Shortened conditioned eyeblink response latency in male but not female Wistar-Kyoto hyperactive rats.

Reductions in the volume of the cerebellum and impairments in cerebellar-dependent eyeblink conditioning have been observed in attention-deficit/hyperactivity disorder (ADHD). Recently, it was reported that subjects with ADHD as well as male spontaneously hypertensive rats (SHR), a strain that is frequently employed as an animal model in the study of ADHD, exhibit a parallel pattern of timing deficits in eyeblink conditioning. One criticism that has been posed regarding the validity of the SHR strain as an animal model for the study of ADHD is that SHRs are not only hyperactive but also hypertensive. It is conceivable that many of the behavioral characteristics seen in SHRs that seem to parallel the behavioral symptoms of ADHD are not solely due to hyperactivity but instead are the net outcome of the interaction between hyperactivity and hypertension. We used Wistar-Kyoto Hyperactive (WKHA) and Wistar-Kyoto Hypertensive (WKHT) rats (males and females), strains generated from recombinant inbreeding of SHRs and their progenitor strain, Wistar-Kyoto (WKY) rats, to compare eyeblink conditioning in strains that are exclusively hyperactive or hypertensive. We used a long-delay eyeblink conditioning task in which a tone conditioned stimulus was paired with a periorbital stimulation unconditioned stimulus (750-ms delay paradigm). Our results showed that WKHA and WKHT rats exhibited similar rates of conditioned response (CR) acquisition. However, WKHA males displayed shortened CR latencies (early onset and peak latency) in comparison to WKHT males. In contrast, female WKHAs and WKHTs did not differ. In subsequent extinction training, WKHA rats extinguished at similar rates in comparison to WKHT rats. The current results support the hypothesis of a relationship between cerebellar abnormalities and ADHD in an animal model of ADHD-like symptoms that does not also exhibit hypertension, and suggest that cerebellar-related timing deficits are specific to males. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spontaneous recovery but not reinstatement of the extinguished conditioned eyeblink response in the rat.

Reinstatement—the return of an extinguished conditioned response (CR) after reexposure to the unconditioned stimulus (US)—and spontaneous recovery—the return of an extinguished CR with the passage of time—are 2 of 4 well-established phenomena that demonstrate that extinction does not erase the conditioned stimulus (CS)–US association. However, reinstatement of extinguished eyeblink CRs has never been demonstrated, and spontaneous recovery of extinguished eyeblink CRs has not been systematically demonstrated in rodent eyeblink conditioning. In Experiment 1, US reexposure was administered 24 hr prior to a reinstatement test. In Experiment 2, US reexposure was administered 5 min prior to a reinstatement test. In Experiment 3, a long, discrete cue (a houselight), present in all phases of training and testing, served as a context within which each trial occurred to maximize context processing, which in other preparations has been shown to be required for reinstatement. In Experiment 4, an additional group was included that received footshock exposure, rather than US reexposure, between extinction and test, and contextual freezing was measured prior to test. Spontaneous recovery was robust in Experiments 3 and 4. In Experiment 4, context freezing was strong in a group given footshock exposure but not in a group given eye shock US reexposure. There was no reinstatement observed in any experiment. With stimulus conditions that produce eyeblink conditioning and research designs that produce reinstatement in other forms of classical conditioning, we observed spontaneous recovery but not reinstatement of extinguished eyeblink CRs. This suggests that reinstatement, but not spontaneous recovery, is a preparation- or substrate-dependent phenomenon. (PsycINFO Database Record (c) 2011 APA, all rights reserved)