Principles of neuroendocrinology Flashcards
neuroendocrinology
study of physiological processes involved in integrating neural and endocrine functions
brain produces neurohormones
neuroendocrine systems
set of neurons, glands, non-endocrine tissues and neurochemical, hormones, humoral signals they produce and receive, that function in an integrated manner to collectively regulate a physiological or behavioural state
neuroendocrine integration
process by which neuroendocrine signals register/transduce/interpret important signals/internal and external environment & direct adaptive changes in prevailing physiological and behavioural states
what do NTs/neurohormones/hormones cause
AP cause depolarisation of the nerve terminal
increase permeability
Ca2+ influx
NT release via exocytosis
hormones released by endocrine cells into bloodstream act at a distance to target cells
neurosecretion
production and secretion of neurohormones by neurons into the bloodstream
vesicles are larger (100-400um) longer AP duration = more Ca2+ influx per AP
neurosecretory cells
posterior pituitary (cell bodies in SON/PVN)
similar structure to other neurons/dendrites/perikarya/axons
different morphology for specialised function
peptidergic
peptides with varying size 3-50AA chains
peptide synthesised in cell body (larger inactive precursor polypeptide) on RER
golgi packages precursor material into granules, transported to terminals by axonal transport - copackaged peptidase enzyme processes the final secretory product within vesicles
e.g magnocellular neurons in PVN/SON product OT/AVP
neuropeptide processing
neuropeptide - prepro - pro - hormone
evidence for neuropeptide processing
cysteine (aa) associated with OT/AVP
radiolabelled cysteine injected in rat cerebral ventricles
radioactivity accumulates in SON/PVN of hypothalamus - radioactivity in pituitary stalk and posterior lobe
rat given hypertonic salt solution (for AVP secretion) causes faster accumulation and cysteine transport
axonal transport via radioactive phosphorus is identical
excitation/secretion coupling
depolarisation (AP) causes AVP secretion
depolarisation by increasing K+ concentration
increase in Ca2+ conc causes hormone release, agents which block Ca2+ interfere with secretory response
define homeostasis
process requiring co-ordinated control over endocrine, behavioural, autonomic nervous responses to the environment
hypothalamus at the base of the brain - sends projections to circulatory system and higher brain centres
what is the circumventricular organ
present in many sites in the ventricular system
lacks the BBB - endothelial cells are fenestrated allowing diffusion
hormones out/circulating factors in (median eminence)
types of nuclei in the hypothalamus
feeding: ARC/VMH/LH
drinking: PVN/SON
sexual behaviour: pre optic/VMH
stress response: PVN
electrolyte and water balance: SON/PVN
centre concept is outdated - fine tuning
what are the tissues which form the neurohypophysis and adenohypophysis
invagniation of FB (diencephalon) which form the posterior lob (neurohypophysis) - SON/PVN
outgrowth of the buccal cavity (rathke’s pouch) - forms anterior lobe (adenohypophysis) - glandular
pars intermedia forms MSH (not in adult humans)
secretion of the anterior and posterior pituitary
anterior: LH/FSH/TSH/ACTH/PRL/GH
posterior: AVP/OT
appetite hormones
leptin - secreted from adipose, decreases food intake
PYY3-36 - decreases food intake
GLP-1 - releases insulin
ghrelin - increases food intake
hypothalamo-hypopysial portal system
anterior pituitary passes via long/short hypophyseal portal vessels
superior hypophyseal artery supplies the median eminence and stalk
inferior hypophyseal artery supplies the posterior lobe and anterior lobe via short portal vessels
both lobes drain into venous sinuses
milk reflex
suckling activates the afferent nerves
activates efferent nerves in hypothalamus
neurosecretion of oxytocin
oxytocin mediated milk ejection
nipple innervation
contains mechanosensory nerves and sends an AP
increased OT via posterior P milk ejection via contraction
increased prolactin decreased DA (negative feedback)
neuronal reflex
similar to neuromuscular reflex
transient fixed pattern response to a stimulus
e.g. Posterior P OT milk ejection
homeostatic control mechanisms
restrict physiological/behavioural variable around a set point
use negative feedback
hypo-pituitary-endocrine organ axis
food intake
homeostatic neuroendocrine axis 3 Tier
HPT/HPA/HPG
hypothalamus to anterior pituitray via hypothalamus releasing/inhibiting factors
anterior pituitary to end organ by adenohypophysis hormone
end organ signals back to hypothalamus and pituitary
negative feedback via long/short loop feedback
Homeostatic neuroendocrine axis 2 tier
GH/PRL release - acts at multiple target organs, feedback from pituitary more important
hormone secretion mainly under control of short feedback loop (from anterior pituitary)
