Ischemia-induced extracellular release of serotonin plays a role in CA1 neuronal cell death in rats.

BACKGROUND AND PURPOSE: Serotonin, via 5-HT2 receptors, exerts an excitatory effect on CA1 neurons and may play a role in ischemia-induced excitotoxic damage. To evaluate the role of serotonin in ischemia, both neurochemical and histopathological studies were performed. METHODS: Neurochemical studies included rats that were subjected to 12.5 or 20 minutes of normothermic ischemia by two-vessel occlusion plus hypotension, and extracellular serotonin levels were measured in the hippocampus (12.5 minutes' ischemia, n = 5) or striatum (20 minutes' ischemia, n = 13) by microdialysis. In the histopathological study the effect of 8 mg/kg ritanserin, a 5-HT2 antagonist, administered continuously from 30 minutes prior to ischemia until 1 hour of recirculation was evaluated in five rats subjected to 10 minutes of ischemia. After 3 days, the numbers of normal-appearing neurons in the CA1 subregions were counted. RESULTS: Ischemia of 12.5 minutes' duration induced a fourfold increase in serotonin in the hippocampus (mean +/- SEM baseline, 1.86 +/- 0.25 pmol/ml perfusate; during ischemia, 8.14 +/- 0.89 pmol/ml; p < 0.05 by analysis of variance). Twenty minutes of ischemia induced a 25-fold increase in serotonin in the dorsolateral striatum (baseline, 0.98 +/- 0.15 pmol/ml; ischemia, 24.4 +/- 5.93 pmol/ml; p < 0.001). The histopathological study demonstrated severe ischemic damage in all CA1 subregions of nontreated animals (medial, 34 +/- 16 normal-appearing neurons, middle, 52.2 +/- 22.9 neurons; lateral, 56.6 +/- 21.8 neurons). Treatment with ritanserin significantly attenuated ischemic damage (medial, 117.6 +/- 6.5 neurons; middle, 131.4 +/- 4.9 neurons; lateral, 130 +/- 7.5 neurons; p < 0.01 different from nontreated). CONCLUSIONS: Taken together, these results suggest that serotonin plays a detrimental role, mediated by 5-HT2 receptors, in the development of ischemic damage.