We also analyzed Tsc1ΔE18/ΔE18 TCA projections as they traversed the striatum and entered the cortex. Similar to Tsc1ΔE12/ΔE12, there was a qualitative excess of RFP+ Tsc1ΔE18/ΔE18 TCA projections within the deep cortical layers. However, a direct comparison of Tsc1ΔE18/ΔE18 and Tsc1ΔE12/ΔE12 vibrissa barrel innervation was precluded because of their different recombination patterns. Regardless, these thalamocortical projection phenotypes in deep layers are consistent see more with disrupted neuronal processes in response to mTOR dysregulation ( Choi et al., 2008). We uncovered multiple electrophysiological

alterations upon early deletion of Tsc1. The increased input capacitance and reduced input resistance are both consistent with increased membrane as a result of cell growth. Notably, action potential dynamics were also altered, yet spike threshold potentials were unaffected. The altered action potentials of Tsc1ΔE12/ΔE12 neurons may partially compensate for the changes in passive properties. As the input resistance of a neuron falls, larger synaptic currents are required to modify membrane voltage. Mutant Tsc1ΔE12/ΔE12 neurons also have larger amplitude, briefer action potentials with normal thresholds, and rates of rise and fall that are considerably faster than normal. The maximum rate-of-rise

of an action potential is proportional to peak inward sodium current in many neurons ( Cohen et al., 1981). Therefore, these changes in spike kinetics strongly suggest that voltage-gated sodium and potassium channels are altered in the mutant cells. The spike shapes are consistent selleck compound with either higher membrane channel densities or altered single-channel properties, such as subunit composition or phosphorylation, that affect conductance and gating dynamics. In support of these possibilities, the mTOR pathway has been reported to control expression levels and subunit composition Fossariinae of some voltage-gated ion channels ( Raab-Graham et al., 2006). Multiple ion channel involvement is further suggested by changes in both the tonic and burst firing modes of mutant cells. The reduced slope of the tonic frequency/current

relationship in mutant cells is most easily explained as a consequence of their lower input resistance, while more rapid intraburst spiking is likely due to changes in ion channels. In addition to altered spike-related sodium and potassium channels, it is possible that the rapid intraburst spiking in Tsc1ΔE12/ΔE12 cells is caused by altered density or kinetics of low-threshold calcium channels. Additionally, the ectopic production of PV, a protein that acts as a slow Ca2+ buffer, in Tsc1ΔE12/ΔE12 thalamic relay neurons may disrupt internal Ca2+ dynamics, which can affect gene transcription, synaptic function, and membrane potential and could contribute to some of the physiological changes we describe ( Schwaller, 2010).