Hypothalamus Lecture Notes PDF

Hypothalamus is the master and commander of Autonomic Integration “mainspring of primitive existence - vegetative, emotional , reproductive…….man has come to superimpose a cortex of inhibitions”…. Cushing 1929. Lecture 3; 10/11/23 Dr. F. Gomez-Pinilla C144/244 – Fall quarter 2023 Hypothalamus con...

Hypothalamus is the master and commander of Autonomic Integration “mainspring of primitive existence - vegetative, emotional , reproductive…….man has come to superimpose a cortex of inhibitions”…. Cushing 1929. Lecture 3; 10/11/23 Dr. F. Gomez-Pinilla C144/244 – Fall quarter 2023 Hypothalamus controls Autonomic Function • Control of homeostasis (housekeeping mechanisms). • Works in concert with the endocrine system to continuously adjust blood chemistry, respiration, circulation, digestion, immune system, body temperature, sexual function, etc. • Plays a pivotal role controlling emotions. • Coordinates a fast physiological response during emergencies, but • Most of the time is doing housekeeping work F. Gomez-Pinilla, C144/244 Middle or Posterior or F. Gomez-Pinilla, C144/244 F. Gomez-Pinilla, C144/244 The hypothalamus integrates neuroendocrine and autonomic functions F. Gomez-Pinilla, C144/244 • • • • • How Hypothalamus can regulate autonomic functions By integrating functions of several regulatory centers. Receives connections from most major divisions of the CNS. Communicates with periphery via the ANS and hormones. Hypothalamus and pituitary form a functional unit. Neurohumoral regulation: release of peptides (hormones) from neurons to peripheral circulation. F. Gomez-Pinilla, C144/244 Circumventricular Organs (CVO): chemosensitive, absence of blood brain barrier; connect brain and body through chemical messengers • • • • Median eminence (ME), inside HP Pituitary (intermediate and post lobes) Vascular organ of lamina terminalis (OVLT), inside HP Subfornical Organ (SFO), connect with HP. Chemosensitive neurons control fluid dynamics (kidney). • Area postrema (AP), connect to HP via NTS. Regulate food intake, cardiovascular, vomiting. • Subcommissural organ (SCO) • Pineal gland F. Gomez-Pinilla, C144/244 Lack of BBB enabling transfer of chemical, hormones, etc, across peripheral and brain blood vessels is key feature of CVOs F. Gomez-Pinilla, C144/244 The posterior lobe of the pituitary is a CVO. Its lack of BBB enables transfer of hormones from neurons to body circulation Posterior lobe receives axon terminals of secretory neurons (tuberohypophyseal tract) from SON and PVN. Oxytocin: milk letdown reflex Vasopresin: water homeostasis F. Gomez-Pinilla, C144/244 The median eminence (ME) of the pituitary is a CVO which lack of BBB enables transfer of hormones into portal blood vessels Axons from arcuate and PVN secrete regulatory hormones (releasing factors) and DA to portal vessels in ME which transport them into the anterior lobe. Example: arcuate nucleus releases growth hormone-releasing hormone to portal vessels to stimulate release of growth hormone from ant. Lobe cells F. Gomez-Pinilla, C144/244 hypothalamus has the ability to use electrophysiological activity (action potentials) to release hormones into periphery F. Gomez-Pinilla, C144/244 • • • • • • Hypothalamic Connections Integrate Sensory and Nonsensory Information Olfaction, to several HP regions from olfactory regions. Important for survival and reproduction in many vertebrates. Photic (visual), projections from eye to suprachiasmatic nucleus (SCN). Part of circadian timing system. Visceral sensation, nucleus solitary tract (NTS) <-----> PVH and LHA. Integrates visceral, cardiorespiratory, cardiovascular, taste – using cranial nerves IX and X. Multimodal brainstem afferents, bidirectional projections to diverse brain regions via medial forebrain bundle. Projections from limbic regions (hippocampus, amygdala, septum), regulates neuroendocrine, ingestive, and