Lickometry: A novel and sensitive method for assessing functional deficits in rats after stroke

Abstract

The need for sensitive, easy to administer assessments of long-term functional deficits is crucial in pre-clinical stroke research. In the present study, we introduce lickometry (lick microstructure analysis) as a precise method to assess sensorimotor deficits up to 40 days after middle cerebral artery occlusion in rats. Impairments in drinking efficiency compared to controls, and a compensatory increase in the number of drinking clusters were observed. This highlights the utility of this easy to administer task in assessing subtle, long-term deficits, which could be likened to oral deficits in patients.

Keywords: Animal models; behaviour (rodent); experimental; focal ischaemia; stroke.

Figure 1.

Representative NeuN stained sections from the median animal of the MCAO group, with the lesion outlined (a) and control group (b). (c) Ipsilateral striatal volume between 90 and 100 days post surgery. (d) Amount of fluid consumed, (e) total number of licks, (f) lick volume, (g) number of licks per cluster, (h) total number of clusters, (i) average ILI, (j) inter-lick variability (controls, n = 30 and MCAO, n = 22). The data are presented as mean and standard deviation. ** indicates p values of < 0.01 and ***p values of < 0.001.

Figure 2.

Lick volume correlated with brain atrophy (a) and total number of licks (b) for the MCAO animals (n = 22). Lick efficiency (c) and total water consumption (d) in control and MCAO animals with striatal only (n = 13) and striatal and cortex lesions (n = 9). (e) Body weight of all rats prior to surgery and at time of lickometry (30–40 days post-MCAO). (f) Food consumption in 1 h, 2 weeks following lickometry. Body weight did not correlate with lick efficiency (g) or total water consumption (h) in the control rats (n = 30). (i) The relative variability (measured by co-efficient of variation) of the lickometry measures in comparison to other behavioural tasks performed in the same group of rats (published in Trueman et al.). Bilateral asymmetry (adhesive removal or sticky dot) measures the latency to contact and remove a sticky label from the forepaws. Apomorphine induced rotations counts the circling over 90 min following administration of 1 mg/kg of apomorphine. The disengage task measures the latency to respond to stimulation with and without a distractor (food). Paw reaching measures the number of pellets the rat is able to retrieve with each paw in staircase chambers. Sample size calculations were performed to establish the group sizes needed to see a treatment effect: 50% or 75% improvement (with control performance = 100%, MCAO group performance = 0%), based on the standard deviation of the MCAO group, alpha = 0.05 and power = 0.80. The data are presented as mean and standard deviation. ** indicates p values of < 0.01 and ***p values of < 0.001. Controls, n = 30 and MCAO, n = 22.