Regulation of tyrosine hydroxylase gene expression in mesencephalic dopamine neurons: effect of imipramine treatment

Individual differences in the expression of tyrosine hydroxylase mRNA in neurosecretory neurons of the human paraventricular and supraoptic nuclei: positive correlation with vasopressin mRNA

Previous studies indicated that in the human paraventricular nucleus (PVN) and in the supraoptic nucleus (SON) tyrosine hydroxylase (TH) - the first and rate-limiting enzyme in catecholamine synthesis - is localized mainly in magnocellular neurosecretory neurons. Individual differences were observed among control subjects in number and distribution of TH-immunoreactive (IR) perikarya, indicating that antemortem factors may regulate TH expression. Since a large number of TH-IR perikarya were observed in subjects who suffered from somatic illnesses leading to prolonged osmotic or nonosmotic stimulation of vasopressin (VP) release, we suggested that TH expression is related to the activation of VP neurons. The purpose of our study was to apply (1) in situ hybridization for TH mRNA on human PVN and SON to investigate how the previously reported individual differences in TH protein expression are depicted at the transcriptional level and (2) quantitative TH immunohistochemistry and in situ hybridization for VP mRNA throughout the dorsolateral part of the SON (dl-SON) in order to elucidate whether indeed expression of TH in neurosecretory nuclei depends on activation of VP neurons. Postmortem formalin-fixed, paraffin-embedded hypothalamic sections of 16 control subjects were studied for TH protein and TH and VP mRNAs. For 6 of the above cases, the number of TH-IR neurons and the total VP mRNA levels were estimated throughout the entire dl-SON using an image analysis system. Individual variation was observed in TH mRNA expression which appears to parallel the expression of TH-protein. Using Spearman's bivariate test, a positive correlation was found between the number of TH-IR- and TH-mRNA-expressing neurons in both PVN and SON (p < 0.01) as well as between the number of TH-IR neurons and the total VP mRNA in the dl-SON (p < 0.05). Our results show (1) that the individual variability in the number of TH-IR neurons within the neurosecretory nuclei might be due to differential expression and/or stability of TH mRNA and (2) that expression of TH-immunoreactivity in human PVN and SON depends on the activation of VP neurons.

Increased expression of tyrosine hydroxylase immunoreactivity in paraventricular and supraoptic neurons in illnesses with prolonged osmotic or nonosmotic stimulation of vasopressin release

Our previous studies indicated that in the human paraventricular (PVN) and supraoptic (SON) nuclei, tyrosine hydroxylase (TH)--the first and rate-limiting enzyme in catecholamine synthesis--is localized mainly in magnocellular neurons and that antemortem factors regulate its expression. The purpose of the present study was to investigate the distribution of TH-immunoreactive (TH-IR) perikarya of the hypothalami of a large sample of well-documented adult subjects without neurological, psychiatric or endocrinological disease in order to identify factors that could regulate the expression of TH in the human neurosecretory neurons. Our material consisted of the hypothalami of 38 subjects studied immunohistochemically for TH using the peroxidase-antiperoxidase method. Striking individual differences were observed among the subjects studied concerning the number and distribution of TH-IR perikarya within the PVN and SON. These differences were evident throughout the entire rostrocaudal length of the hypothalamus and appeared to be related neither to the age or sex of the subjects nor to the postmortem interval or staining procedures. In the sample studied, a large number of TH-IR perikarya were observed specifically in all subjects that had suffered from right-sided heart failure due to pulmonary hypertension, liver cirrhosis or dehydration. In all the above illnesses, increased production and secretion of vasopressin (VP) are reported to occur due to a decrease in 'effective' blood volume or to osmotic stimulation. We conclude that somatic illnesses leading to prolonged osmotic or nonosmotic stimulation of VP release may induce increased expression of TH immunoreactivity in the human neurosecretory neurons related to neuronal activation.