Altered functional connectivity and network excitability in a model of cortical dysplasia

Abstract Focal cortical dysplasias (FCDs) are malformations of cortical development that often result in medically refractory epilepsy, with a greater incidence in the pediatric population. The relationship between the disturbed cortical morphology and epileptogenic activity of FCDs remains unclear. We used the BCNU (carmustine 1-3-bis-chloroethyl-nitrosourea) animal model of cortical dysplasia to evaluate neuronal and laminar alterations and how these result in altered activity of intracortical networks in early life. We corroborated the previously reported morphological anomalies characteristic of the BCNU model, comprising slightly larger and rounder neurons and abnormal cortical lamination. Next, the neuronal activity of live cortical slices was evaluated through large field-of-view calcium imaging as well as the neuronal response to a stimulus that leads to cortical hyperexcitability (pilocarpine). Examination of the joint activity of neuronal calcium time series allowed us to identify intracortical communication patterns and their response to pilocarpine. The baseline power density distribution of neurons in the cortex of BCNU-treated animals was different from that of control animals, with the former showing no modulation after stimulus. Moreover, the intracortical communication pattern differed between the two groups, with cortexes from BCNU-treated animals displaying decreased inter-layer connectivity as compared to control animals. Our results indicate that the altered anatomical organization of the cortex of BCNU-treated rats translates into altered functional networks that respond abnormally to a hyperexcitable stimulus and highlight the role of network dysfunction in the pathophysiology of cortical dysplasia

The role of pituitary melanocortin receptor 3 (MC3) in regulation of hormone output

Introduction/Aim: Of the five melanocortin receptors (MCs: MC1-5) identified to date, the focus of neuroendocrine studies has principally been on MC3 and MC4 due to their role in regulating body weight: a role presumed to be mediated by hypothalamic actions in response to melanocyte stimulating hormone (MSH). Recently, MC3 has been shown to have roles in regulating both statural growth and the timing of puberty: possibly mediated by MC3 expression identified in arcuate growth hormone releasing hormone (GHRH) and kisspeptin neurones, respectively (1). It has long been known that MC3 is expressed in the anterior pituitary and may mediate paracrine interactions within the gland (2). It was the aim of this series of studies to determine the potential impact of mouse pituitary MC3 on physiology: specifically the role of MC3 in pituitary gland function, the pattern of expression of the receptor and potential modifications of function by expression of interacting proteins. Methods/Results: We have determined the impact of loss of MC3 expression on anterior pituitary function using MC3 knockout mice: in adult male mice loss of MC3 leads to a significant reduction in the pituitary content of growth hormone (GH), gonadotrophins and prolactin, with no effect on adrenocorticotrophic hormone (ACTH) or thyroid stimulating hormone; in adult females the reduction is restricted to GH, however, a trend of decrease in gonadotrophins was also found. RNAScope in situ hybridisation showed that MC3 is co-expressed in a large proportion of somatotrophs and gonadotrophs and, consistent with this, imaging showed that ACTH stimulates a rise in intracellular calcium in these cell types. We have also studied the interaction of melanocortin receptor accessory proteins (MRAPs) and found that MRAP2 modifies MC3 response to ACTH but not MSH and results in bias G-protein coupled signalling. RNAScope for MRAP2 revealed that it is co-expressed in a significant proportion of MC3 positive cells. Conclusions: The effects of global knockout of MC3 on pituitary hormone contents suggest that aspects of the body weight, growth and pubertal timing roles of the receptor may also be mediated by its pituitary expression. Furthermore, the interactions of MC3 and MRAPs with the growth hormone secretagogue receptor (3) would be consistent with a pituitary role in growth hormone regulation. (1) Lam et al. (2021) Nature 599:436-441. (2) Roudbaraki et al. (1999) Endocrinol. 140:4874-4885. (3) Rediger et al. (2011) J Biol Chem. 286:39623-31

Synaptic communication mediates the assembly of a self-organizing circuit that controls reproduction

