Efeitos agudos e repetidos da cocaína em ratas em diferentes condições hormonais: estudo dos mecanismos inibitórios e tóxicos no sistema nervoso central / Acute and repeated effects of cocaine in rats under different hormonal conditions: study of inhibitory and toxic mechanisms in the central nervous system

A sensibilização comportamental à cocaína consiste no aumento da resposta após uso repetido intermitente da substância, e tem sido apontada como um dos principais fatores que aumentam o risco do desenvolvimento da dependência. Indivíduos do sexo feminino têm mostrado efeitos mais intensos em resposta ao uso de psicoestimulantes do que os do sexo masculino, influenciados por diferenças hormonais. Além da neurotoxicidade induzida por sua ação nos sistemas dopaminérgico e glutamatérgico (excitatórios), a cocaína influencia a atividade dos sistemas inibitórios cerebrais (GABA e taurina), que se contrapõe aos sistemas acima. Objetivamos, portanto, verificar a influência dos hormônios femininos na neurotoxicidade da cocaína e nas adaptações dos sistemas inibitórios cerebrais, secundárias ao uso deste psicoestimulante em fêmeas. Para tanto, foram utilizadas ratas intactas hormonalmente ou ratas ovariectomizadas, recebendo reposição hormonal (progesterona e/ou estradiol) ou não. Estas foram sensibilizadas com doses repetidas de cocaína e seu comportamento (atividade locomotora e estereotipias) foi monitorado. Para avaliar a influência dos hormônios na neurotoxicidade da cocaína, foi realizado Teste Cometa em diferentes regiões cerebrais, para verificar lesão de DNA na célula neuronal. Para verificar a influência destes hormônios nos níveis extracelulares de GABA (e seus precursores, glutamato e glutamina) e de taurina no córtex pré-frontal medial, os animais foram submetidos a sessões de microdiálise após realização de cirurgia estereotáxica. Os resultados de comportamento indicaram apenas as fêmeas com presença endógena de estradiol e progesterona desenvolveram tanto sensibilização locomotora quanto estereotipia. Já a reposição de estradiol aumentou os comportamentos estereotipados após desafio à cocaína, enquanto as ratas que receberam reposição de progesterona, associada ou não ao estradiol, apresentaram menor escore de estereotipia após cocaína repetida. Tanto a exposição aguda quanto a sensibilização à cocaína induziram dano no DNA em diferentes regiões cerebrais das ratas, exceto no hipotálamo, onde o dano foi comparado ao das ratas que não receberam cocaína. A presença endógena de estrógeno e progesterona diminuiu o dano provocado pela administração de cocaína em todas as regiões cerebrais, mostrando que uma maior sensibilização em fêmeas pode estar relacionada ao desenvolvimento de neuroplasticidade nas regiões avaliadas. Os níveis extracelulares de GABA, de seus precursores e de taurina também sofreram alteração após exposição à cocaína. A administração aguda deste psicoestimulante aumentou os níveis de GABA, glutamato e taurina e diminuiu os níveis de glutamina no CPFm, de forma diferente se for considerada a condição hormonal. Já a sensibilização à cocaína provocou menor alteração nos níveis de GABA e de taurina e consequente aumento nos níveis de glutamato no CPFm das ratas com presença hormonal endógena. Estes resultados sugerem que uma maior sensibilização à cocaína em fêmeas pode estar relacionada a uma hipofuncionalidade dos sistemas inibitórios cerebrais decorrentes da presença endógena dos hormônios sexuais femininos. Portanto, a sensibilização à cocaína em fêmeas com presença hormonal (principalmente o estrógeno) está relacionada ao desenvolvimento de neuroplasticidade e a uma menor atividade dos sistemas inibitórios cerebrais, com consequente aumento na atividade excitatória no CPFm, uma das regiões cerebrais mais importantes no desenvolvimento da adição.

Behavioral sensitization to cocaine is an increased response after repeated intermittent use of the substance, and has been identified as one of the main factors that increase the risk of developing addiction. Females have shown higher effects in response to psychostimulant use than males, influenced by hormonal differences. In addition to the induction of dopaminergic and glutamatergic (excitatory) neurotoxicity, cocaine influences the activity of brain systems inhibitory (GABA and taurine), which is opposite to the above systems. We aim therefore to investigate the influence of female hormones on cocaine neurotoxicity and in brain adaptations, secondary to this psychostimulant use in inhibitory systems of female rats. In this sense, we used hormonally intact rats or ovariectomized rats receiving hormone replacement therapy (progesterone and/or estrogen) or not. These were sensitized with repeated doses of cocaine and its behavior (locomotor activity and stereotypies) was monitored. To evaluate the influence of hormones on the neurotoxicity of cocaine, Comet Assay was performed in different brain areas, to verify DNA damage in neuronal cell. To check the influence of these hormones in extracellular levels of GABA (and its precursors, glutamate and glutamine) and taurine in the medial prefrontal cortex (mPFC), the animals were subjected to microdialysis session after performing stereotactic surgery. The behavior results indicated that only females with endogenous presence of both estrogen and progesterone developed sensitization by hyperlocomotion and stereotypy. The estradiol replacement increased stereotypic behaviors after cocaine challenge, while the rats that received progesterone replacement, associated or not with estradiol, had lower scores of stereotypy after repeated cocaine. Both acute exposure and sensitization to cocaine induced DNA damage in different brain areas of female rats, except in the hypothalamus , where the damage was compared to the rats that did not receive cocaine. The presence of endogenous estrogen and progesterone decreased the damage caused by the administration of cocaine in all brain areas, showing that greater sensitization in females may be associated to neuroplasticity development in the evaluated areas. Extracellular levels of GABA, its precursors and taurine also been changed after cocaine exposure. Acute administration of cocaine increased levels of GABA, glutamate and taurine and decreased glutamine levels in mPFC, differently according with the hormonal condition. Already cocaine sensitization caused less change in the levels of GABA and taurine and subsequent increased levels of glutamate in the mPFC of rats with endogenous hormonal presence. These results suggest that greater sensitization to cocaine in females may be related to a hypofunction of brain inhibitory systems resulting from the presence of endogenous female sex hormones. Therefore, sensitization to cocaine in females with hormonal presence (especially the estrogen) is related to the neuroplasticity development and a lower inhibitory activity of brain systems, with a consequent increase in excitatory activity in the mPFC, one of the most important brain areas involved in the drug addition.

Genetic deletion of MT(1) and MT(2) melatonin receptors differentially abrogates the development and expression of methamphetamine-induced locomotor sensitization during the day and the night in C3H/HeN mice.

This study explored the role of the melatonin receptors in methamphetamine (METH)-induced locomotor sensitization during the light and dark phases in C3H/HeN mice with genetic deletion of the MT(1) and/or MT(2) melatonin receptors. Six daily treatments with METH (1.2 mg/kg, i.p.) in a novel environment during the light phase led to the development of locomotor sensitization in wild-type (WT), MT(1)KO and MT(2)KO mice. Following four full days of abstinence, METH challenge (1.2 mg/kg, i.p.) triggered the expression of locomotor sensitization in METH-pretreated but not in vehicle (VEH)-pretreated mice. In MT(1)/MT(2)KO mice, the development of sensitization during the light phase was significantly reduced and the expression of sensitization was completely abrogated upon METH challenge. During the dark phase the development of locomotor sensitization in METH-pretreated WT, MT(1)KO and MT(2)KO mice was statistically different from VEH-treated controls. However, WT and MT(2)KO, but not MT(1)KO mice receiving repeated VEH pretreatments during the dark phase expressed a sensitized response to METH challenge that is of an identical magnitude to that observed upon 6 days of METH pretreatment. We conclude that exposure to a novel environment during the dark phase, but not during the light phase, facilitated the expression of sensitization to a METH challenge in a manner dependent on MT(1) melatonin receptor activation by endogenous melatonin. We suggest that MT(1) and MT(2) melatonin receptors are potential targets for pharmacotherapeutic intervention in METH abusers.