The Structure of Skilled Forelimb Reaching in the Rat: A Movement Rating Scale

Abstract

Skilled reaching for food is an evolutionary ancient act and is displayed by many animal species, including those in the sister clades of rodents and primates. The video describes a test situation that allows filming of repeated acts of reaching for food by the rat that has been mildly food deprived. A rat is trained to reach through a slot in a holding box for food pellet that it grasps and then places in its mouth for eating. Reaching is accomplished in the main by proximally driven movements of the limb but distal limb movements are used for pronating the paw, grasping the food, and releasing the food into the mouth. Each reach is divided into at least 10 movements of the forelimb and the reaching act is facilitated by postural adjustments. Each of the movements is described and examples of the movements are given from a number of viewing perspectives. By rating each movement element on a 3-point scale, the reach can be quantified. A number of studies have demonstrated that the movement elements are altered by motor system damage, including damage to the motor cortex, basal ganglia, brainstem, and spinal cord. The movements are also altered in neurological conditions that can be modeled in the rat, including Parkinson's disease and Huntington's disease. Thus, the rating scale is useful for quantifying motor impairments and the effectiveness of neural restoration and rehabilitation. Because the reaching act for the rat is very similar to that displayed by humans and nonhuman primates, the scale can be used for comparative purposes. from a number of viewing perspectives. By rating each movement element on a 3-point scale, the reach can be quantified. A number of studies have demonstrated that the movement elements are altered by motor system damage, including damage to the motor cortex, basal ganglia, brainstem, and spinal cord. The movements are also altered in neurological conditions that can be modeled in the rat, including Parkinson's disease and Huntington's disease. Thus, the rating scale is useful for quantifying motor impairments and the effectiveness of neural restoration and rehabilitation.

Short-Term Treatment with Silymarin Improved 6-OHDA-Induced Catalepsy and Motor Imbalance in Hemi-Parkisonian Rats

“…In rotarod, which is considered as a standard test for evaluation of motor-balance, performance is measured by the period of time that an animal stays up and walks on the rod and the latency to fall off the drum was recorded. 20,25,36 In 6-OHDA-lesioned rats loss of dopaminergic neurons and reduction of striatal dopamine levels is an essential cause of motor incoordination. In fact, unilateral lesion of SNc obliges animal to change its weight irregularly for movement and balance; therefore this lead to motor disturbance and asymmetry.…”

Comparing Staircase and Skilled Forelimb Reaching Tests After Endothelin-1-Induced Stroke

“…Rats were placed in a clear acrylic box with a 1cm wide slit opening onto a shelf containing divots to hold 45mg sugar pellets for 10 minutes per session (Figure 1b) [12,13]. The divots are placed lateral to the opening so that the rat cannot reach a pellet placed in the right divot with his right paw or a pellet placed in the left divot with his left paw.…”

“…Redundant reaching (i.e., reaching without a pellet present) was discouraged by having the rat approach an empty shelf and not placing a pellet on the shelf until he performed a complete trial (approach and turn) without reaching [12]. …”

“…Two of the most widely used behavioral tests in rodent models of stroke for addressing fi ne motor skills function and recovery include the Montoya staircase test and the skilled forelimb reaching task (also known as the single pellet reaching test) [11][12][13]. A brief search of PubMed using the terms stroke, rodent, staircase, and skilled reaching yields more than 500 results.…”

“…While the test may be recorded for detailed kinematic analysis of the reach, it is most often employed as a quantitative test, reporting only the percent success rate [18,19]. In the skilled forelimb reaching test, the animal is placed in a box and learns, after extensive training, to extend its dominant forepaw through a vertical slit to retrieve a food item from a fi xed location [12,14,17,18]. The rat is allowed to choose which paw it prefers to use, thus handedness must be taken into account when designing the study [13].…”