Final INTRONS

• Point-to-point communication


  Restricted synaptic activation of target cells and signals of brief duration
• Secretory hypothalamus


  Neurons affect their many targets by releasing hormones directly into the bloodstream
• Autonomic nervous system (ANS)


  Networks of interconnected neurons can work together to activate tissues all over the body
• Diffuse modulatory systems


  Extend their reach throughout the brain with widely divergent axonal projections
• The hypothalamus forms the wall of the third ventricle and sits below the dorsal thalamus
• Functional zones of the hypothalamus


  • Lateral
  • Medial
  • Periventricular

  
• Periventricular zone of hypothalamus


  • Receives inputs from other zones, the brain stem, and the telencephalon
  • Neurosecretory cells secrete hormones into the bloodstream
  • Other cells control the autonomic nervous system

  
• Hypothalamic neurosecretory cells


  • Magnocellular
  • Parvocellular

  
• Magnocellular neurosecretory cells


  Secrete oxytocin and vasopressin directly into capillaries in the posterior lobe of the pituitary

  
• Parvocellular neurosecretory cells


  Secrete hypophysiotropic hormones into specialized capillary beds of the hypothalamo-pituitary portal circulation, which travel to the anterior lobe of the pituitary to trigger the release of pituitary hormones

  
• Communication between kidneys and brain


  1. Kidney secretes renin into bloodstream

  2. Renin promotes synthesis of angiotensin II

  3. Angiotensin II excites neurons in subfornical organ

  4. Neurons stimulate hypothalamus to increase ADH production and cause thirst

  
• Stress response


  1. Periventricular hypothalamus secretes CRH into hypothalamo-pituitary portal circulation

  2. CRH triggers release of ACTH into general circulation

  3. ACTH stimulates release of cortisol from adrenal cortex

  4. Cortisol can act on hypothalamic neurons and other neurons in the brain

  
• Hormones released from hypothalamic neurons and pituitary endocrine cells


  • Oxytocin
  • Vasopressin
  • Corticotropin-releasing hormone (CRH)
  • Adrenocorticotropin (ACTH)
  • Gonadotropin-releasing hormone (GnRH)
  • Luteinizing hormone (LH)
  • Follicle-stimulating hormone (FSH)
  • Growth hormone-releasing hormone (GHRH)
  • Growth hormone (GH)
  • Thyrotropin-releasing hormone (TRH)
  • Thyroid-stimulating hormone (TSH, also called thyrotropin)
  • Prolactin
  • Somatostatin
  • Dopamine
• Oxytocin and vasopressin are also released from synaptic terminals elsewhere as peptide neurotransmitters
• Neural outputs of the CNS


  • Somatic motor system (lower motor neurons in ventral horn of spinal cord and brain stem)
  • Sympathetic division of ANS (post-ganglionic neurons in autonomic ganglia)
  • Parasympathetic division of ANS (post-ganglionic neurons in autonomic ganglia)

  
• Nucleus of the solitary tract


  • Receives input from primary taste and visceral sensory afferents
  • Sends projections to gustatory nucleus in ventral posterior thalamus
  • Provides input to primary visceral motor nuclei
  • Projects to "premotor" autonomic centers in medullary reticular formation and to higher integrative centers in amygdala and hypothalamus

  
• Parabrachial nucleus


  Relays visceral sensory information to the hypothalamus, amygdala, thalamus, and medial prefrontal and insular cortex

  
• The hypothalamus integrates visceral sensory input and higher-order visceral motor signals

  
• Divisions of the autonomic nervous system


  • Sympathetic
  • Parasympathetic
• Sympathetic division


  • Uses norepinephrine as the postganglionic neurotransmitter (except for sweat glands and vascular smooth muscle within skeletal muscle, which use acetylcholine)
  • Most active during crisis, real or perceived
  • Behaviors related to it are fight, flight, fright, and sex
• Parasympathetic division


  • Uses acetylcholine as the postganglionic neurotransmitter
  • Facilitates non-crisis processes like digestion, growth, immune responses, and energy storage
• The effects of visceral motor activation are remarkably varied due to the challenge of maintaining homeostasis across the many organ systems of the body
• The enteric division of the autonomic nervous system is a unique neural system embedded in the lining of the digestive organs, consisting of the myenteric (Auerbach's) plexus and submucous (Meissner's) plexus