International audienceMigration of gonadotropin-releasing hormone (GnRH) neurons from their birthplace in the nasal placode to their hypothalamic destination is critical for vertebrate reproduction and species persistence. While their migration mode as individual GnRH neurons has been extensively studied, the role of GnRH-GnRH cell communication during migration remains largely unexplored. Here, we show in awake zebrafish larvae that migrating GnRH neurons pause at the nasal-forebrain junction and form clusters that act as interhemisphere neuronal ensembles. Within the ensembles, GnRH neurons create an isolated, spontaneously active circuit that is internally wired through monosynaptic glutamatergic synapses into which newborn GnRH neurons integrate before entering the brain. This initial phase of integration drives a phenotypic switch, which is essential for GnRH neurons to properly migrate toward their hypothalamic destination. Together, these experiments reveal a critical step for reproduction, which depends on synaptic communication between migrating GnRH neurons

Addition of a carboxy-terminal tail to the normally tailless gonadotropin-releasing hormone receptor impairs fertility in female mice

Gonadotropin-releasing hormone (GnRH) is the primary neuropeptide controlling reproduction in vertebrates. GnRH stimulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) synthesis via a G-protein-coupled receptor, GnRHR, in the pituitary gland. In mammals, GnRHR lacks a C-terminal cytosolic tail (Ctail) and does not exhibit homologous desensitization. This might be an evolutionary adaptation that enables LH surge generation and ovulation. To test this idea, we fused the chicken GnRHR Ctail to the endogenous murine GnRHR in a transgenic model. The LH surge was blunted, but not blocked in these mice. In contrast, they showed reductions in FSH production, ovarian follicle development, and fertility. Addition of the Ctail altered the nature of agonist-induced calcium signaling required for normal FSH production. The loss of the GnRHR Ctail during mammalian evolution is unlikely to have conferred a selective advantage by enabling the LH surge. The adaptive significance of this specialization remains to be determined.Diabetes mellitus: pathophysiological changes and therap

Genetic approaches identify adult pituitary stem cells

Adult tissues undergo continuous cell turnover in response to stress, damage, or physiological demand. New differentiated cells are generated from dedicated or facultative stem cells or from self-renewing differentiated cells. Here we describe a different stem cell strategy for tissue maintenance, distinct from that observed for dedicated or facultative stem cells. We report the presence of nestin-expressing adult stem cells in the perilumenal region of the mature anterior pituitary and, using genetic inducible fate mapping, demonstrate that they serve to generate subsets of all six terminally differentiated endocrine cell types of the pituitary gland. These stem cells, while not playing a significant role in organogenesis, undergo postnatal expansion and start producing differentiated progeny, which colonize the organ that initially entirely consisted of differentiated cells derived from embryonic precursors. This generates a mosaic organ with two phenotypically similar subsets of endocrine cells that have different origins and different life histories. These parallel but distinct lineages of differentiated cells in the gland may help the maturing organism adapt to changes in the metabolic regulatory landscape

S100a4-Cre-mediated deletion of Patched1 causes hypogonadotropic hypogonadism: role of pituitary hematopoietic cells in endocrine regulation

Hormones produced by the anterior pituitary gland regulate an array of important physiological functions, but pituitary hormone disorders are not fully understood. Herein we report that genetically-engineered mice with deletion of the hedgehog signaling receptor Patched1 by S100a4 promoter-driven Cre recombinase (S100a4-Cre;Ptch1fl/fl mutants) exhibit adult-onset hypogonadotropic hypogonadism and multiple pituitary hormone disorders. During the transition from puberty to adult, S100a4-Cre;Ptch1fl/fl mice of both sexes develop hypogonadism coupled with reduced gonadotropin levels. Their pituitary glands also display severe structural and functional abnormalities, as revealed by transmission electron microscopy and expression of key genes regulating pituitary endocrine functions. S100a4-Cre activity in the anterior pituitary gland is restricted to CD45+ cells of hematopoietic origin, including folliculo-stellate cells and other immune cell types, causing sex-specific changes in the expression of genes regulating the local microenvironment of the anterior pituitary. These findings provide in vivo evidence for the importance of pituitary hematopoietic cells in regulating fertility and endocrine function, in particular during sexual maturation and likely through sexually dimorphic mechanisms. These findings support a previously unrecognized role of hematopoietic cells in causing hypogonadotropic hypogonadism and provide inroads into the molecular and cellular basis for pituitary hormone disorders in humans