Michaela M. Kraus

The nitric oxide system modulates the in vivo release of acetylcholine in the nucleus accumbens induced by stimulation of the hippocampal fornix/fimbria-projection

Nerve signals from the hippocampus to the nucleus accumbens (NAc) are transmitted through a glutamatergic pathway via the fornix/fimbria fibres. The aim of the present study was to investigate whether cholinergic neurons are activated by this projection and whether the nitric oxide (NO) system is also involved in the signal transduction within this nucleus. For this purpose, the NAc of urethane‐anaesthetized rats was superfused, by the push‐pull technique, with compounds that influence the NO system while the fornix/fimbria was electrically stimulated for short periods. The amount of acetylcholine (ACh) released in the superfusate was then determined. Electrical stimulation of the fornix/fimbria increased the ACh output in the NAc. This effect was abolished by superfusion with tetrodotoxin and decreased by superfusion with the glutamate receptor antagonists AP‐5 and DNQX indicating the involvement of action potentials and glutamate. Superfusion with the inhibitor of neuronal NO synthase, NS 2028 also diminished stimulation‐evoked ACh release. The NO donor PAPA/NO increased basal release. Simultaneous application of PAPA/NO and electrical stimulation led to an over‐additive increase of ACh release. The effect of PAPA/NO on stimulation‐evoked release was also abolished by NS 2028. The selective inhibitor of phosphodiesterase type 5 (PDE 5), 5‐[2‐ethoxy‐5‐(morpholinylacetyl)phenyl]‐1,6‐dihydro‐1‐methyl‐3‐propyl‐7H‐pyrazolo[4,3‐d]pyrimidin‐7‐one methanesulphanate monohydrate also enhanced stimulation‐induced release of ACh. Our findings indicate, that action potentials propagated by the fornix/fimbria to the NAc release glutamate which increases ACh release predominantly via NMDA receptors. In addition, nitrergic neurons are activated to enhance NO synthesis. The released NO seems to exert, via cGMP, a potent facilitatory role in the transduction and processing of signals from the hippocampus within the NAc, while the PDE 5 decreases the effects of NO.

Influence of NOS inhibitors on changes in ACH release and NO level in the brain elicited by amphetamine neurotoxicity.

We studied the possible role of neurotoxicity in the d,l-amphetamine (AMPH)-induced release of acetylcholine (ACH) in the nucleus accumbens (Nac) and the involvement of endogenous NO in this process. For determination of ACH release the Nac was superfused using the push-pull-technique. NO was directly measured using the electron paramagnetic resonance technique. Repeated administration of AMPH increased ACH release by about 400%. N-nitro-L-arginine (L-NNA) and 7-nitroindazole (7-NI) nearly abolished the AMPH-induced increase in ACH release. AMPH increased NO as well as lipid peroxidation (LPO) products in the cortex. L-NNA and 7-NI substantially diminished NO increase. AMPH-evoked LPO was only slightly reduced by these compounds. It is concluded that AMPH enhances ACH release through increased NO synthesis and induces neurotoxicity via NO and by LPO independent NO generation.

Influence of the hippocampus on amino acid utilizing and cholinergic neurons within the nucleus accumbens is promoted by histamine via H1 receptors

The influence of the neurotransmitter histamine on spontaneous and stimulation‐evoked release of glutamate, aspartate, GABA and ACh in the nucleus accumbens (NAc) was investigated in vivo.

