Acute effects of prolactin on hypothalamic prolactin receptor expressing neurones in the mouse

The anterior pituitary hormone, prolactin, is a fundamental regulator of lactation, and also plays a role in many other physiological processes including maternal behaviour, reproduction, immune response and even energy balance. Indeed, prolactin receptors (Prlr) are widely distributed throughout the body, including a number of different brain regions, further attesting to its pleiotropic nature. Within the brain, previous research has identified key areas upon which prolactin exerts effects on gene transcription through the canonical JAK2/STAT5 pathway downstream of the Prlr. In some neurones, however, such as the tuberoinfundibular dopamine neurones that control prolactin secretion, prolactin can also exert rapid actions to stimulate neuronal activity. While prolactin-induced activation of STAT5 has been described in a wide variety of brain regions, its capacity for acute modulation of electrical properties of many Prlr-expressing neurones remains to be elucidated. To investigate how widespread these rapid actions of prolactin are in various Prlr-expressing neurones, we utilised a transgenic mouse line in which Cre recombinase is specifically expressed in the coding region of the prolactin long form receptor gene ( Prlr-iCre ). This mouse line was crossed with a Cre-dependent calcium indicator (GCaMP6f) transgenic mouse, allowing us to visually monitor the electrical activity of Prlr-expressing neurones in ex vivo 200μm brain slice preparations. Here, we survey hypothalamic regions implicated in prolactin’s diverse physiological functions such as: the arcuate (ARC) and paraventricular nuclei of the hypothalamus (PVN), and the medial preoptic area (MPOA). We observe that in both males and virgin and lactating females, bath application of prolactin is able to induce electrical changes in a subset of Prlr-expressing cells in all of these brain regions. The effects we detected ranged from rapid or sustained increases in intracellular calcium to inhibitory effects, indicating a heterogeneous nature of these Prlr-expressing populations. These results enhance our understanding of mechanisms by which prolactin acts on hypothalamic neurones and provide insights into how prolactin might influence neuronal circuits in the mouse brain. ### Competing Interest Statement The authors have declared no competing interest.