Quantitative immunogold evidence that glutamate is a neurotransmitter in afferent synaptic terminals within the isthmo-optic nucleus of the pigeon centrifugal visual system
D. Miceli et al., Quantitative immunogold evidence that glutamate is a neurotransmitter in afferent synaptic terminals within the isthmo-optic nucleus of the pigeon centrifugal visual system, BRAIN RES, 868(1), 2000, pp. 128-134
A quantitative electron microscopic analysis of glutamate (GLU) immunoreact
ivity using the post-embedding immunogold technique was carried out within
the isthmo-optic nucleus (ION) of the pigeon centrifugal visual system (CVS
). Measurements were performed in each of eight different categories of axo
n terminals, including those that were GABA-immunoreactive (-ir), considere
d representing control profiles and identified using a single or double-lab
el immunocytochemical procedure. The results demonstrated that the glutamat
e immunogold particle densities for both mitochondrial and vesicular pools
and for total surface area of bouton profiles were significantly higher in
P1a. P1b and P2b terminals and not significantly different in P4 and P5 ter
minals compared to those recorded in control GABA-ir terminals (P2a, P2c, P
3). Moreover, the values measured in GLU-ir positive profiles were all sign
ificantly higher than in either P4 or P5 terminals. The results suggest tha
t tectal neurons, which provide the main input to the ION cells, are either
inhibitory GABA-ir possibly associated with P2c and/or P3 terminals or exc
itatory GLU-ir via P1a, P1b and P2b terminals. Such differential effects of
tectal afferents may be the basis for the modulation of centrifugal activi
ty and consequently of end target retinal ganglion cell responses. The data
are relevant to hypotheses Implicating the avian CVS in mechanisms of sele
ctive enhancement of visual attention to either novel or meaningful stimuli
within the visual held. (C) 2000 Elsevier Science B.V. All rights reserved
.