Differential effects of intracerebroventiricular colchicine administration on the expression of mrnas for neuropeptides and neurotransmitter enzymes, with specila emphasis on galanin: An in situ Hybridization Study

Abstract

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).

Distribution of galanin messenger RNA-expressing cells in murine brain and their regulation by leptin in regions of the hypothalamus

“…This contrasts with studies of this region in the rat (without colchicine pretreatment), where galanin mRNA is not apparently expressed and the peptide is detected only with the use of certain antibodies. 6,14,22,34,41 In primate studies, galanin-containing neurons are found throughout the hippocampal formation, in contrast to the discrete localization in the dentate gyrus found in our study of the mouse. 17 Within the hypothalamus, most nuclei exhibited at least moderate labeling, with notable exceptions being the ventromedial and suprachiasmatic nuclei, which had no detectable signal for galanin mRNA.…”

“…6,14,34 As in the rat, the highest numbers of galanin mRNAexpressing cells were observed in the diencephalon and rhombencephalon, with moderate labeling in the telencephalon and mesencephalon. In the forebrain, the presence of galanin mRNA within all of the major basal forebrain areas that contain cholinergic neurons suggests that galanin plays a similar role in modulating acetylcholine synthesis and release in the mouse as has been postulated for the rat and primate (reviewed in Refs 27 and 29).…”

“…A notable and curious ®nding in the mouse is the apparent lack of galanin message in the cortex and striatumÐ areas that have been reported to contain both galanin mRNA and peptide in primates (Cebus monkeys, baboons and humans) 17 and rats. 6,23,41 One major difference between several of these studies and ours is that the mice used in our study did not receive colchicine pretreatment, whereas the majority of rat studies have used colchicine to enhance galanin peptide levels. Colchicine has been shown to induce the expression of neuropeptide genes, including galanin, 6 and since the studies in the rat where galanin has been reported to be expressed in the cortex and striatum entailed colchicine as a pretreatment, any direct comparison between the results we have obtained in the mouse and these earlier Adult male C57BL6/J £ 129SV mice (n 3) brains were examined by using 35 Slabeled riboprobes complementary to mouse galanin mRNA.…”

“…6,23,41 One major difference between several of these studies and ours is that the mice used in our study did not receive colchicine pretreatment, whereas the majority of rat studies have used colchicine to enhance galanin peptide levels. Colchicine has been shown to induce the expression of neuropeptide genes, including galanin, 6 and since the studies in the rat where galanin has been reported to be expressed in the cortex and striatum entailed colchicine as a pretreatment, any direct comparison between the results we have obtained in the mouse and these earlier Adult male C57BL6/J £ 129SV mice (n 3) brains were examined by using 35 Slabeled riboprobes complementary to mouse galanin mRNA. In situ hybridization assays were performed from the olfactory bulb through the brain to the caudal extent of the medulla, and all sections were analysed for the presence of silver grain clusters representing galanin-expressing cells.…”

Galanin transgenic mice display cognitive and neurochemical deficits characteristic of Alzheimer's disease

“…We propose that up-regulation of galanin occurs as a consequence of the primary underlying pathology of the disease. Up-regulation of galanin mRNA is consistently seen after neuronal damage, including axotomy, inflammation, tetrodotoxin, reserpine, and colchicine treatments (58)(59)(60)(61). Compensatory and possibly neuroprotective actions of galanin are implied by reports that galanin pretreatment attenuates the physiological consequences of ischemia, concussion, and seizures (7,62,63).…”