Pulled this off a supplement research site. Has a LOT of pubmed references on agmatine, this is a portion of its effect on neurology.
Agmatine is currently considered to be a relatively new neurotransmitter, since it has its metabolism (both creation[75] and destruction[76]) regulated in neurons and is stored presynaptically in these neurons;[39][77] following transport to nerve terminals,[78][79][77][80] agmatine is released upon depolarization of the neuron which is mandatory for neurotransmitters.[77][80] Agmatine can also be taken up by and stored in astrocytes.[81]
Agmatine is also sometimes referred to as a neuromodulator. This is likely related to the observations that agmatine can positively modulate signalling through the NMDA receptor (via putrescine[82]), α2 adrenergic receptors,[83] and serotonergic receptors (5-HT1A/1B)[84] at low concentrations while inhibiting binding at the polyamine binding site[85] (that putrescine acts via binding to[86]), competitively inhibiting the α2 adrenergic receptors,[83] and being antagonistic with 5-HT1A/1B signalling[87] at higher concentrations.
77.Goracke-Postle CJ, et al. Release of tritiated agmatine from spinal synaptosomes. Neuroreport. (2006)
78.Sastre M, Regunathan S, Reis DJ. Uptake of agmatine into rat brain synaptosomes: possible role of cation channels. J Neurochem. (1997)
79.Goracke-Postle CJ, et al. Potassium- and capsaicin-induced release of agmatine from spinal nerve terminals. J Neurochem. (2007)
80.Goracke-Postle CJ, et al. Agmatine transport into spinal nerve terminals is modulated by polyamine analogs. J Neurochem. (2007)
81.Regunathan S, et al. Agmatine (decarboxylated arginine) is synthesized and stored in astrocytes. Neuroreport. (1995)
82.Zomkowski AD, Santos AR, Rodrigues AL. Putrescine produces antidepressant-like effects in the forced swimming test and in the tail suspension test in mice. Prog Neuropsychopharmacol Biol Psychiatry. (2006)
83.Molderings GJ, et al. Dual interaction of agmatine with the rat alpha(2D)-adrenoceptor: competitive antagonism and allosteric activation. Br J Pharmacol. (2000)
84.Dias Elpo Zomkowski A, et al. Evidence for serotonin receptor subtypes involvement in agmatine antidepressant like-effect in the mouse forced swimming test. Brain Res. (2004)
85.Gibson DA, et al. Radioligand binding studies reveal agmatine is a more selective antagonist for a polyamine-site on the NMDA receptor than arcaine or ifenprodil. Brain Res. (2002)
86.Lewin AH, et al. Molecular features associated with polyamine modulation of NMDA receptors. J Med Chem. (1998)