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.

Origin of endogenous nitric oxide released in the nucleus accumbens under real-time in vivo conditions.

AIMS: Nitric oxide (NO), is a simple but multifarious molecule. It is implicated in physiological and pathological processes within the striatum, mainly in the nucleus accumbens (NAc). The aim of the present study was to determine the origin of NO in the NAc of anaesthetized rats by applying various compounds known to modulate the release of NO when applied either systemically or locally. MAIN METHODS: Real-time monitoring of NO was carried out by introducing an amperometric NO sensor into the outer tubing of a push-pull cannula. For local application of substances, the push-pull superfusion technique was used. KEY FINDINGS: An overdose of urethane (i.p.) or superfusion of the NAc with tetrodotoxin (TTX) led to a fall of NO release in the NAc. The NO synthase (NOS) inhibitors 7-nitroindazolmonosodiumsalt (7-NINA, neuronal NOS selective) and N-nitro-L-arginine (L-NNA, NOS selective) decreased release of NO when applied i.p. or locally. Superfusion of the NAc with N-methyl-D-aspartate (NMDA) elicited a dose dependent increase of NO release. SIGNIFICANCE: Combination of an amperometric NO sensor for real-time monitoring of NO release with the push-pull superfusion technique showed that NO released in the NAc is, at least to a great extent, of neuronal origin. The enhanced release of NO elicited by locally applied NMDA demonstrates that activation of NMDA receptors facilitates NO synthesis, thus underlining the functionality of NO targets within the NAc.

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 Parkinson's 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.

Effect of early compared with delayed enteral nutrition on endocrine function in patients with traumatic brain injury: an open-labeled randomized trial.

BACKGROUND: Traumatic brain injury (TBI) results in a hypermetabolic and hypercatabolic status in which adequate nutrition support is essential to improve clinical outcome. The endocrine system of a patient with TBI is also affected and may play a critical role in either the metabolic or the immunologic response to the trauma. In the present study, the effect of standard, delayed enteral feeding (DEF), compared with early (within 24-48 hours) enteral feeding (EEF), on the endocrine function of patients with TBI was investigated. METHODS: This comparative, prospective, open-labeled, randomized study included TBI patients admitted to the intensive care unit (ICU). Injury severity was assessed by the Glasgow Coma Scale and predicted mortality by the Acute Physiology and Chronic Health Evaluation II. Twenty-five patients received DEF and 34 patients received EEF. The effect of the onset of nutrition on pituitary, thyroidal, gonadal, and adrenal function was investigated on days 6 and 12 after admission to the hospital. RESULTS: Levels of thyroid-stimulating hormone, free triiodothyronine, free thyroxine, and testosterone (in males) of DEF patients declined in comparison to levels of the day of admission to the ICU. The decrease of hormonal values was less pronounced in the EEF group. Cortisol concentrations rose in the DEF group; a lesser hormonal change was found in the EEF group. Deaths during the study for the DEF group and EEF group were 2 and 3, respectively. CONCLUSIONS: EEF may exert beneficial effects on the hormonal profile of TBI patients, possibly contributing to a better clinical outcome in this patient group.

Chronic aortic denervation decreases anxiety and impairs social memory in rats.

AIMS: The present study investigates anxiety-like behaviour and social cognitive performance in rats with chronic aortic denervation. MAIN METHODS: The aortic depressor nerve was bilaterally transected in Wistar rats, causing an almost complete disruption of baroreceptors. Bilateral aortic denervated (bAD), sham-operated (SHAM), and intact (CTRL) rats performed an elevated plus-maze test and an olfactory social memory test, one and three months after operation. Blood pressure and heart rate were monitored in all animals. KEY FINDINGS: Systolic blood pressure, blood pressure lability and heart rate were elevated in bAD rats compared to SHAM and CTRL rats. In the elevated plus-maze test, bAD rats spent clearly more time in investigating open arms and performed more open arm entries than SHAM and CTRL rats during both testing sessions. The olfactory social memory test revealed that acquisition time during first contact with a juvenile rat did not differ between the groups of rats. The recognition time spent by SHAM and CTRL group of rats was distinctly decreased in comparison to the acquisition time, an indication of social memory. bAD rats investigated the juvenile rat during the second contact to a similar extent than during the first contact, both one and three months after denervation. SIGNIFICANCE: These results suggest that bilateral aortic denervation induces chronic neurogenic hypertension and elevated blood pressure lability, decreases anxiety-like behaviour and deteriorates social memory in rats while acquiring of social information is not affected.

Nandrolone abuse decreases anxiety and impairs memory in rats via central androgenic receptors.

Anabolic androgenic steroids (AASs) affect areas of the central nervous system, which are involved in emotional and cognitive responses such as sexuality, anxiety, and memory. In the present study we imitated the abuse of AASs by administering high doses of the AAS nandrolone decanoate (ND) to rats. Thereafter rats were exposed to an elevated plus-maze and an olfactory social memory test to evaluate their anxiety-like and cognitive behaviour. To reveal whether these emotional and cognitive changes evoked by ND were caused via direct activation of androgenic receptors (ARs) in the brain, the AR antagonist flutamide (FL) was administered intracerebroventricularly (i.c.v.). Male rats were randomly divided in four groups, one group received 15 mg/kg ND subcutaneously, once daily for 6 wk (ND group). In the second group, in addition to ND, a daily dose of 5 microg FL was injected i.c.v. also for 6 wk (ND+FL group). The third group of rats received only FL and in the control group the vehicle was injected. The ND group clearly spent more time investigating the open arms in the maze test and recognizing the juvenile during the olfactory social memory test in comparison to the control group. In the ND+FL group rats showed similar emotional behaviour and cognitive ability to that of the control group. Injection of FL alone did not affect either anxiety or memory. These results indicate that repeated, high-dose administration of ND decreases anxiety and impairs memory in rats via direct activation of central ARs.

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.