Activation of the NO-ergic system of the nucleus accumbens on presentation of contextual danger signals.

Studies in Sprague-Dawley rats using intracerebral microdialysis combined with HPLC showed that presentation of the animals with a chamber in which they had previously acquired a conditioned reflex fear reaction (combination of a tone and electric shocks) led to increases in extracellular citrulline (a co-product of NO synthesis) in the medial segment of the nucleus accumbens. This increase was prevented by local administration of the NO synthase inhibitor 7-nitroindazole (0.5 mM).

[Sound signals of danger activate the nitrergic system of the medial nucleus accumbens].

It was shown in Sprague-Dawley rats by means of in vivo microdialysis combined with HPLC analysis that presentations to the animals in a home cage of a tone previously paired with a footshock in an experimental chamber produced an increase in extracellular levels of citrulline (an NO co-product) in the medial n. accumbens. The increase was prevented by intraaccumbal infusions of 7-nitroindasole (0.

Effects of blockade of dopamine D2 receptors on extracellular citrulline levels in the nucleus accumbens during performance of a conditioned reflex fear response.

Vital microdialysis studies on Sprague-Dawley rats using HPLC showed that performance of a conditioned reflex fear response was accompanied by an increase in the extracellular level of citrulline (a coproduct of nitric oxide synthesis) in the nucleus accumbens. Administration of the dopamine D(2) receptor antagonist raclopride (10 microM) into the nucleus accumbens decreased the magnitude of the increase in the extracellular citrulline level in this structure during performance of the conditioned reflex fear response but had no effect on its behavioral measures (the level of freezing). Doses increased investigative activity in a novel context which had been inhibited by acquisition of the conditioned reflex fear response, without affecting the investigative behavior of control animals.

[NO-ergic system activation in the nucleus accumbens during presentation of contextual signals of danger].

In Spregue-Dawley rats by means of in vivo microdialysis combined with HPLC analysis, presentation of a chamber in which a conditioned fear response was previously acquired (tone(+) +footshock), resulted in an increase in extracellular level of citrulline (an NO co-product) in the medial nucleus accumbens. This increase was prevented by intraaccumbal infusion of 7-nitraindazole (0.5 mM), an NO synthase inhibitor.

Dopamine D1 receptors regulate the extracellular citrulline level in the nucleus accumbens during performance of a conditioned reflex fear reaction.

Intracerebral microdialysis studies on Sprague-Dawley rats using HPLC showed that performance of a conditioned reflex fear reaction was accompanied by an increase in the extracellular citrulline (a co-product of nitric oxide synthesis) level in the nucleus accumbens. Administration of the selective D1 receptor antagonist SCH-23390 (100 microM) into the nucleus accumbens had no long-lasting effect on the extracellular citrulline level in this structure, but reduced the magnitude of the increase in the citrulline level seen on performance of the conditioned reflex fear reaction. These data suggest that the dopaminergic input of the nucleus accumbens acts via D1 receptors to increase NO synthase activity and nitric oxide production during performance of the conditioned reflex fear reaction.