Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

Hypothalamus

Hypothalamus

• “Older” part of the brain (Primitive)– Maintenance of homeostasis

• Reception of external and internal signals• Incorporation of signals to generate appropriate

responses– Endocrine– Autonomic– Behavioral

• Reception of feedback– Hormones

Anatomy of hypothalamus

• Landmarks– Anterior (front)

• Optic chiasm (crossing of optic nerve fibers)

– Posterior (dorsal/back)• Mamillary body

– Superior (cranial)• Third ventricle

– Inferior• Pituitary

stalk/infundiblum

• Neural organization of hypothalamus– Clusters of neurons

• Nucleus/nuclei

– Different section of hypothalamus contains different nuclei

Median eminence

• The center of the tuber cinereum (floor of the third ventricle)– Blood vessels– Nerve endings

• Functional link between hypothalamus and pituitary gland– Site where the pituitary portal vessels arise

• Extensive network of “arterialized” venus capillaries• Microcirculation between hypothalamus and anterior pituitary

• Three zones– Ependymal layer

• Cells with microvilli• Tanycytes

– Forms barrier between CSF and blood– Prevention of diffusion of hypothalamic factors

– Internal zone• Axons of hypothalamic neurons (supraoptic and

paraventricular)– Extended to the posterior pituitary

• Three zones– External zone

• Peptinergic neurons– Thyrotropin-releasing hormone (TRH)– Corticotropin-releasing hormone (CRH/CRF)– Gonadotropin-releasing hormone (GnRH/LHRH)

• Neurons that release monoamines – Serotonin and dopamine

• Portal vessels

• Release of hypothalamic peptides– Depolarization of

neural cells– Supporting elements

• Non-neural cells

– Coordinated regulation by interaction of neurons

• Hypothalamic• CNS

Types of neurosecretory system

• Magnocellular neurons– Neural cells located within hypothalamus

• Paraventricular hypothalamic nuclei• Supraoptic nuclei

– Axon extend through median eminence and enter the posterior pituitary gland

– Hormones produced by the neural cells in hypothalamus and transported to the posterior pituitary gland to be released

• Oxytocin• Vasopressin

• Parvicellular hypophyseotropic neurons– Nuerons within Paraventricular hypothalamic

nuclei and arcuate nuclei– Axons terminate in median eminence

• Portal plexus

– Factors released in portal circulation• Triggers secretion of anterior pituitary hormones

• Hypothalamic projection neurons– Communication between neurons

• Hypothalamic neurons– Paraventricular hypothalamus– Lateral hypothalamic area– Arcuate nuclei

• Target neurons– Preganglionic neurons in spinal cord

• Use of hormones as neural signals

Regulation of hypothalamic hormone secretion

• Role of neurons within the brain– Intrinsic and extrinsic cues

• Sensory neurons• Neurotransmitters

– Excitatory

– Inhibitory

– Neurotransmitters• Monoamines

– Dopamine, Nor, Epi, Serotonin, Histamine, and acetulcholine

• Amino acids– Gamma-aminobutyric acid (GABA), glycine, and glutamate

Regulation of hypothalamic hormone secretion

• Role of neurons within the brain– Neurotransmitters

• Excitation or inhibition depend on the type of receptor present on the peptinergic neurons

• Feedback system– Production of hormones by target tissue

• Release of TSH from hypothalamus results in release of TRH from pituitary gland and subsequently production of T3 and T4 by thyroid gland

– Hypothalamus and pituitary gland• Target tissue to steroid and thyroid hormones

• Types of feedback– Long-loop

• From target organ to hypothalamus, pituitary, or higher brain

– Short-loop• Between hypothalamus

and pituitary• Retrograde flow of

pituitary hormones to hypothalamus

– Autofeedback (autoinhibition)

• Within the hypothalamus

• Result of feedback– Inhibition of pituitary hormone release

• Prevent action of hypothalamic hormones– Inhibitor production

• Alteration of cell population• Alteration of cellular sensitivity to hypothalamic

hormones– GnRH receptor concentrations increase in response to

estradiol– TRH receptor concentrations decrease in response to

thyroxin

Regulation of secretory rhythm/pattern

• Biological clock– Circadian rhythm

• Diurnal activity• Light-dark cycle (Day/night)

– Changes in external environment

– Regulated by supraoptic nuclei

• Pituitary hormones– Episotic/pulsatile secretion

• Critical for normal function

Action of hypothalamic hormones

• Anterior pituitary gland– Heterogeneous population of cells

• Several secretory cells

• Hypothalamic hormones– Elicit/inhibit action potential

• Ca-dependent

– Induce/inhibit cAMP production• Activity of adenylcyclase