Effects of serotonin on neurite outgrowth from thalamic neurons in vitro
Section snippets
Substrate preparation
Glass coverslips (12 mm diameter; Fisher) were acid cleaned, sterilized and placed in 0.25 ml of poly-d-lysine (0.01%; 70,000–100,000 mol wt in sterile water; Sigma). After 30 min, excess poly-d-lysine was removed and coverslips were allowed to air dry in a sterile hood. All cultures were grown in neural basal medium (NB; Gibco) that also contained 10% defined supplemented fetal bovine serum (Hyclone).
Culture preparation
Rat pups (Zivic-Miller Laboratories, Sprague–Dawley rats) no more than 12 h old (postnatal day 0,
Controls
An adequate test of the hypothesis that 5-HT influences neurite development by VB neurons in vitro requires that basal levels of 5-HT in the cultures approach zero and that added 5-HT remains available in the culture for the duration of the test period. Both of these conditions were fulfilled in the study. The NB used for the tissue culture experiments contained trace amounts (0.07±10 ng/μl) of 5-HT, as measured by HPLC. Assessment of 5-HT levels in culture wells demonstrated that the amine was
Discussion
The present results demonstrate that increasing concentrations of 5-HT increase process outgrowth for thalamic cells maintained in tissue culture in the absence of their cortical targets. The results suggest a curvilinear relationship between 5-HT concentration and neurite outgrowth. Specifically, the 25 μM 5-HT concentration had the greatest effect on all of the variables analysed, and both lower and higher concentrations were not significantly different from controls with respect to any of the
Conclusions
In summary, the present results indicate that 5-HT significantly influences neurite outgrowth of thalamic neurons, and this effect is independent of any interaction between the axons of these neurons and their cortical targets. The mechanism(s) underlying these effects of 5-HT remain(s) to be determined.
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