Abstract
ObjectiveInterference with the transmission of sensory signals along visual and auditory pathways has been implicated in the pathogenesis of hallucinations. The relay centres for vision (the lateral geniculate nucleus) and hearing (the medial geniculate nucleus) appear to be susceptible to the uptake of circulating mercury. We therefore investigated the distribution of mercury in cells of both these geniculate nuclei.Materials and methodsParaffin-embedded tissue sections containing the lateral geniculate nucleus were obtained from 50 adults (age range 20–104 years) who at autopsy had a variety of clinicopathological conditions, including neurological and psychiatric disorders. The medial geniculate nucleus was present in seven sections. Sections were stained for mercury using autometallography. Laser ablation-inductively coupled plasma-mass spectrometry was used to confirm the presence of mercury.ResultsTen people had mercury in cells of the lateral geniculate nucleus, and in the medial geniculate nucleus of three of these. Medical diagnoses in these individuals were: none (3), Parkinson disease (3), and one each of depression, bipolar disorder, multiple sclerosis, and mercury self-injection. Mercury was distributed in different groups of geniculate capillary endothelial cells, neurons, oligodendrocytes, and astrocytes. Mass spectrometry confirmed the presence of mercury.ConclusionMercury is present in different combinations of cell types in the lateral and medial geniculate nuclei in a proportion of people from varied backgrounds. This raises the possibility that mercury-induced impairment of the function of the geniculate nuclei could play a part in the genesis of visual and auditory hallucinations. Although these findings do not provide a direct link between mercury in geniculate cells and hallucinations, they suggest that further investigations into the possibility of toxicant-induced hallucinations are warranted.
Highlights
Visual and auditory hallucinations, perceptions that occur in the absence of corresponding sensory stimuli, can arise from a wide range of drug-induced, medical and psychiatric conditions, as well as in the general population [1]
Paraffin-embedded tissue sections containing the lateral geniculate nucleus were obtained from 50 adults who at autopsy had a variety of clinicopathological conditions, including neurological and psychiatric disorders
The medial geniculate nucleus was present in seven sections
Summary
Perceptions that occur in the absence of corresponding sensory stimuli, can arise from a wide range of drug-induced, medical and psychiatric conditions, as well as in the general population [1]. The thalamic lateral geniculate nucleus (LGN) is the main relay centre in the visual pathway, and the nearby medial geniculate nucleus (MGL) in the auditory pathway. These geniculate nuclei are candidate sites for damage that could result in overactivity of the primary visual and auditory cortices. In monkeys exposed to methylmercury, average tissue levels of mercury were higher in the LGN than in other regions of the brain [10]. Monkeys exposed to methylmercury had ultrastructural changes in neurons of the LGN [11]. Damage to LGN neurons has been described in a mercury-exposed dog [12], and bismuth has been seen to accumulate in the MGN of mice [13]. In rats exposed to various forms of mercury, mercury was visible in the LGN and MGN, though usually only at higher levels of exposure [14,15,16]
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