Histamine levels and activity of histidine decarboxylase (HD) and histamine-methyltransferase (HMT) in neonate and adult human brain

Formaldehyde Stress Responses in Bacterial Pathogens

Formaldehyde is the simplest of all aldehydes and is highly cytotoxic. Its use and associated dangers from environmental exposure have been well documented. Detoxification systems for formaldehyde are found throughout the biological world and they are especially important in methylotrophic bacteria, which generate this compound as part of their metabolism of methanol. Formaldehyde metabolizing systems can be divided into those dependent upon pterin cofactors, sugar phosphates and those dependent upon glutathione. The more prevalent thiol-dependent formaldehyde detoxification system is found in many bacterial pathogens, almost all of which do not metabolize methane or methanol. This review describes the endogenous and exogenous sources of formaldehyde, its toxic effects and mechanisms of detoxification. The methods of formaldehyde sensing are also described with a focus on the formaldehyde responsive transcription factors HxlR, FrmR, and NmlR. Finally, the physiological relevance of detoxification systems for formaldehyde in bacterial pathogens is discussed.

Diurnal and age-related changes in cerebrospinal fluid tele-methylhistamine levels during infancy and childhood

Histamine is a neurotransmitter participating in many physiological functions and behavior, including control of arousal and modulation of the circadian rhythms. Diurnal variation in cerebrospinal fluid (CSF) levels of tele-methylhistamine (t-MH), the main histamine metabolite, has been detected in several animal studies. In humans, such changes have not been described. Little is known on the development of histaminergic neurons in human brain. In children, the levels of CSF t-MH are not known. Therefore, we have measured the concentrations of CSF t-MH in 81 children, age ranging from 3 months to 14.6 years. t-MH levels were higher in infants, and near adult values were measured in adolescents, the relation between CSF t-MH and age being; CSF t-MH = -0.217 years + 7.31 (n = 81, r = 0.26, p = 0.021). The mean t-MH concentration was higher during the daytime (7.07 +/- 0.46 pmol/ml, mean +/- SEM) than in the night (5.35 +/- 0.60 pmol/ml, p = 0.0019, ANOVA). The results show a development change in the concentration of t-MH during childhood and a difference in t-MH levels between the daytime and night indicating a more active metabolism of brain HA in the waking period.