Neuropeptide tyrosine in the rat adrenal gland--immunohistochemical and in situ hybridization studies

Effect of reserpine and colchicine on neuropeptide mRNA levels in the rat hypothalamic paraventricular nucleus

Using in situ hybridization and immunohistochemistry, we have studied mRNA and peptide levels in the hypothalamic paraventricular nucleus (PVN) 24 h after a single large dose of reserpine (10 mg/kg, i.p.) and 24 h after an intraventricular (i.c.v.) injection of colchicine (120 microliters/20 microliters saline). Sections of the PVN were hybridized using synthetic oligonucleotide probes complementary to mRNA for corticotropin-releasing hormone (CRH), neurotensin (NT), enkephalin (ENK), vasoactive intestinal polypeptide (VIP) and thyrotropin-releasing hormone (TRH). For immunohistochemistry rabbit antisera to CRH, NT, ENK, VIP and TRH were used. In situ hybridization showed a clear increase in CRH mRNA as compared to control rats after both treatments. Also NT and VIP mRNA could be seen in parvocellular neurons in reserpine and in colchicine-treated rats, whereas we so far have not been able to demonstrate these mRNAs in untreated rats. No changes in TRH mRNA could be detected after reserpine of colchicine. These results provide final evidence that subpopulations of parvocellular PVN neurons can synthesize not only CRH and ENK, but also NT and VIP, in agreement with earlier immunohistochemical results. With immunochemistry, after reserpine, many CRH-, but no NT- or VIP- positive neurons could be observed in the parvoecellular part of the PVN. The present results demonstrate that treatment with two drugs, the monoamine depleting drug reserpine and the mitosis inhibitor colchicine, causes increased levels of mRNA for several peptides in neurons of the PVN, located almost exclusively in its parvocellular part and being part of the hypothalamo-pituitary adrenal axis.

Effects of central nervous system lesions on the expression of galanin: a comparative in situ hybridization and immunohistochemical study

We have used in situ hybridization and immunohistochemistry to study the expression of galanin mRNA and galanin-like immunoreactivity after decortication and lesions of the ventral hippocampus. After decortication the levels of both galanin mRNA and galanin-like immunoreactivity were increased in the dorsal raphe nucleus. In addition, in decorticated rats, but not in controls, galanin mRNA could be seen in dorsal and ventral nuclei of the thalamus and in the remaining parts of the cortex. Increases in galanin mRNA and galanin-like immunoreactivity were also observed in the septum-vertical diagonal band after electrocoagulation lesions of the ventral hippocampus. In contrast, no changes were found after ibotenic acid lesions of the same hippocampal area. These results suggest that increases in the expression of galanin occur in certain neuron populations after direct lesion of their axons and/or terminal fields.

Transplantation of adrenal tissue into the central nervous system

Adrenal medullary tissue can survive transplantation to the central nervous system. Such survival has been obtained experimentally with grafts to the anterior eye chamber, to the brain and to the spinal cord, using medullary tissue from the recipient animal or unrelated animals of the same or, in some cases, different species. Appropriately placed grafts have been shown, under certain conditions, to interact with the host nervous system, exerting behavioral effects including amelioration of experimentally-induced parkinsonian symptoms. Such effects may be enhanced by administration of nerve growth factor to the grafts. On the basis of such findings, adrenal medullary tissue has been grafted to the brain of Parkinson's disease patients. Both animal and human experiments raise important questions about mechanisms of graft action and about factors that influence the outcome of these procedures.

Differential effects of intracerebroventricular colchicine administration on the expression of mRNAs for neuropeptides and neurotransmitter enzymes, with special emphasis on galanin: an in situ hybridization study

The axonal transport blocker colchicine has been extensively used in immunohistochemical studies to induce accumulation of neuroactive compounds, especially neuropeptides, in neuronal somata and thus improve their visualization. To assess whether colchicine might, in addition, influence the synthesis of such compounds, we have now used in situ hybridization to examine the levels of mRNAs encoding for several neuropeptides (galanin [GAL], cholecystokinin [CCK], somatostatin [SOM], neuropeptide Y [NPY]) and neurotransmitter-synthesizing enzymes (choline acetyltransferase [ChAT], tyrosine hydroxylase [TH], amino acid decarboxylase [AADC], and glutamic acid decarboxylase [GAD]) after intraventricular administration of the drug. The results show that colchicine differentially modifies the levels of several mRNA species in different brain areas. Thus GAL mRNA levels increase in virtually all regions examined, including the basal forebrain, hypothalamus, dorsal raphe nucleus, locus coeruleus, and nucleus tractus solitarii. In addition, after colchicine treatment, GAL mRNA appears to be induced in the ipsilateral hemisphere in regions such as the cortex, hippocampus, striatum, lateral septum, and some nuclei of the thalamus as well as within white matter, where it cannot be detected in control animals. Although GAL mRNA in the vast majority of cases is neuronal, some findings indicate a possible glial localization. In parallel, colchicine depletes ChAT mRNA and increases GAD mRNA in the basal forebrain and striatum and decreases AADC mRNA in the dorsal raphe nucleus and locus coeruleus. In the latter nucleus, NPY and TH mRNA levels are increased by colchicine. In contrast, TH mRNA and also CCK mRNA levels decrease in the substantia nigra. In the cortex, hippocampus, and thalamus ipsilateral to colchicine injection CCK mRNA levels are markedly decreased, whereas SOM mRNA is decreased and NPY mRNA increased in the hippocampus but unchanged in the cortex. The results are discussed with reference to the possible artifacts that the use of colchicine might induce in immunohistochemical mapping studies and in relation to possible neurotoxic actions of colchicine, in some cases perhaps related to impaired retrograde transport of growth factor(s).

