Summary
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.
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Abbreviations
- A:
-
Cerebral aqueduct
- CP:
-
Posterior commissure
- DK:
-
Nucleus of Darkschewitsch
- DMN:
-
Deep mesencephalic nucleus
- DTN:
-
Dorsal terminal nucleus, accessory optic system
- HITr:
-
Habenulointerpeduncular tract
- IGL:
-
Intergeniculate leaflet
- INC:
-
Interstitial nucleus of Cajal
- inSFp:
-
Interstitial nucleus, superior fasciculus, posterior fibers
- LGNd:
-
Dorsal lateral geniculate nucleus
- LGNv:
-
Ventral posterior nucleus
- LP:
-
Lateral posterior nucleus
- LTN:
-
Lateral terminal nucleus, accessory optic system
- MB:
-
Mammillary body
- MGN:
-
Medial geniculate nucleus
- ML:
-
Medial lemniscus
- MTNd:
-
Medial terminal nucleus, dorsal subdivision, accessory optic system
- MTNv:
-
Medial terminal nucleus, ventral subdivision, accessory optic system
- NOT:
-
Nucleus of the optic tract
- NPC:
-
Nucleus of posterior commissure
- OT:
-
Optic tract
- PA:
-
Anterior pretectal nucleus
- PAG:
-
Periaqueductal gray
- pbp:
-
Nucleus parabrachialis pigmentosus
- pC:
-
Cerebral peduncle
- PM:
-
Medial pretectal nucleus
- pn:
-
Nucleus paranigralis
- PO:
-
Pretectal olivary nucleus
- pp:
-
Posterior pretectal nucleus
- PPN:
-
Peripeduncular nucleus
- RNm:
-
Magnocellular division, red nucleus
- RNp:
-
Parvocellular division, red nucleus
- SC:
-
Superior colliculus
- SGP:
-
Stratum griseum profundus, superior colliculus
- SGS:
-
Stratum griseum superficiale, superior colliculus
- SGM:
-
Stratum griseum medium, superior colliculus
- SNc:
-
Substantia nigra, pars compacta
- SNr:
-
Substantia nigra, pars reticulata
- SO:
-
Stratum opticum, superior colliculus
- VB:
-
Ventrobasal complex
- ZI:
-
Zona incerta
- 3N:
-
Oculomotor nerve, root fibers
- 3V:
-
Third ventricle
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Supported by USPHS grants EY03642, NS15669, NS20228, EY03018, and NS15321. C.E.R. is the recipient of a Klingenstein Fellowship in the Neurosciences; R.H.I.B. is a Research Career Development Fellow of the National Eye Institute; and J.H.F. is a Research Career Development Fellow of the National Institutes of Health
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Giolli, R.A., Peterson, G.M., Ribak, C.E. et al. GABAergic neurons comprise a major cell type in rodent visual relay nuclei: an immunocytochemical study of pretectal and accessory optic nuclei. Exp Brain Res 61, 194–203 (1985). https://doi.org/10.1007/BF00235635
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DOI: https://doi.org/10.1007/BF00235635