Biology subjects

Grattan, D. R.

Publications and source records attributed to Grattan, D. R..

6 recordsLinked to original sources

bioRxiv2024

Prolactin-mediates a lactation-induced suppression of arcuate kisspeptin neuronal activity necessary for lactational infertility in mice

The specific role that prolactin plays in lactational infertility, as distinct from other suckling or metabolic cues, remains unresolved. Here, deletion of the prolactin receptor (Prlr) from forebrain neurons or arcuate kisspeptin neurons resulted in failure to maintain normal lactation-induced suppression of estrous cycles. Kisspeptin immunoreactivity and pulsatile LH secretion were increased in these mice, even in the presence of ongoing suckling stimulation and lactation. GCaMP fibre photometry of arcuate kisspeptin neurons revealed that the normal episodic activity of these neurons is rapidly suppressed in pregnancy and this was maintained throughout early lactation. Deletion of Prlr from arcuate kisspeptin neurons resulted in early reactivation of episodic activity of kisspeptin neurons prior to a premature return of reproductive cycles in early lactation. These observations show dynamic variation in arcuate kisspeptin neuronal activity associated with the hormonal changes of pregnancy and lactation, and provide direct evidence that prolactin action on arcuate kisspeptin neurons is necessary for suppressing fertility during lactation in mice.

neuroscience↗

bioRxiv2023

Unexpected plasma gonadal steroid and reproductive hormone levels across the mouse estrous cycle

Despite the importance of the mouse in biomedical research, the levels of circulating gonadal steroids across the estrous cycle are not established with any temporal precision. Using liquid chromatography-mass spectrometry, now considered the gold standard for steroid hormone analysis, we aimed to generate a detailed profile of gonadal steroid levels across the estrous cycle of C57BL/6J mice. For reference, luteinizing hormone (LH) and prolactin concentrations were measured in the same samples by sandwich ELISA. Terminal blood samples were collected at 8-hour intervals (10 am, 6 pm, 2 am) throughout the four stages of the estrous cycle. As expected, the LH surge was detected at 6 pm on proestrus with a mean ({+/-}SEM) concentration of 11{+/-}3 ng/mL and occurred coincident with the peak in progesterone levels (22{+/-}4 ng/mL). Surprisingly, estradiol concentrations peaked at 10 am on diestrus (51{+/-}8 pg/mL), with levels on proestrus 6 pm reaching only two-thirds of this value (31{+/-}5 pg/mL). We also observed a proestrous peak in prolactin concentrations (132.5{+/-}17 ng/mL) that occurred earlier than expected at 2 am. Estrone and androstenedione levels were often close to the LOD and showed no consistent changes across the estrous cycle. Testosterone levels were rarely above the LOD (0.01 ng/mL). These observations provide the first detailed assessment of fluctuating gonadal steroid and reproductive hormone levels across the mouse estrous cycle and indicate that species differences exist between mice and other spontaneously ovulating species.

physiology↗

bioRxiv2021

Prolactin action is necessary for parental behavior in male mice

Parental care is critical for successful reproduction in mammals. In comparison to maternal care, the neuroendocrine mechanisms supporting paternal care are less well-studied. Laboratory mice show a mating-induced suppression of infanticide (normally observed in virgins) and onset of paternal behavior. Using this model, we sought to investigate whether the hormone prolactin plays a role in paternal behavior, as it does for maternal behavior. First, using c-fos immunoreactivity in Prlr-IRES-Cre-tdtomato reporter mouse sires, we show that the circuitry activated during paternal interactions contains prolactin-responsive neurons, including the medial preoptic area, bed nucleus of the stria terminalis, and medial amygdala. To evaluate whether prolactin action is required for the establishment and display of paternal behavior, we conditionally deleted the prolactin receptor (Prlr) from 3 distinct cell types: glutamatergic, GABAergic, and CaMKII-expressing forebrain neurons. Prlr-deletion from CaMKII-expressing forebrain neurons, but not from glutamatergic or GABAergic cells, resulted in a profound effect on paternal behavior, as none of these males completed the pup retrieval task. Finally, although sires do not show an acute increase in circulating prolactin levels in response to pups, pharmacological blockade of prolactin-release at the time of pup exposure resulted in failure to retrieve pups, similar to when the Prlr was deleted from CaMKII neurons, with prolactin administration rescuing this behavior. Taken together, our data show that paternal behavior in sires is dependent on basal levels of circulating prolactin acting at the Prlr on CaMKII-expressing neurons. These new data in male mice demonstrate that prolactin has a similar action in both sexes to promote parental care.

neuroscience↗

bioRxiv2021

Leptin regulates glucose homeostasis via the canonical WNT pathway.

Leptin is a body weight regulatory hormone, but it is arguably even more potent at regulating blood glucose levels. To further our understanding of the molecular mechanisms by which leptin controls glucose homeostasis, we have used transgenic zebrafish models and conditional deletion of beta catenin in the mediobasal hypothalamus of adult mice to show that Wnt signalling in the brain mediates glucoregulatory effects of leptin. In zebrafish, under normal feeding conditions, leptin regulates glucose homeostasis but not adipostasis. In times of nutrient excess, we found that leptin also regulates body weight and size in this species. Using a Wnt signalling reporter fish, we show that leptin directly activates the canonical Wnt pathway in vivo. Pharmacological inhibition of this pathway prevented the leptin-induced improvement in glucose tolerance. In adult mice, conditional deletion of the key Wnt effector molecule, {beta}-catenin, in the mediobasal hypothalamus of male mice confirmed the essential role of the Wnt pathway in mediating leptin action and the neuroendocrine regulation of glucose homeostasis. Adult-onset {beta}-catenin deletion in the mediobasal hypothalamus led to glucose intolerance, exacerbation of caloric intake and body weight gain under high fat diet, as well as resistance to exogenous leptin.

physiology↗

bioRxiv2020

A reduction in voluntary physical activity during pregnancy in mice is mediated by prolactin

As part of the maternal adaptations to pregnancy, mice show a rapid, profound reduction in voluntary running wheel activity (RWA) as soon as pregnancy is achieved. Here, we evaluate the hypothesis that prolactin, one of the first hormones to change secretion pattern following mating, is involved in driving this suppression of physical activity levels during pregnancy. We show that prolactin can acutely suppress RWA in virgin female mice, and that conditional deletion of prolactin receptors (Prlr) from either all forebrain neurons or from GABA neurons prevented the early pregnancy-induced suppression of RWA. Deletion of Prlr specifically from the medial preoptic area, a brain region associated with multiple homeostatic and behavioural roles including parental behaviour, completely abolished the early pregnancy-induced suppression of RWA. Our data demonstrate a key role for prolactin in suppressing voluntary physical activity during early pregnancy, highlighting a novel biological basis for reduced physical activity in pregnancy.

neuroscience↗

bioRxiv2020

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 200m brain slice preparations. Here, we survey hypothalamic regions implicated in prolactins 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.

neuroscience↗