Statistical Analysis 1 Reaction Time Data

Raw data were processed to extract mean reaction times, movement time, latency to collect reward, and error type frequency for each rat. Accuracy of performance was assessed as the proportion of correct responses as a function of all trials (correct and all error responses). Each type of error was also examined separately as a percentage of all trials. The percentage of contralateral responses were also calculated, as a measure of response asymmetry. Mean reaction time, movement time, latency to collect reward, percentage correct and percentage of errors by type were analysed by repeated-measures Analysis of Variance.

The assumption of homogeneity of covariance required by repeated-measures ANOVA was tested using Mauchly’s test of sphericity. If this test indicated that the assumption had been violated, then the F ratio was evaluated with more conservative degrees of freedom adjusted by the Huynh-Feldt correction factor (Howell, 1987). When appropriate, further investigation of significant interactions (p < 0.05) were conducted using post hoc Newman-Keuls comparisons.

Probability density distributions (Silverman, 1986; see Bowman et al., 1993) of reaction times were produced to gain insight into the nature of the significant changes in

by replacing each reaction time with a Gaussian kernel (ct = 40 ms) centred on the

reaction time. The kernels were then summed across trials and the probability of a response per millisecond was plotted against reaction time bins of 10 ms.

2.3.2. Asymmetry Test

Paw reaching (numbers of reaches) and the somatosensory asymmetry test (latency to contact) were also analysed using repeated-measures ANOVA. In addition, an asymmetry score was calculated as the proportion of responses to the contralateral side as a function of total responses, expressed as a percentage where 50 % is no asymmetry, and 100 % is an exclusive contralateral asymmetry.

2.3.3. Controls

Following unilateral 6-OHDA striatal dopamine depletion, unilateral MCA occlusion and excitotoxic unilateral posterior parietal lesion the intact contralateral hemisphere served as a control. Ischemic lesions (MCA and ACA occlusion) also included an operated control group in the analysis.

2.4. Surgery

2.4.1. Anaesthesia

Initial anaesthesia was induced in an anaesthetic chamber using halothane at 4-5 %, delivered in a nitrous oxide/oxygen (3:1) mix. When the pedal reflex could no longer be elicited the rat was placed in a stereotaxic frame with ‘atraumatic’ ear bars (Kopf, Tujunga, CA) and the nose bar set appropriately for the surgery undertaken. Halothane was then reduced to 1.5-2 % for the duration of the surgical procedure. Normal body temperature (37 ± 1 °C) was maintained during surgery using a thermostatically regulated heating blanket (Harvard Apparatus Ltd, Edenbridge, Kent, UK).

2.4.2. Dopamine Depleting Lesions (ô-hydroxydopamine) of the Striatum

Poole, UK) before surgery to enhance the efficacy of 6-OHDA (Breese & Traylor, 1971). Twenty minutes after the injection of pargyline, anaesthesia was induced. The rats were then placed into a stereotaxic frame with the nose bar set at + 5 mm. A midline incision was made along the scalp and the skin and fascia were retracted to reveal the skull. A hole was then drilled in the skull at the co-ordinates A? -f 2.0 mm and L ± 3.0 mm to bregma (lesions were unilateral). A 30 gauge injection cannula containing 8 pg of 6- OHDA base in 2 pi of ascorbate acid saline was then lowered to 6.5 mm below skull, and the 6-OHDA was manually infused at a rate of 0.1 pi every 10 seconds. The cannula was left in place for 3 minutes, before being slowly withdrawn. The incision in the scalp was then closed using sterilised metal clips. Finally the animal was placed in a warm cage to recover before transfer back to a home cage.

2.4.3. Excitotoxic Lesions of Posterior Parietal Cortex

The anaesthetised rat was placed into a stereotaxic frame with the nose plate set at - 3.3 mm. A midline incision was made to permit retraction of the scalp and fascia to expose the skull. A craniotomy was performed on one side of the skull (lesions were unilateral) which exposed the brain between L ± 1.5, AP - 3.8 to - 5.8 mm and at L ± 6.0 mm, AP - 4.3 to - 5.8 mm relative to bregma. Quinolinic acid (Sigma Chemical Co., Poole, UK) was sprinkled directly on to the exposed cortex using a fine brush. The scalp incision was closed and the rat was placed into a warm environment to recover.

2.4.4. Occlusion of the Middle Cerebral Artery - MCAo

The nose plate was set to - 3.7 mm for the procedure. A dorsal craniotomy was performed to allow an injection cannula to be lowered to AP + 0.9 mm, 5.2 mm lateral and - 8.8 mm (- 8.7 mm, comparison of rat strain) at skull below bregma. Injection was accomplished using a 5 pi syringe filled with sterile water and attached to a 31 gauge injection cannula via a polythene tube. A 0.2 pi air bubble was drawn into the tube before the potent vasoconstrictor endothelin-1 was taken up. The position of the air bubble was marked and the movement of the bubble monitored to confirm successful injection. Occlusion of the right MCA was then achieved by manual intracerebral injection of the endothelin-1 (150 pmol in 3 pi 0.9 % sterile saline, Novabiochem, Nottingham, UK) adjacent to the MCA (Sharkey et al. 1993). The endothelin-1 was administered as three

strain endothelin-1 was administered as two injections of 1 pi separated by a 90 second delay (100 pmol in 2 pi 0.9 % sterile saline). The cannula was then left in situ for 5 minutes before being slowly withdrawn. After completely withdrawing the injection cannula the patency of the line was verified. Finally the burr hole in the skull was filled with bone wax and the incision in the scalp closed using sterilised metal clips (suture in experiment examining rat strain). During recovery the rat was placed in a warm

environment to maintain normothermia throughout the recovery period.

All the rats in the study received an intracerebral injection of endothelin-1. Operated controls arise from the surgery as those rats with only needle tract damage and only a small lesion at the site of injection. Any animal that displayed difficulty in feeding or gross abnormality was humanely killed. The importance of high blood glucose levels in aggravating the evolution of an ischemic lesion has been well established in the literature (Duverger & MacKenzie, 1988 & Slivka, 1991) thus rats were always maintained on a standard laboratory diet for at least 48 hours after surgery.

The use of a craniotomy has been criticised for exposing the brain tissue, thereby potentially allowing a fall in brain temperature. A fall as small as 2°^ in brain temperature has been demonstrated to reduce the severity of ischemic injury (Ginsberg et al., 1992). However, Henshall et al. (1995) has recently demonstrated that intracerebral temperature does not fall after the dorsolateral craniotomy performed for stereotaxic administration of endothelin-1.

2.4.5. Occlusion of the Anterior Cerebral Arteries -ACAo

The procedure for occlusion of the middle cerebral artery applicable to chapter 6 was adhered to with the following modifications. The nose plate was set at - 3.3 mm and the injection cannula was positioned according to the co-ordinates AP + 3.0 mm, L 0.0 mm and V - 6.5 mm at skull below bregma. The burr hole was covered with sterile gelfoam rather than bone wax.

2.5. Histology