[Focus on the endocannabinoid system and the reprotoxicity of marijuana in female users]. / Focus sur le système endocannabinoïde et la reprotoxicité du cannabis chez la femme à l'heure du débat sur sa dépénalisation en France.

Among recreative compounds, marijuana is the most used worldwide. Delta9THC binding on brain endocannabinoid receptors drives its psychotropic effects. The endocannabinoid system (ECS) is an endogenous neurohormonal system essential for homeostasis composed of ligands, metabolic enzymes and at least 2 receptors discovered to date. In female reproduction, the ECS regulates the hypothalamic-pituitary axis and many steps of the reproduction process, such as ovulation, tubal transportation and trophoblast implantation. Delta9THC can cross the placental barrier and bind to the fetal endocannabinoid system. In humans, fetal and obstetrical consequences of marijuana use during pregnancy are intrauterine growth restriction and preterm delivery. In the light of legalization projects currently reviewed in several western countries, further research should be conducted to improve knowledge on maternal, fetal and reprotoxic consequences of marijuana use during reproductive age and pregnancy.

Prefrontal synaptic markers of cocaine addiction-like behavior in rats.

Defining the drug-induced neuroadaptations specifically associated with the behavioral manifestation of addiction is a daunting task. To address this issue, we used a behavioral model that differentiates rats controlling their drug use (Non-Addict-like) from rats undergoing transition to addiction (Addict-like). Dysfunctions in prefrontal cortex (PFC) synaptic circuits are thought to be responsible for the loss of control over drug taking that characterizes addicted individuals. Here, we studied the synaptic alterations in prelimbic PFC (pPFC) circuits associated with transition to addiction. We discovered that some of the changes induced by cocaine self-administration (SA), such as the impairment of the endocannabinoid-mediated long-term synaptic depression (eCB-LTD) was similarly abolished in Non-Addict- and Addict-like rats and thus unrelated to transition to addiction. In contrast, metabotropic glutamate receptor 2/3-mediated LTD (mGluR2/3-LTD) was specifically suppressed in Addict-like rats, which also show a concomitant postsynaptic plasticity expressed as a change in the relative contribution of AMPAR and NMDAR to basal glutamate-mediated synaptic transmission. Addiction-associated synaptic alterations in the pPFC were not fully developed at early stages of cocaine SA, when addiction-like behaviors are still absent, suggesting that pathological behaviors appear once the pPFC is compromised. These data identify specific synaptic impairments in the pPFC associated with addiction and support the idea that alterations of synaptic plasticity are core markers of drug dependence.

Group 2 metabotropic glutamate receptors induced long term depression in mouse striatal slices.

We studied the roles of mGlu2/3 receptors (mGlu2/3) in glutamatergic transmission at corticostriatal synapses in mice brain slices. Perfusion of the selective mGlu2/3 agonists LY354740 and L-CCG1 caused the long term depression (LTD) of evoked synaptic responses. Photonic and electronic microscopy showed mGlu2/3 on axonal fibers and glial processes but not on striatal dendrites. mGlu2/3-LTD was independent of synaptic activity and insensitive to specific antagonists of dopamine D1, D2, GABA(B), N-methyl-D-aspartate or adenosine A1 receptors. Manipulation of the cAMP/protein kinase A cascade had no effect on the mGlu2/3-LTD. In contrast, MEK1-2 inhibitors reduced both mGlu2/3 initial depression and LTD suggesting the involvement of the mitogen activated kinase pathway in mGlu2/3-LTD.

Cannabinoids inhibit GABAergic synaptic transmission in mice nucleus accumbens.

In mice nucleus accumbens slices, whole-cell patch clamp recording of medium-spiny neurons revealed that cannabimimetics ((R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphtalenylmethanone) (WIN-2) and ((-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol) inhibit stimulus-evoked gamma-aminobutyric acid mediated inhibitory post-synaptic currents (IPSC). The actions of WIN-2 were reversed by the selective cannabinoid CB(1) receptor antagonist [N-piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride] (SR141716A). WIN-2 modified paired-pulse ratio of evoked IPSCs and decreased miniature IPSC frequency indicating a presynaptic localization of cannabinoid CB(1) receptors.

Localization and mechanisms of action of cannabinoid receptors at the glutamatergic synapses of the mouse nucleus accumbens.

