Loud Noise Exposure Produces DNA, Neurotransmitter and Morphological Damage within Specific Brain Areas.

Exposure to loud noise is a major environmental threat to public health. Loud noise exposure, apart from affecting the inner ear, is deleterious for cardiovascular, endocrine and nervous systems and it is associated with neuropsychiatric disorders. In this study we investigated DNA, neurotransmitters and immune-histochemical alterations induced by exposure to loud noise in three major brain areas (cerebellum, hippocampus, striatum) of Wistar rats. Rats were exposed to loud noise (100 dBA) for 12 h. The effects of noise on DNA integrity in all three brain areas were evaluated by using Comet assay. In parallel studies, brain monoamine levels and morphology of nigrostriatal pathways, hippocampus and cerebellum were analyzed at different time intervals (24 h and 7 days) after noise exposure. Loud noise produced a sudden increase in DNA damage in all the brain areas under investigation. Monoamine levels detected at 7 days following exposure were differently affected depending on the specific brain area. Namely, striatal but not hippocampal dopamine (DA) significantly decreased, whereas hippocampal and cerebellar noradrenaline (NA) was significantly reduced. This is in line with pathological findings within striatum and hippocampus consisting of a decrease in striatal tyrosine hydroxylase (TH) combined with increased Bax and glial fibrillary acidic protein (GFAP). Loud noise exposure lasting 12 h causes immediate DNA, and long-lasting neurotransmitter and immune-histochemical alterations within specific brain areas of the rat. These alterations may suggest an anatomical and functional link to explain the neurobiology of diseases which prevail in human subjects exposed to environmental noise.

Region-specific DNA alterations in focally induced seizures.

We induced brief secondarily generalized seizures of limbic origin in Sprague-Dawley rats by bicuculline microinfusion into the anterior piriform cortex. After 1 h or 5 days we performed comet assay, a sensitive marker for DNA damage, within entorhinal cortex, hippocampus (limbic areas recruited by seizure spreading) and striatum (which is not recruited). DNA damage occurred selectively in the ipsilateral entorhinal cortex and hippocampus at 1 h, but not at 5 days. These data shed new light on molecular genetics as a marker during limbic seizures, the most common in epileptic patients.

A systematic study of brainstem motor nuclei in a mouse model of ALS, the effects of lithium.

Transgenic mice expressing the human superoxide dismutase 1 (SOD-1) mutant at position 93 (G93A) develop a phenotype resembling amyotrophic lateral sclerosis (ALS). In fact, G93A mice develop progressive motor deficits which finally lead to motor palsy and death. This is due to the progressive degeneration of motor neurons in the ventral horn of the spinal cord. Although a similar loss is reported for specific cranial motor nuclei, only a few studies so far investigated degeneration in a few brainstem nuclei. We recently reported that chronic lithium administration delays onset and duration of the disease, while reducing degeneration of spinal motor neuron. In the present study, we extended this investigation to all somatic motor nuclei of the brain stem in the G93A mice and we evaluated whether analogous protective effects induced by lithium in the spinal cord were present at the brain stem level. We found that all motor but the oculomotor nuclei were markedly degenerated in G93A mice, and chronic treatment with lithium significantly attenuated neurodegeneration in the trigeminal, facial, ambiguus, and hypoglossal nuclei. Moreover, in the hypoglossal nucleus, we found that recurrent collaterals were markedly lost in G93A mice while they were rescued by chronic lithium administration.

Activation of brain metabolism and fos during limbic seizures: the role of locus coeruleus.

The noradrenergic nucleus Locus Coeruleus (LC) densely innervates limbic structures. In rats, the damage to LC by the neurotoxin DSP-4, converts episodic limbic seizures induced by bicuculline infusion in the anterior piriform cortex (APC) into self-sustaining status epilepticus (SE). SE induced by this approach is similar to SE induced by co-infusing cyclothiazide and bicuculline into APC in rats bearing an intact LC. As opposed to other commonly used rat SE models (e.g. systemic kainate or pilocarpine), this approach allows one to analyze the effects of SE on brain regions which are solely due to spreading of seizure activity, rather than to direct effect of systemic chemoconvulsant. We evaluated the expression of Fos protein (an immediate early gene product), and the local cerebral metabolic rates for [14C] 2-deoxyglucose (lCMRglc), in rats following SE induced either by cyclothiazide+bicuculline or by DSP-4+bicuculline. We demonstrated that regional Fos expression after SE does not parallel the increase in lCMRglc, in LC-lesioned rats. In DSP-4+bicuculline rats there is an overall lower expression of the protein as compared with the cyclothiazide+bicuculline or bicuculline alone groups; even more, such a difference co-exists with an higher lCMRglc in the DSP-4+bicuculline-treated rats in some regions, as compared with the other groups. These data show that LC neurons play an important role in determining immediate early genes expression even in conditions of strong pathological activation, such as limbic SE. This might have relevant effects in the plastic mechanisms related with epileptogenesis.