS do not contribute to nicotine-induced responses, and 4) EAARs in the NTS are not involved in mediating responses to nicotine.     

Mecamylamine blockade of nicotine enhanced noradrenaline turnover in rat brain.

The administration of nicotine significantly enhanced the depletion in noradrenaline (NA) observed in the brains of male Sprague-Dawley rats following alpha methyl-para-tyrosine (αMPT) administration. These data indicate that nicotine enhances the turnover of NA in the rat brain. This effect of nicotine was completely blocked by mecamylamine administration while mecamylamine alone had no observed effect on NA content or turnover. These data are consistent with the action of mecamylamine as an effective antagonist of the action of nicotine in the rat brain.     

A central link between angiotensinergic and cholinergic systems; role of vasopressin

Participation of central cholinergic system in the effects of intracerebroventricular (i.c.v.) injection of angiotensin II (Ang II) on blood pressure and heart rate was studied in conscious, freely moving rats. Ang II dose-dependently increased blood pressure and decreased heart rate. Both atropine and mecamylamine (i.c.v.) pretreatments prevented the cardiovascular effects of Ang II. Pretreatment with a vasopressin V1 antagonist also prevented the cardiovascular responses to Ang II. Our data suggest that the central pressor effect of Ang II is mediated in part by central acetylcholine via both muscarinic and nicotinic receptors, and vasopressin participates in this effect through V1 receptors.     

Nicotine increases the expression of high affinity nerve growth factor receptors in both in vitro and in vivo

Impairment in nerve growth factor (NGF)-mediated support to basal forebrain cholinergic neurons may represent an initial insult to certain neural cells in Alzheimer's disease (AD). High affinity NGF receptor (TrkA) levels are decreased in AD brains as compared to age-matched control brains. One of the approaches suggested for the treatment of AD exploits the ability of small molecular substances to enhance the expression of endogenous growth factors and/or their receptors. The purpose of this study was to determine whether treatment with nicotine in both in vitro and in vivo settings would increase the neural expression of TrkA receptors. Using a differentiated PC12 neuronal-like system, chronic nicotine treatment increased cell surface TrkA receptor expression. Nicotine's action was blocked by co-treatment with either the non-competitive nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine or with the alpha7 nAChR-selective antagonist methyllycaconitine. Surprisingly, certain low doses of mecamylamine alone also increased TrkA receptor levels. Rats prepared with chronic indwelling intravenous catheters were continuously infused with nicotine to deliver a total dose of 12 mg/kg over 24 hr. This treatment resulted in a significant 44% increase in TrkA receptor expression in the hippocampus. As in the cell experiments, mecamylamine also increased hippocampal TrkA receptor expression. In fact, the ratio of the maximal mecamylamine response to the maximal nicotine response that was measured in vitro, i.e., 0.43 was remarkably similar to that for the in vivo experiment, i.e., 0.47. Since in our previous studies the increase in TrkA expression produced by nicotine was shown to be related to its cytoprotective actions, these results suggest that nicotine's neuroprotective actions might also be mediated through the drug's interaction with central alpha7 nAChRs and subsequent increase in TrkA receptor expression.     

Ethanol withdrawal tremor potentiates the tremorogenic action of nicotine

The tremorogenic effect of nicotine was studied in control rats and in rats withdrawn for 16-48 h from six to nine days' ethanol administration. The frequency and the intensity of tremor were measured electronically. A single dose of nicotine 5 mg/kg caused shortlasting (2-3 min) convulsions within 1 min after injection in control rats. Tremor occurred first after five repeated injections of nicotine (5 mg/kg) at half-hour intervals. This tremor encompassed peak frequencies of 6, 10 and 15 Hz. Hexamethonium at a dose of 10 mg/kg did not inhibit the tremor but eliminated the highest peak frequency (15 Hz) and tended to increase the intensity. Propranolol 5 mg/kg completely abolished the nicotine-induced tremor in control rats. Rats withdrawn from repeated ethanol administration showed a marked hypersensitivity to the tremorogenic action of nicotine so that a single dose of 1 mg/kg of nicotine caused clear tremor. The frequency spectra of this tremor showed peak frequencies at 6, 10 and 12 Hz. Hexamethonium did not change these frequencies. Furthermore, it tended to increase the intensity of nicotine-induced tremor in ethanol-withdrawn rats. Propranolol did not inhibit the tremor although it eliminated the 12 Hz peak frequency. The results suggest that the hypersensitivity to the tremorogenic action of nicotine in ethanol-withdrawn rats is not mediated by a sympathetic beta-adrenergic mechanism.     

