Early-life perfluorooctanoic acid exposure disrupts the function of dopamine transporter protein with glycosylation changes implicating the links between decreased dopamine levels and disruptive behaviors in larval zebrafish

Exposure to perfluorooctanoic acid (PFOA) during early embryonic development is associated with the increased risk of developmental neurotoxicity and neurobehavioral disorders in children. In our previous study, we demonstrated that exposure to PFOA affected locomotor activity and disrupted dopamine-related gene expression in zebrafish larvae. Consequently, we continue to study the dopaminergic system with a focus on dopamine levels and dopamine's effect on behaviors in relation to PFOA exposure. In the present study, we found a decrease in dopamine levels in larval zebrafish. We studied the dopamine transporter (DAT) protein, which is responsible for regulating dopamine levels through the reuptake of dopamine in neuronal cells. We demonstrated that exposure to PFOA disrupted the glycosylation process of DAT, inhibited its uptake function, and induced endoplasmic reticulum (ER) stress in dopaminergic cells. Besides, we conducted a light-dark preference test on larval zebrafish and observed anxiety/depressive-like behavioral changes following exposure to PFOA. Dopamine is one of the most prominent neurotransmitters that significantly influences human behavior, with low dopamine levels being associated with impairments such as anxiety and depression. The anxiety-like response in zebrafish larvae exposure to PFOA implies the link with the reduced dopamine levels. Taken together, we can deduce that glycosylation changes in DAT lead to dysfunction of DAT to regulate dopamine levels, which in turn alters behavior in larval zebrafish. Therefore, alternation in dopamine levels may play a pivotal role in the development of anxiety/depressive-like behavioral changes induced by PFOA.

Electrophysiologic changes in ventral midbrain dopaminergic neurons resulting from (+/-) -3,4-methylenedioxymethamphetamine (MDMA-"Ecstasy")

BACKGROUND

Although dopamine (DA) has been implicated in the psychostimulant properties of 3,4-methylenedioxymethamphetamine (MDMA), there is no detailed information on its modalities of action on single ventral midbrain dopaminergic neurons.

METHODS

We examined the actions of MDMA on intracellularly recorded dopaminergic neurons maintained in slices.

RESULTS

At 1 micromol/L, MDMA depolarized and excited the cells; at 3 micromol/L, either excited or inhibited the neurons. Interestingly, higher concentrations (10-30 micromol/L) inhibited firing through membrane hyperpolarization or caused an outward current. Whereas MDMA's excitatory effects were antagonized by pindolol, indicating involvement of 5-HT 1B receptors, the inhibitory effects were counteracted by sulpiride indicating involvement D2 receptors. Treatment of the cells with carbidopa eliminated MDMA-induced firing inhibition and membrane hyperpolarization. MDMA enhanced DA-induced cellular responses but reduced those of amphetamine. Cocaine-induced outward currents were not affected by MDMA. These actions are consistent with inhibition of the DA transporter. Moreover, MDMA depressed the GABA(B) IPSP by activating 5-HT 1B receptors.

CONCLUSIONS

Our data demonstrate that 3-30 micromol/L MDMA preferentially inhibits the dopaminergic cells via indirect activation of D2 autoreceptors due to increased extracellular concentration of DA. In contrast, reduction of the GABA(B) IPSP could partially account for excitation caused by 1-3 micromol/L drug.