Increase in pituitary dopaminergic receptors after monosodium glutamate treatment

Area of Science:

• Neuroendocrinology
• Reproductive Biology

Background:

• Dopamine (DA) in the arcuate nucleus regulates prolactin (PRL) secretion from the anterior pituitary.
• Neonatal exposure to monosodium glutamate (MSG) is known to destroy dopaminergic neurons in the arcuate nucleus.

Purpose of the Study:

• To investigate the effect of reduced arcuate nucleus DA levels, induced by neonatal MSG treatment, on anterior pituitary DA receptors in adult male rats.
• To determine if changes in DA receptor binding capacity or affinity occur in response to altered DAergic tone.

Main Methods:

• Neonatal rats were treated with MSG or a vehicle control.
• Hypothalamic and circulating hormone levels (DA, norepinephrine, epinephrine, PRL) were measured in adulthood.
• Dopamine receptor binding characteristics in anterior pituitary membranes were analyzed using Scatchard analysis with [3H]spiperone.

Main Results:

• MSG treatment significantly reduced medial basal hypothalamic DA levels and increased circulating PRL.
• No significant changes were observed in hypothalamic norepinephrine or epinephrine concentrations.
• Scatchard analysis revealed a significant increase in DA receptor binding capacity in MSG-treated rats, with no alteration in receptor affinity.
• The number of anterior pituitary DA receptors increased following neonatal MSG-induced destruction of the arcuate nucleus.

Conclusions:

• Neonatal MSG treatment leads to a compensatory upregulation of anterior pituitary dopamine receptors in adult male rats.
• This increase in DA receptor number is likely a direct consequence of reduced dopaminergic input to the anterior pituitary.
• The findings highlight the dynamic regulation of anterior pituitary DA receptors in response to altered neuroendocrine conditions.