Many neural control systems are at least roughly optimized, but how is optimal control learned in the brain? There are algorithms for this purpose, but in their present forms they aren’t suited for biological neural networks because they rely on a type of communication that isn’t available in the brain, namely weight transport — transmitting the strengths, or “weights”, of individual synapses to other synapses and neurons. Here I show how optimal control can be learned without weight transport. I explore three complementary approaches. In the first, I show that the control-theory concept of feedback linearization can form the basis for a simple mechanism that learns roughly optimal control, at least in some sensorimotor tasks. Second, I describe a method based on Pontryagin’s Minimum Principle of optimal control, by which a network without weight transport might achieve optimal open-loop control. Third, I describe a mechanism for building optimal feedback controllers, without weight transport, by a method based on generalized Hamilton-Jacobi-Bellman equations. Finally, I argue that the issues raised in these three projects apply quite broadly, i.e. most control algorithms rely on weight transport in many different ways, but it may be possible to recast them into forms that are free of such transport by the mechanisms I propose.

Retrospective epidemiological studies of British cohorts have found an inverse relationship between birth size and rates of mortality from cardiovascular disease and stroke. Subsequently, further studies in humans and in animals have demonstrated that there is an inverse relationship with a combination of suboptimal prenatal and postnatal environments and the development of the metabolic syndrome (insulin resistance, hypertension, obesity and dyslipidemia). However, recently it has been reported that not all individuals exposed to these environments develop these conditions, suggesting that an individual’s genotype may contribute to the eventual outcome. Phylogenetically distinct, murine strains allow the genetic dissection of complex phenotypic traits; however, to date, they have not been utilized to evaluate the gene-environment interaction underlying these inverse relationships. Thus, A/J and C57BL/6J mice were subjected to prenatal undernutrition, to model an adverse intra-uterine environment, and although prenatal undernutrition resulted in fetal growth restriction of equal magnitude, remarkable strain differences were observed. At the end of gestation C57BL/6J mice showed significant alterations in fetal organ weights (liver, kidneys and placenta) and glucocorticoids (elevation). Postnatally, C57BL/6J offspring demonstrated catch-up growth, obesity, impaired glucose tolerance, insulin resistance, increased blood pressure, liver dysfunction and altered cardiovascular function compared to strain and gender matched controls. The A/J strain was resistant to the development of prenatal and postnatal pathologies, except they also demonstrated alterations in cardiovascular function. Females of both strains displayed a more moderate phenotype than the males. Although feeding undernutrition mice an atherogenic diet postnatally did not exacerbate the phenotype, postnatal dietary supplementation of omega-3 long chain unsaturated fatty acids completely reversed the undernutrition induced altered metabolic phenotype in C57BL/6J. Microarray analysis revealed that adult A/J and C57BL/6J mice have distinct gene expression profiles, under control dietary conditions, and that this differential strain expression profile changes in adult offspring in response to prenatal undernutrition. The expression profiles predicted onset of metabolic and liver diseases within the C57BL/6J strain, clearly linking the observed phenotype to alterations in gene expression. These expression differences were also linked to inherent strain differences in the genetic code where a disproportionate number of differential expressed genes had function altering polymorphisms.

