A Nafion(5 pre-coats/2 dip-coats)-modified Pt sensor developed for real-time neurochemical monitoring has now been characterised in vitro for the sensitive and selective detection of nitric oxide (NO). A potentiodynamic profile at bare Pt established +0.9 V (vs. SCE) to be the most appropriate applied potential for NO oxidation. The latter was confirmed using oxyhaemoglobin and N(2), both of which reduced the NO signal to baseline levels. Results indicated enhanced NO sensitivity at the Nafion(5/2) sensor (1.67 +/- 0.08 nA microM(-1)) compared to bare Pt (1.08 +/- 0.20 nA microM(-1)) and negligible interference from a wide range of endogenous electroactive interferents such as ascorbic acid, dopamine and its metabolites, NO(2)(-) and H(2)O(2). The response time of 33.7 +/- 2.7 s was found to improve (19.0 +/- 3.4 s) when the number of Nafion layers was reduced to 2/1 and an insulating outer layer of poly(o-phenylenediamine) added. When tested under physiological conditions of 37 degrees C the response time of the Nafion(5/2) sensor improved to 14.00 +/- 2.52 s. In addition, the NO response was not affected by physiological concentrations of O(2) despite the high reactivity of the two species for each other. The limit of detection (LOD) was estimated to be 5 nM while stability tests in lipid (phosphatidylethanolamine; PEA) and protein (bovine serum albumin; BSA) solutions (10%) found an initial ca. 38% drop in sensitivity in the first 24 h which remained constant thereafter. Preliminary in vivo experiments involving systemic administration of NO and L-arginine produced increases in the signals recorded at the Nafion(5/2) sensor implanted in the striatum of freely-moving rats, thus supporting reliable in vivo recording of NO.

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The increasing scientific interest in nitric oxide (NO) necessitates the development of novel and simple methods of synthesising NO on a laboratory scale. In this study we have refined and developed a method of NO synthesis, using the neutral Griess reagent, which is inexpensive, simple to perform, and provides a reliable method of generating NO gas for in-vivo sensor calibration. The concentration of the generated NO stock solution was determined using UV-visible spectroscopy to be 0.28±0.01 mmol L À1 . The level of NO 2 À contaminant, also determined using spectroscopy, was found to be 0.67±0.21 mmol L À1 . However, this is not sufficient to cause any considerable increase in oxidation current when the NO stock solution is used for electrochemical sensor calibration over physiologically relevant concentrations; the NO sensitivity of bare Pt-disk electrodes operating at +900 mV (vs. SCE) was 1.08 nA lmol À1 L, while that for NO 2 À was 5.9·10 À3 nA lmol À1 L. The stability of the NO stock solution was also monitored for up to 2 h after synthesis and 30 min was found to be the time limit within which calibrations should be performed.

Recent theories propose that both GABA and glutamate signaling are compromised in patients with schizophrenia. These deficits can be observed in several brain regions including the prefrontal cortex (PFC), an area extensively linked to the cognitive dysfunction in this disease and notably affected by NMDA receptor antagonists such as phencyclidine (PCP). We have previously demonstrated that inhibition of the nitric oxide (NO) pathways in the brain, particularly in the PFC, prevents a wide range of PCP-induced behavioral deficits including disruption of prepulse inhibition (PPI). This study investigated the role of GABA(B) receptor signaling and NO in the effects of PCP on PPI. Mice received systemic or prefrontal injections of the GABA(B) receptor agonist baclofen (2.5-5 mg/kg and 1 mM) before PCP treatment (5 mg/kg) and were thereafter tested for PPI. GABA/NO interactions were studied by combining baclofen and the NO synthase inhibitor L-NAME (20 mg/kg) in subthreshold doses. The role of GABA(B) receptors for NO production in vivo was assessed using NO-sensors implanted into the rat PFC. PCP-induced PPI deficits were attenuated in an additive manner by systemic baclofen treatment, whereas prefrontal microinjections of baclofen completely blocked the effects of PCP, without affecting PPI per se. The combination of baclofen and L-NAME was more effective in preventing the effects of PCP than any compound by itself. Additionally, baclofen decreased NO release in the PFC in a dose-related manner. This study proposes a role for GABA(B) receptor signaling in the effects of PCP, with altered NO levels as a downstream consequence. Thus, prefrontal NO signaling mirrors an altered level of cortical inhibition that may be of importance for information processing deficits in schizophrenia.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. a b s t r a c tA reliable method of directly measuring endogenously generated nitric oxide (NO) in real-time and in various brain regions is presented. An extensive characterisation of a previously described amperometric sensor has been carried out in the prefrontal cortex and nucleus accumbens of freely moving rats. Systemic administration of saline caused a transient increase in signal from baseline levels in both the prefrontal cortex (13 ± 3 pA, n = 17) and nucleus accumbens (12 ± 3 pA, n = 8). NO levels in the prefrontal cortex were significantly increased by 43 ± 9 pA (n = 9) following administration of l-arginine. A similar trend was observed in the nucleus accumbens, where an increase of 44 ± 9 pA (n = 8) was observed when compared against baseline levels. Systemic injections of the non-selective NOS inhibitor l-NAME produced a significant decrease in current recorded in the prefrontal cortex (24 ± 6 pA, n = 5) and nucleus accumbens (17 ± 3 pA, n = 6). Finally it was necessary to validate the sensors functionality in vivo by investigating the effect of the interferent ascorbate on the oxidation current. The current showed no variation in both regions over the selected time interval of 60 min, indicating no deterioration of the polymer membrane. A detailed comparison identified significantly greater affects of administrations on NO sensors implanted in the striatum than those inserted in the prefrontal cortex and the nucleus accumbens.