Effects of systemic administration of saxitoxin on serotonin levels in some discrete rat brain regions.

The present study is related with the toxicity of Saxitoxin (STX), a neurotoxic compound, produced by certain dinoflagellates. Its main toxicological activity is observed through the blockage of the sodium channels. It might originate a reduction of the amplitude and speed of conduction of the action potentials by the peripheral and central nerves, as well as weakening of the skeletal muscular contraction. The aim of this study was to analyze the effect of STX on serotonin (5-HT) levels in some discrete rat brain regions after acute intraperitoneal (i.p.) administration of 5 and 10 microg Kg(-1) STX body weight. 5-HT levels were analyzed at 30, 60 and 120 min after the administration of 5 microg Kg(-1) of STX, and 30 min after administration of 10 microg K(-1) of the toxin. Animals were sacrificed by cervical dislocation and the brains were removed and dissected in seven regions. Tissue samples were analyzed by using a chromatographic technique with electrochemical detection (HPLC/ED). Our results suggest that systemic administration of the STX reaches the brain producing alterations in neurotransmission increasing the levels of 5-HT in all the brain regions studied. With respect to the serotonin metabolite, 5-hidroxiindoleacetic acid (5-HIAA), we observed an increase in its levels in all the brain regions studied with the high dose of toxin, whereas different alterations were observed with the low dose of toxin.

Evaluation of in vivo and in vitro recovery rate of anatoxin-a through the microdialysis probe.

In vivo microdialysis is a versatile sampling technique commonly employed to observe changes in neurotransmitters levels that occur in response to different treatments, being these treatments administered through a microdialysis probe implanted into a specific brain region in living animals. In previous works we have used this technique to study the effects of the drug anatoxin-a, a nicotinic acetylcholine receptor agonist, on dopamine release in striatum. The aim of the present study was to assess the recovery of anatoxin-a through the microdialysis probe. This information allows knowing the exact amount of the drug crossing the microdialysis membrane, acting on extracellular tissue. High Performance Liquid Chromatography (HPLC) with Fluorescence Detection (FLD) has been used for the analysis of anatoxin-a. We observed that the recovery of anatoxin-a was about 0.5%. Under our experimental conditions, the results suggest that anatoxin-a can be used as an important tool in the study of neuronal nicotinic receptors by in vivo microdialysis technique and also show a reliable estimation of the anatoxin-a recovery through the microdialysis probe under both in vivo and in vitro conditions.