Type 2 diabetes is hallmarked by insufficient beta-cell insulin secretion and inappropriate alpha-cell glucagon secretion concomitant to peripheral insulin resistance. However, the mechanisms underlying dysregulation of pancreatic beta- and alpha-cells in type 2 diabetes require further investigation. Whereas triglycerides and saturated free fatty acids have been well recognized to cause beta-cell dysfunction, the physiological and/or pathological role of cholesterol on beta- and alpha-cells is less well examined. Cholesterol is the major component of membrane microdomains, termed lipid rafts. Numerous signaling and transport proteins have been found to be targeted to lipid raft microdomains, where the function of the associated membrane proteins could be distinctly regulated. I have identified the expression of lipid raft constituent proteins, caveolin-1/2 in pancreatic beta-cells; and caveolin-2 in alpha-cells. A variety of membrane proteins (ion channels and SNARE proteins) critical for beta- and alpha-cell stimulus-secretion coupling were found to be associated with cholesterol-rich lipid raft microdomians, and the properties of those ion channels (Kv2.1, Kv4.1/4.3, and Cav1.2 channels) and SNARE proteins were closely regulated by cholesterol-rich lipid rafts. Acute depletion of cholesterol from the plasma membrane with methyl-beta-cyclodextrin caused an elevated basal hormone secretion from both beta- and alpha-cells and a loss of glucose-stimulated insulin secretion, implicating that cholesterol-rich lipid rafts play an important role in regulating exocytosis of these two types of islet cells. Chronic pharmacological inhibition of beta-cell endogenous cholesterol biosynthesis with squalene epoxidase inhibitor caused an impairment of both Cav channels and SNARE protein exocytotic machinery, indicating that intracellular cholesterol and its homeostasis are critical for maintaining normal beta-cell function. The work presented in this thesis provided clear evidence that cholesterol-rich lipid rafts play a critical role in maintaining the normal function of pancreatic ion channels and SNARE proteins to regulate pancreatic beta- and alpha-cells stimulus-secretion coupling. Manipulation of cholesterol level of beta- and alpha-cells could be a potential target for a therapeutic intervention in the treatment of type 2 diabetes.

Type 2 diabetes is hallmarked by insufficient beta-cell insulin secretion and inappropriate alpha-cell glucagon secretion concomitant to peripheral insulin resistance. However, the mechanisms underlying dysregulation of pancreatic beta- and alpha-cells in type 2 diabetes require further investigation. Whereas triglycerides and saturated free fatty acids have been well recognized to cause beta-cell dysfunction, the physiological and/or pathological role of cholesterol on beta- and alpha-cells is less well examined. Cholesterol is the major component of membrane microdomains, termed lipid rafts. Numerous signaling and transport proteins have been found to be targeted to lipid raft microdomains, where the function of the associated membrane proteins could be distinctly regulated. I have identified the expression of lipid raft constituent proteins, caveolin-1/2 in pancreatic beta-cells; and caveolin-2 in alpha-cells. A variety of membrane proteins (ion channels and SNARE proteins) critical for beta- and alpha-cell stimulus-secretion coupling were found to be associated with cholesterol-rich lipid raft microdomians, and the properties of those ion channels (Kv2.1, Kv4.1/4.3, and Cav1.2 channels) and SNARE proteins were closely regulated by cholesterol-rich lipid rafts. Acute depletion of cholesterol from the plasma membrane with methyl-beta-cyclodextrin caused an elevated basal hormone secretion from both beta- and alpha-cells and a loss of glucose-stimulated insulin secretion, implicating that cholesterol-rich lipid rafts play an important role in regulating exocytosis of these two types of islet cells. Chronic pharmacological inhibition of beta-cell endogenous cholesterol biosynthesis with squalene epoxidase inhibitor caused an impairment of both Cav channels and SNARE protein exocytotic machinery, indicating that intracellular cholesterol and its homeostasis are critical for maintaining normal beta-cell function. The work presented in this thesis provided clear evidence that cholesterol-rich lipid rafts play a critical role in maintaining the normal function of pancreatic ion channels and SNARE proteins to regulate pancreatic beta- and alpha-cells stimulus-secretion coupling. Manipulation of cholesterol level of beta- and alpha-cells could be a potential target for a therapeutic intervention in the treatment of type 2 diabetes.

