Ontogeny of sensorimotor gating and short-term memory processing throughout the adolescent period in rats

Different maturation patterns for sensorimotor gating and startle habituation deficits in male and female RHA vs RLA rats

Neurodevelopmental anomalies are thought to play a crucial role in the emergence of schizophrenia. The Roman high-avoidance (RHA) rats exhibit impaired prepulse inhibition (PPI), as well as other behavioral and cognitive singularities related to schizophrenia syndromes compared to the Roman low-avoidance (RLA) rats. In the present study, we aimed at elucidating whether PPI deficits in the RHA rats take place during prepubescence, adolescence, or adulthood. Thus, we evaluated the levels of PPI of both strains and both sexes during these three developmental phases. Additionally, we also investigated the onset of startle habituation deficits in the same groups. The results showed that male RHA rats exhibit a clear-cut PPI reduction compared to their RLA counterparts in adulthood. In female RHA rats, we observed lower levels of PPI since adolescence and through adulthood. We also found no differences between PPI percentages among the three ages in RHA male rats. Contrarily, in male RLA rats, PPI levels were increased in adults compared to their adolescent and prepubescent counterparts. Finally, a deficit in startle habituation was observed in adulthood of both male and female RHA rats, although in the latter case the disturbance in startle habituation was more profound. These results further the description of the maturational trajectory of cognitive markers relevant to schizophrenia prodrome and they add face validity to the RHA rats as a model of schizophrenia-relevant phenotypes.

Positive symptom phenotypes appear progressively in "EDiPS", a new animal model of the schizophrenia prodrome

An increase in dopamine (DA) synthesis capacity in the dorsal striatum (DS) during the prodromal stage of schizophrenia becomes more pronounced as patients progress to the full disorder. Understanding this progression is critical to intervening in disease course. We developed an animal model-Enhanced Dopamine in Prodromal Schizophrenia (EDiPS)-which uses a genetic construct to increase DA synthesis capacity in the DS of male rats. We assessed pre-pulse inhibition (PPI) and amphetamine (AMPH)-induced locomotion (0.6 mg/kg) in EDiPS animals longitudinally after post-natal day 35 (when the EDiPS construct is administered). We also assessed their response to repeated acute restraint stress. In adult EDiPS animals, we measured baseline and evoked extracellular DA levels, and their stereotyped responses to 5 mg/kg AMPH. AMPH-induced hyperlocomotion was apparent in EDiPS animals 6-weeks after construct administration. There was an overall PPI deficit in EDiPS animals across all timepoints, however the stress response of EDiPS animals was unaltered. Adult EDiPS animals show normal baseline and potassium-evoked DA release in the DS. These findings suggest that key behavioural phenotypes in EDiPS animals show a progressive onset, similar to that demonstrated by patients as they transition to schizophrenia. The EDiPS model could therefore be used to investigate the molecular mechanisms underlying the prodrome of schizophrenia.

Young spontaneously hypertensive rats (SHRs) display prodromal schizophrenia-like behavioral abnormalities

The Spontaneously Hypertensive Rat (SHR) strain has been suggested as an animal model of schizophrenia, considering that adult SHRs display behavioral abnormalities that mimic the cognitive, psychotic and negative symptoms of the disease and are characteristic of its animal models. SHRs display: (I) deficits in fear conditioning and latent inhibition (modeling cognitive impairments), (II) deficit in prepulse inhibition of startle reflex (reflecting a deficit in sensorimotor gating, and associated with psychotic symptoms), (III) diminished social behavior (modeling negative symptoms) and (IV) hyperlocomotion (modeling the hyperactivity of the dopaminergic mesolimbic system/ psychotic symptoms). These behavioral abnormalities are reversed specifically by the administration of antipsychotic drugs. Here, we performed a behavioral characterization of young (27-50 days old) SHRs in order to investigate potential early behavioral abnormalities resembling the prodromal phase of schizophrenia. When compared to Wistar rats, young SHRs did not display hyperlocomotion or PPI deficit, but exhibited diminished social interaction and impaired fear conditioning and latent inhibition. These findings are in accordance with the clinical course of schizophrenia: manifestation of social and cognitive impairments and absence of full-blown psychotic symptoms in the prodromal phase. The present data reinforce the SHR strain as a model of schizophrenia, expanding its validity to the prodromal phase of the disorder.