The interplay between 5-HT2C and 5-HT3A receptors in the dorsal periaqueductal gray mediates anxiety-like behavior in mice.

The monoamine neurotransmitter serotonin (5-HT) modulates anxiety by its activity on 5-HT2C receptors (5-HT2CR) expressed in the dorsal periaqueductal gray (dPAG). Here, we investigated the presence of 5-HT3A receptors (5-HT3AR) in the dPAG, and the interplay between 5-HT2CR and 5-HT3AR in the dPAG in mediating anxiety-like behavior in mice. We found that 5-HT3AR is expressed in the dPAG and the blockade of these receptors using intra-dPAG infusion of ondansetron (5-HT3AR antagonist; 3.0 nmol) induced an anxiogenic-like effect. The activation of 5-HT3ABR by the infusion of mCPBG [1-(m-Chlorophenyl)-biguanide; 5-HT3R agonist] did not alter anxiety-like behaviors. In addition, blockade of 5-HT3AR (1.0 nmol) prevented the anxiolytic-like effect induced by the infusion of the 5-HT2CR agonist mCPP (1-(3-chlorophenyl) piperazine; 0.03 nmol). None of the treatment effects on anxiety-like behaviors altered the locomotor activity levels. The present results suggest that the anxiolytic-like effect exerted by serotonin activity on 5-HT2CR in the dPAG is modulated by 5-HT3AR expressed in same region.

An overview of preparation and characterization of solid binary system and its application on transdermal film with variation of plasticizers

Chemotherapy induced nausea and vomiting (CINV) and post-operative nausea and vomiting (PONV) is a problem, often occurs in patient. Inspite of high bioavailability, the demerits such as: hepatic first pass metabolism and invasive nature of oral and parenteral dosage forms can be avoided with anti-emetic therapy of transdermal device. The major objective of the present study is to modify the hydrochloride (HCl) form of Ondansetron (OND) to the base form followed by improvement of solubility and permeability of OND by employing solid dispersion (SD) loaded patches. Preformulation study, as observed, begins with an approach to enthuse solubility of OND by SD technique choosing different carriers. The choice of carriers was rationalized by phase solubility study. Several combinations of transdermal films were prepared with pure drug, carriers and SDs with plasticizer Ka values of OND-HPßCD binary system were found lower (54.43 to 187.57 M-1) than that of OND-PVP K-30 binary system (1156.77 to 12203.6 M-1). The drug content of SDs and patches were found satisfactory. Better permeation rate (236.48±3.66 µg/3.935 cm2) with promising flux enhancement (8.30 fold) was found with DBP loaded SD patch (P6*). Hence, enhancement of solubility and permeability of P6* ensures that it can successfully enhance the bioavailability

Varenicline blocks ß2*-nAChR-mediated response and activates ß4*-nAChR-mediated responses in mice in vivo.

INTRODUCTION: The smoking cessation aid, varenicline, has higher affinity for the alpha4beta2-subtype of the nicotinic acetylcholine receptor (α4ß2*-nAChR) than for other subtypes of nAChRs by in vitro assays. The mechanism of action of acute varenicline was studied in vivo to determine (a) subtype activation associated with physiological effects and (b) dose relationship as an antagonist of nicotine. METHODS: Acute doses of saline, nicotine, and varenicline were given to mice, and locomotor depression and hypothermia were measured. Subunit null mutant mice as well as selective antagonists were used to study mode of action of varenicline as an agonist. Varenicline as an antagonist of nicotine was also investigated. RESULTS: Varenicline evokes locomotor depression and hypothermia at higher doses than necessary for nicotine. Null mutation of the α7- or ß2-nAChR subunit did not decrease the effectiveness of varenicline; however, null mutation of the ß4 subunit significantly decreased the magnitude of the varenicline effect. Effects of the highest dose studied were blocked by mecamylamine (general nAChR antagonist) and partially antagonized by hexamethonium (largely peripheral nAChR antagonist). No significant block was seen with ondansetron antagonist of 5-hydroxytryptamine 3 receptor. Using a dose of nicotine selective for ß2*-nAChR subtype effects with these tests, dose-dependent antagonism by varenicline was seen. Effective inhibitory doses were determined and appear to be in a range consistent with binding affinity or desensitization of ß2*-nAChRs. CONCLUSIONS: Varenicline acts as a functional antagonist of ß2*-nAChRs, blocking certain effects of nicotine. At higher doses, varenicline is an agonist of ß4*-nAChRs producing physiological changes in mice.

A comparative analysis of the potential of cannabinoids and ondansetron to suppress cisplatin-induced emesis in the Suncus murinus (house musk shrew).