Retrospective epidemiological studies of British cohorts have found an inverse relationship between birth size and rates of mortality from cardiovascular disease and stroke. Subsequently, further studies in humans and in animals have demonstrated that there is an inverse relationship with a combination of suboptimal prenatal and postnatal environments and the development of the metabolic syndrome (insulin resistance, hypertension, obesity and dyslipidemia). However, recently it has been reported that not all individuals exposed to these environments develop these conditions, suggesting that an individual’s genotype may contribute to the eventual outcome. Phylogenetically distinct, murine strains allow the genetic dissection of complex phenotypic traits; however, to date, they have not been utilized to evaluate the gene-environment interaction underlying these inverse relationships. Thus, A/J and C57BL/6J mice were subjected to prenatal undernutrition, to model an adverse intra-uterine environment, and although prenatal undernutrition resulted in fetal growth restriction of equal magnitude, remarkable strain differences were observed. At the end of gestation C57BL/6J mice showed significant alterations in fetal organ weights (liver, kidneys and placenta) and glucocorticoids (elevation). Postnatally, C57BL/6J offspring demonstrated catch-up growth, obesity, impaired glucose tolerance, insulin resistance, increased blood pressure, liver dysfunction and altered cardiovascular function compared to strain and gender matched controls. The A/J strain was resistant to the development of prenatal and postnatal pathologies, except they also demonstrated alterations in cardiovascular function. Females of both strains displayed a more moderate phenotype than the males. Although feeding undernutrition mice an atherogenic diet postnatally did not exacerbate the phenotype, postnatal dietary supplementation of omega-3 long chain unsaturated fatty acids completely reversed the undernutrition induced altered metabolic phenotype in C57BL/6J. Microarray analysis revealed that adult A/J and C57BL/6J mice have distinct gene expression profiles, under control dietary conditions, and that this differential strain expression profile changes in adult offspring in response to prenatal undernutrition. The expression profiles predicted onset of metabolic and liver diseases within the C57BL/6J strain, clearly linking the observed phenotype to alterations in gene expression. These expression differences were also linked to inherent strain differences in the genetic code where a disproportionate number of differential expressed genes had function altering polymorphisms.

Doctor of Philosophy / Department of Anatomy and Physiology / Thomas J. Barstow / The primary aim of this dissertation was to evaluate the factors that contribute to the cardiorespiratory and vascular responses following exercise conditioning and microgravity deconditioning. The first study of this dissertation (Chapter 2) revealed that exercise training in the head down tilt posture, which places increases central blood volume compared to upright, results in cardiorespiratory adaptations in both upright and head down tilt postures which are not completely expressed with exercise training in the upright posture. These findings suggest that augmentation of the ventricular volume load during exercise training may result in adaptations that transfer across multiple body positions. In the second and third studies measurements of blood velocity and flow were performed via Doppler ultrasound. In Chapter 3 we observed that in the brachial and femoral arteries blood moves with a slightly blunted parabolic velocity profile that is very stable across a range of mean arterial pressures and downstream limb resistances. We concluded that these findings support the current calculations of shear rate based on the assumptions of laminar flow. With these assumptions confirmed, the investigation in Chapter 4 could be performed. We observed that acute exposure to a sustained antegrade shear rate, via unilateral forearm heating, increased measurements of flow-mediated dilation and the overall rate of adjustment for forearm blood flow and vascular conductance during dynamic handgrip exercise. These findings suggest that one potential stimulus for improvements in vascular function and health following exercise conditioning may be exposure to elevations in antegrade shear. Lastly in Chapter 5 we changed focus to the cardiorespiratory deconditioning following long-duration microgravity exposure. We retrospectively reviewed and analyzed previous investigations of microgravity deconditioning and demonstrated that the decrease in maximal O2 consumption ( O2max) occurs as a function of duration of exposure and that both convective and diffusive O2 transport pathways substantially contribute to this decline. In addition we reviewed the current literature and highlighted potential mechanisms, across several organ systems, which may contribute to this decline in O2max. Collectively, these studies revealed the breath of plasticity for cardiorespiratory adaptations to a variety of stressors.