Interactive effects of nicotine and MPTP on striatal tetrahydrobiopterin in mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin known to cause dopamine (DA) neuron degeneration, while the psychoactive compound nicotine is known to excite DA neurons. Tetrahydrobiopterin is the cofactor for tyrosine hydroxylase (TOH) in the regulation of DA biosynthesis. The present study investigated the interactions between nicotine and MPTP on striatal biopterin, DA and TOH activity in BALB/c mice. The results indicated that both acute and chronic nicotine administrations at various concentrations significantly increased biopterin and DA levels in the striatum, while MPTP markedly decreased these measures. Pretreatment with nicotine at a dose having no significant effect alone, partially protected against MPTP's toxicity on biopterin and DA. Increasing the dose of nicotine did not have a further protective action. The toxicity of MPTP on TOH was also prevented by nicotine. Further, the above effects of nicotine were probably mediated through the cholinergic nicotinic receptors since mecamylamine reversed the effects of nicotine. These results suggest that nicotine interacts with the dopaminergic system probably at the level of DA biosynthesis through activating TOH and its coenzyme tetrahydrobiopterin.     

Preproenkephalin mRNA and Methionine-Enkephalin Content Are Increased in Mouse Striatum After Treatment with Nicotine

Abstract: A single dose of nicotine increased methionine-enkephalin (Met-Enk) immunoreactivity in the striatum of mice in a time-dependent manner. Met-Enk content reached a maximum by ∼1 h after nicotine and returned to control values by 6 h. The response to nicotine was blocked by pretreating animals with the nicotinic receptor antagonist mecamylamine. In contrast, pretreating mice with the muscarinic receptor antagonist atropine or the dopamine receptor antagonist haloperidol did not block the response. A single dose of nicotine also increased mRNA for the precursor peptide preproenkephalin (PPE). The increase of PPE mRNA preceded that of Met-Enk and reached a maximum by ∼30 min after nicotine. PPE mRNA levels returned to near normal by ∼3 h and increased again by 6 h after nicotine. Daily administration of nicotine for 14 days increased Met-Enk content and PPE mRNA in the striatum of mice as well. Taken together, our results suggest that nicotinic receptors modulate Met-Enk content and PPE mRNA in the mouse striatum.     

Effects of a beta-sympathomimetic drug on the foetal and maternal cardiovascular system in a chronic sheep model

The effects of the beta-sympathomimetic agent terbutalin (1-/3.5 dihydroxyphenyl/-allilaminoethane sulphonate) on maternal and foetal circulation were studied in 11 ewe at 110-130 days of pregnancy. None of them exhibited uterine contractions. Catheters were implanted in the carotid artery and jugular vein, together with four stainless steel electrodes on the limbs. Terbutalin was added intravenously in Ringer-lactate (5%) infusion (1 ml/min). The following maternal and foetal parameters were measured simultaneously: heart rate, central arterial pressure, blood glucose levels, ECG. Intravenous administration of 100 micrograms terbutalin resulted in a 19% increase of maternal and 10% enhancement of foetal heart rate. Maternal systolic blood pressure rose by 9%, whereas diastolic blood pressure fell by 7%. Maternal and foetal blood glucose levels was fairly constant during the entire experiment. In further six experiments terbutalin was administered into the foetal circulation (1 ml/3 min). The same effects on foetal heart rate and pulse pressure were observed as after injecting into the maternal circulation, however but the time necessary for the maximum action to develop was significantly shorter.     

Effects of Menthol on Nicotine Pharmacokinetic,Pharmacology and Dependence in Mice

Although menthol, a common flavoring additive to cigarettes, has been found to impact the addictive properties of nicotine cigarettes in smokers little is known about its pharmacological and molecular actions in the brain. Studies were undertaken to examine whether the systemic administration of menthol would modulate nicotine pharmacokinetics, acute pharmacological effects (antinociception and hypothermia) and withdrawal in male ICR mice. In addition, we examined changes in the brain levels of nicotinic receptors of rodents exposed to nicotine and menthol. Administration of i.p. menthol significantly decreased nicotine’s clearance (2-fold decrease) and increased its AUC compared to i.p. vehicle treatment. In addition, menthol pretreatment prolonged the duration of nicotine-induced antinociception and hypothermia (2.5 mg/kg, s.c.) for periods up to 180 min post-nicotine administration. Repeated administration of menthol with nicotine increased the intensity of mecamylamine-precipitated withdrawal signs in mice exposed chronically to nicotine. The potentiation of withdrawal intensity by menthol was accompanied by a significant increase in nicotine plasma levels in these mice. Western blot analyses of α4 and β2 nAChR subunit expression suggests that chronic menthol impacts the levels and distribution of these nicotinic subunits in various brain regions. In particular, co-administration of menthol and nicotine appears to promote significant increase in β2 and α4 nAChR subunit expression in the hippocampus, prefrontal cortex and striatum of mice. Surprisingly, chronic injections of menthol alone to mice caused an upregulation of β2 and α4 nAChR subunit levels in these brain regions. Because the addition of menthol to tobacco products has been suggested to augment their addictive potential, the current findings reveal several new pharmacological molecular adaptations that may contribute to its unique addictive profile.     

