Hippocampus lead distribution

Hi-receptors in the adrenal medulla stimulates the release of the two catecholamines noradrenaline and adrenaline as well as enkephalins. In the heart, histamine produces negative inotropic effects via Hr receptor stimulation, but these are normally masked by the positive effects of H2-receptor stimulation on heart rate and force of contraction. Histamine Hi-receptors are widely distributed in human brain and highest densities are found in neocortex, hippocampus, nucleus accumbens, thalamus and posterior hypothalamus where they predominantly excite neuronal activity. Histamine Hrreceptor stimulation can also activate peripheral sensory nerve endings leading to itching and a surrounding vasodilatation ( flare ) due to an axonal reflex and the consequent release of peptide neurotransmitters from collateral nerve endings. 

Although the distribution of these receptors is widespread in the brain, they are found postsynaptically in high concentrations in the hippocampus, septum and amygdala and also on cell bodies of 5-HT neurons in the Raphe nuclei. They are negatively coupled, via Gj/o/z proteins, to adenylyl cyclase such that their activation reduces production of cAMP. In turn, this leads to an increase in K+ conductance and hyperpolarisation of... 

Chen HH, Ma T, Hume AS, et al. 1998. Developmental lead exposure alters the distribution of protein kinase C activity in the rat hippocampus. Biomed Environ Sci 11 61-69. 

Among the soft tissues, lead is distributed to the bone marrow, liver and kidney (Barry 1975, Skerfving etal. 1993). Lead does, to some extent, pass the blood-brain barrier into the nervous system and, according to animal experiments, such passage is most likely higher in infants than in adults (Mahaffey 1983). Distribution in the central nervous system (CNS) is uneven, with higher levels in the hippocampus and amygdala. Lead concentrations in the cerebrospinal fluid are very low, and seem to correlate positively with plasma lead concentrations rather than with B-Pb. 

HT RECEPTORS 5-HT receptors are widely distributed throughout the body. In the CNS, the receptors are found on neurons of the superior and inferior colliculi and in the hippocampus. In the GI tract, 5-HT receptors are located on neurons of the myenteric plexus and on smooth muscle and secretory cells. The 5-HT receptor is thought to evoke secretion in the alimentary tract and to facilitate the peristaltic reflex. 5-HT receptors couple to G to activate adeny-lyl cyclase, leading to a rise in intracellular levels of cyclic AMP, possibly accounting for the utility of prokinetic benzamides in GI disorders (see Chapter 37). 

Once absorbed from the intestines, lead enters the blood stream and is rapidly distributed throughout the body, to the erythrocytes, bones, and soft tissue (10). In adults, 90-95% of the total lead body burden is found in bone (5, 435, 436), resulting in a mean level of 14 pg Pb/g of skeletal bone ash (14 ppm) in middle-aged adults in the United States today (27, 437) (Table XVI). In children, the percent of total body lead that resides in bone is closer to 70-80% (436). By contrast, lead concentrations in soft tissues are typically 0.5 ppm (438) and lead concentrations in brain are usually <0.2 ppm, with the highest levels being found in the hippocampus and frontal cortex (10). The average concentration of lead in whole blood for people in the United States in 1999 was 1.6 pg/dL (16 ppb) (18) 94—99% of blood lead is found in the erythrocytes and only 1-6% is in the plasma (10, 27). (Methods for the analysis of lead content in blood are discussed in Section Vl.E.)... 

Huang, E., W.Y. Ong and J.R. Connor. (2004) Distribution of divalent metal transporter-1 in the monkey basal gangha. Neuroscience 128 487-496 Huang, E. and W.Y. Ong. (2005) Distribution of ferritin in the rat hippocampus after kainate-induced neuronal injury. Exp. Brain Res. 161 502-511 Ide-Ektessabi, A., Y. Ota, R. Ishihara, Y. Mizuno and T. Takeuchi. (2005) Distribution of lead in the brain tissues from DNTC patients using synchrotron radiation microbeams. Nucl. Instrum. Methods Phys. Res. B 241 681-684... 

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