PHY3181 Neuroendocrinology, PHY3181:
Neuroendocrinology Exam Study Guide
Describe the HPG axis pathway, creating GnRH to gonadotrope (L7, P4) - ANSWER 1.
Start at the hypothalamus for GnRH synthesis
2. GnRH is then stored and released at the Median Eminence
3. The GnRH is then transported from the Portal Blood System
4. The Anterior Pituitary is the location in where GnRH exerts its action
Difference between GnRH and GnRH neurons? (L7, P5) - ANSWER GnRH is a hormone
secreted by neuroendocrine cells in the hypothalamus that reaches the anterior
pituitary via the hypothalamopituitary portal blood vessels.
GnRH neurons are the cells in the brain that control the release of reproductive
hormones from the pituitary
Where are GnRH neurons located? (L7, P8) - ANSWER primarily located in the medial
preoptic area, but are sparsely distributed throughout the pre-optic area and
mediobasal hypothalamus
What makes GnRH neurons different to other neuroendocrine cells? (L7, P8) - ANSWER
GnRH do NOT form a tight grouping
Characteristics of GnRH neurons (L7, P11) - ANSWER - are relatively small (10-20µm)
- are oval or fusiform in shape
- have "rough" cell bodies and proximal dendrites with spiny processes
- have dendrites that extend from one or both poles, both receiving and transmitting
information
- talk to each other via dendrites
- must act in concert to create pulses
How do dendrites of GnRH neurons interact? (L7, P12) - ANSWER 1. wrapped around
each other on the same axis (vertical dendritic bundling)
(or)
2. intercepted other GnRH neuron dendrites in a perpendicular fashion (horizontal
dendritic intersection)
,Do GnRH neurons possess axons? (L7, P13) - ANSWER Classical axonal or dendritic
markers are not detectable in the projection of GnRH neurons to the median eminence
to control pituitary hormone secretion.
What are dendrons? (L7, P13) - ANSWER - GnRH neurons posses dendrons, which are
thread-like long-range extensions of the cytoplasm of a neuron that function as an axon
and dendrite simultaneously
- they typically branch into treelike processes and compose most of the receptive
surface of a neuron.
Where are the GnRH terminals located? (L7, P17) - ANSWER in the median eminence
What is the median eminence? (L7, P17) - ANSWER highly specialised structure where
GnRH neurons project to the external zone of the median eminence to receive synaptic
input
What makes portal vessels efficient in transportation of GnRH? (L7, P18) - ANSWER
Portal vessels of the primary capillary bed of the hypophyseal portal system are
fenestrated, allowing rapid transport of hypothalamic substances to the anterior
pituitary.
How is GnRH secretion triggered? (L7, P20) - ANSWER GnRH secretion is triggered by
periodically brief action potentials bursts in GnRH neurons in the hypothalamus
What is the relationship between the GnRH secretion and LH secretion? (L7, P20) -
ANSWER There is a one-to-one relationship between GnRH secretion from the
hypothalamus and LH secretion from the anterior pituitary
Does continuous GnRH stimulate LH and/pr FSH secretion? (L7, P22) - ANSWER
Continuous GnRH does not stimulate LH or FSH secretion.
What is the relationship between GnRH and LH secretion? (L7, P22) - ANSWER Pulsatile
input of GnRH to the pituitary gland is essential for LH secretion
Is FSH secretion passive or active? (L7, P22) - ANSWER FSH secretion is passive (ie. not
pulsatile)
What is the relationship between GnRH and FSH synthesis? (L7, P22) - ANSWER GnRH
is required for the maintenance of FSH synthesis, but FSH secretion does not require
pulsatile GnRH input
Why is pulsatile GnRH secretion important? (L7, P22) - ANSWER Pulsatile GnRH
secretion is important because the cells of the anterior pituitary that secrete the
gonadotropins will not respond to GnRH if the plasma concentration of this hormone
remains elevated over time.
How is GnRH controlled? (L7, P24) - ANSWER by a closed feedback loop system
, Stimulus (GnRH) -> Effector (LH/FSH) -> Sensor (Sex steroids)
What are the negative feedback hormones? (L7, P25) - ANSWER Estrogen,
Progesterone, Testosterone
What are the positive feedback hormones? (L7, P25) - ANSWER Estrogen
What are the feedback effects of gonadal sex steroids? (L7, P25) - ANSWER Feedback
effects of gonadal sex steroids may involve changes in the frequency and/ or amplitude
of GnRH pulses.
What are the sex differences in negative feedback effects? (L7, P26) - ANSWER -
Estrogen has a short-term negative feedback effect in the early follicular phase to
reduce GnRH pulse amplitude
- Progesterone reduces GnRH pulse frequency in the luteal phase
- Testosterone reduces GnRH pulse frequency in males
When does estrogen switch its negative feedback to positive feedback? (L7, P28) -
ANSWER Late follicular phase
What are convergent pathways? (L8, P7) - ANSWER Convergent pathways act as a
gating system to allow information to be integrated up so only one combined signal is
sent to GnRH neurons
How is GnRH neurons modulated? (L8, P8) - ANSWER By neuronal afferents that provide
direct and/or relayed input from various regions of the brain
Why is the convergent pathway used for GnRH neurons? (L8, P8) - ANSWER Prevents
information overload at a single neuron and allows neurons to act in concert.
List (2) what is involved in relaying steroid feedback to GnRH neurons (L8, P10) -
ANSWER the neuropeptides - Kisspeptin and gonadotropin inhibitory hormone (GnIH)
that express the relevant receptors
What are kisspeptins (metastin)? (L8, P11) - ANSWER family of proteins that are
essential for fertility.
