Fewer driver synapses in higher order than in first order thalamic relays

Abstract We used electron microscopy to determine the relative numbers of the three synaptic terminal types, RL (round vesicle, large terminal), RS (round vesicles, small terminal), and F (flattened vesicles), found in several representative thalamic nuclei in cats chosen as representative examples...

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Bibliographic Details
Published in:Neuroscience 2007-04, Vol.146 (1), p.463-470
Main Authors: Van Horn, S.C, Sherman, S.M
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Cats
corticocortical communication
Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation
Fundamental and applied biological sciences. Psychology
gamma-Aminobutyric Acid - metabolism
medial geniculate nucleus
Microscopy, Electron, Transmission - methods
Microscopy, Immunoelectron - methods
Neural Pathways - anatomy & histology
Neurology
neuromodulators
Neurons - metabolism
Neurons - ultrastructure
posterior nucleus
Synapses - physiology
Synapses - ultrastructure
Thalamus - cytology
ventral posterior nucleus
Vertebrates: nervous system and sense organs
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Summary:Abstract We used electron microscopy to determine the relative numbers of the three synaptic terminal types, RL (round vesicle, large terminal), RS (round vesicles, small terminal), and F (flattened vesicles), found in several representative thalamic nuclei in cats chosen as representative examples of first and higher order thalamic nuclei, where the first order nuclei relay subcortical information mainly to primary sensory cortex, and the higher order nuclei largely relay information from one cortical area to another. The nuclei sampled were the first order ventral posterior nucleus (somatosensory) and the ventral portion of the medial geniculate nucleus (auditory), and the higher order posterior nucleus (somatosensory) and the medial portion of the medial geniculate nucleus (auditory). We found that the relative percentage of synapses from RL terminals varied significantly among these nuclei, these values being higher for first order nuclei (12.6% for the ventral posterior nucleus and 8.2% for the ventral portion of the medial geniculate nucleus) than for the higher order nuclei (5.4% for the posterior nucleus, and 3.5% for the medial portion of the medial geniculate nucleus). This is consistent with a similar analysis of first and higher order nuclei for the visual system (the lateral geniculate nucleus and pulvinar, respectively). Since synapses from RL terminals represent the main information to be relayed, whereas synapses from F and RS terminals are modulatory in function, we conclude that there is relatively more modulation of the thalamic relay in the cortico-thalamo-cortical higher order pathway than in first order relays.
ISSN:0306-4522
1873-7544
DOI:10.1016/j.neuroscience.2007.01.026