Norepinephrine

Norepinephrine or noradrenaline is a hormone and a neurotransmitter. [The terms noradrenaline and norepinephrine are interchangeable]. 

As a stress hormone, norepinephrine affects parts of the brain, such as the amygdala, where attention and responses are controlled. It can affect our mood inducing fear or grief.  At overdose proportions it can result in extreme emotion, which is a major mechanism of spiritual experience.

One of the most important functions of norepinephrine is its role as the neurotransmitter released from the sympathetic neurons affecting the heart. An increase in norepinephrine from the sympathetic nervous system increases the rate of contractions.  Norepinephrine is a beta 1 agonist.  Beta 1 agonists increase the heart rate.  So, it makes our heart beat faster.  Overdose on norepinephrine and it makes the heart truly thump – palpitate.

Along with epinephrine, norepinephrine also underlies the fight-or-flight response, not only directly increasing heart rate, but triggering the release of glucose from energy stores, and increasing blood flow to skeletal muscle.  BUT,  in the true fight or flight response what blood flow exists is diverted from other non-essential organs to skeletal muscle.  You may feel hugely energised, even hyperactive with an over dose.

So despite the increase of blood, it does not go to the brain and can at overdose proportions produce light headed ness, confusion and dizziness – all the by-products of hypoxia.

Norepinephrine also  increases the  blood pressure by increasing vascular tone (tension of muscles) through alpha-adrenergic receptor activation; this causes a compensatory reflex that results in a drop in heart rate, "reflex bradycardia".  In effect the blood pressure can soar to extraordinary levels.  At overdose levels this merely serves to exacerbate the hypoxia.