  
• Optogenetic activation of the glossopharyngeal nerve branch that collects input from the carotid sinus (site 3) or the vagus nerve branch that collects input from the aortic arch (site 2), but not the vagus nerve before the joining of the aortic arch branch (site 1)


  Causes reductions in blood pressure and heart rate

  
• Stimulation at site 2 in wild-type mice not expressing ChR2 has no effect
• Enteric division of the ANS


  A unique neural system embedded in the lining of the esophagus, stomach, intestines, pancreas, and gallbladder, consisting of two complicated networks (myenteric plexus and submucous plexus) that control many physiological processes involved in the transport and digestion of food
• The enteric division of the ANS contains about 500 million neurons, the same number of neurons as the entire spinal cord
• Enteric division of the ANS


  • Can operate with a great deal of independence
  • Enteric sensory neurons monitor tension and stretch of the gastrointestinal walls, the chemical status of stomach and intestinal contents, and hormone levels in the blood
  • This information is used by enteric interneuronal circuits and motor neurons to govern smooth muscle motility, the production of mucous and digestive secretions, and the diameter of the local blood vessels

  
• Diffuse modulatory systems


  • Typically have a small set of neurons (several thousand) in the core
  • Neurons arise from the central core of the brain, most from the brain stem
  • Each neuron can influence many others because each one has an axon that may contact more than 100,000 postsynaptic neurons spread widely across the brain
  • Synapses release transmitter molecules into the extracellular fluid so they can diffuse to many neurons rather than be confined to the vicinity of the synaptic cleft
  • Many psychoactive drugs affect these modulatory systems, and the systems figure prominently in current theories about the biological basis of some psychiatric disorders
• Noradrenergic diffuse modulatory system arising from the locus coeruleus


  Locus coeruleus neurons are most strongly activated by new, unexpected, nonpainful sensory stimuli in the animal's environment, and may participate in a general arousal of the brain during interesting events in the outside world
• Serotonergic diffuse modulatory systems arising from the Raphe nuclei


  Raphe nuclei cells fire most rapidly during wakefulness, when an animal is aroused and active, and are intimately involved in the control of sleep-wake cycles and different stages of sleep
• Cholinergic diffuse modulatory systems arising from the basal forebrain and brain stem


  The basal forebrain complex provides cholinergic innervation of the hippocampus and neocortex, while the pontomesencephalotegmental complex acts mainly on the dorsal thalamus to regulate the excitability of the sensory relay nuclei

  
• Dopaminergic diffuse modulatory systems


  One group of dopaminergic cells in the substantia nigra projects to the striatum and facilitates the initiation of voluntary movements, while another group in the ventral tegmental area (VTA) innervates the frontal cortex and parts of the limbic system, and is involved in a "reward" system that reinforces adaptive behaviors
• Animals are motivated to behave in ways that stimulate the release of dopamine in the basal forebrain area


  Arising from a group of cells that lie in the ventral tegmental area (VTA)
• Self-stimulation reveals the existence of reward pathways


  • Rats will self-stimulate when electrodes are placed in certain reward centers
  • Rats will withstand more foot shock when crossing a grid for electrical stimulation than they do when crossing for food after food deprivation
  • Transgenic rats expressing Cre in dopamine neurons show robust nose poking at an active port that results in photostimulation of the VTA
• Drugs of abuse increase dopamine action at VTA dopamine neuron targets, nucleus accumbens (NAc) and prefrontal cortex
• Reward prediction error signals in dopamine neurons of the VTA


  • Events that are "better than expected" cause dopamine neurons to fire, those that are "worse than expected" cause them to be inhibited, and those that occur "as expected" cause no change in firing
  • Behaviors that cause expected or better-than-expected outcomes are repeated; those with outcomes that are worse than expected are not
  • Dopamine is intimately involved in the mechanism behind this learning, as synaptic connections active during and shortly before a rise in dopamine are persistently changed to store this memory
• Nucleus of the solitary tract


  Part of this nucleus is a gustatory relay, receiving input from primary taste afferents (cranial nerves VII, IX, and X) and sending projections to the gustatory nucleus in the ventral posterior thalamus
• Nucleus of the solitary tract

  Caudal visceral sensory part provides input to primary visceral motor nuclei, such as the dorsal motor nucleus of the vagus nerve and the nucleus ambiguus
• Nucleus of the solitary tract

  Projects to "premotor" autonomic centers in the medullary reticular formation and to higher integrative centers in the amygdala and hypothalamus