Despite the role of excitatory transmission to the nucleus accumbens (NAc) in the actions of most drugs of abuse, the presence and functions of cannabinoid receptors (CB1) on the glutamatergic cortical afferents to the NAc have never been explored. Here, immunohistochemistry has been used to show the localization of CB1 receptors on axonal terminals making contacts with the NAc GABAergic neurons. Electrophysiological techniques in the NAc slice preparation revealed that cannabimimetics [WIN 55,212,2 (WIN-2) and CP55940] strongly inhibit stimulus-evoked glutamate-mediated transmission. The inhibitory actions of WIN-2 were dose-dependent (EC(50) of 293 +/- 13 nm) and reversed by the selective CB1 antagonist SR 141716A. In agreement with a presynaptic localization of CB1 receptors, WIN-2 increased paired-pulse facilitation, decreased miniature EPSC (mEPSC) frequency, and had no effect on the mEPSCs amplitude. Perfusion with the adenylate cyclase activator forskolin enhanced glutamatergic transmission but did not alter presynaptic CB1 actions, suggesting that cannabinoids inhibit glutamate release independently from the cAMP-PKA cascade. CB1 did not reduce evoked transmitter release by inhibiting presynaptic voltage-dependent Ca(2+) currents through N-, L-, or P/Q-type Ca(2+) channels, because CB1 inhibition persisted in the presence of omega-Conotoxin-GVIA, nimodipine, or omega-Agatoxin-IVA. The K(+) channel blockers 4-aminopyridine (100 micrometer) and BaCl(2) (300 micrometer) each reduced by 40-50% the inhibitory actions of WIN-2, and their effects were additive. These data suggest that CB1 receptors are located on the cortical afferents to the nucleus and can reduce glutamate synaptic transmission within the NAc by modulating K(+) channels activity.

Cellular and synaptic adaptations mediating opioid dependence.

Although opioids are highly effective for the treatment of pain, they are also known to be intensely addictive. There has been a massive research investment in the development of opioid analgesics, resulting in a plethora of compounds with varying affinity and efficacy at all the known opioid receptor subtypes. Although compounds of extremely high potency have been produced, the problem of tolerance to and dependence on these agonists persists. This review centers on the adaptive changes in cellular and synaptic function induced by chronic morphine treatment. The initial steps of opioid action are mediated through the activation of G protein-linked receptors. As is true for all G protein-linked receptors, opioid receptors activate and regulate multiple second messenger pathways associated with effector coupling, receptor trafficking, and nuclear signaling. These events are critical for understanding the early events leading to nonassociative tolerance and dependence. Equally important are associative and network changes that affect neurons that do not have opioid receptors but that are indirectly altered by opioid-sensitive cells. Finally, opioids and other drugs of abuse have some common cellular and anatomical pathways. The characterization of common pathways affected by different drugs, particularly after repeated treatment, is important in the understanding of drug abuse.

Regulation of central synaptic transmission by 5-HT(1B) auto- and heteroreceptors.

Although 5-HT(1B) receptors are believed to be expressed on nerve terminals, their precise mode of action is not fully understood because of the lack of selective antagonists. The 5-HT(1B) receptor knockout mouse was used in the present investigation to assess the function of 5-HT(1B) receptors in the modulation of synaptic transmission in three areas of the central nervous system: the dorsal raphe, the ventral midbrain, and the nucleus accumbens. N-(3-Trifluoromethylphenyl)piperazine, a 5-HT(1B) receptor agonist, potently inhibited 5-HT(1A) receptor-mediated slow inhibitory postsynaptic potentials (IPSPs) in the dorsal raphe of wild-type but not knockout mice. Both synaptically released 5-HT and exogenous 5-HT caused a presynaptic inhibition that outlasted the postsynaptic hyperpolarization only in wild-type mice. In the ventral midbrain, 5-HT(1B) receptor-dependent inhibition of gamma-aminobutyric acid(B) IPSPs in dopamine neurons was present in wild-type animals and absent in knockout animals. Similar results were obtained in the nucleus accumbens measuring glutamate-mediated excitatory postsynaptic currents in medium spiny neurons. Finally, cocaine, which blocks 5-HT uptake, inhibited IPSPs in the dorsal raphe and the ventral midbrain of wild-type but not knockout mice, whereas cocaine produced comparable inhibition of excitatory postsynaptic currents in the nucleus accumbens of both types of animals. These results indicate that 5-HT(1B) receptors function as autoreceptors and heteroreceptors to exert presynaptic inhibition of transmitter release in the central nervous system. Furthermore, this study underscores the role played by presynaptic 5-HT(1B) receptors in mediating the effects of cocaine on synaptic transmission.

