The subfornical organ: A novel site for prolactin action

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Abstract
Prolactin (PRL) is a peptide hormone that performs over 300 biological functions, including those that require binding to prolactin receptor (PRL‐R) in neurones within the central nervous system (CNS). To enter theCNS, circulatingPRLmust overcome the blood‐brain barrier. Accordingly, areas of the brain that do not possess a blood‐brain barrier, such as the subfornical organ (SFO), are optimally positioned to interact with systemicPRL. TheSFOhas been classically implicated in energy and fluid homeostasis but has the potential to influence oestrous cyclicity and gonadotrophin release, which are also functions ofPRL. We aimed to confirm and characterise the expression ofPRL‐R in theSFO, as well as identify the effects ofPRLapplication on membrane excitability of dissociatedSFOneurones. Using a quantitative real‐time polymerase chain reaction, we found thatPRL‐RmRNAin theSFOof male and female Sprague Dawley rats did not significantly differ between juvenile and sexually mature rats (P = .34), male and female rats (P = .97) or across the oestrous cycle (P = .54). Patch‐clamp recordings were obtained in juvenile male rats to further investigate the actions ofPRLat theSFO. DissociatedSFOneurones perfused with 1 μmol L‐1PRLresulted in 2 responsive subpopulations of neurones; 40% depolarised (n = 15/43, 11.3 ± 1.7mV) and 14% hyperpolarised (n = 6/43, −6.7 ± 1.4mV) toPRLapplication. Within the range of 10 pmol L‐1to 1 μmol L‐1, the concentrations ofPRLwere not significantly different in either the magnitude (P = .53) or proportion (P = .19) of response. Furthermore,PRLapplication significantly reduced the transient K+current in 67% ofSFOneurones in voltage‐clamp configuration (n = 6/9,P = .02). The stability in response toPRLand expression ofPRL‐R in theSFOsuggests thatPRLfunction is conserved across physiological states and circulatingPRLconcentrations, prompting further investigations aiming to clarify the nature ofPRLfunction in the SFO.
Funding Information
  • Canadian Institutes of Health Research (MOP 12192)

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