Table 3.

Reported in vivo dialysate concentrations of neurotransmitters as measured by microdialysis in rats unless otherwise noted.

Neurotransmitter	Approx. extracellular concentration	Brain region
Glutamate	1 μM[7], 1.4 μM[13]	striatum
γ-aminobutyric acid	0.2 μM[7], 0.17 μM[13]	striatum
Glycine	1.6 μM[7], 6 μM[13]	striatum
Aspartate	0.3 μM[7]	striatum
Taurine	26 μM[13]	striatum
L-Serine, D-Serine	28 μM[13], 15 μM[13]	striatum
Dopamine	26 nM,[74] 40 nM[75]	nucleus accumbens, striatum
Dorepinephrine	12 nM[76]	striatum
Epinephrine	~ 10% of NE[77]	Not reported
Serotonin	70 nM[75], 68 nM[76]	striatum
Met-enkephalin	127 ± 16 pM[78], 110, 50 pM[79]	striatum
Leu-enkephalin	51 ± 9 pM[78], 36, 23 pM[79]	striatum
Dynorphin	78 ± 7 pM[78]	striatum
β-endorphin	109 ± 7 pM[78]	striatum
Endomorphin 2	1259 ± 297 pM[80]	spinal cord
Vasopressin	~ 25 pM[81]	anterior pituitary
Corticotrophin releasing hormone	~ 25–40 pM[81]	anterior pituitary
Growth hormone releasing hormone	40 pg/mL[82, 83] ~ 8 pM	hypothalamus (cattle)
Somatostatin	333 ± 8 pM[84]	striatum
Substance P	23.5 pM[85]	CSF (human)
Neurokinin α	2.31/2.24 nM[86]	CSF (human)
Neuropeptide tyrosin	26.1 ± 3.5 pM[87]	ventral stiatum
Vasoactive intestinal polypeptide	25.5 ± 7.5 pmol per gram of tissue[88]	cerebral cortex tissue
Neurotensin	49.7 ± 7.0 pM[87]	ventral stiatum
Nociceptin/orphanin FQ	63 ± 12 pM/60 ± 8 pM [89]	hippocampus/thalamus
Cholecystokinin	2.3 ± 0.1 pM[90]	anterior cingulated cortex
Galanin	7.9 pM[91]	spinal cord
Hypocretins/orexins	~ 60 pM (BF) ~ 75 pM (HYP) ~ 45 pM (LC) [92]	basal forebrain, perifornical hypothalamus, and locus ceruleus
Angiotensin	46 pM [93]	globus pallidus/ventral pallidum
Acetylcholine	0.4–4 nM,[94] 2.8 μM[95]	hippocampus, prefrontal cortex
Adenosine triphophosphate	0.5–10 μM[96]	dorsal spinal horn (frog)
Adenosine	200 nM[97]	Not reported
Nitric oxide	92 nM[98]	striatum