Role of 5-HT 1A and 5-HT 2C receptors of the dorsal periaqueductal gray in the anxiety- and panic-modulating effects of antidepressants in rats

• Published in: Behavioural brain research 2021-04, Vol.404, p.113159
• Main Authors: Vilela-Costa, Heloisa H, Maraschin, Jhonatan Christian, Casarotto, Plinio C, Sant'Ana, Ana Beatriz, de Bortoli, Valquiria C, Vicente, Maria Adrielle, Campos, Alline Cristina, Guimarães, Francisco S, Zangrossi, Jr, Helio
• Format: Article
• Language: English
• Subjects: Aminopyridines - pharmacology; Animals; Antidepressive Agents - pharmacology; Anxiety - drug therapy; Blotting, Western; Elevated Plus Maze Test; Fluoxetine - pharmacology; Imipramine - pharmacology; Indoles - pharmacology; Male; Open Field Test - drug effects; Panic - drug effects; Periaqueductal Gray - drug effects; Periaqueductal Gray - metabolism; Periaqueductal Gray - physiology; Piperazines - pharmacology; Pyridines - pharmacology; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT1A - drug effects; Receptor, Serotonin, 5-HT1A - metabolism; Receptor, Serotonin, 5-HT1A - physiology; Receptor, Serotonin, 5-HT2C - drug effects; Receptor, Serotonin, 5-HT2C - metabolism; Receptor, Serotonin, 5-HT2C - physiology; Serotonin 5-HT1 Receptor Antagonists - pharmacology
• ISSN: 1872-7549

Antidepressant drugs are first-line treatment for panic disorder. Facilitation of 5-HT receptor-mediated neurotransmission in the dorsal periaqueductal gray (dPAG), a key panic-associated area, has been implicated in the panicolytic effect of the selective serotonin reuptake inhibitor fluoxetine. However, it is still unknown whether this mechanism accounts for the antipanic effect of other classes of antidepressants drugs (ADs) and whether the 5-HT interaction with 5-HT receptors in this midbrain area (which increases anxiety) is implicated in the anxiogenic effect caused by short-term treatment with ADs. The results showed that previous injection of the 5-HT receptor antagonist WAY-100635 in the dPAG blocked the panicolytic-like effect caused by chronic systemic administration of the tricyclic AD imipramine in male Wistar rats tested in the elevated T-maze. Neither chronic treatment with imipramine nor fluoxetine changed the expression of 5-HT receptors in the dPAG. Treatment with these ADs also failed to significantly change ERK1/2 (extracellular-signal regulated kinase) phosphorylation level in this midbrain area. Blockade of 5-HT receptors in the dPAG with the 5-HT receptor antagonist SB-242084 did not change the anxiogenic effect caused by a single acute injection of fluoxetine or imipramine in the Vogel conflict test. These results reinforce the view that the facilitation of 5-HT receptor-mediated neurotransmission in the dPAG is a common mechanism involved in the panicolytic effect caused by chronic administration of ADs. On the other hand, the anxiogenic effect observed after short-term treatment with these drugs does not depend on 5-HT receptors located in the dPAG.