Age and Sex Differences in the Effects of Nicotine on Tyrosine Hydroxylase Protein Levels and DARPP-32 Phosphorylation at Ser130 in Mice

Nicotine causes dysregulation of the dopaminergic system. Tyrosine hydroxylase (TH) and Dopamine-and-cAMP-regulated phosphoprotein (DARPP-32) are proteins that play important roles in dopamine synthesis, and dopamine signaling, respectively. TH is the rate-limiting enzyme for the synthesis of catecholamines (including dopamine). Nicotine acts directly on nicotinic acetylcholine receptors (nACHRs) in the brain, indirectly stimulates TH gene transcription, and stimulates dopamine release from mesocorticolimbic neurons. DARPP-32 integrates both glutamatergic and dopaminergic signaling via phosphorylation events at distinct sites within the DARPP-32 protein. In particular, nAChR signaling affects DARPP-32 phosphorylation by stimulating a combination of nicotinic, dopaminergic, and glutamatergic signaling that stimulates Ca2+ signaling. The dephosphorylation of PP-2B activates CK1 (Cegielska et al. 1998), which phosphorylates DARPP-32 at Ser130. In our study, both TH protein levels and phosphorylation of DARPP-32 at Ser130 were measured in the ventral tegmentum (VT), ventral striatum (VS), and medial prefrontal cortex (mPFC) of adolescent and adult mice after subcutaneous nicotine injections. In the VT, we found a highly-significant nicotineinduced decrease in TH in adult males, but not in adult females. These findings were presumably influenced by the suppressive effect of androgens on tyrosine hydroxylase expression in the VT. In the mPFC, nicotine injections decreased TH protein in prepubertal adolescent females, but increased TH protein in adult females, possibly due to the stimulatory effects of estrogen levels on TH expression. DARPP-32 phospho-Ser130 decreased in the VT after repeated nicotine injections in adolescent males and adult females. This decrease was also significant in adult females after just a single nicotine injection. This may reflect sex-and-age specific nicotine responses of dopaminergic neurons that impact addiction liability. In the VS, nicotine decreased DARPP-32 Ser130 phosphorylation in every age and sex group, which may contribute to increased nicotine dependence. In the mPFC, nicotine injections decreased DARPP-32 phospho-Ser130 in adult males, but increased it in adult females, possibly due to sex differences in the PFC regulation of dopamine release. To our knowledge this is the first analysis of age and sex differences in the effects of nicotine on these proteins. Overall, the responses to these two genes were surprisingly different, and may therefore provide complementary information about differences in nicotine vulnerability and dose escalation. Our findings of both significant age and sex effects highlight the importance of studying the responses to drugs of abuse in multiple age and sex categories.

Author

• Proffitt, Tresa L S

• dopamine
• nicotine
• adolescents
• sex differences

Identifier

hdl:1920/14991

OAI identifier oai:identifier

oai:MARS:1920/14991