Models in neuroendocrinology

Nanotechnological advances in the treatment of epilepsy: a comprehensive review

Epilepsy is one of the most prevalent chronic neurological disorders characterized by frequent unprovoked epileptic seizures. Epileptic seizures can develop from a broad range of underlying abnormalities such as tumours, strokes, infections, traumatic brain injury, developmental abnormalities, autoimmune diseases, and genetic predispositions. Sometimes epilepsy is not easily diagnosed and treated due to the large diversity of symptoms. Undiagnosed and untreated seizures deteriorate over time, impair cognition, lead to injuries, and can sometimes result in death. This review gives details about epilepsy, its classification on the basis of International League Against Epilepsy, current therapeutics which are presently offered for the treatment of epilepsy. Despite of the fact that more than 30 different anti-epileptic medication and antiseizure drugs are available, large number of epileptic patients fail to attain prolonged seizure independence. Poor onsite bioavailability of drugs due to blood brain barrier poses a major challenge in drug delivery to brain. The present review covers the limitations with the state-of-the-art strategies for managing seizures and emphasizes the role of nanotechnology in overcoming these issues. Various nano-carriers like polymeric nanoparticles, dendrimers, lipidic nanoparticles such as solid lipid nanoparticles, nano-lipid carriers, have been explored for the delivery of anti-epileptic drugs to brain using oral and intranasal routes. Nano-carries protect the encapsulated drugs from degradation and provide a platform to deliver controlled release over prolonged periods, improved permeability and bioavailability at the site of action. The review also emphasises in details about the role of neuropeptides for the treatment of epilepsy.

The Effects of Chronic Lead Exposure on Testicular Development of Japanese Quail (Coturnix japonica): Histopathological Damages, Oxidative Stress, Steroidogenesis Disturbance, and Hypothalamus-Pituitary-Testis Axis Disruption

Lead (Pb) becomes a global public health concern for its high toxicology. Birds are sensitive to environmental pollution and Pb contamination exerts multiple negative influences on bird life. Pb also impacts on avian reproductive system. Thus, in this study, we attempted to determine toxicological effects and possible mechanistic pathways of Pb on avian testicular development by using the model species-Japanese quail (Coturnix japonica). Male quail chicks of 1-week-old were exposed to 0, 50, 500, and 1000 ppm Pb concentrations in drinking water for 5 weeks when reaching sexual maturation. The results showed that high Pb doses (500 and 1000 ppm) induced testis atrophy and cloacal gland shrinkage. Microstructural damages of both hypothalamus and testis indicated the disruption of the hypothalamus-pituitary-gonadal (HPG) axis by Pb exposure. The decrease of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and testosterone (T) may also imply HPG axis disruption. Moreover, excess testicular oxidative damages featured by increasing reactive oxygen species (ROS) and malondialdehyde (MDA) and decreasing catalase (CAT), glutathione (GSH), superoxide dismutase (SOD), glutathione-S-transferase (GST), and total antioxidant capacity (T-AOC) indicated increasing risks of reproductive dysfunction by Pb. Furthermore, increasing apoptosis and upregulation of gene expression associated with cell death suggested testicular abnormal development. In addition, molecular signaling involved with steroidogenesis in the testis was disturbed by Pb treatment. The study showed that Pb could impair testicular development and reproductive function by morphological and histological injury, hormone suppression, oxidative stress, cell death, and HPG axis disruption.

State-dependent activity dynamics of hypothalamic stress effector neurons

The stress response necessitates an immediate boost in vital physiological functions from their homeostatic operation to an elevated emergency response. However, the neural mechanisms underlying this state-dependent change remain largely unknown. Using a combination of in vivo and ex vivo electrophysiology with computational modeling, we report that corticotropin releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN), the effector neurons of hormonal stress response, rapidly transition between distinct activity states through recurrent inhibition. Specifically, in vivo optrode recording shows that under non-stress conditions, CRH_PVN neurons often fire with rhythmic brief bursts (RB), which, somewhat counterintuitively, constrains firing rate due to long (~2 s) interburst intervals. Stressful stimuli rapidly switch RB to continuous single spiking (SS), permitting a large increase in firing rate. A spiking network model shows that recurrent inhibition can control this activity-state switch, and more broadly the gain of spiking responses to excitatory inputs. In biological CRH_PVN neurons ex vivo, the injection of whole-cell currents derived from our computational model recreates the in vivo-like switch between RB and SS, providing direct evidence that physiologically relevant network inputs enable state-dependent computation in single neurons. Together, we present a novel mechanism for state-dependent activity dynamics in CRH_PVN neurons.

Transgenic approaches to opening up new fields of vasopressin and oxytocin research

Transgenic approaches have been applied to generate transgenic rats that express exogenous genes in arginine vasopressin (AVP)- and oxytocin (OXT)-producing magnocellular neurosecretory cells (MNCs) of the hypothalamic-neurohypophyseal system (HNS). First, the fusion gene that expresses AVP-enhanced green fluorescent protein (eGFP) and OXT-monomeric red fluorescent protein 1 (mRFP1) was used to visualize AVP- and OXT-producing MNCs and their axon terminals in the HNS under fluorescence microscopy. Second, the fusion gene that expresses c-fos-eGFP and c-fos-mRFP1 was used to identify activated neurons physiologically in the central nervous system, including MNCs, circumventricular organs and spinal cord. In addition, AVP-eGFP x c-fos-mRFP1 and OXT-mRFP1 × c-fos-eGFP double transgenic rats were generated to identify activated AVP- and OXT-producing MNCs using appropriate physiological stimuli. Third, the fusion gene that expresses AVP-chanelrhodopsin 2 (ChR2)-eGFP and AVP-hM3Dq-mCherry was used to activate AVP- and OXT-producing MNCs by optogenetic and chemogenetic approaches. In each step, these transgenic approaches in rats have provided new insights on the physiological roles of AVP and OXT not only in the HNS, but also in the whole body. In this review, we summarize the transgenic rats that we generated, as well as related physiological findings.

Mathematical modeling approaches of cellular endocrinology within the hypothalamo-pituitary-gonadal axis

The reproductive neuroendocrine axis, or hypothalamo-pituitary-gonadal (HPG) axis, is a paragon of complex biological system involving numerous cell types, spread over several anatomical levels communicating through entangled endocrine feedback loops. The HPG axis exhibits remarkable dynamic behaviors on multiple time and space scales, which are an inexhaustible source of studies for mathematical and computational biology. In this review, we will describe a variety of modeling approaches of the HPG axis from a cellular endocrinology viewpoint. We will in particular investigate the questions raised by some of the most striking features of the HPG axis: (i) the pulsatile secretion of hypothalamic and pituitary hormones, and its counterpart, the cell signaling induced by frequency-encoded hormonal signals, and (ii) the dual, gametogenic and glandular function of the gonads, which relies on the tight control of the somatic cell populations ensuring the proper maturation and timely release of the germ cells.

Mathematical Modelling of Endocrine Systems

Hormone rhythms are ubiquitous and essential to sustain normal physiological functions. Combined mathematical modelling and experimental approaches have shown that these rhythms result from regulatory processes occurring at multiple levels of organisation and require continuous dynamic equilibration, particularly in response to stimuli. We review how such an interdisciplinary approach has been successfully applied to unravel complex regulatory mechanisms in the metabolic, stress, and reproductive axes. We discuss how this strategy is likely to be instrumental for making progress in emerging areas such as chronobiology and network physiology. Ultimately, we envisage that the insight provided by mathematical models could lead to novel experimental tools able to continuously adapt parameters to gradual physiological changes and the design of clinical interventions to restore normal endocrine function.