Quantitative changes in monoamines in visual brain structures (visual cortex, colliculus superior, and lateral geniculate dorsales) in an experimental model of retinal pigmentary dystrophy

Abstract

Introduction. Retinal pigment dystrophy is characterized not only by degeneration of peripheral photoreceptors but also by disruption of neuromodulatory balance in the central structures of the visual analyzer.
Purpose. The specific aim of the study was to determine quantitative changes in serotonin (5-HT), norepinephrine (NA), and dopamine (DA) levels in the visual cortex (VC), superior colliculus (CS), and lateral geniculate dorsales (LGD) under experimentally induced retinal pigment dystrophy (RPD).
Methods. The study was conducted on rabbits, where a dystrophy model was induced by injection of monoiodoacetic acid. The concentration of monoamines in brain structures was determined using a fluorometric analysis method.
Results. Under normal conditions, 5-HT had the highest value (410±7 ng/g in VC, 380±10 ng/g in CS, 405±5 ng/g in LGD). A noticeable increase in 5-HT (420±10 ng/g) and DA (390±10 ng/g) was observed in the CS, while a decrease in 5-HT (365±5 ng/g) and NA (320±10 ng/g) was recorded in the VC. In the LGD, dopamine levels decreased significantly to 310±6 ng/g (p < 0.05). 
Under experimental retinal pigment dystrophy, significant and structure-specific alterations in monoamine levels were observed in the central visual structures. In the CS, the levels of 5-HT, NA, and DA increased from 380±10 to 420±10 ng/g, from 325±7 to 360±10 ng/g, and from 335±6 to 390±10 ng/g, respectively (p < 0.05). In contrast, DA levels in the LGD decreased from 340±6 to 310±6 ng/g (p < 0.05), while 5-HT levels in the VC decreased from 410±7 to 365±5 ng/g. These findings indicate differential monoaminergic responses across the central visual structures during retinal pigment dystrophy, suggesting that retinal degeneration is accompanied by region-specific alterations in central neuromodulatory mechanisms. The observed changes in 5-HT-ergic, NA-ergic, and DO-ergic systems may reflect adaptive and/or compensatory processes associated with impaired retinal input and altered central–peripheral visual integration. Preservation of monoaminergic homeostasis within the central visual system may therefore represent an important consideration in strategies aimed at maintaining neuronal function and visual processing under dystrophic conditions.