autonomic behaviors important for emotions, motivation. Circumventricular organs (CVO, 7), chemosensitive regions, absence of blood brain barrier allows peripheral signals influence CNS. F. Gomez-Pinilla, C144/244 Hypothalamus can also affect immune function F. Gomez-Pinilla, C144/244 Hypothalamic Functions • • • • • • • Central Integration of autonomic function achieved by coordinating ascending and descending projections to other integrative centers. Reproductive, control of sexual function (glands and organs) Immune, via endocrine and ANS, e.g., ANS action on spleen Behavioral state, timing of behaviors, e.g., sleep-wake cycle via SCN; and caudal hypothal control arousal. Narcolepsy (defect in hypocretin receptor) Neuroendocrine regulation: ant and post pituitary. Thermoregulation, in conjunction with circadian rhythms and environmental signals; dysfunction=fever. Fluid homeostasis and thirst, OVLT, SFO, NST Food intake, via integration of a variety sensory stimuli (neural/hormonal) to viscera F. Gomez-Pinilla, C144/244 Hypothalamic disorders • • • • • • • • Eating disorders (anorexia, diabetes, obesity) Blood vessel problems in brain (aneurysm) Circadian rhythm dysregulation, sleep disorders Body temperature dysregulation Developmental problems Kallmann syndrome Problems in fertility Intellectual and emotional disabilities Metabolism: fatigue, weakness F. Gomez-Pinilla, C144/244 Hypothalamus integrates autonomic reflexes • Autonomic reflexes: coordinates function of various organs such as mouth, stomach, intestines, pancreas after a meal • Hypothalamus integrates reflexes using bidirectional communication via ascending and descending pathways. Bidirectional projections to brainstem integrative centers such as nucleus tract solitarius (NST), rostroventrolateral medula (RVLM regulates cardiovascular function), and to spinal cord. • Hypothalamus links autonomic reflexes with somatic events -e.g., cardiovascular and postural adjustment • Hypothalamus coordinates Autonomic adjustments in response to environmental events F. Gomez-Pinilla, C144/244 Pathways that communicate hypothalamus with upper and lower centers (brainstem and spinal cord) F. Gomez-Pinilla, C144/244 Hypothalamus has bidirectional communication with periphery via ascending and descending pathways Ascending pathways linking periphery with hypothalamus and other brain centers that regulate Autonomic function • spinal lamina V connects with Nucleus solitary tract (NST) and then with midbrain central gray, hypothalamus, amygdala, nucleus of stria terminalis F. Gomez-Pinilla, C144/244 Descending pathways from hypothalamus and other brain regions to brain stem and spinal cord • Descending projections from supraspinal centers to preganglionic neurons in brain stem and spinal cord • For example, hypothalamic paraventricular nucleus (PVN) projects to vagal neurons, nucleus of solitary tract (NST), and Spinal laminae (lam. V) and then to intermediolateral cell column • And from there to peripheral organs F. Gomez-Pinilla, C144/244 The hypothalamus exerts its functions using Central Network that regulates autonomic and endocrine functions • Hypothalamus • Limbic regions (hippocampus, amygdala, nucleus of stria terminalis, cingulate cx, orbital frontal cx, insular cx, and rhinal cx., septal region) • Central grey • Paramedian regions of mesencephalon F. Gomez-Pinilla, C144/244 The hypothalamus regulates emotions using limbic system pathways Limbic regions (hippocampus, amygdala, nucleus of stria terminalis, cingulate cx, orbital frontal cx, insular cx, and rhinal cx., septal region) F. Gomez-Pinilla, C144/244 Feeding reflex: coordinates mouth, stomach, intestines, pancreas after a meal F. Gomez-Pinilla, C144/244 Example of autonomic integration important for regulation of circadian clock F. Gomez-Pinilla, C144/244 Regulation of circadian timing system F. Gomez-Pinilla, C144/244