Neurochemical and behavioural characterization of milnacipran, a serotonin and noradrenaline reuptake inhibitor in rats.
BACKGROUND
The prefrontal cortex is implicated in the pathophysiology of depression, and hypoactivity of this brain area has been found in depressed patients. Reduced function of the serotonergic and noradrenergic systems is another feature of depression.


OBJECTIVE
The present study was aimed at characterizing neurochemically and behaviorally the serotonin and noradrenaline reuptake inhibitor (SNRI), milnacipran, in the prefrontal cortex in comparison with tricyclic antidepressants and selective serotonin reuptake inhibitors.


METHODS
Sodium-dependent monoamine uptake measurement, radioligand binding assays, microdialysis procedure, forced swimming test and conditioned fear stress test were carried out in rats.


RESULTS
Milnacipran selectively inhibited sodium-dependent [(3)H]serotonin (5-hydroxytryptamine, 5-HT) and [(3)H]noradrenaline (NA) uptake into the synaptosomes from rat cerebral cortex (IC(50)=28.0 and 29.6 nM, respectively) without any affinities for various neuroreceptors. In the medial prefrontal cortex, milnacipran (10 and 30 mg/kg, PO) caused a dose-related increase in the extracellular levels of 5-HT and NA with similar potency, whereas imipramine (10 and 30 mg/kg, PO) caused a dominant increase in the output of NA compared to 5-HT. Milnacipran (30 and 60 mg/kg, PO) significantly reduced the duration of both the immobility time in the forced swimming test and the freezing time in the conditioned fear stress test in rats, which are animal behavioral models for depression and anxiety, respectively. Imipramine and maprotiline were active in the former test, but not in the latter. Fluoxetine and fluvoxamine on the other hand were more active in the conditioned fear test.


CONCLUSIONS
These findings show that milnacipran acts as a SNRI in vitro and in vivo and may be useful for the treatment of anxiety as well as depression.
Asahi Kasei Corporation, 9-1 Kanda, Mitoshiro-cho, Chiyoda-ku, Tokyo 101-8481, Japan. mochizuki.db@om.asahi-kasei.co.jp
Daisuke
D
Mochizuki
Ryuichi
R
Tsujita
Shinji
S
Yamada
Koh
K
Kawasaki
Yuji
Y
Otsuka
Shinji
S
Hashimoto
Tsuyoshi
T
Hattori
Yoshihisa
Y
Kitamura
Naomasa
N
Miki
D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D003213:Conditioning, Psychological; D003521:Cyclopropanes / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005239:Fear / Q000187:drug effects / Q000523:psychology; D005473:Fluoxetine / Q000494:pharmacology; D016666:Fluvoxamine / Q000494:pharmacology; D007099:Imipramine / Q000494:pharmacology; D008297:Male; D008376:Maprotiline / Q000494:pharmacology; D017551:Microdialysis; D000078764:Milnacipran; D008995:Monoamine Oxidase / Q000187:drug effects / Q000378:metabolism; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D009638:Norepinephrine / Q000493:pharmacokinetics; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D011956:Receptors, Cell Surface / Q000378:metabolism; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism / Q000493:pharmacokinetics; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D013550:Swimming; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors
D018759:Adrenergic Uptake Inhibitors; D003521:Cyclopropanes; D005473:Fluoxetine; D016666:Fluvoxamine; D007099:Imipramine; D008376:Maprotiline; D000078764:Milnacipran; D008995:Monoamine Oxidase; D008996:Monoamine Oxidase Inhibitors; D009638:Norepinephrine; D011956:Receptors, Cell Surface; D011985:Receptors, Serotonin; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors