Effect of domoic acid on metabolism of 5-hydroxytryptamine in rat brain

Acute aluminum chloride toxicity revisited: Study on DNA damage and histopathological, biochemical and neurochemical alterations in rat brain. Life Sci. 2019;217:202-211. [PMID: 30528774 DOI: 10.1016/j.lfs.2018.12.009]

AIMS

Due to rapid increase in industrialization in the last few years, use of aluminum (Al) and its alloys have been increased in different industrial fields. Ample evidence supports the neurotoxic effects of chronic aluminum chloride (AlCl₃) administration in rats but acute Al toxicity has been less described so the present study was aimed to investigate the neurotoxic effects of acute AlCl₃.

MAIN METHODS

To investigate such effects 12 male albino Wistar rats were randomly divided into control and test rats. AlCl₃ at a dose of 150 mg/kg was intraperitoneally injected to test rats for 7 days. Rats were subjected to behavioral assessments 24 h after last dose and after behavioral assessment rats were sacrificed to collect brain samples for further neurochemical, biochemical and histopathological examinations.

KEY FINDINGS

In the present study acute administration of AlCl₃ resulted in noticeable behavioral deficits. Cognitive deficits and neuropsychiatric disturbances were evident in AlCl₃ injected rats. Test rats also exhibited marked antioxidant enzymes, cholinergic, serotonergic and dopaminergic dysfunctions and DNA fragmentation. Histopathological alterations were observed in hippocampus and cortex of rats injected with AlCl₃.

SIGNIFICANCE

The observed effects may be due to pro-oxidant nature of Al and its participation in free radical mediated cellular injury. Al by promoting oxidative stress, impairing antioxidant defense system and altering brain neurochemistry may act as a potent neurotoxic agent as evident from observed histopathological alterations in brain of test rats. This investigation may further confirm and shed some more light on deleterious effects of acute Al intoxication on brain.

Subclinical effects of saxitoxin and domoic acid on aggressive behaviour and monoaminergic turnover in rainbow trout (Oncorhynchus mykiss)

The algal produced neurotoxins saxitoxin and domoic acid may have serious effects on marine life and can be responsible for the intoxication of for instance sea mammals, sea birds and fish. Given that farmed fish cannot escape algal blooms, they may be more susceptible to intoxication than wild stocks. In the present study, subclinical effects of saxitoxin and domoic on aggressive behaviour and monoaminergic systems in the brain of the rainbow trout (Oncorhynchus mykiss) were investigated. The resident-intruder test was used to measure aggression where only the resident fish were subjected to the toxins and analysed for monoamines and their metabolites. The resident-intruder test was carried out on two consecutive days. On day one basal aggression was measured in the four groups. On day two three of the groups were injected with subclinical doses of one of the following: saxitoxin (1.752 microg/kg bw), domoic (0.75 mg/kg bw) or 0.9% saline solution. This was performed 30 min prior to the aggression test. Handling stress and injection affected aggressive behaviour, cortisol and the serotonergic system in telencephalic brain regions. Cortisol levels were elevated in all of the injected groups when compared to the control group. An increase in serotonergic turnover was evident when all injected groups were pooled and compared to the control group. All together this suggests that the handling stress in connection with the injection was similar in all of the three injected groups. In contrast to both the undisturbed control group and the toxin-injected groups, the saline-injected group displayed a reduction in aggressive behaviour which was evident in increased attack latency. Furthermore the domoic injected group displayed more aggressive attacks towards their conspecifics than the saline-injected group. Consequently the two toxins appear to mask the stress induced alteration in aggressive behaviour. Monoamine levels and monoaminergic turnover could not be demonstrated to be directly affected by the two toxins at the given doses in the investigated brain regions (dorsal and ventral parts of telencephalon, optic tectum, locus coeruleus, raphe nucleus, molecular and granular layer of cerebellum). This could indicate that the toxins mediate aggressive behaviour either through other systems than the monoaminergic systems, such as neuroactive amino acids, or that the mediation occurs in other brain regions.

Domoic acid-induced neurotoxicity in the hippocampus of adult rats

Domoic acid (DA), an agonist of non-N-methyl-D-aspartate (non-NMDA) receptor subtype including kainate receptor, was identified as a potent neurotoxin showing involvement in neuropathological processes like neuronal degeneration and atrophy. In the past decade evidence indicating a role for excitatory amino acids in association with neurological disorders has been accumulating. Although the mechanisms underlying the neuronal damage induced by DA are not yet fully understood, many intracellular processes are thought to contribute towards DA-induced excitotoxic injury, acting in combination leading to cell death. In this review article, we report the leading hypotheses in the understanding of DA-induced neurotoxicity, which focus on the role of DA in neuropathological manifestations, the formation of the retrograde messenger molecule nitric oxide (NO) for the production of free radicals in the development of neuronal damage, the activation of glial cells (microglia and astrocytes) in response to DA-induced neuronal damage and the neuroprotective role of melatonin as a free radical scavenger or antioxidant in DA-induced neurotoxicity. The possible implications of molecular mechanism underlying the neurotoxicity in association with necrosis, apoptosis, nitric oxide synthases (nNos and iNOS) and glutamate receptors (NMDAR1 and GluR2) related genes and their expression in DA-induced neuronal damage in the hippocampus have been discussed.

Aluminium-induced changes in the rat brain serotonin system

Aluminium exposure, apart from producing cholinotoxicity, can include changes in other neurotransmitter levels since neurotransmitter levels are closely interrelated. Reports of aluminium (Al) effects on brain neurotransmitters are limited. To investigate the effect of Al on the rat brain serotonergic system, the present study was conducted to explore brain region-specific changes and duration-specific changes. Male Wistar albino rats were exposed orally to Al chloride (AlCl(3).6H(2)O; 320 mg/kg body weight) daily for up to 60 days and changes in the 5-hydroxytrytamine (5-HT) and its metabolite 5-hydroxyindole acetic acid (5-HIAA) levels were observed after 4, 14 and 60 days of exposure in olfactory lobe (OLB), cerebellum (CBL), pons (PON), medulla oblongata (MOB), spinal cord (SPI), hypothalamus (HYP), hippocampus (HIP), striatum (STR), midbrain (MBR) and cortex (COR) brain regions. Significantly increased 5-HT levels observed in brain regions OLB (60 days), HIP (4,14 days), STR (14 days), HYP (14, 60 days), MBR (4 and 14 days), PON (4 days), MOB (4 days) and SPI (4, 14 and 60 days) following Al exposure may be due to Al deactivating 5-HT system by decreased release and subsequent breakdown of 5-HT. Decreased 5-HT levels observed in cerebral COR, HIP (60 days) and in CBL after 4 and 60 days of exposure suggest an inhibitory effect of Al on the 5-HT system due to withdrawal of cholinergic input in these brain regions. 5-HIAA level changes correlate with 5-HT level changes in many brain regions studied. The results reveal that the neurochemical changes due to Al were dependent on the duration of exposure and are brain-region-specific. The observed changes may be related to the cholinergic toxicity of Al.

In vivo release of dopamine and its metabolites from rat striatum in response to domoic acid

The microdialysis technique was used to examine the effect of the neurotoxin domoate, an analog of glutamic acid, on striatal dopamine activity. Our results show that the intracerebral administration of different concentrations of domoate (100 and 500 microM) produced increases in the extracellular levels of dopamine associated to decreases in the extracellular levels of its metabolites dihydroxyphenylacetate and homovanillate from rat striatum. These changes seem to be related according to a time sequence, indicating a possible effect on the metabolism of dopamine. Changes were also observed in locomotor activity (cycling behavior, sniffing around and chewing) in rats during the domoate infusion. The physiological mechanism by which domoate increased dopamine release remains to be worked out.