The physiological mechanisms that control energy homeostasis are reciprocally linked to reproduction. However, the neuroendocrine circuitry that registers endocrine cues to direct homeostatic responses in energy balance and reproduction remain unknown. Neuropeptide Y (NPY) neurons have emerged as a key central target of estrogen and leptin that are capable of modulating both reproduction and energy balance. The hypothesis was generated that NPY neuronal subpopulations act as an integration centre to regulate the effects of estrogen and leptin on these important physiological processes through specific signaling pathways. Using hypothalamic cell lines that express the leptin receptor (Ob-R), estrogen receptor (ER) and NPY, this hypothesis was tested in three aims. 17β-estradiol (E2) was previously demonstrated to biphasically regulate NPY mRNA in the mHypoE-38 neuronal cell line; where 24 h E2 exposure induced NPY gene expression that our group proposed may be involved in the gonadotropin-releasing hormone (GnRH) preovulatory surge. E2 also acts as an anorexigenic hormone through unknown hypothalamic targets. E2 directly decreased NPY secretion in the mHypoE-42 and mHypoA-2/12 neuronal cell lines through ER-α. The anorexigenic action of E2 was mediated through the energy sensing 5’ AMP-activated protein kinase (AMPK) and the phosphoinositide-3-kinase (PI3K) pathway. NPY secretion was also decreased by leptin in mHypoA-59 and NPY-GFP cell models through AMPK- and PI3K-dependent mechanisms. Prolonged exposure to leptin in NPY-GFP cell lines prevented AMPK signaling and the leptin-mediated reduction in NPY secretion, indicating NPY neuronal resistance with prolonged leptin exposure. Leptin also stimulated NPY secretion in mHypoE-38 neurons, which was blocked by pharmacological inhibitors of the mitogen-activated protein kinase (MAPK) and PI3K pathways. Importantly, conditioned medium from the mHypoE-38 NPY neuronal cells induced GnRH transcripts in GT1-7 neurons, which was inhibited by Y1-receptor antagonists. Pharmacological inhibitors of the MAPK and PKA signal transduction pathways attenuated the NPY-mediated increase in GnRH transcription. Based upon these findings, I propose NPY neurons in the hypothalamus consist of a heterogeneous population of neurons, and provide the first evidence of intrinsically different responses to function as physiological integrators for two different systems: NPY secretion can be suppressed to decrease food intake and induced to stimulate GnRH neurons.

GLP-2 is a potent intestinotrophic peptide that can increase mucosal growth, intestinal blood flow, and nutrient absorption when administered exogenously. We aimed to delineate the effects of endogenous GLP-2R signalling in conditions of nutrient deprivation and excess. Using a mouse with a targeted genetic deletion of the Glp2r gene (Glp2r-/-), we addressed the hypothesis that the known GLP-2R is required for intestinal adaptation to nutrient deprivation and excess. In Chapter 2, we demonstrate that Glp2r−/− mice fasted for 24 hours and re-fed for 24 hours failed to increase intestinal growth and jejunal crypt cell proliferation compared to littermate Glp2r+/+ mice. Administration of EGF to Glp2r−/− during the re-feeding period rescued this re-feeding defect. Wildtype mice re-fed for 30, 90, and 180 minutes following a 24 hour fast displayed increased jejunal mRNA levels of the ErbB ligands amphiregulin, epiregulin and HB-EGF. Treatment with the pan ErbB inhibitor CI-1033 inhibited induction of these ErbB ligands in jejunum of mice in association with prevention of crypt cell proliferation. Re-feeding also caused an increase in jejunal p-Akt levels and treatment with CI-1033 prevented increased p-Akt levels. Moreover, re-fed Glp2r−/− mice failed to increase ErbB ligands or p-Akt levels 90 minutes following re-feeding when compared to Glp2r+/+ littermates. Therefore, the GLP-2R is essential for re-feeding induced intestinal adaptation by activating the ErbB network and p-Akt to increase crypt cell proliferation. In Chapter 3, we show that the known GLP-2R is not required for intestinal adaptation to a perceived nutrient deprivation challenge (STZ-induced diabetes) or chronic nutrient excess (high-fat diet induced glucose intolerance). Although exogenous GLP-2 administration has been previously shown to stimulate glucagon secretion, glucose homeostasis was normal in STZ-diabetic and high fat fed Glp2r−/− mice. We also developed a third model of diabetes and glucose intolerance: ob/ob: Glp2r−/−. In the absence of GLP-2R signalling, ob/ob mice display improved oral but impaired intraperitoneal glucose tolerance, elevated fed and fasted glucose levels, increased circulating glucagon, decreased beta cell and increased alpha cell mass. Taken together, these results suggest that endogenous GLP-2R signalling is essential for intestinal and islet adaptation to conditions of nutrient deprivation and excess.

