Anxiolytic-like effect of way-100635 microinfusions into the median (but not dorsal) raphe nucleus in mice exposed to the plus-maze: influence of prior test experience.
Studies in several laboratories have confirmed the anxiolytic potential of a wide range of 5-HT(1A) receptor antagonists in rats and mice, with recent evidence pointing to a postsynaptic site of action in the ventral hippocampus. It would, therefore, be predicted that blockade of 5-HT(1A) somatodendritic autoreceptors in the midbrain raphe nuclei should produce anxiogenic-like effects. To test this hypothesis, we investigated the effects of WAY-100635 microinfusions (0, 1.0 or 3.0 microg in 0.1 microl) into the dorsal (DRN) or median (MRN) raphe nuclei on behaviours displayed by male Swiss-Webster mice in the elevated plus-maze. As this test is sensitive to prior experience, the effects of intra-raphe infusions were examined both in maze-naive and maze-experienced subjects. Sessions were videotaped and subsequently scored for conventional indices of anxiety (open arm avoidance) and locomotor activity (closed arm entries), as well as a range of ethological measures (e.g. risk assessment). In maze-naive mice, intra-MRN (but not intra-DRN) infusions of WAY-100635 (3.0 microg) increased open arm exploration and reduced risk assessment. Importantly, these effects could not be attributed to a general reduction in locomotor activity. A similar, though somewhat weaker, pattern of behavioural change was observed in maze-experienced animals. This unexpected anxiolytic effect of 5-HT(1A) autoreceptor blockade in the MRN cannot be accounted for by a disinhibition of 5-HT release in forebrain targets (e.g. hippocampus and amygdala), where stimulation of postsynaptic 5-HT(1A) receptors enhances anxiety-like responses. However, as the MRN also projects to the periaqueductal gray matter (PAG), an area known to be sensitive to the anti-aversive effects of 5-HT, it is argued that present results may reflect increased 5-HT release at this crucial midbrain locus within the neural circuitry of defense.
Canto-de-Souza
Azair
A
Department Psicologia, Universidade Federal de São Carlos-UFSCar, São Carlos, SP, Brazil.
Luiz Nunes-de-Souza
Ricardo
R
Rodgers
Robert John
RJ
D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D001007:Anxiety / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008845:Microinjections; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology*; D011725:Pyridines / Q000494:pharmacology*; D011903:Raphe Nuclei / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000378:metabolism; D044263:Receptors, Serotonin, 5-HT1; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology*
D014151:Anti-Anxiety Agents; D010879:Piperazines; D011725:Pyridines; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists; D012701:Serotonin; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide