Modelo neurodesenvolvimental de esquizofrenia induzida pela administração neonatal de cetamina em ratos: avaliação da influência do sexo e efeito antipsicótico

Abstract

Schizophrenia is a severe psychiatric disorder, and maybe, because of this, one of the most researched. Despite the important advances achieved in the studies about the physiopathology of the disease during the last century, few benefits were significant in the treatment of these patients. The construction of new animal models of schizophrenia is an important tool for the comprehension of the physiopathology of the disease and the development of new therapies, since even the atypical antipsychotics did not show the expected results regarding the improvement of negative and cognitive symptoms. The objective of this research was to investigate the effects of ketamine in the central nervous system as a possible agent in a neurodevelopmental model of schizophrenia. We sought to determinate the behavioral changes and oxidative stress by the neonatal administration of ketamine, as well as the reversion and prevention of these effects by the treatment with clozapine, an atypical antipsychotic. We also conducted an analysis of the role of sex at the development of schizophrenia, dividing the females by the estrous cycle, that includes phases presenting high and low concentrations of estrogen, proestrus and diestrus, respectively, since estrogen presents a neuroprotective effect. The experimental design followed the criteria to determine an animal model: the face validity (where one seeks to mimic the characteristic behavior of the disease in the animal), construct validity (the physiopathology of the disease) and predictive validity (if the established medicines for the disease are able to reverse and prevent the effects that the researched drug induces). The animals used at the experimental protocol were Wistar rats, divided in six groups and treated with saline or ketamine intraperitoneal (i.p.) for five days (7th-11th day after birth). Group 1: (males treated with saline) Group 2 (females treated with saline); Group 3 (males treated with ketamine 2,5mg/kg); Group 4 (females treated with ketamine 2,5mg/kg); Group 5 (males treated with ketamine 5 mg/kg); Group 6 (females treated with ketamine 5 mg/kg).The tests of prepulse inhibition and y-maze (behavioral tests) were conducted in adolescence (35 days after birth), and repeated at the adult phase (65 days after birth). At the adult phase, the females were divided according with the estrous cycle (diestrus and proestrus) to observe the influence of estrogen. At the 66th day after birth, the animals trated with ketamine 5 mg/kg were submitted to a reversion treatment by clozapine 10 mg/kg i.p. once a day during 10 days. After this period, the behavioral and neurochemical (dosage of BDNF and GSH) tests were performed. The animals treated with ketamine 2,5 mg/kg did not show any significant difference in the behavioral tests conducted in the adult phase when compared with the animals treated with saline and, therefore, the dose selected to measure the other parameters was 5,0 mg/kg. The treatment with ketamine 5 mg/kg significantly reduced the parameters observed at the behavioral tests, both in adult males and females at the diestrus. The males and females at the diestrus also presented a significant reduction in the GSH levels. The adult males treated with ketamine 5 mg/kg presented a significant increase in BDNF, whereas the females at the diestrus presented a reduction in this parameter. The females at the proestrus achieved a better performance in all tests. In the prevention protocol, the treatment with clozapine 10mg/kg reverted the effects of ketamine in the tests of prepulse inhibition and in the neurochemical testes in males and females in the diestrus that were treated with ketamine 5 mg/kg.The results observed in the behavioral and neurochemical tests showed that ketamine induced the parameters of schizophrenia, presenting itself as a new tool available to the research of animal models of neonatal schizophrenia. The developed model succeeded for the first time in mimicking the differences between the phases of the estrous cycle of the animals, in a close approximation of what happens in humans.