Presynaptic regulation of glutamate release in the ventral tegmental area during morphine withdrawal.

The regulation of glutamate (Glu) release from the excitatory input to dopamine cells in the ventral tegmental area (VTA) during acute withdrawal from morphine was studied in slices from animals treated for 6-7 d with morphine. EPSCs were inhibited by opioid agonists acting at micro-subtype receptors but not by selective delta- or kappa-subtype agonists. The opioid inhibition was reduced by 65% with the potassium channel blocker 4-aminopyridine (4-AP; 100 microM) and a 12-lipoxygenase inhibitor, baicalein (5 microM), suggesting that opioids acted via a transduction pathway involving activation of a voltage-dependent potassium conductance by lipoxygenase metabolites as has been shown in the periaqueductal gray (). During withdrawal, neither the potency nor the efficacy of D-Ala-Met-enkephalin-Gly-ol (DAMGO) were changed; however, the blockade of micro-opioid inhibition by both 4-AP and baicalein was reduced. In addition, the potency of baclofen to depress EPSCs by GABA-B receptors and the effects of the GABA-uptake inhibitor NO-711 (10 microM) were increased in withdrawn rats. Finally, group 2 (but not group 4 or 1) metabotropic glutamate receptor-mediated presynaptic inhibition was also enhanced in morphine-withdrawn rats. These results suggest that one of the consequences of withdrawal from chronic morphine is an enhanced presynaptic inhibition of the excitatory inputs to the dopamine cells of the VTA. Inhibition of glutamate release during acute withdrawal would add to the inhibition of dopamine cells that is mediated by an augmented release of GABA ().

Decreased presynaptic sensitivity to adenosine after cocaine withdrawal.

The nucleus accumbens (NAc) is a site mediating the rewarding properties of drugs of abuse, such as cocaine, amphetamine, opiates, nicotine, and alcohol (Wise and Bozarth, 1987; Koob, 1992; Samson andHarris, 1992; Woolverton and Johnson, 1992; Self and Nestler, 1995; Pontieri et al., 1996). Acute cocaine has been shown to decrease excitatory synaptic transmission mediated by the cortical afferents to the NAc (Nicola et al., 1996), but the effects of long-term cocaine treatment and withdrawal have not been explored. Here, we report that long-term (1 week) withdrawal from chronic cocaine reduced the potency of adenosine to presynaptically inhibit glutamate (Glu) release by activating adenosine A1 receptors. Adenosine A1 receptors were not desensitized, because the potency of the metabolically stable adenosine analog N6-cyclopentyl-adenosine was unchanged after chronic cocaine withdrawal. When adenosine transporters were blocked, the potency of adenosine to inhibit Glu release from naive and cocaine-withdrawn NAc slices was similar. These results suggest that one of the long-term consequences of cocaine withdrawal is an augmented uptake of adenosine. This long-lasting change expressed at the presynaptic excitatory inputs to the medium spiny output neurons in the NAc may help identify new therapeutic targets for the treatment of drug abuse.

Visualization of cyclic AMP-regulated presynaptic activity at cerebellar granule cells.

Adenylyl cyclase (AC) modulation of vesicular cycling was visualized at cultured cerebellar granule cell synapses using the sequential uptake of antibodies directed against the intraluminal domain of synaptotagmin I. Vesicle recycling due to spontaneous transmitter release in the absence of action potentials was increased by the AC/protein kinase A (PKA) activators forskolin and CPT-cAMP. These effects were blocked by the PKA inhibitor Rp-cAMPs. Cyclic AMP elevation also induced new cycling at previously silent sites. Activation of L-AP4-sensitive mGluR reduced the cAMP/PKA enhancement at preexisting synapses downstream of both AC and calcium channels. Modulation of the turnover and the number of vesicular release sites provide one mechanism that may underlie cAMP-dependent cerebellar long-term potentiation.

Metabotropic glutamate receptors in the rat nucleus accumbens.

