Fluorescence histochemical observations on the distribution of exogenous dihydroisoquinoline in the rat brain

Salsolinol Protects SH-SY5Y Cells Against MPP+ Damage and Increases Enteric S100-Immunoreactivity in Wistar Rats

A dopamine derivative, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, known as salsolinol (SAL), has increasingly gained attention since its first detection in the urine of Parkinson's disease patients treated with levodopa, and has been proposed as a possible neurotoxic contributor to the disease. Yet, so far, the neurobiological role of SAL remains unclear. Thus, the main aims of our study were to compare the neurotoxic potential of SAL with MPP⁺ (1-methyl-4-phenylpyridinium ion) in vitro, and to examine intestinal and metabolic alterations following intraperitoneal SAL administration in vivo. In vitro, SH-SY5Y neuroblastoma cell line was monitored following MPP⁺ and SAL treatment. In vivo, Wistar rats were subjected to SAL administration by either osmotic intraperitoneal mini-pumps or a single intraperitoneal injection, and after two weeks, biochemical and morphological parameters were assessed. SH-SY5Y cells treated with MPP⁺ (1000 μM) and SAL (50 µM) showed increase in cell viability and fluorescence intensity in comparison with the cells treated with MPP⁺ alone. In vivo, we predominantly observed decreased collagen content in the submucosal layer, decreased neuronal density with comparable ganglionic area in the jejunal myenteric plexus, and increased glial S100 expression in both enteric plexuses, yet with no obvious signs of inflammation. Besides, glucose and triglycerides levels were lower after single SAL-treatment (200 mg/kg), and low- to high-density lipoprotein (LDL/HDL) ratio and aspartate to alanine aminotransferases (AST/ALT) ratio levels were higher after continuous SAL-treatment (200 mg/kg in total over 2 weeks). Low doses of SAL were non-toxic and exhibited pronounced neuroprotective properties against MPP⁺ in SH-SY5Y cell line, which supports the use of SAL as a reference compound for in vitro studies. In vivo results give insight into our understanding of gastrointestinal remodeling following intraperitoneal SAL administration, and might represent morphological correlates of a microglial-related enteric neurodegeneration and dopaminergic dysregulation.

Salsolinol: an Unintelligible and Double-Faced Molecule-Lessons Learned from In Vivo and In Vitro Experiments

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a tetrahydroisoquinoline derivative whose presence in humans was first detected in the urine of Parkinsonian patients on l-DOPA (l-dihydroxyphenylalanine) medication. Thus far, multiple hypotheses regarding its physiological/pathophysiological roles have been proposed, especially related to Parkinson’s disease or alcohol addiction. The aim of this review was to outline studies related to salsolinol, with special focus on in vivo and in vitro experimental models. To begin with, the chemical structure of salsolinol together with its biochemical implications and the role in neurotransmission are discussed. Numerous experimental studies are summarized in tables and the most relevant ones are stressed. Finally, the ability of salsolinol to cross the blood–brain barrier and its possible double-faced neurobiological potential are reviewed.

The route and significance of endogenous synthesis of alkaloids in animals

There is now substantial evidence that several TIQs and beta-carbolines are present in vivo and increase during certain pathological conditions. It still remains to be determined, however, precisely what roles they play in endogenous functions and whether or not they are critical for the expression of these pathological conditions. Accumulating biochemical information continues to support the notion that these compounds can act as false transmitters. The exciting new findings, which will certainly receive a great deal more attention, concern the interaction of some of the beta-carbolines with the benzodiazepine receptor. Determining if a beta-carboline is an endogenous receptor ligand will attract further research interest on the theoretical and specifically clinically-directed levels. Biochemical, morphological, and behavioral data indicate that some of the condensation products can act as neurotoxins. Very few experiments have included an examination of long-term effects of exposure to one of these alkaloids, so the amount of information on this issue is limited. Chronic rather than acute administration of an alkaloid is more likely to mimic the pathological states in which these compounds are hypothesized to play a role. Biochemically, both the dopaminergic and serotonergic systems have been shown to be affected by chronic treatments with certain alkaloids. Progressive and long-term behavioral alterations also have been reported. Such changes may reflect an adaptation to an increase or decrease in activity of particular systems or a neurotoxic action.