In vivo exposure to lead does not influence muscarinic receptors in the frontal cortex of the mouse brain

Alzheimer's disease and metals: a review of the involvement of cellular membrane receptors in metallosignalling

Alzheimer's disease (AD) is a debilitating form of dementia. The hallmark protein associated with the disease is the amyloid beta (Aβ) peptide. Aggregation of Aβ has been shown to depend on interactions with metals. The recent studies now demonstrate that metals also play additional important roles in the disease process. Consequently, there may be benefit from modulating metal homeostasis. However, the role and subcellular location of metals within neurons is not well understood. There is growing evidence to suggest that metals can act at the site of cellular membrane receptors and affect cellular signaling by modulating the signal transduction of those receptors. The glutamatergic and cholinergic receptor systems, both well-known neurotransmitter systems affected in AD, have well-documented metal interactions, as do the tropomyosin-receptor kinase (Trk) family of receptors and the epidermal growth factor (EGF) receptor. In this paper, the metal interactions with these membrane receptor systems will be explored and thus the potential for membrane receptors as an intervention point in AD will be assessed.

Histological and histochemical alterations in the kidney induced by lead

BACKGROUND

Although lead intoxication is one of the most common forms of metal intoxication, the histochemical alterations in the renal tissues due to chronic lead exposure is limited and has not yet been well identified.

SUBJECTS AND METHODS

A total of 60 male Wistar albino rats (Rattus norvegicus) were exposed to lead acetate trihydrate (0.0, 0.25, 0.5, 1.0 and 2% for 1 to 12 months) in drinking water to investigate the histological and histochemical alterations in the renal tissues due to lead.

RESULTS

Chronic exposure to subtoxic doses of lead produced distinct progressive tubular, glomerular and interstitial damages. Tubular changes occurred earlier than glomerular and interstitial ones, and included anisokaryosis, nuclear pyknosis, karyomeglay, development of intranuclear and cytoplasmic inclusions together with tubular dilation, necrosis, vacuolization, tubular hyperplasia and solid tubular adenoma. The glomerular alterations were mainly mesangial hypercellularity, segmental proliferation, focal and segmental glomeruloscleriosis, glomerural hyalinization and glomerular tuft alterations.

CONCLUSIONS

The findings indicate that lead produces significant histological and histochemical changes in the kidney that lead to severe complications.

Interaction of metals with muscarinic cholinoceptor and adrenoceptor binding, and agonist-stimulated inositol phospholipid hydrolysis in rat brain

In vitro mercury (Hg) or lead (Pb) effectively inhibited the binding of 3H-quinuclidinyl-benzilate (QNB) (a muscarinic cholinoceptor antagonist) and 3H-prazosin (an alpha 1-adrenoceptor antagonist) to their receptors in cerebellar and cerebral cortex membranes in a concentration-dependent manner. Hg was more potent than Pb. When the rats were treated with Hg (5 mg/kg body wt) or Pb (25 mg/kg body wt) for 24 hr, a decrease in 3H-prazosin and an increase in 3H-QNB receptor binding were observed in cerebral cortex. There was no alteration in 3H-prazosin binding in cerebellum with the above treatment of metals, but 3H-QNB binding in cerebellum was significantly inhibited by Hg. However, both 3H-prazosin and 3H-QNB receptor bindings were significantly decreased in cerebellum of rats treated for 7 days with Hg (1 mg/kg body wt/day) or Pb (25 mg/ kg body wt/day). But in cerebral cortex of rats treated with these metals for 7 days, a decrease in 3H-prazosin and an increase in 3H-QNB receptor binding activities were noticed. There was a significant decrease in phospholipid content in cerebral cortex but not in cerebellum of rats treated with these metals for 7 days. At 100 microM concentration carbachol or acetylcholine or norepinephrine stimulated 3H-inositol incorporation and 3H-inositol phosphate (IP) formation in rat cerebral cortical slices. Hg or Pb in vitro though increased the agonist-stimulated 3H-inositol incorporation, 3H-IP formation was not significantly altered. The present investigation demonstrates the differential responses by alpha 1-adrenoceptor and muscarinic cholinoceptor in cerebellum and cerebral cortex of rat to in vitro and in vivo effects of Hg or Pb.

In vitro and in vivo effects of lead on specific 3H-PN200-110 binding to dihydropyridine receptors in the frontal cortex of the mouse brain

It is assumed that several neurotoxic substances interfere with neuronal calcium channels. Therefore, we studied the effects of the heavy metals, cadmium, copper, lead, manganese, and zinc on the L-type calcium channels in the mouse brain. Characterization of the calcium channels was carried out using binding studies on homogenates from the frontal cortex with the DHP (dihydropyridine)-derivative, 3H-PN200-110, which binds with high affinity to the DHP-receptor inside the L-type calcium channel. Furthermore, the in vivo effects of lead on the DHP-receptors were investigated in perinatally exposed mice. In these animals, the analysis of saturation experiments with 3H-PN200-110 showed no changes in receptor density or ligand affinity due to the lead exposure. In vitro, 3H-PN200-110 binding is absolutely dependent on the presence of calcium. Divalent cations, such as magnesium or manganese, which normally block the physiological effects of calcium, also enhance DHP-receptor binding. Interestingly, ions such as lead, cadmium and copper stimulate 3H-PN200-110 binding at low concentrations (0.1-10 microM), but inhibit binding at higher concentrations. In contrast, zinc blocked DHP-receptor binding at low concentrations (< 100 microM) without any stimulating effects. These results suggest that modulation of the L-type calcium channel by heavy metal cations is one possible mechanism by which the regulation of calcium homeostasis in neurons is altered.