The effects of glutamate metabotropic receptors (mGluRs) on excitatory transmission in the nucleus accumbens were investigated using electrophysiological techniques in rat nucleus accumbens slices. The broad-spectrum mGluR agonist (1S,3R)-1-aminocyclopentyl-1,3-dicarboxylate, the mGluR group 2 selective agonists (S)-4-carboxy-3-hydroxyphenylglycine, (1S,3S)-ACPD) and (2S,1'S,2'S)-2-(2'-carboxycyclopropyl)glycine (L-CCG1), and the mGluR group 3 specific agonist L-2-amino-4-phosphonobutyrate (L-AP4) all reversibly inhibited evoked excitatory synaptic responses. The specific group 1 mGluR agonist (R,S)-3,5-dihydroxyphenylglycine [(R,S)-DHPG] did not depress transmission. Dose-response curves showed that the rank order of agonist potencies was: L-CCG1 > L-AP4 > (1S,3S)-ACPD. Group 2 and 3 mGluRs inhibited transmission via a presynaptic mechanism, as they increased paired-pulse facilitation, decreased the frequency of miniature excitatory postsynaptic currents and had no effect on their amplitude. The mGluRs did not inhibit transmitter release by reducing voltage-dependent Ca2+ currents through N- or P-type Ca2+ channels, as inhibition persisted in the presence of omega-conotoxin-GVIA or omega-Aga-IVA. The depression induced by mGluRs was not affected by specific antagonists of dopamine D1, GABA-B or adenosine A1 receptors, indicating direct effects. Finally, (R,S)-DHPG specifically blocked the postsynaptic afterhyperpolarization current (I(AHP)). Our results represent the first direct demonstration of functional mGluRs in the nucleus accumbens of the rat.

Metabotropic glutamate receptors inhibiting excitatory synapses in the CA1 area of rat hippocampus.

In the CA1 region of hippocampal slices prepared from young adult rats, we studied the ability of several specific agonists of metabotropic glutamate receptors (mGluRs) to depress excitatory synaptic transmission at the CA3-CA1 pyramidal cell synapses. Three groups of mGluRs have been described: group 1 (mGluR1 and 5) receptors are positively coupled to phospholipase C whereas group 2 (mGluR2 and 3) and group 3 (mGluR4, 6, 7 and 8) receptors are negatively coupled to adenylate cyclase. We found that the broad-spectrum agonist (1S,3R)-1-aminocyclopentyl-1,3-dicarboxylate and the group 1-specific agonist (R,S)-dihydroxyphenylglycine both reversibly inhibited evoked field excitatory postsynaptic potentials, indicating the involvement of group 1 mGluRs. (R,S)-3,5-dihydroxyphenylglycine presumably inhibited transmission via a presynaptic mechanism, as whole-cell voltage-clamp recordings revealed that inhibition of the synaptic transmission was always accompanied with an increase in paired-pulse facilitation. Treatment with a specific blocker of mGluR1 receptors, the phenylglycine derivative (S)-4-carboxyphenylglycine, was without effect on the (1S,3R)-1-amino-cyclopentyl-1,3-dicarboxylate-induced depression of the field excitatory postsynaptic potentials, strongly suggesting that mGluR5 receptors are responsible for the (1S,3R)-1-aminocyclopentyl-1,3-dicarboxylate effect. Two selective agonists of group 2 mGluRs, (2S,1's,2's)-2-(2'-carboxycyclopropyl)glycine and 4-carboxy-3-hydroxyphenylglycine, were totally ineffective in blocking CA3-CA1-evoked synaptic transmission, excluding the involvement of mGluR2/3 subtypes at this developmental stage.

Pharmacology of metabotropic glutamate receptors at the mossy fiber synapses of the guinea pig hippocampus.

