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VOL. 73 (4), 1127-1157, 2007 PHYSIOLOGICAL ROLE OF EXTRACELLULAR...

or catecholamines has been reported (55-61). Figure 4 shows the
exocytotic release from rat midbrain synaptic terminals, after
stimulation. It can be observed that the quantity of neurotransmitter
released by mg of protein from synaptosomal preparation mirrors
the relative abundance of eah specific type of terminal, being
glutamatergic the most abundant. The dose response curves reported
in Figure 4 have been obtained with ATP in the presence of Mg2+ ion
and correspond in a great extent to secretion mediated by P2X3
presynaptic receptors. Later the secretory responses mediated by
P2X3 compared to P2X7 will be reported in cultured granule neurons.

Presynaptic ionotropic receptors functionality is something that
has recently appeared and very insistently, as the mean to regulate
in a drastic way the secretory capacity of terminals and essentially
all ionotropic receptors described in neural soma have been now
characterized in the neural secreting area (55-63). This could be the
case for NMDA, AMPA, GABAA and especially nicotinic and,
nucleotidic neural receptors wich role on the control of synaptic
terminals secretion, synaptic plasticity, recovery and stability, or long
term depression or potentiation, has to be settled (57, 58, 60, 61, 64-

FIGURE 4. P2X receptor activation induces glutamate, GABA and
acetylcholine release from presynaptic terminals. Synaptic terminals isolated

from rat midbrain were stimulated with increasing ATP concentrations. The
amount of glutamate and GABA in the extrasynaptosomal media were measured
by HPLC. Extrasynaptosomal acetylcholine was quantified by the luminometric

protocol described by Israel and Lesbats (85).

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