Proceedings of The Physiological Society

Physiology 2012 (Edinburgh) (2012) Proc Physiol Soc 27, PC236

Poster Communications

Experience-dependent, layer-specific development of divergent thalamocortical connectivity

S. Brown1, J. Isaac2, M. Daw1

1. CIP, University of Edinburgh, Edinburgh, Please Select, United Kingdom. 2. Lilly UK, Windlesham, Surrey, United Kingdom.

The main sensory pathway from the whiskers to layer 4 (L4) of the cortex is shaped by experience during a critical period in the first postnatal week. The thalamocortical axons that comprise the final stage of this pathway also make a much weaker input to layer 6 (L6). The developmental profile of the relative input strengths to these 2 layers is currently unknown. To study this we made whole-cell recordings (perforated patch for LTP experiments) from thalamocortical slices from mice aged postnatal day (P) 3-9. Using simultaneous recordings we show that thalamocortical input strength to L4 and 6 is similar in neonates (EPSC amp L4 36 ±13 pA, L6 36 ± 14 pA, n = 10) and the dominance of the L4 input is established during the first postnatal week (EPSC amp L4 67 ±19 pA, L6 28 ± 7 pA, n = 7). This relative change is associated with the selective expression of thalamocortical LTP in L4 (EPSC amp after pairing 206 ± 46% baseline, n = 12), but not L6 (98 ±14% n = 18). This increased input to L4 is mediated not by an increase in the input strength of each thalamocortical axon (P3-5 37 ± 6 pA, n = 18, P 8-9 37 ± 6, n = 26), but by an increase in the proportion of L4 cells contacted by each axon (P3-5 9%, n = 11, P 8-9 55%, n = 11). Furthermore this increase in thalamocortical connectivity is experience-dependent in that it is absent in whisker trimmed mice (P8-9 whisker trimmed 9%, n=11). Thus early experience acts via synaptic plasticity and leads to a layer specific increase in thalamocortical input strength. All values mean ± s.e.m.

Where applicable, experiments conform with Society ethical requirements