RATIONALE: The 5-HT3 antagonist, ondansetron (OND), and the cannabinoid, delta9-tetrahydrocannabinol (delta9-THC), have been shown to interfere with emesis; however, their relative and/or combined effectiveness in suppressing vomiting produced by the chemotherapeutic agent, cisplatin, is unknown. OBJECTIVE: To evaluate the potential of: 1) a broad range of doses of delta9-THC and OND to prevent cisplatin-induced vomiting and retching in the Suncus murinus (house musk shrew), 2) combined treatment with ineffective individual doses of delta9-THC and OND to prevent cisplatin-induced vomiting and retching, 3) the CB1 receptor antagonist, SR141716, to reverse the antiemetic effects of OND, and 4) cannabidiol (CBD), the principal non-psychoactive component of marijuana, to reverse cisplatin-induced vomiting in the shrew. METHODS: Shrews were injected with various doses of OND (0.02-6.0 mg/kg), delta9-THC (1.25-10 mg/kg) and a combination of ineffective doses of each (0.02 mg/kg OND+1.25 mg/kg delta9-THC) prior to being injected with cisplatin (20 mg/kg) which induces vomiting. Shrews were also injected with CBD (5 mg/kg and 40 mg/kg) prior to an injection of cisplatin. RESULTS: OND and delta9-THC both dose-dependently suppressed cisplatin-induced vomiting and retching. Furthermore, a combined pretreatment of doses of the two drugs that were ineffective alone completely suppressed vomiting and retching. CBD produced a biphasic effect, suppressing vomiting at 5 mg/kg and potentiating it at 40 mg/kg. CONCLUSIONS: A low dose of the non-intoxicating cannabinoid CBD may be an effective anti-emetic treatment and combined doses of OND and delta9-THC that are ineffective alone suppresses cisplatin-induced emetic reactions in shrews.

Retrograde carbon monoxide is required for induction of long-term potentiation in rat superior cervical ganglion.

Carbon monoxide (CO), produced in the body by the enzyme heme oxygenase (HO), has been suggested as a retrograde synaptic messenger with a prominent role in the long-term potentiation (LTP) of certain areas of the brain. LTP of sympathetic ganglia is 5-HT(3) receptor-dependent and has been shown to require nitric oxide for the maintenance, but not for the induction, phase. We investigated the possibility of CO being required for the induction of ganglionic LTP. Pretreatment of rat isolated superior cervical ganglia with oxyhemoglobin (25-100 microm) completely blocked LTP. In the same ganglia, prolonged washout of oxyhemoglobin did not uncover any potentiation of the compound action potential. Oxyhemoglobin had no significant effect on the maintenance phase in ganglia with established LTP. Pretreatment of ganglia with the HO inhibitor zinc protoporphyrin-IX (ZnPP) (10 microm) completely and irreversibly prevented the expression of tetanus-evoked LTP. However, in the same ganglia, after superfusion of CO in the presence of ZnPP, tetanic stimulation readily evoked LTP. No effect was seen on the maintenance phase when ZnPP was superfused on ganglia with established LTP. Pretreatment of ganglia with the 5-HT(3) receptor antagonist ondansetron (0.4 microm) alone completely and irreversibly blocked LTP. However, in the presence of CO, ondansetron did not block LTP. These results suggest that activation of 5-HT(3) receptors may be involved in the production of CO. The results also suggest that CO, probably originating outside the presynaptic nerve terminal, is involved in the induction of LTP.

Fluoxetine treatment comprises the antiemetic efficacy of ondansetron in cancer patients.

Fluoxetine (Prozac) is an effective and increasingly widely used antidepressant. It is a 5-hydroxytryptamine (5-HT) re-uptake inhibitor. It produces its pharmacological effects by preventing the elimination of the 5-HT produced at nerve synapses, thus increasing its concentration at that location. Ondansetron (Zofran), is a 5-HT3 antagonist, which produces its pharmacological effect by competing with 5-HT receptors at the synapse. When both fluoxetine and ondansetron are used together, there is the possibility that the accumulation of 5-HT resulting from the use of fluoxetine may compete with ondansetron at the receptors, potentially reducing the antiemetic effects of ondansetron. Clinically, this has been observed in three patients treated with both compounds at the same time, while they were receiving carboplatin combination chemotherapy. The possibility that concurrent administration of the 5-HT re-uptake inhibitors, fluoxetine, may reduce the antemetic effectiveness of ondansetron is relevant to the established role of antidepressants in the management of patients with malignant disease, in whom the prevention of emesis is also important. Further investigation of this possible interaction is recommended.

Differential profile of the CCKB receptor antagonist CI-988 and diazepam in the four-plate test.

The cholecystokininB receptor antagonist CI-988 ([R-(R*,R*)]-4-[[2-[[3-(1H-indol-3-yl)-2-methyl-1-oxo-2- [[(tricyclo[3.3.1.1(3,7)]dec-2-yloxy)carbonyl]amino]- propyl]amino]-1-phenylethyl]amino]-4-oxobutanoic acid compound with 1-deoxy-1-(methylamino)-D-glucitol (1:1)) and the benzodiazepine receptor agonist diazepam were tested for potential anxiolytic effects on punished exploratory behavior in the four-plate test using mice. Diazepam (0.31-5 mg/kg PO) increased the number of shocks taken in a dose-dependent manner, an effect blocked by the benzodiazepine receptor antagonist flumazenil. CI-988 (0.00001-1 mg/kg PO) tended to increase the number of delivered shocks over the chosen dose range; this effect was, however, not dose-related or as large as that produced by diazepam. A limited testing of the 5-hydroxytryptamine3 receptor antagonist ondansetron (0.1 and 1 mg/kg PO) suggested an effect similar to CI-988. These results indicate that distinct and contrasting dose-response profiles exist for these classical and atypical drugs in an animal model of anxiety based on electric shock.