26 With regard to transgenic rats, the observation that gene transfers were performed after development only had transient consequences on 5-HTT and 5-HT reuptake underlines the limits of that particular model.33 Finally, autoradiographic experiments conducted with the rat sublines differing for platelet 5-HTT protein expression and function suggest that these two sublines may not differ with regard Inhibitors,research,lifescience,medical to central 5-HTT protein expression.34 Detection of strain differences in 5-HTT: behavioral response Taking into account these observations, we performed two scries of experiments.

The first series of experiments took advantage of the finding that WKY do not respond acutely to the tricyclics imipramine Inhibitors,research,lifescience,medical and desipramine when examined in the forced swimming test. Thus, one hypothesis

could be that 5-HTT and/or NA transporters are hyposensitive to the 5-HT reuptake (imipramine) and NA reuptake (imipramine and desipramine) inhibitory properties of these antidepressants. Accordingly, we used in vitro, in vivo, and ex vivo methods to examine the 5-HTT in WKY, SHR, and LEW35 Acute administration of the SSRI citalopram (1-10 mg/kg, IP 1 h before an elevated plus-maze test) to SHR, LEW, and WKY promoted anxiety and/or hypoactivity in SHR Inhibitors,research,lifescience,medical and LEW, but not in WKY. This initially reinforced the hypothesis that WKY 5-HTTs are hyposensitive to drugs endowed with 5-HT reuptake properties.

Inhibitors,research,lifescience,medical However, the pretreatment with citalopram increased central 5-HT levels and/or decreased 5-HIAA levels in all strains. Hippocampal, but not midbrain or striatal, [3H]citalopram binding at 5-HTTs was lower in WKY than in SHR, whereas the [3H]5-HT reuptake kinetics and the potencies of citalopram (1-1000 nM) needed to inhibit [3H]5-HT reuptake into hippocampal and striatal Inhibitors,research,lifescience,medical synaptosomes did not differ between strains. This was confirmed in vivo by means of microdialysis in the hippocampus of freely moving rats. Thus, although LEW displayed a three- to fourfold higher baseline level of extracellular 5-HT in the hippocampus, compared with SHR and WKY, local perfusion with 1 μM citalopram promoted relative increases first in extracellular 5-HT levels over baseline that were similar in all strains. Acute IP administration of 3.3 mg/kg citalopram (1 h beforehand) decreased [3H]5-HT reuptake into hippocampal synaptosomes to a similar extent in SHR and WKY, check details thereby indicating that the systemic administration of the SSRI has strain-independent effects at hippocampal 5-HT nerve terminals. This study thus failed to detect strain differences in the 5-HTT or in its sensitivity to an SSRI, further indicating that genetic differences in the behavioral responses to SSRIs may involve 5-HTT-independent mechanisms.