We measured the concentrations of the three major monoamine neurotransmitters noradrenaline, dopamine, and serotonin, their metabolites, and receptor binding sites in autopsied brain of three patients with narcolepsy. As compared with the controls, concentrations of the noradrenaline and serotonin metabolites MHPG and 5-HIAA, respectively, were markedly elevated in cerebral cortical subdivisions of the narcolepsy patients together with a trend for above-normal neurotransmitter/metabolite "turnover" ratio. A moderately reduced number of alpha 1-adrenoceptors, as judged by the reduced levels of 3H-prazosin binding, was observed in cerebral cortex of two of the three patients with narcolepsy. Mean striatal levels of dopamine and its metabolite homovanillic acid were normal, whereas the concentration of dopamine's second metabolite, dihydroxyphenylacetic acid, was markedly reduced by 50% or greater. This was accompanied by a marked increase (+125%) in mean 3H-spiperone binding to the D2 dopamine receptor in both caudate and putamen; in contrast, the levels of 3H-SCH 23390 binding to the striatal D1 dopamine receptor were in the normal range. Our data provide evidence for altered brain monoaminergic neurotransmitter function in human narcolepsy.

1 After physical (knife-cut) or chemically-mediated (tetrodotoxin 300nm, 1.5p1; 1.Oplmin-1) interruption of nerve conduction in the nigrostriatal tract, there was a marked increase in the synthesis and metabolism of dopamine in the isolated dopaminergic nerve terminals of the striatum. The effect peaked at 4h post-transection, at which time 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were increased by 300% and 700% respectively (DOPAC: 27+13 vs 80+17nmolg-1; HVA: 6.66+3.57 vs 54+18nmolg 1). The increases in dopamine content and metabolism are secondary to an increase in the rate of synthesis on the lesioned side, versus the intact, control side. 2 In both experimental situations, haloperidol (1.0mgkg-1, i.p.) retained its known ability to induce a significant increase in DOPAC and HVA in the striatum, despite the interruption of nerve conduction in the nigrostriatal tract. 3 Six days after cutting the left nigrostriatal tract, dopamine in the left striatum was reduced to < 5% of the control value, and DOPAC and HVA were not detectable. In the denervated, left striatum, the synthesis of dopamine (from injected L-DOPA), and its metabolism to DOPAC and HVA, occurred to the same degree as in the intact right side. In these DOPA-treated rats, haloperidol (1.Omgkg-1, i.p.) caused a further increase in DOPAC and HVA in the intact striatum, but not in the denervated striatum. 4 Under non-stressful conditions, using a combination of anaesthetic treatments, electrical stimulation (400 yA, 0.4 ins, 15 Hz, 15 min) of the nigrostriatal tract did not increase DOPAC or HVA in the striatum on the stimulated side.5 It is concluded (a) that there is a significant presynaptic, and/or local circuit mechanism capable of activating the synthesis and metabolism of dopamine in the isolated, striatal, dopaminergic nerve terminals. Furthermore, haloperidol can act directly on the striatal, dopaminergic nerve terminal, to cause an increase in the synthesis and metabolism of striatal dopamine. (b) After degeneration of the striatal dopaminergic nerves, the denervated striatum retains the ability to synthesize (from L-DOPA) and metabolize dopamine, to the same degree as the intact, innervated, contralateral striatum. (c) When stress is minimized, and release of dopamine is induced by electrical stimulation of the medial forebrain bundle, the catabolism of dopamine (to DOPAC and HVA) during the release-uptake cycle may not be a significant factor under physiological conditions. (d) When dopamine synthesis is increased in the striatum, the normal blood concentration of tyrosine is adequate to sustain the increased synthesis, and precursor availability is not a limiting factor. (e) These results suggest that some of the basic concepts about the neurochemical/neurophysiological regulation of monoaminergic neurones may require further reevaluation.