Infusion of bicuculline methiodide into the tectum: model specificity of pro- and anticonvulsant actions

Microinjection of drugs, such as muscimol, into the substantia nigra pars reticulata (SNpr) can inhibit several types of experimental seizures. Some findings suggested that this was a result of disinhibition of neurons receiving input from GAB Aergic nigrotectal cells. Indeed, it was reported that bicuculline methiodide (BMI), infused into the tectal region that was reported to receive nigral input, produced an anticonvulsant effect against maximal electroshock (MES) convulsion. Since previous work had suggested that the anticonvulsant effect of intranigral muscimol depended on the particular experimental seizure used, three different experimental seizures were used in the present study to evaluate the effects of BMI infusion into the tectum. Guide cannulas aimed at the tectal region receiving nigral innervation were stereotaxically implanted in rats a week before testing. Bilateral intratectal infusions of BMI (25 ng/ side) had an anticonvulsant effect against MES convulsions, confirming a previous report. In contrast, the same BMI pretreatment worsened convulsions produced by either systemic pentylenetetrazol (40 mg/kg i.p.) or bicuculline (0.5 mg/kg i.V.). The effects of intratectal BMI were seizure model-dependent, suggesting different functional interconnections between tectum and those pathways responsible for generalization of MES as compared to PTZ or bicuculline convulsions.