- Neuropeptide encoded by the KISS1 gene
- Acts on Kisspeptin receptor (KISS1R)
Neuroendocrinology Exam Study Guide
Describe the HPG axis pathway, creating GnRH to gonadotrope (L7, P4) - ANSWER 1.
Start at the hypothalamus for GnRH synthesis
2. GnRH is then stored and released at the Median Eminence
3. The GnRH is then transported from the Portal Blood System
4. The Anterior Pituitary is the location in where GnRH exerts its action
Difference between GnRH and GnRH neurons? (L7, P5) - ANSWER GnRH is a hormone
secreted by neuroendocrine cells in the hypothalamus that reaches the anterior
pituitary via the hypothalamopituitary portal blood vessels.
GnRH neurons are the cells in the brain that control the release of reproductive
hormones from the pituitary
Where are GnRH neurons located? (L7, P8) - ANSWER primarily located in the medial
preoptic area, but are sparsely distributed throughout the pre-optic area and
mediobasal hypothalamus
What makes GnRH neurons different to other neuroendocrine cells? (L7, P8) - ANSWER
GnRH do NOT form a tight grouping
Characteristics of GnRH neurons (L7, P11) - ANSWER - are relatively small (10-20µm)
- are oval or fusiform in shape
- have "rough" cell bodies and proximal dendrites with spiny processes
- have dendrites that extend from one or both poles, both receiving and transmitting
information
- talk to each other via dendrites
- must act in concert to create pulses
How do dendrites of GnRH neurons interact? (L7, P12) - ANSWER 1. wrapped around
each other on the same axis (vertical dendritic bundling)
(or)
2. intercepted other GnRH neuron dendrites in a perpendicular fashion (horizontal
dendritic intersection)
,Do GnRH neurons possess axons? (L7, P13) - ANSWER Classical axonal or dendritic
markers are not detectable in the projection of GnRH neurons to the median eminence
to control pituitary hormone secretion.
What are dendrons? (L7, P13) - ANSWER - GnRH neurons posses dendrons, which are
thread-like long-range extensions of the cytoplasm of a neuron that function as an axon
and dendrite simultaneously
- they typically branch into treelike processes and compose most of the receptive
surface of a neuron.
Where are the GnRH terminals located? (L7, P17) - ANSWER in the median eminence
What is the median eminence? (L7, P17) - ANSWER highly specialised structure where
GnRH neurons project to the external zone of the median eminence to receive synaptic
input
What makes portal vessels efficient in transportation of GnRH? (L7, P18) - ANSWER
Portal vessels of the primary capillary bed of the hypophyseal portal system are
fenestrated, allowing rapid transport of hypothalamic substances to the anterior
pituitary.
How is GnRH secretion triggered? (L7, P20) - ANSWER GnRH secretion is triggered by
periodically brief action potentials bursts in GnRH neurons in the hypothalamus
What is the relationship between the GnRH secretion and LH secretion? (L7, P20) -
ANSWER There is a one-to-one relationship between GnRH secretion from the
hypothalamus and LH secretion from the anterior pituitary
Does continuous GnRH stimulate LH and/pr FSH secretion? (L7, P22) - ANSWER
Continuous GnRH does not stimulate LH or FSH secretion.
What is the relationship between GnRH and LH secretion? (L7, P22) - ANSWER Pulsatile
input of GnRH to the pituitary gland is essential for LH secretion
Is FSH secretion passive or active? (L7, P22) - ANSWER FSH secretion is passive (ie. not
pulsatile)
What is the relationship between GnRH and FSH synthesis? (L7, P22) - ANSWER GnRH
is required for the maintenance of FSH synthesis, but FSH secretion does not require
pulsatile GnRH input
Why is pulsatile GnRH secretion important? (L7, P22) - ANSWER Pulsatile GnRH
secretion is important because the cells of the anterior pituitary that secrete the
gonadotropins will not respond to GnRH if the plasma concentration of this hormone
remains elevated over time.
How is GnRH controlled? (L7, P24) - ANSWER by a closed feedback loop system
, Stimulus (GnRH) -> Effector (LH/FSH) -> Sensor (Sex steroids)
What are the negative feedback hormones? (L7, P25) - ANSWER Estrogen,
Progesterone, Testosterone
What are the positive feedback hormones? (L7, P25) - ANSWER Estrogen
What are the feedback effects of gonadal sex steroids? (L7, P25) - ANSWER Feedback
effects of gonadal sex steroids may involve changes in the frequency and/ or amplitude
of GnRH pulses.
What are the sex differences in negative feedback effects? (L7, P26) - ANSWER -
Estrogen has a short-term negative feedback effect in the early follicular phase to
reduce GnRH pulse amplitude
- Progesterone reduces GnRH pulse frequency in the luteal phase
- Testosterone reduces GnRH pulse frequency in males
When does estrogen switch its negative feedback to positive feedback? (L7, P28) -
ANSWER Late follicular phase
What are convergent pathways? (L8, P7) - ANSWER Convergent pathways act as a
gating system to allow information to be integrated up so only one combined signal is
sent to GnRH neurons
How is GnRH neurons modulated? (L8, P8) - ANSWER By neuronal afferents that provide
direct and/or relayed input from various regions of the brain
Why is the convergent pathway used for GnRH neurons? (L8, P8) - ANSWER Prevents
information overload at a single neuron and allows neurons to act in concert.
List (2) what is involved in relaying steroid feedback to GnRH neurons (L8, P10) -
ANSWER the neuropeptides - Kisspeptin and gonadotropin inhibitory hormone (GnIH)
that express the relevant receptors
What are kisspeptins (metastin)? (L8, P11) - ANSWER family of proteins that are
essential for fertility.
- Neuropeptide encoded by the KISS1 gene
- Acts on Kisspeptin receptor (KISS1R)
