Practical feline behaviour understanding cat behaviour and improving welfare

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Health and Behaviour 83


The sympathetic–adrenal medullary axis (SAM axis)


This involves the autonomic nervous system that is part of the peripheral nervous
system responsible for the regulation of bodily functions not under conscious control,
such as breathing, heartbeat and digestion. It is made up of two halves: the sympa-
thetic and the parasympathetic. Under normal circumstances both systems work
together to maintain a state of homeostasis but during the stress response sympathetic
activity is increased and parasympathetic activity decreased. This takes place via the
following process:


● Information received via the senses is sent to the amygdala – a group of neurons
located within the limbic system of the brain.
● If a potential threat or challenge is perceived, the amygdala sends a message to the
hypothalamus, which in turn sends signals to the adrenal glands – two small
endocrine glands situated just above the kidneys.
● Chemicals known as catecholamines, predominantly adrenaline (epinephrine)
and noradrenaline (norepinephrine), are then released into the blood stream from
the adrenal medulla (the centre of the adrenal gland).
● The effects of adrenaline and noradrenaline are to prepare the animal for ‘fight or
flight’ by activating the following physiological effects:
● Increased heart rate and blood pressure, which increases blood flow to the muscles.
● Narrowing of some blood vessels to reduce blood flow to non-essential organs.
● Widening of air passages to allow increased intake of oxygen.
● Increased hydrolysis of glycogen to glucose to increase energy availability.


The hypothalamus–pituitary–adrenal axis (HPA axis)


● When a signal of potential threat reaches the hypothalamus it also releases corti-
cotropin releasing hormone (CRH).
● CRH acts on the pituitary gland stimulating increased synthesis and release of
adrenocorticotropic hormone (ACTH).
● ACTH is carried to the adrenal glands where it stimulates the release of glucocor-
ticoids (also known as glucocorticosteriods) into the blood stream from the adre-
nal cortex (the outer part of the adrenal gland).
● Glucocorticoids play an important role in creating energy from the metabolism of
carbohydrates, proteins and fats, although they may also have other roles in the
stress response that are not as yet fully understood (Sapolsky et al., 2000).
● Once an optimum level in the bloodstream is reached, glucocorticoids are trans-
mitted back to the hypothalamus in a ‘negative feedback loop’ where they shut
down the production of CRH and stop both the SAM and HPA axes.
● However, chronic stress can disrupt this negative feedback cycle, resulting in the
continued release of glucocorticoids (Mizoguchi et al., 2003).


The stress response performs an important function in that it increases the individu-
al’s ability to escape from, or defend itself against, an actual or potential danger. But
if stress is persistent or frequently repeated over an extended period the emotional

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