7-nitroindazole, nNOS inhibitor, attenuates amphetamine-induced amino acid release and nitric oxide generation but not lipid peroxidation in the rat brain

Summary.The aim of the present study was to elucidate whether amphetamine modulates the output of the neurotransmitters glutamate, aspartate, GABA and acetylcholine (ACh) in nucleus accumbens (NAc) as well as the formation of lipid peroxidation (LPO) and nitric oxide (NO). D,L-amphetamine (AMPH, 5 mg/kg, i.p., 4 times every 2 h) was injected into anaesthetized rats and the release of neurotransmitters in the NAc, tissue content of NO and LPO products were determined.While AMPH increased the release of aspartate, GABA and ACh in the NAc, the glutamate release was not affected. Levels of NO and LPO products were elevated in striatum and cortex. Pretreatment with the neuronal NO synthase inhibitor 7-nitroindazole (50 mg/kg, i.p.) was highly effective in abating the rise of the neurotransmitter release and NO generation but failed to influence the intensity of LPO elicited by the AMPH administration.These findings suggest that activation of NO synthesis is a potent factor in the AMPH-induced neurotransmitter release and that activation of NO synthesis and LPO by AMPH are not parallel processes.

Dizocilpine inhibits amphetamine-induced formation of nitric oxide and amphetamine-induced release of amino acids and acetylcholine in the rat brain.

Glutamate receptor activation participates in mediation of neurotoxic effects in the striatum induced by the psychomotor stimulant amphetamine. The effects of the non-competitive NMDA receptor antagonist dizocilpine (MK-801) on amphetamine-induced toxicity and formation of nitric oxide (NO) in both striatum and cortex and on induced transmitter release in the nucleus accumbens were investigated. Repeated, systemic application of amphetamine elevated striatal and cortical lipid peroxidation and NO production. Moreover, amphetamine caused an immediate release of acetylcholine and aspartate and a delayed release of GABA in the nucleus accumbens. Surprisingly, glutamate release was not affected. Dizocilpine abolished the amphetamine-induced lipid peroxidation and NO production in striatum and cortex and diminished the elevation of neurotransmitter release. These findings suggest that amphetamine evokes neurotoxic effects in both striatal and cortical brain areas that are prevented by inhibiting NMDA receptor activation. The amphetamine-induced acetylcholine, aspartate and GABA release in the nucleus accumbens is also mediated through NMDA receptor-dependent mechanisms. Interestingly, the enhanced aspartate release might contribute to NMDA receptor activation in the nucleus accumbens, while glutamate does not seem to mediate amphetamine-evoked transmitter release in this striatal brain area.

Comparative effects of NO-synthase inhibitor and NMDA antagonist on generation of nitric oxide and release of amino acids and acetylcholine in the rat brain elicited by amphetamine neurotoxicity

Abstract: The aim of this study was to clarify the role of nitric oxide (NO) and lipid peroxidation (LPO) processes as well as the contribution of various neurotransmitters in pathophysiological mechanisms of neurotoxicity induced by amphetamine (AMPH). NO level was determined directly in brain tissues using electron paramagnetic resonance spectroscopy technique. The content of the products of lipid peroxidation (LPO) was measured spectrophotometrically as thiobarbituric acid reactive species (TBARS). The output of neurotransmitter amino acids (glutamate, aspartate, and GABA) and acetylcholine (ACH) was monitored in nucleus accumbens (NAc) by push‐pull technique with HPLC detection. Repeated, systemic application of AMPH elevated striatal and cortical NO generation and LPO production. Moreover, administration of AMPH led to a marked and long‐lasting increase of ACH release. Surprisingly, while glutamate output was not affected, aspartate release was enhanced 30 to 50 min after each AMPH injection. The release rate of GABA was also elevated. The selective NO‐synthase inhibitor 7‐nitroindazole (7‐NI) was highly effective in abating the rise in the neurotransmitter release induced by the AMPH. The NOS inhibitor also abolished the increase of NO generation produced by AMPH, but did not influence the intensity of LPO elicited by the AMPH administration. Pretreatment with the noncompetitive NMDA receptor antagonist dizocilpine (MK‐801) completely prevented increase of NO generation and TBARS formation induced by multiple doses of AMPH. Dizocilpine also abolished the effect of the psychostimulant drug on the release of neurotransmitters ACH, glutamate, aspartate, and GABA in the NAc. Our findings suggest a key role of NO in AMPH‐induced transmitter release, but not in the formation of LPO products. It appears that AMPH enhances release of ACH and neurotransmitter amino acids through increased NO synthesis and induces neurotoxicity via NO and also by NO‐independent LPO.

