Chromatic modulation of luminance visual evoked potential latencies in healthy subjects and patients with mild vision disorders.

OBJECTIVE: To study whether and how color modulates luminance visual evoked potentials (VEPs). METHODS: We studied pattern-reversal luminance VEPs to red/black and blue/black checkerboards with identical luminance contrast values (mixed luminance and chromatic components) (isocontrast color VEP, in brief, IVEPs) in 25 healthy subjects and two groups of patients with mild vision disorders (23 with glaucoma and 25 with optic neuritis). We then compared these with the standard color VEPs to pure chromatic contrast red/green and blue/yellow gratings (CVEPs). RESULTS: In healthy subjects, VEPs to red/black checkerboards and red/green gratings were slower than those obtained with blue/black checkerboards and blue/yellow gratings. Both procedures (IVEPs and CVEPs) differentiated patients with vision disorders from healthy subjects and distinguished between the two different vision disorders. Red/black checkerboards and red-green gratings elicited slower VEPs in patients with optic neuritis and blue/black checkerboards and blue/yellow gratings elicited slower VEPs in patients with glaucoma. IVEPs appeared more stable and ample than CVEPs. The contrast indices normalized CVEP and IVEP latencies in the same subject and showed a positive correlation between CVEP and IVEP latencies in healthy subjects and in patients with optic neuritis, but not in patients with glaucoma. CONCLUSIONS: Our study confirms the usefulness of CVEPs in detecting and differentiating mild vision disorders. IVEPs to colored pattern-reversal luminance checkerboards are equally effective in distinguishing between various vision disorders possibly because colors can modulate VEP latencies to luminance contrast stimuli. SIGNIFICANCE: IVEPs can be useful in differentiating the various vision disorders and are easier than CVEPs to test in a routine clinical setting.

Intravenous morphine increases glucose utilization in the shell of the rat nucleus accumbens.

The [14C]2-deoxyglucose method was applied to measure the effects of the acute intravenous administration of morphine sulphate (0.2-0.4 mg/kg) on cerebral glucose utilization in rats. Morphine produced dose-dependent increases of glucose metabolism in the shell of the nucleus accumbens, without affecting functional activity in any other brain area. These results provide further evidence for the preferential effects of intravenously abused substances in the shell of the nucleus accumbens.

Functional correlates of repeated administration of cocaine and apomorphine in the rat.

The [14C]2-deoxyglucose method was applied to measure the effects of repeated (8 consecutive days) administration of apomorphine (0.5 mg/kg/day s.c.) or cocaine (15 mg/kg/day i.p.) on cerebral glucose utilization in freely moving rats. Altered rates of glucose utilization were measured in extrapyramidal motor areas, such as the globus pallidus, entopeduncular nucleus, subthalamic nucleus, substantia nigra and lateral habenula of both cocaine- and apomorphine-treated rats. Furthermore, cocaine-treated animals displayed increased glucose metabolism in the mesolimbic dopaminergic projections, such as nucleus accumbens and olfactory tubercle, and in the hippocampus. These results suggest that altered functional activity within the dopaminergic mesolimbic system may play a role in the process of sensitization to psychomotor stimulant drugs.

Psychostimulant drugs increase glucose utilization in the shell of the rat nucleus accumbens.

The nucleus accumbens (NAc) is a heterogeneous area, divided into a 'shell' and a 'core' on the basis of morphological and histochemical criteria. Moreover, the two portions have different anatomical connections. In order to test whether the two portions of NAc are functionally distinct, we measured local cerebral glucose utilization in rats administered intravenously with cocaine (1 mg kg-1) or amphetamine (0.5 mg kg-1). The results of the study show that, at these dosages, both drugs increase glucose utilization in the shell, but not in the core of NAc. This differential effect might reflect functional differences between the two portions of NAc, probably relevant to the abuse liability of psychostimulants.