Rapid increase in enzyme and peptide mRNA in sympathetic ganglia after electrical stimulation in humans

Thoracic ganglia in humans were studied after electrical, preganglionic stimulation using in situ hybridization with synthetic oligonucleotide probes against the catecholamine-synthesizing enzymes tyrosine hydroxylase (EC 1.14.16.2) and dopamine beta-hydroxylase (EC 1.14.17.1) and neuropeptide tyrosine. Immunohistochemical analysis was also performed. Following short peroperative stimulation a severalfold increase in all three mRNAs was found in principal ganglion cells, whereas no definite changes could be detected in enzyme or peptide levels with immunohistochemistry. The results suggest a very rapid and sensitive regulation of genes involved in signal transmission in the sympathetic nervous system of humans. Moreover, they indicate that electrical stimulation of neurons and/or pathways combined with in situ hybridization may be used as a method to define neuronal projections by visualizing increases in mRNAs for transmitter enzymes and/or peptide in target cells.

Distribution of TRH-like immunoreactivity with special reference to coexistence with other neuroactive compounds

During the last years, several important advancements have been made that are of importance for our understanding of the distribution and localization of neurons and cells producing TRH-LI. As detailed in other chapters in this volume, the precursor for TRH has been characterized that has allowed production of antibodies raised against specific sequences of this precursor. This, in turn, has provided new tools for the immunohistochemical elucidation of TRH systems in the CNS. The TRH precursor has also been cloned, leading to possibilities for studying the localization of TRH mRNA with in situ hybridization. Finally, as shown in this paper, improvement of the fixation technique has made it possible to visualize extensive TRH-immunoreactive cell body and fiber systems with antiserum raised against the TRH tripeptide. The results from the latter studies and those with antisera directed to the TRH precursor and in situ hybridization are in good agreement, with some minor exceptions. It should be pointed out that some of the systems described here, for example TRH positive-cell bodies in cortical areas and the hippocampal formation, contain only a very weak immunoreactivity. As always with immunohistochemical techniques, the possibility of crossreactivity with TRH-like peptides or TRH-like sequences within larger proteins must be considered. The present results confirm the presence of TRH-LI in the insulin-producing beta cells of the pancreas, which with the improved technique can be demonstrated also in early adulthood in rats and guinea pigs. Moreover, it could be established that TRH-LI is present in neurons in the gastrointestinal tract as well as in a population of endocrine cells in the antrum of the stomach of the guinea pig. These cells seem at least partly to be identical to the well-known gastrin-producing cells. TRH-LI has been observed to occur in neurons already containing a classical transmitter and/or other peptides. Of particular importance here seems to be a descending bulbospinal system that in addition to TRH co-contains 5-HT, substance P-LI, galanin-LI, human growth hormone immunoreactive material, and proctolin-like material. The significance of this coexistence is not well understood, but interesting interactions have been observed. Attempts to manipulate the TRH phenotype in these medullary neurons by transplantation to other sites in the brain has so far shown that the expression of this peptide seems fairly stable.(ABSTRACT TRUNCATED AT 400 WORDS)

Coexistence and gene expression of phenylethanolamine N-methyltransferase, tyrosine hydroxylase, and neuropeptide tyrosine in the rat and bovine adrenal gland: effects of reserpine

Expression and regulation of the catecholamine-synthesizing enzymes phenylethanolamine N-methyltransferase (PNMTase; S-adenosyl-L-methionine:phenylethanolamine N-methyltransferase, EC 2.1.1.28) and tyrosine hydroxylase [TyrOHase; tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] and the coexisting neuropeptide tyrosine (NPY) were studied in rat and bovine adrenal medulla. By using both immunohistochemistry and in situ hybridization, PNMTase- and NPY-positive cells exhibited a close overlap in bovine medulla and were preferentially localized in the outer two-thirds of the medulla. Although TyrOHase and its mRNA were observed in virtually all medullary gland cells, TyrOHase mRNA levels were much higher in the PNMTase- and NPY-positive cells. After administration of the catecholamine-depleting drug reserpine to rats, a brief increase, followed by a dramatic decrease, in the level of PNMTase mRNA was observed in the adrenal medulla. In contrast, mRNA for both TyrOHase and NPY only exhibited an increase, whereby the TyrOHase mRNA peak preceded that of NPY mRNA. Different regulatory mechanisms may thus operate for these three compounds coexisting in the adrenal medulla.