Figure 1.
The synthesis and degradation of dopamine.
Enzymes involved in the synthesis and catabolism of dopamine are highlighted in green. Dopamine is synthesised from tyrosine via L-DOPA (the rate-limiting step being the conversion of tyrosine to L-DOPA, mediated by tyrosine hydroxylase [TH]). Dopamine can be converted to noradrenaline, via the action of dopamine β-hydroxylase (DBH) or catabolised by the joint action of the enzymes COMT, monoamine oxidase (MAO) and aldehyde dehydrogenase (AH). Other abbreviations: dopamine decarboxylase (DDC); 3-methoxytyramine (3-MT); 3,4 dihydrophenylacetaldehyde (DHPA); 3-methoxy-4-hydroxyphenylacetaldehyde (MHPA).
Figure 2.
Tolcapone increased tissue dopamine levels in the rat hippocampus, but not other regions.
Tissue levels of dopamine (expressed as ng/g tissue) are shown in the striatum, PFC, cerebellum and hippocampus. There were no main effects of sex, nor sex*treatment interactions. *p<0.05.
Figure 3.
Tolcapone did not affect tissue noradrenaline levels in the rat brain.
Tissue levels of noradrenaline (expressed as ng/g tissue) are shown in the striatum, PFC, cerebellum and hippocampus. There were no main effects of drug treatment or sex, nor sex*treatment interactions in any region.
Figure 4.
Tolcapone increased rat tissue DOPAC levels in all regions.
Tissue levels of DOPAC (expressed as ng/g tissue) are shown in the striatum, PFC, cerebellum and hippocampus. For clarity, only main effects of drug treatment are shown. However, there were main effects of sex, and sex*treatment interactions, in the PFC and cerebellum (see text for details). ***p<0.0005.
Figure 5.
Tolcapone decreased tissue HVA levels in the rat striatum and PFC, but not the cerebellum and hippocampus.
Tissue levels of HVA (expressed as ng/g tissue) are shown in the striatum, PFC, cerebellum and hippocampus. For clarity, only main effects of drug treatment are shown. However, there were trend effects of sex, and sex*treatment interactions, in the PFC and striatum (see text for details). *p<0.005; ***p<0.0005.