Influence of parafascicular thalamic input on neuronal activity within the nucleus accumbens is mediated by nitric oxide — An in vivo study

AIMS Thalamostriatal fibers are involved in cognitive tasks such as acquisition, learning, processing of sensory events, and behavioral flexibility and might play a role in Parkinsons disease. The aim of the present study was the in vivo electrochemical characterization of the projection from the lateral aspect of the parafascicular thalamus (Pfl) to the dorsolateral aspect of the nucleus accumbens (dNAc). Since nitric oxide (NO) plays a crucial role in striatal synaptic transmission, its implication in Pfl-evoked signaling within the dNAc was investigated. MAIN METHODS The Pfl was electrically stimulated utilizing paired pulses and extracellular potentials were recorded within the dNAc. Simultaneously, the dNAc was superfused using the push-pull superfusion technique for local application of compounds and for assessing the influence of NO on release of glutamate, aspartate and GABA. KEY FINDINGS Stimulation of the Pfl evoked a negative-going component at 9-14 ms followed by a positive-going component at 39-48 ms. The early response was current-dependent and diminished by superfusion of the dNAc with tetrodotoxin, kynurenic acid or N(G)-nitro-l-arginine methyl ester (L-NAME), while 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPA/NO) increased this evoked potential. Transmitter release was inhibited by L-NAME and facilitated by PAPA/NO. SIGNIFICANCE This study describes for the first time in vivo extracellular electrical responses of the dNAc on stimulation of the Pfl. Synaptic transmission within the dNAc on stimulation of the Pfl seems to be facilitated by NO.

Facilitation of short-term memory by histaminergic neurons in the nucleus accumbens is independent of cholinergic and glutamatergic transmission

Here, we have investigated whether learning and/or short‐term memory was associated with release of ACh and glutamate in the rat nucleus accumbens (NAc). Additionally, neurotransmitter release in the NAc was assessed during facilitation of cognitive processes by antagonists of inhibitory histamine autoreceptors.

Modulation of acetylcholine release by histamine in the nucleus accumbens

Cholinergic neuron systems of the brain seem to play a key role in cognitive processes such as attention, learning and mnemonic function. However, other neurotransmitter systems, including histaminergic neurons, also influence cognition. We have shown that H3 receptor antagonists improve memory in rats [1]. Improvement of memory by other histaminergic drugs has also been shown [2–4]. The role of histaminergic neurons in the nucleus accumbens (Nac) is of special interest since this brain region possesses a high number of cholinergic neurons and a dense network of histaminergic fibers which tightly surround neuronal cell bodies. The Nac seems also to be involved in several forms of learning [4]. The aim of the present study was to investigate the influence of histaminergic neurons on the release of acetylcholine (ACh) in the Nac of freely moving rats.

Use of Push-Pull Superfusion Technique for Identifying Neurotransmitters Involved in Brain Functions: Achievements and Perspectives

The push-pull superfusion technique (PPST) is a procedure for in vivo examination of transmitter release in distinct brain areas. This technique allows to investigate dynamics of transmitter release both under normal and experimentally evoked conditions. The PPST can be modified so that it is possible to determine release of endogenous transmitters simultaneously with electroencephalogram (EEG) recordings, recordings of evoked potentials or the on-line determination of endogenous nitric oxide (NO) released into the synaptic cleft. Because of the good time resolution, the method provides further the possibility to modify the collection periods of superfusates depending on the neuronal function that is analyzed. For instance, investigation of central cardiovascular control, behavioral tasks or mnemonic processes requires very short collection periods, because changes in transmitter release occur within seconds. Even more important is the time resolution when rates of transmitter release are correlated with evoked extracellular potentials or EEG recordings. This review provides an overview of the different devices which might be combined with the PPST and perspectives for future work.