The decrease in hypothalamic dopamine secretion induced by suckling: comparison of voltammetric and radioisotopic...

Area of Science:

• Neuroendocrinology
• Lactation Physiology
• Dopamine Signaling

Background:

• Dopamine in the median eminence is implicated in regulating prolactin secretion.
• Previous studies suggested dopamine release into portal blood during mammary nerve stimulation, but lacked direct evidence.

Purpose of the Study:

• To investigate the relationship between dopamine release in the median eminence and dopamine secretion into the hypophysial portal circulation during mammary nerve stimulation.
• To provide direct experimental support for dopamine's role in the neuroendocrine control of lactation.

Main Methods:

• In vivo voltammetry measured median eminence dopamine release in anesthetized lactating rats.
• [3H]dopamine was used to trace dopamine secretion into sequential hypophysial portal blood samples.
• Mammary nerves were stimulated, and dopamine levels and electrochemical signals were monitored.

Main Results:

• Mammary nerve stimulation caused a simultaneous, transient decrease (35-70%) in median eminence dopamine and [3H]dopamine in portal blood.
• Following the initial decrease, dopamine levels increased in pulses, mirroring portal blood concentrations.
• These changes occurred within minutes of initiating nerve stimulation.

Conclusions:

• Mammary nerve stimulation induces a rapid, substantial decline in hypothalamic dopamine secretion.
• This dopamine decrease is directly linked to release into the hypophysial portal circulation.
• The findings support dopamine's role as a key regulator, inhibiting prolactin release during suckling-induced responses.