Day/night variation of 5-hydroxyindole acetic acid concentration in rat cerebrospinal fluid after acute and long-term administration of a selective serotonin reuptake inhibitor, fluvoxamine

The selective serotonin reuptake inhibitor fluvoxamine suppresses post-feeding hyperactivity induced by food restriction in rats

Previous studies demonstrated that rats allowed access to running wheel with food restriction schedules run excessively. This hyperactivity consisted of a pre-feeding activity (an increase in running activity before the feeding time, also termed food-anticipatory activity: FAA) and a post-feeding activity (an increase in running activity after the feeding time, succeeding activity: SA). Here we evaluated the effect of fluvoxamine, a selective serotonin reuptake inhibitor, on food restriction-induced hyperactivity in rats. Furthermore, the effect of fluvoxamine on each of the FAA and the SA was also investigated. Rats were individually housed in a running-wheel cage under food restriction for 3 h per day, and running activity was measured for 7 consecutive days. This restricted feeding significantly increased the running activity and decreased body weight. Simultaneous administration of fluvoxamine (50 mg/kg/day, p.o.) for 7 days suppressed the increase in running activity (P<0.05) with no modification of the decrease in body weight or food intake. Analysis of each activity revealed that fluvoxamine's efficacy was observed only in the SA (p<0.01). These results suggest that repeated treatment with fluvoxamine attenuates the hyperactivity, which is exclusively dependent on the substantial reduction in the SA.

Cerebrospinal fluid monoamine and metabolite concentrations and aggression in rats

In humans and other primates low cerebrospinal fluid (CSF) levels of the major serotonin (5-HT) metabolite 5-hydroxyindoleacetic acid (5-HIAA) have been correlated to high aggressiveness. This finding forms the basis of the 5-HT deficiency hypothesis of aggression. Surprisingly, this correlation has not been confirmed in rodents so far, while manipulation studies aimed to investigate the link between 5-HT and aggressive behaviour are mostly carried out in rodents. In this study the relation between aggression and CSF monoamine and metabolite concentrations was investigated in male Wildtype Groningen rats. In sharp contrast to the hypothesis and our expectation, a clear positive correlation was found between the individual level of trait-like aggressiveness and CSF concentrations of 5-HT, 5-HIAA, norepinephrine (NE), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC). Shortly after the acute display of aggressive behaviour (as a state-like phenomenon), decreased 5-HT levels and an increase in 5-HIAA/5-HT ratio and NE concentrations were found. Surprisingly, pharmacological challenges known to influence 5-HT transmission and aggressive behaviour did not affect CSF 5-HT and 5-HIAA concentrations, only the NE level was increased. Lesioning 5-HT terminals by 5,7-dihydroxytryptamine (5,7-DHT) administration caused a decrease in CSF 5-HT and 5-HIAA, but without affecting aggressive behaviour. The observed positive correlation between CSF 5-HIAA and trait aggressiveness makes it questionable whether a direct extrapolation of neurobiological mechanisms of aggression between species is justified. Interpretation of CSF metabolite levels in terms of activity of neural substrates requires a far more detailed knowledge of the dynamics and kinetics of a neurotransmitter after its release.

Uptake across the blood-brain barrier and tissue distribution of enterostatin after peripheral administration in rats

Enterostatin, the N-terminal activation pentapeptide of procolipase that is produced by the pancreas, reduces food intake from high-fat diet when injected either peripherally or centrally to rats. We investigated uptake across the blood-brain barrier (BBB) and tissue distribution of enterostatin by giving radioactive-labeled enterostatin (3H-VPDPR) intravenously. Low levels of 3H-VPDPR were detected in many areas of the brain, with greatest radioactivity in the frontal cortex, hippocampus and cerebellum. Radioactivity was found in the plasma and all tissues, with the highest amount detected in the pancreas.