Experimental Brain Research

, Volume 61, Issue 1, pp 194–203 | Cite as

GABAergic neurons comprise a major cell type in rodent visual relay nuclei: an immunocytochemical study of pretectal and accessory optic nuclei

  • R. A. Giolli
  • G. M. Peterson
  • C. E. Ribak
  • H. M. McDonald
  • R. H. I. Blanks
  • J. H. Fallon


The enzyme glutamic acid decarboxylase (GAD) has been localized in sections of rodent brains (gerbil, rat) using conventional immunocytochemical techniques. Our findings demonstrate that large numbers of GAD-positive neurons and axon terminals (puncta) are present in the visual relay nuclei of the pretectum and the accessory optic system. The areas of highest density of these neurons are in the nucleus of the optic tract (NOT) of the pretectum, the dorsal and lateral terminal accessory optic nuclei (DTN, LTN), the ventral and dorsal subdivisions of the medial terminal accessory optic nucleus (MTNv, MTNd), and the interstitial nucleus of the posterior fibers of the superior fasciculus (inSFp). The findings indicate that 27% of the NOT neurons are GAD-positive and that these neurons are distributed over all of the NOT except the most superficial portion of the NOT caudally. The GAD-positive neurons of the NOT are statistically smaller (65.9 μm2) than the total population of neurons of the NOT (84.3 [j,m2) but are otherwise indistinguishable in shape from the total neuron population. The other visual relay nuclei that have been analyzed (DTN, LTN, MTNv, MTNd, inSFp) are similar in that from 21% to 31% of their neurons are GAD-positive; these neurons are smaller in diameter and are more spherical than the total populations of neurons. The data further show that a large proportion of the neurons in these visual relay nuclei are contacted by GAD-positive axon terminals. It is estimated that approximately one-half of the neurons of the NOT and the terminal accessory optic nuclei receive a strong GABAergic input and have been called “GAD-recipient neurons”. Further, the morphology of the GAD-positive neurons combined with their similar distribution to the GAD-recipient neurons suggest that many of these neurons are acting as GABAergic, local circuit neurons. On the other hand, the large number of GAD-positive neurons in the NOT and MTN (20–30%) in relation to estimates of projection neurons (75%) presents the possibility that some may in fact be projection neurons. The overall findings provide morphological evidence which supports the general conclusion that GABAergic neurons play a significant role in modulating the output of the visually related NOT and terminal accessory optic nuclei.

Key words

GABAergic neurons Accessory optic nuclei Pretectal nuclei Gerbil Rat Visual system 

Abbreviations to Figures


Cerebral aqueduct


Posterior commissure


Nucleus of Darkschewitsch


Deep mesencephalic nucleus


Dorsal terminal nucleus, accessory optic system


Habenulointerpeduncular tract


Intergeniculate leaflet


Interstitial nucleus of Cajal


Interstitial nucleus, superior fasciculus, posterior fibers


Dorsal lateral geniculate nucleus


Ventral posterior nucleus


Lateral posterior nucleus


Lateral terminal nucleus, accessory optic system


Mammillary body


Medial geniculate nucleus


Medial lemniscus


Medial terminal nucleus, dorsal subdivision, accessory optic system


Medial terminal nucleus, ventral subdivision, accessory optic system


Nucleus of the optic tract


Nucleus of posterior commissure


Optic tract


Anterior pretectal nucleus


Periaqueductal gray


Nucleus parabrachialis pigmentosus


Cerebral peduncle


Medial pretectal nucleus


Nucleus paranigralis


Pretectal olivary nucleus


Posterior pretectal nucleus


Peripeduncular nucleus


Magnocellular division, red nucleus


Parvocellular division, red nucleus


Superior colliculus


Stratum griseum profundus, superior colliculus


Stratum griseum superficiale, superior colliculus


Stratum griseum medium, superior colliculus


Substantia nigra, pars compacta


Substantia nigra, pars reticulata


Stratum opticum, superior colliculus


Ventrobasal complex


Zona incerta


Oculomotor nerve, root fibers


Third ventricle


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Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • R. A. Giolli
    • 1
  • G. M. Peterson
    • 1
  • C. E. Ribak
    • 1
  • H. M. McDonald
    • 1
  • R. H. I. Blanks
    • 1
  • J. H. Fallon
    • 1
  1. 1.Departments of Anatomy and SurgeryCalifornia College of Medicine, University of CaliforniaIrvineUSA

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