Conflict behavior and dynamics of monoamines of various brain nuclei in rats

Hippocampal serotonergic system is involved in anxiety-like behavior induced by corticotropin-releasing factor

To clarify the interaction between anxiety-like behavior produced by corticotropin-releasing factor (CRF) and the 5-HT system, we investigated the effects of intracerebroventricular (i.c.v.) administration of CRF on an elevated plus-maze performance as indices of anxiety, measuring extracellular levels of 5-HT in the ventral hippocampus using an in vivo brain dialysis method in rats. The time spent in the open arms of the maze and the number of open arm entries were decreased in a dose-dependent manner by the administration of CRF (0.3-1.0 microg/rat). These effects of CRF were prevented by pretreatment with a 5-HT(1A) receptor agonist, 8-OH-DPAT (0.5 mg/kg, s.c.). In biochemical studies, CRF increased 5-HT release about 150-250% above baseline in the ventral hippocampus and this elevation was significantly inhibited by a CRF receptor antagonist, alpha-Helical CRF(9-41) (50 mug/rat), and 5-HT(1A) receptor agonist, 8-OH-DPAT (0.5 mg/kg, s.c.). These results suggested that the anxiety-like effect produced by CRF may have involved increased 5-HT transmission in the ventral hippocampus. Taken with the evidence for hypersecretion of CRF in patients with depression and anxiety-related disorders, our findings lead to the intriguing hypothesis that interaction between CRF and 5-HT, especially in the ventral hippocampus, plays a role in the etiology of affective and anxiety disorders.

Nitric oxide participates in the stimulatory and neurotoxic action of endothelin on rat striatal dopaminergic neurons

1. Our method of real-time monitoring of dopamine release from rat striatal slices revealed that endothelin (ET)-3-induced dopamine release was inhibited by NG-methyl-L-arginine (L-NMMA; 1 mM), an inhibitor of nitric oxide (NO) synthase, while NG-methyl-D-arginine (D-NMMA; 1 mM), an inactive isomer of L-NMMA, had no effect. 2. The inhibition of L-NMMA (0.1 mM) became apparent when tissues were pretreated with tetrodotoxin (1 microM) for 30 min and subsequently exposed to ET-3 (4 microM). 3. L-NMMA (0.1 and 1 mM) dose dependently protected against ET-3-triggered hypoxic/hypoglycemic impairment of striatal responses to high K+. 4. Thus, NO may work as a promoter in mediation of the stimulatory and neurotoxic action of ET-3 on the striatal dopaminergic system, presumably by interacting with interneurons in the striatum.

Conflict situation increases serotonin release in rat dorsal hippocampus: in vivo study with microdialysis and Vogel test

The release of serotonin (5-hydroxytryptamine, 5-HT) in the dorsal hippocampus was measured using an in vivo microdialysis method in rats subjected to the Vogel type conflict test. The conflict situation significantly increased 5-HT release in the dorsal hippocampus. Midazolam (0.75 and 1.5 mg/kg i.p.) suppressed the dosage-dependently this increased 5-HT release, an inhibition closely associated with the attenuation of conflict behavior. These findings suggest that the activation of serotonergic neuronal activity in the dorsal hippocampus is linked to mediation of anxiety-related behavior.

Serotonergic innervation of the hippocampus and nucleus accumbens septi and the anxiolytic-like action of the 5-HT3 receptor antagonists

The roles of hippocampus (HP) and the nucleus accumbens septi (NAS) in the anxiolytic activity of two 5-HT3 receptor antagonists were studied in two animal models of anxiety, in rats. Injection of tropisetron (0.005 and 0.01 microgram) or ondansetron (1.0 and 2.5 micrograms) into the hippocampus increased punished consumption of water in the Vogel conflict test. In the open field test neither 5-HT3 receptor antagonists had anxiolytic-like effects. Tropisetron (0.01 and 0.025 microgram) injected into the NAS caused a marked increase in punished drinking, while ondansetron (0.01-15.0 micrograms) had no effect. In the open field test, tropisetron (0.001, 0.005 and 0.01 microgram) and ondansetron (1.0 and 2.5 micrograms) given to the NAS increased the number of entries into the central part of the open-field, and the time spent in the central sector of the arena. Depletion of 5-HT significantly enhanced the anxiolytic-like effect of intra-NAS-injected tropisetron in the open field, at the dose of 0.005 microgram. Moreover, 5,7-DHT lesions produced a tendency to increase motor activity in tropisetron-treated rats. Both hippocampal and accumbens 5-HT3 receptors seem to contribute to the anxiolytic-like effects of 5-HT3 antagonists in the Vogel test. It also appears that this effect of 5-HT3 receptor antagonists is related to their action on postsynaptic 5-HT3 receptors within the NAS, and depends on the functional state of the 5-HT innervation ascending from the raphe nuclei. Thus, the present data add more arguments for the more specific involvement of this limbic nucleus in emotional control.

Nebracetam (WEB 1881FU) prevents N-methyl-D-aspartate receptor-mediated neurotoxicity in rat striatal slices

The effects of nebracetam were investigated on N-methyl-D-aspartate (NMDA) receptor- and voltage-operated Ca2+ channels (VOCC)-mediated neural dysfunction by directly monitoring the real-time dynamics of dopamine released from rat striatal slices. Nebracetam (10(-5) and 10(-4) M) completely protected against striatal dopaminergic impairment induced by L-glutamate and NMDA, respectively. BAY K-8644-evoked striatal dysfunction was not blocked by nebracetam (10(-4) M). Therefore, nebracetam seems to produce a neuroprotective action by interacting, at least in part, with NMDA receptor-operated Ca2+ channels.