[Decrease in the Activity of Striatal-Enriched Protein-Tyrosine-Phosphatase (STEP) in the Brain of Danio rerio Treated with p-Chlorophenylalanine and Pargyline]

Effect of Prolonged Exposure to Short Daylight and a Tryptophan Hydroxylase Inhibitor on the Behavior and Brain Serotonin System in Danio rerio

We studied the effect of reduced tryptophan hydroxylase (TPH) activity and short daylight exposure on the behavior and the 5-HT system of the brain in D. rerio. Male and female D. rerio were exposed for 30 days to standard (12:12 h light:dark) and short (4:20 h light:dark) photoperiods in the presence or absence of TPH inhibitor (p-chlorophenylalanine, pCPA, 5 mg/liter). On day 31, the fish behavior in the "novel tank diving" test, their sex and body weight were determined, and the levels of pCPA, 5-HT, and its metabolite 5-HIAA were measured by HPLC; the levels of the key genes encoding metabolism enzymes (Tph1a, Tph1b, Tph2, and Mao) and receptors of 5-HT (Htr1aa, Htr2aa) were assessed by real-time PCR with reverse transcription. The short daylight exposure caused masculinization of females, reduced body weight, and motor activity in the "novel tank diving" test, but did not affect the 5-HT system of the brain. Long-term pCPA treatment had no effect on sex and body weight, significantly reduced the 5-HIAA level, but increased Tph1a and Tph2 gene expression in the brain. No effects of the interaction of short daylight and pCPA exposure on the sex, body weight, behavior, and 5-HT system of the brain were found. Thus, a moderate decrease in TPH activity cannot potentiate the negative effects of short daylight exposure on the sex, body weight, behavior, and 5-HT system of D. rerio.

Tryptophan Hydroxylase 2 Deficiency Modifies the Effects of Fluoxetine and Pargyline on the Behavior, 5-HT- and BDNF-Systems in the Brain of Zebrafish (Danio rerio)

The mechanisms of resistance to antidepressant drugs is a key and still unresolved problem of psychopharmacology. Serotonin (5-HT) and brain-derived neurotrophic factor (BDNF) play a key role in the therapeutic effect of many antidepressants. Tryptophan hydroxylase 2 (TPH2) is the rate-limiting enzyme in 5-HT synthesis in the brain. We used zebrafish (Danio rerio) as a promising model organism in order to elucidate the effect of TPH2 deficiency caused by p-chlorophenylalanine (pCPA) on the alterations in behavior and expression of 5-HT-related (Tph2, Slc6a4b, Mao, Htr1aa, Htr2aa) and BDNF-related (Creb, Bdnf, Ntrk2a, Ngfra) genes in the brain after prolonged treatment with two antidepressants, inhibitors of 5-HT reuptake (fluoxetine) and oxidation (pargyline). In one experiment, zebrafish were treated for 72 h with 0.2 mg/L fluoxetine, 2 mg/L pCPA, or the drugs combination. In another experiment, zebrafish were treated for 72 h with 0.5 mg/L pargyline, 2 mg/L pCPA, or the drugs combination. Behavior was studied in the novel tank diving test, mRNA levels were assayed by qPCR, 5-HT and its metabolite concentrations were measured by HPLC. The effects of interaction between pCPA and the drugs on zebrafish behavior were observed: pCPA attenuated “surface dwelling” induced by the drugs. Fluoxetine decreased mRNA levels of Tph2 and Htr2aa genes, while pargyline decreased mRNA levels of Slc6a4b and Htr1aa genes. Pargyline reduced Creb, Bdnf and Ntrk2a genes mRNA concentration only in the zebrafish treated with pCPA. The results show that the disruption of the TPH2 function can cause a refractory to antidepressant treatment.

Age-Related Alterations in the Behavior and Serotonin-Related Gene mRNA Levels in the Brain of Males and Females of Short-Lived Turquoise Killifish (Nothobranchius furzeri)

Short-lived turquoise killifish (Nothobranchius furzeri) have become a popular model organism for neuroscience. In the present paper we study for the first time their behavior in the novel tank diving test and the levels of mRNA of various 5-HT-related genes in brains of 2-, 4- and 6-month-old males and females of N. furzeri. The marked effect of age on body mass, locomotor activity and the mRNA level of Tph1b, Tph2, Slc6a4b, Mao, Htr1aa, Htr2a, Htr3a, Htr3b, Htr4, Htr6 genes in the brains of N. furzeri males was shown. Locomotor activity and expression of the Mao gene increased, while expression of Tph1b, Tph2, Slc6a4b, Htr1aa, Htr2a, Htr3a, Htr3b, Htr4, Htr6 genes decreased in 6-month-old killifish. Significant effects of sex on body mass as well as on mRNA level of Tph1a, Tph1b, Tph2, Slc6a4b, Htr1aa, 5-HT2a, Htr3a, Htr3b, Htr4, and Htr6 genes were revealed: in general both the body mass and the expression of these genes were higher in males. N. furzeri is a suitable model with which to study the fundamental problems of age-related alterations in various mRNA levels related with the brains 5-HT system.