Mirtazapine enhances frontocortical dopaminergic and corticolimbic adrenergic, but not serotonergic, transmission by blockade of α2‐adrenergic and serotonin2C receptors: a comparison with citalopram

Apr 13, 2000The European journal of neuroscience

Mirtazapine boosts dopamine and adrenaline signaling in thinking and emotion areas by blocking specific receptors, unlike citalopram

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Abstract

Mirtazapine showed marked affinity for human alpha2A-adrenergic receptors and serotonin 5-HT2C receptors.

Mirtazapine blocked noradrenaline-induced stimulation at alpha2A-adrenergic receptors.
It abolished serotonin-induced phosphoinositide generation at 5-HT2C receptors.
Mirtazapine demonstrated antagonist properties in vivo, affecting pain response and penile erections.
In freely moving rats, mirtazapine elevated levels of noradrenaline, and dopamine in the frontal cortex, while serotonin levels remained unchanged.
Citalopram increased serotonin levels but did not affect dopamine or noradrenaline.
The differential effects of mirtazapine and citalopram suggest that mirtazapine enhances dopaminergic and adrenergic transmission without influencing serotonergic activity.

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Mirtazapine displayed marked affinity for cloned, human alpha2A-adrenergic (AR) receptors at which it blocked noradrenaline (NA)-induced stimulation of guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]-GTPgammaS) binding. Similarly, mirtazapine showed high affinity for cloned, human serotonin (5-HT)2C receptors at which it abolished 5-HT-induced phosphoinositide generation. Alpha2-AR antagonist properties were revealed in vivo by blockade of UK-14,304-induced antinociception, while antagonist actions at 5-HT2C receptors were demonstrated by blockade of Ro 60 0175-induced penile erections and discriminative stimulus properties. Mirtazapine showed negligible affinity for 5-HT reuptake sites, in contrast to the selective 5-HT reuptake inhibitor, citalopram. In freely moving rats, in the dorsal hippocampus, frontal cortex (FCX), nucleus accumbens and striatum, citalopram increased dialysate levels of 5-HT, but not dopamine (DA) and NA. On the contrary, mirtazapine markedly elevated dialysate levels of NA and, in FCX, DA, whereas 5-HT was not affected. Citalopram inhibited the firing rate of serotonergic neurons in dorsal raphe nucleus, but not of dopaminergic neurons in the ventral tegmental area, nor adrenergic neurons in the locus coeruleus. Mirtazapine, in contrast, enhanced the firing rate of dopaminergic and adrenergic, but not serotonergic, neurons. Following 2 weeks administration, the facilitatory influence of mirtazapine upon dialysate levels of DA and NA versus 5-HT in FCX was maintained, and the influence of citalopram upon FCX levels of 5-HT versus DA and NA was also unchanged. Moreover, citalopram still inhibited, and mirtazapine still failed to influence, dorsal raphe serotonergic neurons. In conclusion, in contrast to citalopram, mirtazapine reinforces frontocortical dopaminergic and corticolimbic adrenergic, but not serotonergic, transmission. These actions reflect antagonist properties at alpha2A-AR and 5-HT2C receptors.

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Mirtazapine enhances frontocortical dopaminergic and corticolimbic adrenergic, but not serotonergic, transmission by blockade of α2‐adrenergic and serotonin2C receptors: a comparison with citalopram

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