Anterior thalamic lesions are thought to produce covert pathology in retrosplenial cortex, but the causes are unknown. strong evidence for covert pathology (i.e. a functional lesion where there is no pathology detectable by standard histological means) as there is no overt pathology in the retrosplenial cortex following anterior thalamic nuclei lesions (van Groen hybridization was used to validate one further gene, hybridization (Exp. 2). All experiments were performed in accordance with the UK Animals (Scientific Procedures) Take action (1986) and associated guidelines. Experiment 1 Subjects Male pigmented rats (total n = 12, Dark Agouti strain; Harlan, UK) were housed in pairs under a 13 hour light/11 hour dark cycle with access to food and water. Each animal was extensively habituated to handling. The weight of the animals was monitored (212-248 g at the time of surgery). Surgery Unilateral lesions were placed in the anterior thalamic MYO5C nuclei as the projections to the retrosplenial cortex remain ipsilateral, making it possible to have within-subject comparisons between the Lesion (ipsilateral to the thalamic lesion) and the Intact (contralateral to the thalamic lesion) hemispheres. Excitotoxic lesions were made with the goal of minimizing damage to fibers of passage. Animals (n=12) were first anaesthetized with an intraperitoneal injection of pentobarbitone sodium (Sagatal, 75mg/kg), and then placed in a stereotaxic frame (David Kopf Instruments, CA). A craniotomy was made over both hemispheres. Excitotoxic lesions were produced by injecting 0.19 l of N-methyl-D-aspartate (NMDA; Sigma Chemicals UK; 0.12 M in phosphate buffered saline (PBS), pH 7.2) into two sites in the same hemisphere using a 1 l syringe (Hamilton, Switzerland). The stereotaxic coordinates were as follows: anterio-posterior, ?0.5 from bregma; medio-lateral, 1.0 and 1.7 from the midline; dorso-ventral, ?6.3 and ?5.7 from the top of the dura for the medial and lateral injections, respectively. The incisor bar was set at +5.0. Antibiotic powder (Aureomycin, Fort Dodge Animal Health, Southampton, UK) was subsequently applied topically and all rats also received a 5 ml AR-231453 subcutaneous injection of glucose saline. Paracetamol was dissolved in the rats drinking water, and they were observed daily until recovery. A period of six to nine weeks preceded tissue sampling. Behavioral Procedures Five days preceding tissue extraction, the animals were individually housed. In order to minimize unwanted disruption the rats were first habituated daily to a separate holding room in which there were no other rats. AR-231453 Twenty-four hours prior to tissue extraction, the animals were placed in this new holding room, under the standard feeding regimen and light cycle. The next day, the animals were individually placed for 20 minutes in a novel, larger cage with different flooring in a novel environment of different dimensions and containing different visual stimuli. The purpose of this manipulation was to increase the likelihood of transcript expression, and so minimize floor effects. Retrosplenial tissue from animals with unilateral anterior thalamic lesions was sampled at three time points following exposure to the novel environment (30 min, 2 and 8hrs from onset of exposure, Fig.1a), but at comparable occasions AR-231453 of day. The three delays allowed the detection of changes in genes that are expressed early and late after stimulation (e.g. Cavallaro DNA polymerase and reaction buffer provided in the QuantiTect SYBR Green kit (Qiagen, UK). All QPCR assays used an initial 15 min., 95C step to activate polymerase, followed by 35-40 cycles of denaturation 95C, 15 sec., annealing 56C, 20 sec. and extension 72C, 10 sec. The fluorescence of the accumulating product was acquired each cycle.