Role of serotonergic mechanism in the regulation of blood-brain barrier in anaesthetised cats and dogs has been investigated. In cats, the circulant used was Evans blue. The drugs as well as the circulant were administered through the left carotid artery. The staining of the brain substance was scored at autopsy. 5-Hydroxytryptamine (5-HT), 5-hydroxytryptophan (5-HTP), 5-HT uptake-inhibitors, citalopram and fluvoxamine, as well as normal saline produced no staining whereas hypertonic sodium chloride solution produced significant staining of the brain substance. In experiments on dogs, sodium fluorescein was injected intravenously and the cerebrospinal fluid (CSF) was collected through a needle put in the cisterna magna for estimation of the dye. Normal saline, 5-HT, citalopram, fluvoxamine and methysergide failed to affect the entry of sodium fluorescein in the CSF while hypertonic sodium chloride solution increased it significantly. Furthermore, 5-HT did not affect the increased entry of sodium fluorescein induced by hypertonic sodium chloride. It is concluded that serotonergic mechanism does not play a significant role in the regulation of blood-brain barrier.
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