Cardiovascular effects produced by choline injected into the lateral cerebral ventricle of the unanesthetized rat

Intracerebroventricular (icv) injection of choline (50–150 μg) causes a transient increase in blood pressure and a more prolonged decrease in heart rate (HR) in conscious rats. The bradycardia results from a centrally mediated increase in vagal tone. The cardiovascular effects do not appear to involve endogenous brain acetylcholine since there is no significant difference in the responses induced by choline before and after icv injection of hemicholinium-3. Intracerebroventricular ventricular injection of atropine or mecamylamine, alone, failed to influence the choline effect. However, atropine and mecamylamine, given together, abolished the reduction of HR, but still failed to modify the pressor response. The changes in blood pressure and HR appear to be due to effects of choline on post-synaptic receptors in different brain regions.     

Genetic correlations between nicotine reinforcement‐related behaviors and propensity toward high or low alcohol preference in two replicate mouse lines

Common genetic factors may contribute to the high comorbidity between tobacco smoking and alcohol use disorder. Here, we assessed behavioral and biological effects of nicotine in replicate mouse lines selectively bred for high (HAP2/3) or low alcohol preference (LAP2/3). In Experiment 1, free‐choice (FC) oral nicotine and quinine intake were assessed in HAP2/3 and LAP2/3 mice. Effects of nicotinic acetylcholine receptor blockade by mecamylamine on nicotine intake in HAP2 mice were also examined. In Experiment 2, HAP2/3 and LAP2/3 mice were tested for differences in sensitivity to nicotine‐induced taste conditioning. In Experiment 3, the effects of a single nicotine injection on nucleus accumbens (NAc) and dorsal striatum monoamine levels in HAP2/3 and LAP2/3 mice were tested. In Experiment 1, HAP2/3 mice showed greater nicotine intake and intake ratio than LAP2/3 mice. There were no line differences in quinine intake. Mecamylamine reduced nicotine intake and intake ratio in HAP2 mice. In Experiment 2, HAP2/3 mice showed weaker nicotine‐induced conditioned taste aversion (CTA) compared with LAP2/3 mice. In Experiment 3, nicotine treatment increased NAc dopamine turnover across both HAP2/3 and LAP2/3 mouse lines. These results show that there is a positive genetic correlation between oral alcohol intake (high alcohol intake/preference selection phenotype) and oral nicotine intake and a negative genetic correlation between oral alcohol intake and sensitivity to nicotine‐induced CTA.     

Dose-Response Relationship for Nicotine-Induced Up-Regulation of Rat Brain Nicotinic Receptors

Abstract: The chronic administration of nicotine to animals has been shown to result in an increase in brain nicotinic acetylcholine receptor (nAChR) density. It has been suggested that this agonist-induced receptor up-regulation is a consequence of long-term nAChR desensitization in vivo. In this study, the effects of different nicotine doses and administration schedules as well as the resulting blood and brain nicotine levels were determined to assess the effect of in vivo nicotine concentration on nAChR density in the brain. Rats with indwelling subcutaneous cannulas were infused for 10 days with 0.6–4.8 mg/kg/day nicotine either 2×, 4×, or 8×/day or by constant infusion. The nAChR density in cortical, striatal, and hippocampal tissue measured by [³H]cytisine binding as well as the corresponding plasma and brain nicotine levels measured by GC analysis were determined. The results showed a dose-dependent increase in nAChR density with significant increases achieved at 2.4 mg/kg/day in all three brain areas. It is surprising that at this dose there was little difference between the constant infusion of nicotine and twice-daily administration, whereas more frequent periodic injections were actually less effective at up-regulating nAChRs. An analysis of the blood and brain levels of nicotine compared with the concentrations that produce nAChR desensitization suggests that in vivo desensitization alone is not sufficient for nAChR up-regulation to occur.     

Nicotine-induced alteration in Tyr-Gly-Gly and Met-enkephalin in discrete brain nuclei reflects altered enkephalin neuron activity