We have tested the ability of several specific agonists of glutamate metabotropic receptors (mGluRs) to depress synaptic transmission at mossy fiber synapses in the CA3 region of the guinea pig hippocampus. 1S,3R-1-amino-cyclopentyl-1,3-dicarboxylate (ACPD) reversibly inhibited monosynaptic mossy fiber field potentials, presumably by a presynaptic mechanism, with an EC50 of 2.0 +/- 0.4 microM (n = 3), suggesting the presence of mGluRs on mossy fiber synaptic terminals of the group 1 or 2 category. L-2-amino-4-phosphono butanoate (L-AP4) also inhibited responses with an EC50 of 1.1 +/- 0.2 microM suggesting that mGluRs of the group 3 (mGluR4, 6, 7 and 8) category of receptors are also present on mossy fiber terminals. Both (2S,1'S,2'S)-2-(2'-carboxycyclopropyl)glycine (L-CCG1) and (S)-4-carboxy-3-hydroxy phenylglycine (4C3HPG) were also efficacious at blocking mossy fiber transmission, with an EC50 of 1.1 +/- 0.1 microM (n = 4) and 4.8 +/- 0.6 microM (n = 3) respectively. The latter finding indicates the involvement of mGluRs belonging to the group 2 (mGluR2, 3) category of receptors. The effects of L-AP4 and L-CCG1 were both antagonized by (+)-alpha-methyl-4-carboxyphenylglycine [(+)MCPG]. MAP4, an antagonist of group 3 mGluRs in other systems, blocked the effect of L-AP4, but not the effect of L-CCG1, while MCCG, an antagonist of group 2 mGluRs in other systems, blocked the effect of L-CCG1, but not the effect of L-AP4. These pharmacological findings provide strong evidence for the coexistence of group 2 and 3 mGluRs on the terminals of mossy fibers in the guinea pig.

Vasopressin stimulates steroid secretion in human adrenal glands: comparison with angiotensin-II effect.

Autoradiographic experiments using iodinated vasopressin analog revealed the presence of specific vasopressin-binding sites in the human adrenal cortex (zona glomerulosa and zona fasciculata). These receptors exhibited a good affinity for arginine vasopressin (3.3 nM), with classical V1a pharmacology and densities of 65 and 135 fmol/mg protein-enriched membranes from zona glomerulosa and fasciculata, respectively. Vasopressin receptors present in both glomerulosa and fasciculata cell-enriched primary cultures were coupled to phospholipase C (ED50, 0.9 and 1.8 nM; maximal stimulation, 4.3- and 5.8-fold, respectively). Vasopressin also stimulated an increase in intracellular calcium through at least two distinct mechanisms: the mobilization of intracellular pools via vasopressin-stimulated inositol phosphate accumulation and the activation of calcium influx. In glomerulosa cell-enriched primary cultures, vasopressin increased aldosterone secretion (ED50, 0.4 nM; maximal stimulation, 2.5-fold) and was found to be as potent as angiotensin-II in stimulating aldosterone secretion, phosphoinositide turnover, and calcium mobilization. In fasciculata cells, vasopressin and angiotensin-II were also able to stimulate cortisol secretion and inositol phosphate accumulation. Moreover, perifusion experiments demonstrated that vasopressin was released from the adrenal medulla. Together, these results indicate that vasopressin can be considered a potent paracrine modulator of adrenal steroid secretion in man.

Dual effects of nordidemnin on WRK1 cells: inhibition of phosphoinositide metabolism and cell proliferation.

Nordidemnin (NorD), a cyclodepsipeptide isolated from marine invertebrates, exhibits antiproliferative and antitumoral properties identical to didemnin B on many cell lines. On WRK1 cells, a rat mammary tumor cell line, NorD considerably reduced the vasopressin-stimulated accumulation of inositol phosphates. This effect was more pronounced on dividing cells and of weak amplitude on quiescent ones. It was observed with nanomolar concentrations of NorD and became significative after 3 hr of incubation at 37 degrees C. The maximal effect was observed after a 14-hr incubation period. In contrast, the inactive analog epinordidemnin, as well as the structurally related immunosuppressive cyclosporin A, had no significant effect on phosphoinositide metabolism. More detailed analysis demonstrated that NorD reduced the amounts of all intracellular inositol phosphate isomers, including inositol pentakisphosphate and inositol hexakisphosphate. Vasopressin-stimulated inositol (1,4,5)-trisphosphate accumulation was reduced by 80% and, as a consequence, the intracellular calcium mobilization was strongly affected. Similarly, NorD reduced both the level of inositol (1,4,5)-trisphosphate and the intracellular free calcium concentration of unstimulated cells. NorD blocked phosphoinositide metabolism by reducing the myoinositol transporter and, by a consequence, the pool of inositol lipids. NorD also strongly inhibited WRK1 cell proliferation with the same EC50 as that observed for the effect on phosphoinositide metabolism. Epinordidemnin, which was unable to inhibit inositol phosphate accumulation, had no effect on cell growth. Cyclosporin A, which slightly inhibited WRK1 cell growth, did not significantly affect the calcium-phosphatidylinositol cascade. Taken together, these results suggest that NorD might interfere with WRK1 cell growth by inhibiting phosphoinositide turnover.

Release of adenosine by activation of NMDA receptors in the hippocampus.

Adenosine is present in the mammalian brain in large amounts and has potent effects on neuronal activity, but its role in neural signaling is poorly understood. The glutamate receptor agonist N-methyl-D-aspartate (NMDA) caused a presynaptic depression of excitatory synaptic transmission in the CA1 region of guinea pig hippocampal slices. This depression was blocked by an adenosine A1 receptor antagonist, which suggests that activation of the NMDA subtype of glutamate receptor raises the concentration of extracellular adenosine, which acts on presynaptic inhibitory A1 receptors. Strong tetanic stimulation caused a heterosynaptic inhibition that was blocked by both NMDA and A1 receptor antagonists. Enkephalin, which selectively inhibits interneurons, antagonized the heterosynaptic inhibition. These findings suggest that synaptically released glutamate activates NMDA receptors, which in turn releases adenosine, at least in part from interneurons, that acts at a distance to inhibit presynaptically the release of glutamate from excitatory synapses. Thus, interneurons may mediate a widespread purinergic presynaptic inhibition.

MCPG antagonizes metabotropic glutamate receptors but not long-term potentiation in the hippocampus.

In the CA1 and CA3 regions of the guinea pig hippocampus, we have tested the ability of the new antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) to inhibit the well-known effects of (trans)-1-amino-cyclopentyl-1,3-dicarboxylate (ACPD), a specific agonist of glutamate metabotropic receptors. Whole-cell recordings showed that MCPG was able to antagonize the blocking action of ACPD on IAHP in the CA1 region. In addition, we report here that MCPG also antagonized the presynaptic inhibitory actions of ACPD on field excitatory postsynaptic potentials in both areas CA1 and CA3. Thus, MCPG proved to be an effective tool for determining physiological roles of the glutamate metabotropic receptors in synaptic transmission in the hippocampus. We next tested the possible effects of this antagonist on long-term potentiation (LTP). In completely blind experiments MCPG was without effect on LTP in both areas CA1 and CA3. In conclusion, our results suggest that, although MCPG is a valuable antagonist of the ACPD-sensitive receptors, it has no inhibitory effect on LTP.

Nitric oxide synthase activity endogenously modulates NMDA receptors.

We tested the possibility that endogenous nitric oxide synthase activity regulated NMDA receptors in primary cultured striatal neurons. We monitored NMDA-induced increase in intracellular Ca2+ levels with fura-2 ratio imaging, while nitric oxide synthase activity was either increased with L-arginine (the natural substrate of nitric oxide synthase) or inhibited using nitro-L-arginine (a specific inhibitor of nitric oxide synthase). We found that the NMDA receptor effect was slowly but strongly diminished after an L-arginine (1 mM, 15 min) treatment (L-arginine preincubation reduced the 100 microM NMDA-induced maximal effect by 30-50%). The L-arginine blockade of NMDA receptors was long-lasting but could be partially reversed by hemoglobin (100 microM, 10 min), which binds nitric oxide. This was not observed when the neurons were treated with L-arginine together with nitro-L-arginine. Our data strongly suggest that physiological nitric oxide synthase activity could regulate NMDA receptors.

Stimulation by glutamate receptors of arachidonic acid release depends on the Na+/Ca2+ exchanger in neuronal cells.

In primary cultures of striatal neurons, stimulation of N-methyl-D-aspartic acid (NMDA) receptors or associative activation (but not separate activation) of (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and metabotropic glutamate receptors (mGluR) strongly increased arachidonic acid (AA) release via activation of phospholipase A2 (PLA2). Depolarizing agents, such as veratridine, were as potent as NMDA in stimulating AA release. However, increasing the intracellular Ca2+ concentration via voltage-sensitive Ca2+ channels did not result in a significant stimulation of PLA2. Substitution of sodium by lithium, a monovalent cation that does not participate in the Na+/Ca2+ exchanger activity but permeates ionotropic glutamate receptor channels, blocked AA release induced by veratridine or AMPA plus mGluR agonists. It also reduced the NMDA-induced AA release, to a lesser extent. The contribution of the Na+/Ca2+ exchanger to the activation of PLA2 after veratridine, NMDA receptor, or AMPA receptor plus mGluR stimulation was confirmed by using a selective inhibitor of the Na+/Ca2+ exchanger.