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Peter W Campbell, William Guido; Development of Intrathalamic Connections Between dLGN and TRN. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2594.
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© ARVO (1962-2015); The Authors (2016-present)
The reciprocal connections between the dorsal lateral geniculate nucleus (dLGN) and the thalamic reticular nucleus (TRN) play an important role in regulating thalamocortical activity during different behavioral states such as attention, wakefulness, and sleep. Axon collaterals of thalamocortical neurons provide feedforward excitatory input onto GABAergic TRN neurons, which in turn convey feedback inhibition to dLGN relay neurons. Here we examined when and how these circuits arise during early postnatal life.
We employed mouse transgenics to visualize when inputs appear and optogenetics to assess when functional patterns of connectivity emerge. To determine when projections arrived in their target nucleus, we examined coronal sections across multiple early-postnatal ages using confocal microscopy. We also studied when these connections became functional by combining optogenetics with in vitro whole cell patch clamp physiology.
Our results show that TRN terminals arrive in dLGN at early postnatal ages and span the entire nucleus in a diffuse but dense plexus by the end of the first postnatal week. Weak inhibitory postsynaptic activity from TRN to dLGN appears during the first postnatal week, and grows steadily in amplitude to reach adult-like levels by the third postnatal week. Feedforward excitatory connections from dLGN to TRN begin to arrive near the end of the first postnatal week. Soon after, weak excitatory responses appear and mature rapidly, reaching adult-like levels by the third postnatal week.
Taken together, these data suggest that reciprocal connections between dLGN and TRN develop in a coordinated manner, with feedback inputs arising somewhat earlier that feedforward ones. The emergence of this intrathalamic loop occurs well after retino-geniculate and geniculo-cortical connections are established and at about the same time as descending corticothalamic connections are made with TRN and dLGN. Thus it would appear that circuits involved in the state dependent modulation of sensory signal transmission are assembled after primary visual pathways are established.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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