Nicotine acts in CNS, but the pathways and mechanisms of its actions are poorly understood. Recent studies suggest an interaction between brain nicotinic receptors and endogenous opioid peptides. Acute administration of nicotine may alter enkephalin release without affecting brain enkephalin level. Tyr-Gly-Gly has been shown previously to be an extraneuronal metabolite of opioid peptides derived from proenkephalin A. Concentrations of Tyr-Gly-Gly in brain were used to provide an index of enkephalin release in vivo. Thus we examined the thesis that nicotine alters brain neuronal enkephalin release, by measuring Tyr-Gly-Gly levels in specific brain nuclei from rats treated with nicotine 0.3 mg/kg SC 10 min before decapitation. Of 30 brain regions investigated, acute nicotine increased Tyr-Gly-Gly immunoreactivity in nucleus accumbens and in lower brain stem areas including dorsal raphe, pontine reticular formation, gigantocellular reticular formation, locus coeruleus, sensory trigeminal nucleus and the caudal part of ventrolateral medulla oblongata. Concomitantly, nicotine produced a significant decrease in native Met-enkephalin in central amygdala, flocculo-nodular lobe of cerebellum, caudal part of the ventrolateral medulla and intermediolateral cell column of the spinal cord. It is probable that the effects of nicotine to increase Tyr-Gly-Gly and alter Met-enkephalin concentration are mediated by nicotine-induced release of enkephalin at these brain sites. Furthermore, some of the physiologic and pharmacologic effects of nicotine may be mediated by such enkephalin release.     

Nicotinic receptor agonists and antagonists increase sAPPα secretion and decrease Aβ levels in vitro

We have earlier reported that Aβ were significantly reduced in brains of smoking Alzheimer patients and control subjects compared with non-smokers, as well as in nicotine treated APPsw transgenic mice. To examine the mechanisms by which nicotine modulates APP processing we here measured levels of secreted amyloid precursor protein (sAPPα), total sAPP, Aβ40 and Aβ42 in different cell lines expressing different nicotinic receptor (nAChR) subtypes or no nAChRs. Treatment with nicotine increased release of sAPPα and at the same time lowered Aβ levels in both SH-SY5Y and SH-SY5Y/APPsw cells expressing α3 and α7 nAChR subtypes. These effects could also be evoked by co-treatment with the competitive α7 nAChR antagonists α-bungarotoxin and methyllycaconitine (MLA), and by these antagonists alone, suggesting that binding to the agonist binding site, rather than activation of the receptor, may be sufficient to trigger changes in APP processing. The nicotine-induced increase in sAPPα could only be blocked by co-treatment with the open channel blocker mecamylamine. In addition to nicotine, the agonists epibatidine and cytisine both significantly increased the release of sAPP in M10 cells expressing the α4/β2 nAChR subtype, and this effect was blocked by co-treatment with mecamylamine but not by the α4/β2 competitive antagonist dihydro-β-erythroidine. The lack of effect of nicotine on sAPPα and Aβ levels in HEK 293/APPsw cells, which do not express any nAChRs, demonstrates that the nicotine-induced attenuation of β-amyloidosis is mediated by nAChRs and not by a direct effect of nicotine. Our data show that nicotinic compounds stimulate the non-amyloidogenic pathway and that α4 and α7 nAChRs play a major role in modulating this process. Nicotinic drugs directed towards specific nAChR subtypes might therefore be beneficial for the treatment of AD not only by lowering Aβ production but also by enhance release of neuroprotective sAPPα.     

Brain 2-phenylethylamine as a major mediator for the central actions of amphetamine and methylphenidate.

2-Phenylethylamine (PEA) was measured in rabbit brain by gas-liquid chromatography. D-Amphetamine sulfate (0.65 mg/Kg) initially reduced brain PEA levels to one-third of its usual content (30 min) and subsequently doubled brain PEA (4 hr). Brain PEA levels were reduced (30 min) and subsequently increased (ten-fold at 4 hr) by D-amphetamine sulfate (13 mg/Kg); tolerance to these two effects was observed in rabbits treated for three days with D-amphetamine. Methylphenidate HCl (30 mg/Kg) but not L-amphetamine sulfate (0.65 mg/Kg and 13 mg/Kg) induced a small, non-significant lowering of brain PEA (30 min) followed by a marked augmentation (4 hr) of brain PEA content. D-Amphetamine (30 min or 4 hr prior) increased the recovery of labeled PEA from the brain of rabbits injected intraventricularly with labeled phenylalanine, and reduced the recovery of labeled PEA after its intraventricular injection, suggesting that D-amphetamine accelerates both the synthesis and the disposition of brain PEA. Pretreatment with α-methyldopa (which depletes PEA and other brain amines) or with α-methyldopa hydrazine (which selectively reduces brain PEA content by inhibiting decarboxylase in peripheral tissues only) markedly reduced the CNS effects of D-amphetamine (behavioral stimulation in mice and rabbits, anti-convulsant effect in mice); these decarboxylase inhibitors enhanced the amphetamine-like effects induced by PEA in mice pretreated with a monoamine oxidase inhibitor. The ability of PEA depleters to selectively block the stimulant effects of D-amphetamine, together with the close structural and pharmacological similarities between amphetamine and PEA, and marked influence of amphetamine administration upon PEA brain levels, synthesis and metabolism, suggest to us that many of the central actions of amphetamine may be mediated by endogenous PEA.