Neuroplastic changes in motor representations within the primary motor cortex (M1) have been described after peripheral manipulations and implicated in motor learning and adaptation processes. It is unclear whether dental manipulations, which may result in altered oral sensorimotor functions, are associated with analogous changes within face-M1. This project applied intracortical microstimulation (ICMS) and recordings of evoked muscle electromyographic (EMG) activity to test if changes occur in the ICMS-defined motor representations of tongue-protrusion (genioglossus, GG) and jaw-opening (anterior-digastric, AD) muscles within face-M1 and adjacent face primary somatosensory cortex (face-S1) following trimming or extraction of the rat’s right mandibular incisor, or a change in diet consistency. ICMS mapping was carried out in anaesthetised adult male rats. Consistent with previous findings, AD and GG had extensive motor representations showing considerable overlap in naïve and sham control rats. AD and GG motor representations were also found within face-S1. Left and right AD (LAD, RAD) had significantly larger representations with shorter onset latency of ICMS-evoked EMG responses within contralateral face-M1. A change in diet consistency for 2-3 weeks was not associated with significant changes in AD and GG motor representations within face-M1. Compared to control rats, iii incisor trimming out of occlusion for a period of 1 week resulted, 1 day later, in a significantly longer GG onset latency in ipsilateral than in contralateral face-M1; 1 week later, despite a regain of normal occlusion, GG and GG/AD overlapping representations were significantly larger and the centre of gravity (at AP 4.0) was significantly deeper in contralateral than in ipsilateral face-M1. Incisor extraction was associated, 1 week later, with significantly larger RAD and RAD/GG overlapping representations and a lateral shift of LAD and RAD centre of gravity. Extraction also induced significant changes in AD and GG motor representations within the contralateral face-S1. These novel findings indicate that face-M1 can undergo neuroplastic changes in association with intraoral manipulations and also suggest similar neuroplastic capabilities for face-S1 motor outputs. These findings contribute to our understanding of the role of face-M1 and face-S1 in sensorimotor adaptations to an altered oral state and provide the basis for several future studies.

Pancreatic alpha- and beta-cells play vital roles in maintaining glucose homeostasis. While much work has investigated beta-cell biology, alpha-cell research has been scarce. This is due to limitations in conventional methods of alpha-cell preparation, which expose alpha-cells on the islet mantle to enzymatic and mechanical injury inherent in the preparation. I have employed the pancreas tissue slice preparation, which surmounts these limitations. Pancreas slices can be prepared efficiently, and islet cells examined in situ without requiring culture conditions. Alpha-cells are preserved in their native cellular environment not only in health, but more remarkably, also in disease (type 1 diabetes; T1D) states, which was not previously feasible. In the first part of my study, I deployed this preparation to assess normal mouse alpha-cell physiology. Alpha-cells exhibited well-described features of INa, IKATP, small cell size, low resting membrane conductance, and inducible low and high voltage-activated ICa, the latter correlating with exocytosis determined by capacitance measurements. In contrast to previous reports, our large sampling of alpha-cells revealed a wide-range data distribution of several ion channel parameters. My findings explain the apparent inconsistency of previous reports wherein alpha-cell ion channel properties appeared skewed within narrow portions of this wide distribution, likely caused by different preparations. In the second part of my thesis, I assessed alpha-cell perturbation in streptozotocin-induced T1D in the GluCre-ROSA26EYFP (GYY) mouse. In this T1D model, alpha-cells exhibited more glucagon content per cell, which can be exocytosed in greater quantity upon serial depolarization. Membrane electrical properties revealed larger Na+ current and reduced KV-transient current, which contributed to the apparent increased amplitude and firing frequency of action potentials in membrane electrical recording. These electrical events likely prime alpha-cells to release more glucagon, culminating in larger in vivo glucagon secretory responses to low glucose stimulation in this T1D model. We are now well-positioned to employ this in situ model of pancreas slice preparation to address many other apparently unanswerable questions in alpha-cells in normal and pathophysiologic states, such as diabetes.