Recovery of sensorimotor function following sciatic nerve injury across multiple rat strains.

BACKGROUND: Peripheral nerve injury (PNI) can result in neurodegenerative changes leading to motor, sensory and autonomic dysfunction. Injury to the rat sciatic nerve is used to model pathophysiologic processes following PNI and assess the efficacy of therapeutic interventions. Frequently, temporal changes in the sciatic functional index (SFI), a measure of sensorimotor integration are measured in rats to assess functional recovery following sciatic nerve injury. However, multiple rat strains and behavioral endpoints have been employed to investigate pathophysiology of PNI and impact of therapeutic intervention on recovery, raising the possibility that rat strain may influence the outcome of such studies. NEW METHOD: The temporal course of recovery from sham, sciatic nerve crush or transection injury was assessed using SFI determined by two methods (footprint and DigiGait), and proprioceptive hind limb placement (a measure of proprioceptive integrity) of the sciatic nerve innervation, in male Sprague Dawley, Lewis, Fischer, Wistar and Long Evans rats. RESULTS: The SFI profile, as assessed by both inked footprint analysis and DigiGait, following sciatic nerve injury was remarkably conserved across strains. Dramatic strain-related differences were observed in the latency to place the crush- or transection-injured hind limb following proprioceptive hind limb stimulation. COMPARISON WITH EXISTING METHOD: The novelty of this study is the parallel comparison of multiple strains using existing and novel tests. CONCLUSION: These results suggest that some sensorimotor function tests may be sensitive to the choice of strain, as evidenced by the differences between SFI and proprioceptive function outcomes.

Assessment of ultrasonic vocalizations during drug self-administration in rats.

Drug self-administration procedures are commonly used to study behavioral and neurochemical changes associated with human drug abuse, addiction and relapse. Various types of behavioral activity are commonly utilized as measures of drug motivation in animals. However, a crucial component of drug abuse relapse in abstinent cocaine users is "drug craving", which is difficult to model in animals, as it often occurs in the absence of overt behaviors. Yet, it is possible that a class of ultrasonic vocalizations (USVs) in rats may be a useful marker for affective responses to drug administration, drug anticipation and even drug craving. Rats vocalize in ultrasonic frequencies that serve as a communicatory function and express subjective emotional states. Several studies have shown that different call frequency ranges are associated with negative and positive emotional states. For instance, high frequency calls ("50-kHz") are associated with positive affect, whereas low frequency calls ("22-kHz") represent a negative emotional state. This article describes a procedure to assess rat USVs associated with daily cocaine self-administration. For this procedure, we utilized standard single-lever operant chambers housed within sound-attenuating boxes for cocaine self-administration sessions and utilized ultrasonic microphones, multi-channel recording hardware and specialized software programs to detect and analyze USVs. USVs measurements reflect emotionality of rats before, during and after drug availability and can be correlated with commonly assessed drug self-administration behavioral data such lever responses, inter-response intervals and locomotor activity. Since USVs can be assessed during intervals prior to drug availability (e.g., anticipatory USVs) and during drug extinction trials, changes in affect associated with drug anticipation and drug abstinence can also be determined. In addition, determining USV changes over the course of short- and long-term drug exposure can provide a more detailed interpretation of drug exposure effects on affective functioning.