Omega-3 fatty acid deficient male rats exhibit abnormal behavioral activation in the forced swim test following chronic fluoxetine treatment: association with altered 5-HT1A and alpha2A adrenergic receptor expression

Abstract

Omega-3 fatty acid deficiency during development leads to enduing alterations in central monoamine neurotransmission in rat brain. Here we investigated the effects of omega-3 fatty acid deficiency on behavioral and neurochemical responses to chronic fluoxetine (FLX) treatment. Male rats were fed diets with (CON, n = 34) or without (DEF, n = 30) the omega-3 fatty acid precursor alpha-linolenic acid (ALA) during peri-adolescent development (P21-P90). A subset of CON (n = 14) and DEF (n = 12) rats were administered FLX (10 mg/kg/d) through their drinking water for 30 d beginning on P60. The forced swimming test (FST) was initiated on P90, and regional brain mRNA markers of serotonin and noradrenaline neurotransmission were determined. Dietary ALA depletion led to significant reductions in frontal cortex docosahexaenoic acid (DHA, 22:6n-3) composition in DEF (-26%, p = 0.0001) and DEF + FLX (-32%, p = 0.0001) rats. Plasma FLX and norfluoxetine concentrations did not different between FLX-treated DEF and CON rats. During the 15-min FST pretest, DEF + FLX rats exhibited significantly greater climbing behavior compared with CON + FLX rats. During the 5-min test trial, FLX treatment reduced immobility and increased swimming in CON and DEF rats, and only DEF + FLX rats exhibited significant elevations in climbing behavior. DEF + FLX rats exhibited greater midbrain, and lower frontal cortex, 5-HT1A mRNA expression compared with all groups including CON + FLX rats. DEF + FLX rats also exhibited greater midbrain alpha2A adrenergic receptor mRNA expression which was positively correlated with climbing behavior in the FST. These preclinical data demonstrate that low omega-3 fatty acid status leads to abnormal behavioral and neurochemical responses to chronic FLX treatment in male rats.

Keywords: 5-HT(1A) autoreceptor; Alpha(2A) adrenergic receptor; Docosahexaenoic acid; Fluoxetine; Forced swim test; Omega-3 fatty acid; Serotonin transporter; Tryptophan hydroxylase-2.

Figure 1

PFC DHA (22:6n-3) composition (A), arachidonic acid (AA, 20:4n-6) composition (B), and the AA:DHA ratio (C) in CON, CON+FLX, DEF, and DEF+FLX rats (n=8–10/group). Values (wt % total fatty acids) are group mean ± S.E.M. **P≤0.01, ***P≤0.001 vs. CON and CON+FLX rats.

Figure 2

Cumulative mean immobility (A), swimming (B), and climbing (C) scores during the 15-min pretest in CON, CON+FLX, DEF, and DEF+FLX rats (n=10–17/group). Values are group mean ± S.E.M. *P≤0.05 vs. CON and DEF, ^#P≤0.05 vs. CON+FLX.

Figure 3

Cumulative mean immobility (A), swimming (B), and climbing (C) scores during the 5-min test trial in CON, CON+FLX, DEF, and DEF+FLX rats (n=10–17/group). Values are group mean ± S.E.M. *P≤0.05, **P≤0.01 vs. CON and DEF, ^#P≤0.05 vs. CON+FLX.

Figure 4

5-HT_1A, 5-HT_2A, and 5-HT_2C mRNA expression in the PFC (A), and SERT, TPH-2, and 5-HT_1A mRNA expression in the midbrain (B) of CON, CON+FLX, DEF, and DEF+FLX rats (n=11–14/group). Values (mRNA/GAPDH mRNA) are group mean ± S.E.M. *P≤0.05 vs. CON and DEF, ^##P≤0.01 vs. CON+FLX rats.

Figure 5

Noradrenaline transporter (NAT)(A), alpha2A adrenergic receptor (α_2A)(B), and tyrosine hydroxylase (TH)(C) mRNA expression in the midbrain of CON, CON+FLX, DEF, and DEF+FLX rats (n=11–14/group). Values (mRNA/GAPDH mRNA) are group mean ± S.E.M. *P≤0.05, **P≤0.01 vs. CON, ^#P≤0.05 vs. CON+FLX rats.