BACKGROUND AND PURPOSEDeficient transmission at the glutamate NMDA receptor is considered a key component of the pathophysiology of schizophrenia. However, the effects of antipsychotic drugs on the release of the endogenous NMDA receptor partial agonist,d‐serine, remain to be clarified.EXPERIMENTAL APPROACHWe determined the interaction between antipsychotic drugs (clozapine and haloperidol) and transmission‐modulating toxins (tetanus toxin, fluorocitrate, tetrodotoxin) on the release of L‐glutamate andd‐serine in the medial prefrontal cortex (mPFC) of freely moving rats, using microdialysis, and primary cultures of astrocytes using extreme high‐pressure liquid chromatography.KEY RESULTSRelease of L‐glutamate andd‐serine in the mPFC and in cultured astrocytes was inhibited by tetanus toxin (a synaptobrevin inhibitor) and fluorocitrate (a glial toxin), whereas tetrodotoxin (a voltage‐sensitive Na⁺blocker) inhibited depolarization‐induced L‐glutamate release in the mPFC without affecting that ofd‐serine. Clozapine (1 and 5 mg·kg⁻¹), but not haloperidol (0.5 and 1 mg·kg⁻¹), dose‐dependently increased L‐glutamate andd‐serine release from both astrocytes and mPFC. Clozapine‐induced release of L‐glutamate andd‐serine was also reduced by tetanus toxin and fluorocitrate. Tetrodotoxin reduced clozapine‐induced mPFC L‐glutamate release but not that ofd‐serine. Clozapine‐induced L‐glutamate release preceded clozapine‐inducedd‐serine release. MK‐801 (a NMDA receptor antagonist) inhibited the delayed clozapine‐induced L‐glutamate release without affecting that ofd‐serine.CONCLUSIONS AND IMPLICATIONSClozapine predominantly activated glial exocytosis ofd‐serine, and this clozapine‐inducedd‐serine release subsequently enhances neuronal L‐glutamate release via NMDA receptor activation. The enhancedd‐serine associated glial transmission seems a novel mechanism of action of clozapine but not haloperidol.

AP-3 is a member of the adaptor protein (AP) complex family that regulates the vesicular transport of cargo proteins in the secretory and endocytic pathways. There are two isoforms of AP-3: the ubiquitously expressed AP-3A and the neuron-specific AP-3B. Although the physiological role of AP-3A has recently been elucidated, that of AP-3B remains unsolved. To address this question, we generated mice lacking μ3B, a subunit of AP-3B. μ3B−/− mice suffered from spontaneous epileptic seizures. Morphological abnormalities were observed at synapses in these mice. Biochemical studies demonstrated the impairment of γ-aminobutyric acid (GABA) release because of, at least in part, the reduction of vesicular GABA transporter in μ3B−/− mice. This facilitated the induction of long-term potentiation in the hippocampus and the abnormal propagation of neuronal excitability via the temporoammonic pathway. Thus, AP-3B plays a critical role in the normal formation and function of a subset of synaptic vesicles. This work adds a new aspect to the pathogenesis of epilepsy.

Staphylococcal enterotoxins (SEs) produced by Staphylococcus aureus are the most recognizable bacterial superantigenic toxins causing food poisoning in humans throughout the world. However, it remains unclear how SEs induce emesis and its emetic signal pathway. We investigated a mechanism of SEA-induced emesis using a small emetic animal model, house musk shrew. SEA-induced emesis in the animals was inhibited by a 5-hydroxytryptamine (5-HT) synthesis inhibitor and a 5-HT(3) receptor antagonist. SEA could increase 5-HT release in the small intestine. Pre-treatment with 5,7-dihydroxytryptamine (5,7-DHT) markedly inhibited SEA-induced emesis. SEA-induced emesis was also abolished by surgical vagotomy. Furthermore, cannabinoid (CB) receptor agonists inhibited SEA-induced emesis, and the action was reversed by a CB1 antagonist. Both 5-HT release and CB1 receptor expression were found in the mucosal and myenteric plexus of the intestine. Moreover, a CB1 receptor agonist significantly decreased the 5-HT release in the intestine. These results demonstrate that SEA induces 5-HT release in intestine, rather than in brain, and that the 5-HT(3) receptors on vagal afferent neurons are essential for SEA-stimulated emesis. In addition, SEA-induced emesis is downregulated by the CB system through decreasing 5-HT release in intestine.

To clarify the mechanisms of interaction between adenosineA₁receptor (A1-R) and adenosine A₂receptor (A2-R) on neurotransmitter release, this study determined the functional interactions among adenosine receptors (AD-Rs), voltage-sensitive Ca²⁺channels (VSCCs), protein kinases (PKs), and synaptic proteins [N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors] on hippocampal serotonin release usingin vivomicrodialysis in freely moving rat. Basal serotonin release was regulated by two functional complexes: N-type VSCC (N-VSCC)/calcium-phospholipid-dependent protein kinase (PKC)/syntaxin (major pathway) and P-type VSCC (P-VSCC)/cyclic AMP-dependent protein kinase (PKA)/synaptobrevin (minor pathway). However, K⁺-evoked serotonin release was regulated by N-VSCC/PKC/syntaxin (minor pathway) and P-VSCC/PKA/synaptobrevin (major pathway). A1-R antagonists increased basal serotonin release, which was reduced by inhibitors of N-VSCC, PKC, and syntaxin predominantly and by inhibitors of PKA and synaptobrevin weakly, but was not affected by P-VSCC inhibitor. In the presence of A1-R antagonist, A2-R agonists increased basal serotonin release, which was inhibited by inhibitors of P-VSCC, PKA, and synaptobrevin predominantly and reduced by inhibitors of N-VSCC, PKC, and syntaxin weakly. Under the condition of activation of adenylate cyclase in the absence of A1-R antagonists, A2-R agonists increased basal serotonin release. A1-R antagonist and A2-R agonist enhanced K⁺-evoked serotonin release, which was inhibited by inhibitors of P-VSCC, PKA, and synaptobrevin predominantly. These results suggest that an activation of A1-R suppresses serotonin release via inhibition of both N-VSCC/PKC/syntaxin and P-VSCC/PKA/synaptobrevin pathways, and an activation of A2-R stimulates serotonin release via enhancement of the P-VSCC/PKA/synaptobrevin pathway. Therefore, PKA activity plays an important role in the interaction between A1-R and A2-R on hippocampal serotonin release.