Figure 2 shows such image variations across a rostrocaudal series through the thalamus (Figures 2A and 2B), and the subtraction analysis (e.g., Figure 2C), which separated the experimentally induced MR enhancements from this intrinsic background variation. Figures 2A–2C show results after extensive signal averaging. Figure 2A was acquired during a 14 hr scan using the T1-IR sequence, which yielded the highest image contrast; this was the single ex vivo experiment that we performed. Images in Figures 2B and 2C show the average from 9 scans over 3 scan sessions, from a single in vivo case.

At a threshold of p < 0.002 (uncorrected), the subtraction images (Figure 2C) confirmed PR171 enhanced MR signals (presumptive transport) in thalamic targets VPL, Po, and VM (i.e., the ventromedial thalamic nucleus), consistent with known connections (Koralek et al., 1988, Kaas and Ebner, 1998, Liu and Jones, 1999, Paxinos, 2004, MacLeod and

James, 1984 and Desbois and Villanueva, 2001). Additional enhancement was apparent in the raw images (e.g., Rt, in Figure 2B) but it did not reach statistical significance at p < 0.002, given this level of signal averaging. The lack of significance in Rt (Figure 2C) may also reflect the small size of the nucleus, relative to the limits of brain coregistration processes. A second, simpler strategy for isolating enhancement was to measure MR levels in mirror-symmetric locations in each hemisphere from Selleckchem Dactolisib a common slice, then to use the contralateral hemisphere as a control for that in the injected hemisphere. For example, Figure 3 shows enhancements ipsilateral to the S1 injection site in 4 slices centered on VPL, based on both T1-W (Figures 3A and 3B) and T1-IR (Figures 3C and 3D) sequences. In Figures 3A and 3B, the slice planes included putative Rt. In the T1-W images, enhancement in VPL was

typically 10%–20%. As expected, the background suppression sequence (T1-IR) yielded higher contrast enhancement; in VPL, this amounted to 70%–90%. Our subsequent analyses focused on VPL, because VPL is the largest of S1′s thalamic-recipient nuclei, and it includes somatotopic map variations large secondly enough to be resolved with MRI. Of the 24 animals injected with GdDOTA-CTB into the forepaw region of S1, all showed MR enhancements in the corresponding forepaw representation of VPL. To resolve the time course of this presumptive transport, we rescanned animals at a range of time points following the GdDOTA-CTB injections: days 1–7, 1 week, 3 weeks, 4 weeks, and 8 weeks. Figure 4 shows the level of MR enhancement over time in VPL, in group-averaged data (n = 8). The mean signal remained near baseline through day 2 postinjection. In this data set, the signal increase became statistically significant on day 5 (p = 0.034), and reached a plateau near day 7, approximately 10% above baseline in these T1-W images.