I ve read that metabotropic receptors outnumber ionotropic receptors on
the average neuron. Is that true? Is there a known average number of ionotropic vs metabotropic receptors?

G'Day George: As lists go there are many more metabotropic (e.g., this would include G protein-coupled receptors (GPCRs)) than ionotropic receptors. However the ionotropic receptors tend to be a lot more abundant in the brain in terms of gene and protein expression. There will be various notions of what people consider an ‘average’ neuron and if you take both receptor classes (and their subtypes) there will be brain region-specific expression patterns. Also, some neurons may express most (if not all) of these receptors, but there will be differences in the absolute numbers, perhaps averaging hundreds to thousands of one type of ionotropic (e.g., GluA2) and metabotropic (e.g., mGlu1) receptor per neuron. There will also be variants (e.g., splice) of many types of these receptors.

In terms of gene expression, sequencing of single neurons (i.e., transcriptomic profiles) has been performed in a few brain regions and this reveals a complexity that we may not have imagined based on pharmacological studies alone. For example in some individual hypothalamic (preoptic area) neurons it appears that the genes for over 250 neurotransmitter receptors (mostly GPCRs) and ligand-gated ion channels are expressed - and there are hundreds of additional hormone receptors. In this particular example - see http://www.ncbi.nlm.nih.gov/pubmed/20970451 - there were over 150 different non-olfactory GPCRs and around 90 different ion channels per neuron. Many of these receptors may oligomerise with each other, or to a different receptor type to alter their pharmacology. One challenge for neuroscientists is to establish how many receptors in a neuron are functional.

One of the best sites for information on receptors that people in the field(s) use is - http://www.guidetopharmacology.org/

Last edited by Steve Lolait (29th Oct 2015 15:25:27)