Acute blockade of dopamine receptors with haloperidol: a retinal model to study impairments of dopaminergic transmission

Is there a dysfunction in the visual system of depressed patients?

BACKGROUND: The aim of the current study was to identify a possible locus of dysfunction in the visual system of depressed patients. MATERIALS AND METHODS: Fifty Major Depressive patients aged 21-60 years and 15 age-matched controls took part in the study The diagnosis was obtained with the SCAN v 2.0. The psychometric assessment included the HDRS, the HAS, the Newcastle Scales, the Diagnostic Melancholia Scale and the GAF scale. Flash Electroretinogram and Electrooculogram were performed in all subjects. The statistical analysis included ANCOVA, Student's t-test and Pearson Product Moment Correlation Coefficient were used. RESULTS: The Electro-oculographic findings suggested that all subtypes of depressed patients had lower dark trough and light peak values in comparison to controls (p < 0.001), while Arden ratios were within normal range. Electroretinographic recordings did not reveal any differences between patients and controls or between subtypes of depression. DISCUSSION: The findings of the current study provide empirical data in order to assist in the understanding of the international literature and to explain the mechanism of action of therapies like sleep deprivation and light therapy.

Recording of the fast oscillations in the human electro-oculogram

The fast oscillations (FO) of the electro-oculogram were recorded in 102 eyes of 51 normal subjects. We evaluated the normal range and variability of FO parameters, i.e. Rf, which is the average ratio in percentage of the average amplitude in the dark period (AD) and the average amplitude in the light period (AL), and df, which is the average difference between AD and AL in microV. The standing potential was recorded continuously during six subsequent cycles, each consisting of a one minute period in the dark and one minute period in the light. The mean +/- standard error for Rf was 112.9 +/- 1.3% and 69.6 +/- 5.3 microV for df. There was no statistically significant difference between both genders or different age groups. Rf and df were calculated using a different number of dark-light cycles. In normal subjects both the Rf and df show no difference when only 4 dark-light cycles are used in calculating these values. Therefore there seems no additional advantage in performing as many as 6 cycles. Using 4 dark-light cycles reduces the duration of the examination (8 vs. 12 min) of the fast oscillations and in particular when examining both fast and slow oscillations successively it might be useful to reduce the time of the examination.

Pharmacological modifications in dopaminergic neurotransmission affect the quinpirole-evoked suppression of serotonin N-acetyltransferase activity in chick retina: an impact on dopamine D4-like receptors

Dopamine (DA) plays an important role in the regulation of melatonin biosynthesis in retinas of several vertebrate species. In the retina of chick, the DA receptor controlling melatonin production represents a D4-like subtype. Stimulation of this receptor by quinpirole (QNP) results in a dose-dependent decline of the nighttime activity of serotonin N-acetyltransferase (NAT; a key regulatory enzyme in melatonin biosynthesis) and melatonin level of chick retina. The present study was undertaken to determine whether long-term treatment with antipsychotic drugs (clozapine-30 mg/kg, i.m.; sulpiride-100 mg/kg, i.m.; and raclopride-10 mg/kg, i.p., once daily for 21 days) and L-DOPA (80 mg/kg, i.p., once daily for 7 days) affects the response of the melatonin generating system of chick retina to the suppressive effect of QNP. Chronic administration to chicks of clozapine and sulpiride, but not raclopride, resulted in a markedly increased response of retinal NAT activity to the action of QNP. ED50 values for QNP were 3-times (clozapine) and 4-times (sulpiride) lower than those in the respective vehicle-treated control groups. On the other hand, QNP was significantly less potent in retinas of birds treated with L-DOPA than in control animals; the ED50 value for QNP was 3-times higher in birds injected with L-DOPA than in the vehicle-treated group. These results indicate that long-term treatment with clozapine, sulpiride and L-DOPA may modify the reactivity of D4-like DA receptors regulating NAT activity of chick retina. A possibility of modifications of circadian and electrophysiological processes within the eye following prolonged administration of DA-ergic drugs is discussed.

A role for photoreceptor outer segments in the induction of deprivation myopia

An ultrastructural examination of the outer retina and choroid of hatchling chicks reared for periods of 1, 2 or 4 weeks with opaque occluders (MD) covering one eye, was instigated to elucidate the mechanism of deprivation myopia. Refractive myopia (approximately 20 D), retinal and choroidal thinning were induced in all deprived eyes. Electron microscopy showed significant changes in the MD eyes compared to normals. Cone inner segments were markedly thicker and outer segment lamellae more damaged. The rod outer segments were elongated and thicker than normal, such that their distal tips either directly apposed the basal lamina of the retinal pigment epithelium, or indented the cell nuclei. We hypothesize that this "rod-push" mechanism leads to thinning of the choroid in deprived eyes, and may directly contribute to axial myopia.

Electrophysiological signs of retinal dopamine deficiency in recently diagnosed Parkinson's disease and a follow up study

Electrophysiological studies, including electrooculogram (EOG), and simultaneously recorded flash and pattern evoked electroretinograms (FERG and PERG) and visually evoked potentials (FVEP and PVEP) were made in 1988 on 10 newly diagnosed untreated Parkinson's patients at Stage 1 of the Hoehn and Yahr scale. Follow up studies were made on five out of the 10 patients when their disease had progressed to Stage 2 during 1993. The earliest and only sign of abnormality detected in the Stage 1 of Parkinson's patients in 1988 was a delay in the time to reach the peak light rise in the EOG. When the disease had progressed to Stage 2, not only a delay in the time to reach the peak light rise but also a reduction in the amplitude of the peak light rise in the EOG, together with changes in PERG, FERG and PVEPs were demonstrable. These changes observed in PERG, FERG and PVEPs were generally consistent with those reported by previous studies. It is suggested that the reason for the susceptibility of pigment epithelial function to dopamine deficiency in Parkinson's disease may be due to the pigment epithelium being at the extremity of the diffusion pathway from dopamine release sites at the inner plexiform layer.