The brain produces and exchange millions of neurotransmitters every hour.

Question

I need to support this because this is what I have written in my work and a student brought that up to my attention. Can someone help help support this with a source? I have been trying to find one source but I havent had any luck. A couple sentences supporting the statement above is all I need.

With the billions of neurons in the brain, each with multiple synapses, I can envision more than millions of neurotansmitter exchanges in a much smaller amount of time — like a second.

I searched Google under the key words "neuron number brain" to get these possible sources:

http://faculty.washington.edu/chudler/facts.html#neuron
http://hypertextbook.com/facts/2002/AniciaNdabahaliye2.shtml
http://en.wikipedia.org/wiki/Neuron
http://www.hallym.ac.kr/~neuro/kns/tutor/facts.html

I hope this helps. Thanks for asking.