Intracranial self-stimulation increases differentially in vivo hydroxylation of tyrosine but similarly in vivo hydroxylation of tryptophan in rat medial prefrontal cortex, nucleus accumbens and striatum

We have examined using microdialysis the effect of intracranial self-stimul ation (ICSS) on the in vivo hydroxylation rate of tyrosine and tryptophan i n the medial prefrontal cortex (mPFC), nucleus accumbens (NAC) and striatum (STR). A decarboxylase inhibitor NSD-1015 was included in the perfusate, w hich enabled the simultaneous measurement of 3,4-dihydroxyphenylalanine (DO PA) and 5-hydroxytryptophan (5-HTP) as an index of the in vivo hydroxylatio n level of tyrosine and tryptophan. When rats were exposed to 1 h of ICSS a t the medial forebrain bundle (MFB), their extracellular levels of DOPA sig nificantly increased in the mPFC, NAC and STR, but with a different magnitu de and time course. The same stimulation produced a delayed increase in ext racellular 5-HTP, compared to DOPA, in these brain regions. The profile of 5-HTP response demonstrated no apparent difference among the regions. These findings indicate that ICSS of the MFB can increase differentially the in vivo hydroxylation of tyrosine but similarly the in vivo hydroxylation of t ryptophan in the mPFC, NAC and STR. (C) 2000 Elsevier Science B.V. All righ ts reserved.