Current Review of the Function and Regulation of Tuberoinfundibular Dopamine Neurons

The Hypothalamic Arcuate Nucleus Dopaminergic Neurons: More Than Just Prolactin Secretion

The hypothalamic arcuate nucleus dopaminergic (A12) neurons are well known for their central role in regulating prolactin secretion through a sophisticated negative feedback loop. In this canonical pathway, prolactin stimulates A12 neurons to release dopamine, which suppresses further prolactin release from lactotrophs in the anterior pituitary. However, a collective of recent and past evidence strongly implies that the A12 neurons are far more dynamic and multifaceted than previously appreciated. This minireview discusses the developmental trajectory of A12 neurons, from prenatal origins to postnatal maturation, highlighting their diversity and heterogeneity. Beyond their well-characterized role in prolactin regulation, the A12 neurons contribute to a broader array of hypothalamic functions, including autoregulation, metabolism, and growth. By shedding light on these underexplored roles, this review outlines the expansive significance of A12 neurons as more than mere gatekeepers of prolactin secretion, positioning them as versatile players in endocrine and metabolic homeostasis.

Oxytocin and neuroscience of lactation: Insights from the molecular genetic approach

In mammals, lactation is essential for the health and growth of infants and supports the formation of the mother-infant bond. Breastfeeding is mediated by the neurohormone oxytocin (OT), which is released into the bloodstream in a pulsatile manner from OT neurons in the hypothalamus to promote milk ejection into mammary ducts. While classical studies using anesthetized rats have illuminated the activity patterns of putative OT neurons during breastfeeding, the molecular, cellular, and neural circuit mechanisms driving the synchronous pulsatile bursts of OT neurons in response to nipple stimulation remain largely elusive. Only recently have molecular neuroscience techniques for imaging and manipulating specific genetically defined cells been applied to lactating mice. For instance, fiber photometry has revealed the temporal dynamics of the population pulsatile activity of OT neurons in freely moving dams across various lactation stages, while microendoscopy has provided single-cell level insights. In this review, we introduce the neuroscience of lactation with respect to OT neuron activity, discuss findings from molecular neuroscience approaches, and highlight key unresolved questions.

Hypothalamic neurons fully or partially expressing the dopaminergic phenotype: development, distribution, functioning and functional significance. A review

The hypothalamus is a key link in neuroendocrine regulations, which are provided by neuropeptides and dopamine. Until the late 1980 s, it was believed that, along with peptidergic neurons, hypothalamus contained dopaminergic neurons. Over time, it has been shown that besides dopaminergic neurons expressing the dopamine transporter and dopamine-synthesizing enzymes - tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) - the hypothalamus contains neurons expressing only TH, only AADC, both enzymes or only dopamine transporter. The end secretory product of TH neurons is L-3,4-dihydroxyphenylalanine, while that of AADC neurons and bienzymatic neurons lacking the dopamine transporter is dopamine. During ontogenesis, especially in the perinatal period, monoenzymatic neurons predominate in the hypothalamic neuroendocrine centers. It is assumed that L-3,4-dihydroxyphenylalanine and dopamine are released into the neuropil, cerebral ventricles, and blood vessels, participating in the regulation of target cell differentiation in the perinatal period and the functioning of target cells in adulthood.

Sleep and local field potential effect of the D2 receptor agonist bromocriptine during the estrus cycle and postpartum period in female rats

BACKGROUND

Pituitary lactotrophs are under tonic dopaminergic inhibitory control and bromocriptine treatment blocks prolactin secretion.

METHODS

Sleep and local field potential were addressed for 72 h after bromocriptine treatments applied during the different stages of the estrus cycle and for 24 h in the early- and middle postpartum period characterized by spontaneously different dynamics of prolactin release in female rats.

RESULTS

Sleep changes showed strong dependency on the estrus cycle phase of the drug application. Strongest increase of wakefulness and reduction of slow wave sleep- and rapid eye movements sleep appeared during diestrus-proestrus and middle postpartum treatments. Stronger sleep-wake effects appeared in the dark phase in case of the estrus cycle treatments, but in the light phase in postpartum treatments. Slow wave sleep and REM sleep loss in case of estrus cycle treatments was not compensated at all and sleep loss seen in the first day post-injection was gained further later. In opposition, slow wave sleep loss in the light phase after bromocriptine injections showed compensation in the postpartum period treatments. Bromocriptine treatments resulted in a depression of local field potential delta power during slow wave sleep while an enhancement in beta and gamma power during wakefulness regardless of the treatment timing.

CONCLUSIONS

These results can be explained by the interplay of dopamine D2 receptor agonism, lack of prolactin release and the spontaneous homeostatic sleep drive being altered in the different stages of the estrus cycle and the postpartum period.