Activation by serotonin and noradrenaline of vasopressin and oxytocin expression in the mouse paraventricular and supraoptic nuclei

Abstract

Noradrenaline and serotonin are known to control arginine-vasopressin (AVP) and oxytocin (OT) secretion in the systemic circulation. The aim of the current study was to investigate whether these monoamines are also able to influence AVP and OT expression in the paraventricular (PVN) and supraoptic nuclei (SON). To test this hypothesis, we used the Tg8 transgenic mice KO for the monoamine oxidase-A gene, which present high levels of noradrenaline and serotonin in the brain. AVP and OT expression were evaluated at peptide and mRNA levels by immunohistochemistry, enzyme immunoassay, and in situ hybridization. Compared with wild type, the amounts of AVP, OT, AVP mRNA, and OT mRNA were increased in the PVN and SON in Tg8 mice. To distinguish the respective contributions of noradrenaline and serotonin to these modifications, we treated Tg8 mice with a synthesis inhibitor of either catecholamines [alpha-methylparatyrosine (alpha-MPT)] or serotonin [parachlorophenylalanine (pCPA)]. Administration of alpha-MPT to Tg8 mice induced a decline in the amounts of AVP, OT, and their mRNA in the PVN and SON. The pCPA treatment in Tg8 mice was also associated with a decrease in OT expression in the PVN and SON and in AVP expression in the PVN, but not in the SON. These results suggest that noradrenaline may activate AVP and OT expression in the PVN and SON. Likewise, serotonin is proposed to stimulate AVP and OT expression in the PVN and only OT expression in the SON.

Fig. 1.

Immunohistochemical detection of arginine-vasopressin in the PVN (A–D) and in the SON (E–H) of C3H mice (A, E), Tg8 mice (B, F), α-MPT-treated Tg8 mice (C, G), and pCPA-treated Tg8 mice (D, H). The mutation is associated with an increase in AVP immunoreactivity in the PVN (B vs A) and in the SON (F vs E). No difference was observed between Tg8 and saline-control Tg8 mice. The treatment by α-MPT in Tg8 mice is correlated with a decline in AVP immunoreactivity in the PVN (C) as well as in the SON (G) compared with saline-control Tg8 mice (the same as B, F). In pCPA-treated Tg8 mice the intensity of labeling is also decreased in the PVN (D) and in the SON (H) compared with saline-control Tg8 mice.III, Third ventricle; OC, optic chiasma. Scale bar, 50 μm.

Fig. 2.

Dark-field microphotographs representing thein situ hybridization signal of AVP mRNA on emulsion-coated sections in C3H mice (A, E), Tg8 mice (B, F), α-MPT-treated Tg8 mice (C, G), and pCPA-treated Tg8 mice (D, H). Compared with C3H mice (A, E), the hybridization signal is increased but distributed similarly both in the PVN (B) and the SON (F) in Tg8 mice. No difference was detected between Tg8 mice and saline-control Tg8 mice. In α-MPT-treated Tg8 mice the hybridization signal is decreased in the PVN (C) as well as in the SON (G) compared with saline-control Tg8 mice (the same as B, F). In pCPA-treated Tg8 mice the density of silver grains is decreased in the PVN (D) compared with saline-control Tg8 mice. In contrast, no difference is observed between pCPA-treated Tg8 mice and saline-control Tg8 in the SON (G).III, Third ventricle; OC, optic chiasma. Scale bars, 50 μm.

Fig. 3.

Immunohistochemical detection of oxytocin in the PVN (A–D) and in the SON (E–H) of C3H mice (A, E), Tg8 mice (B, F), α-MPT-treated Tg8 mice (C, G), and pCPA-treated Tg8 mice (D, H). Compared with C3H mice, OT-immunostained neurons are stained more strongly and are more numerous in Tg8 mice both in the PVN (B) and the SON (E). In α-MPT-treated Tg8 mice the intensity of OT immunoreactivity as well as the number of OT-immunopositive neurons declines in the PVN (C) and in the SON (G) compared with saline-control Tg8 mice (the same as B,F). Likewise, the treatment by pCPA in Tg8 mice is associated with a decrease in the number of OT-immunostained cell bodies and in the intensity of OT labeling both in the PVN (D) and the SON (H) compared with saline-control Tg8 mice. III, Third ventricle; OC, optic chiasma. Scale bar, 50 μm.

Fig. 4.

Dark-field microphotographs representing thein situ hybridization signal of OT mRNA on emulsion-coated sections in C3H mice (A, E), Tg8 mice (B, F), α-MPT-treated Tg8 mice (C, G), and pCPA-treated Tg8 mice (D, H). The hybridization signal is enhanced in Tg8 mice both in the PVN (B) and the SON (F) compared with C3H mice (A, E). In α-MPT-treated Tg8 mice the hybridization signal is reduced in the PVN (C) as well as in the SON (G) compared with saline-control Tg8 mice (the same as B, F). In pCPA-treated Tg8 mice the density of silver grains is also decreased in the PVN (D) and in the SON (G) compared with saline-control Tg8 mice. III, Third ventricle; OC, optic chiasma. Scale bar, 50 μm.

Fig. 5.

Immunohistochemical detection of noradrenaline in the PVN (A–C) and in the SON (D, E) of C3H mice (A, D), Tg8 mice (B, E), and α-MPT-treated Tg8 mice (C). Compared with C3H mice (A), both the density of immunostained fibers and the staining intensity are increased in the PVN in Tg8 mice (B). Likewise, the labeling intensity of varicosities surrounding unstained cell bodies is enhanced in the SON of Tg8 mice (arrow, E) compared with C3H mice (D). With the treatment of Tg8 mice by α-MPT, the intensity of NA immunostaining declined in the PVN (C) in comparison with saline-control Tg8 mice (the same as B). III, Third ventricle; OC, optic chiasma. Scale bars, 50 μm.

Fig. 6.

Immunohistochemical detection of serotonin in the PVN (A–C) and in the SON (D, E) of C3H mice (A, D), Tg8 mice (B, E), and pCPA-treated Tg8 mice (C). In Tg8 mice the density of 5-HT-positive varicosities surrounding unstained cell bodies and the labeling intensity are increased in the PVN (A,B, E, arrow) compared with C3H mice (A). In the SON of Tg8 mice the number of 5-HT-immunopositive fibers increases, particularly in the ventral portion of the nucleus (E), compared with C3H mice (D). Treatment by pCPA in Tg8 mice induces a decrease in the density of 5-HT-immunostained varicosities in the PVN (C) compared with saline-control Tg8 mice (the same as B).III, Third ventricle; OC, optic chiasma. Scale bars, 50 μm.

Fig. 7.

Enzyme immunoassay of AVP (A, C) and in situ hybridization of AVP mRNA (B, D) in the PVN (A, B) and the SON (C, D). Data are expressed as picograms of peptide/micrograms of protein (AVP level) or as optical density × surface (cm²) (AVP mRNA) ± SEM; *p< 0.05 and **p < 0.01 compared with C3H mouse value with one-way ANOVA. ^£p < 0.05;^££p < 0.01;^£££p < 0.001; ns^£, nonsignificant compared with saline-control Tg8 mouse value (which was equivalent to that of control Tg8 mice).

Fig. 8.

Enzyme immunoassay of OT (A, C) andin situ hybridization of OT mRNA (B, D) in the PVN (A, B) and the SON (C, D). Data are expressed as picograms of peptide/micrograms of protein (OT level) or as optical density × surface (cm²) (AVP mRNA) ± SEM; *p < 0.05 compared with C3H mouse value, using one-way ANOVA.^£p < 0.05;^££p < 0.01;^£££p < 0.001 compared with saline-control Tg8 mouse value (which was equivalent to that of control Tg8 mice).