Impairment of object recognition, object location and spatial working memory performance in inbred RHA vs. RLA rats

The inbred Roman rat strains, which have been selected and bred for their very high (RHA) or extremely poor (RLA) ability to acquire the two-way active avoidance task, constitute a bidirectional genetic model in which each strain differs from the other and/or from "standard" laboratory rat strains in a large number of behavioral and neurobiological phenotypes. Relative to Roman low-avoidance (RLA) rats, the Roman High-avoidance (RHA) rats exhibit increased mesolimbic dopamine function, social deficits, and impaired attention and cognitive flexibility, besides many other neurobehavioral phenotypes that make them a promising animal model of attention/cognitive-related syndromes, such as schizophrenia or attention deficit/hyperactivity disorder (ADHD). This study aimed to investigate non-spatial working memory and long-term memory in the Roman rat strains using the Object Recognition Test (ORT), a non-spatial declarative memory task that assesses object memory encoding, consolidation, and retrieval. The Object Location Test (OLT), which measures recognition of object location rather than differences between objects, was also used to evaluate short- and long-term memory. Between-strain spatial working memory differences were also evaluated using a delayed-matching-to-place (DMTP) task in the Morris water maze. Findings showed that RHA rats exhibited impaired working memory and long-term memory compared to RLA rats in the ORT. The degree of previous habituation to the testing context significantly affected object recognition memory in RHA rats. RHA rats also exhibited impaired short-term memory in the OLT. In the DMTP task, spatial working memory was also impaired in RHAs. The memory deficits shown by RHA rats seem to be compatible with their known (schizophrenia-like) alterations of the hippocampus and prefrontal cortex. The finding that relatively long habituation to the testing context rescues the long-term object-recognition memory deficit of RHA rats suggests that impaired attention, perhaps related to their relative hyperactivity, might be a factor underlying that deficit. The findings of the present study support the notion that the inbred RHA rat strain presents impairments in both non-spatial and spatial working/short-term memory, aligning with cognitive symptoms observed in patients with schizophrenia or with ADHD.