Purinergic signaling mediated by P2X7 receptors controls myelination in sciatic nerves.

Adenosine-5'-triphosphate, the physiological ligand of P2X receptors, is an important factor in peripheral nerve development. P2X7 receptor is expressed in Schwann cells (SCs), but the specific effects of P2X7 purinergic signaling on peripheral nerve development, myelination, and function are largely unknown. In this study, sciatic nerves from P2X7 knockout mice were analyzed for altered expression of myelin-associated proteins and for alterations in nerve morphology. Immunohistochemical analyses revealed that, in the wild-type peripheral nerves, the P2X7 receptor was localized mainly in myelinating SCs, with only a few immunopositive nonmyelinating SCs. Complete absence of P2X7 receptor protein was confirmed in the sciatic nerves of the knockout mice by Western blot and immunohistochemistry. Western blot analysis revealed that expression levels of the myelin proteins protein zero and myelin-associated glycoprotein are reduced in P2X7 knockout nerves. In accordance with the molecular results, transmission electron microscopy analyses revealed that P2X7 knockout nerves possess significantly more unmyelinated axons, contained in a higher number of Remak bundles. The myelinating/nonmyelinating SC ratio was also decreased in knockout mice, and we found a significantly increased number of irregular fibers compared with control nerves. Nevertheless, the myelin thickness in the knockout was unaltered, suggesting a stronger role for P2X7 in determining SC maturation than in myelin formation. In conclusion, we present morphological and molecular evidence of the importance of P2X7 signaling in peripheral nerve maturation and in determining SC commitment to a myelinating phenotype.

Progesterone and its derivatives are neuroprotective agents in experimental diabetic neuropathy: a multimodal analysis.

One important complication of diabetes is damage to the peripheral nervous system. However, in spite of the number of studies on human and experimental diabetic neuropathy, the current therapeutic arsenal is meagre. Consequently, the search for substances to protect the nervous system from the degenerative effects of diabetes has high priority in biomedical research. Neuroactive steroids might be interesting since they have been recently identified as promising neuroprotective agents in several models of neurodegeneration. We have assessed whether chronic treatment with progesterone (P), dihydroprogesterone (DHP) or tetrahydroprogesterone (THP) had neuroprotective effects against streptozotocin (STZ)-induced diabetic neuropathy at the neurophysiological, functional, biochemical and neuropathological levels. Using gas chromatography coupled to mass-spectrometry, we found that three months of diabetes markedly lowered P plasma levels in male rats, and chronic treatment with P restored them, with protective effects on peripheral nerves. In the model of STZ-induced of diabetic neuropathy, chronic treatment for 1 month with P, or with its derivatives, DHP and THP, counteracted the impairment of nerve conduction velocity (NCV) and thermal threshold, restored skin innervation density, and improved Na(+),K(+)-ATPase activity and mRNA levels of myelin proteins, such as glycoprotein zero and peripheral myelin protein 22, suggesting that these neuroactive steroids, might be useful protective agents in diabetic neuropathy. Interestingly, different receptors seem to be involved in these effects. Thus, while the expression of myelin proteins and Na(+),K(+)-ATPase activity are only stimulated by P and DHP (i.e. two neuroactive steroids interacting with P receptor, PR), NCV, thermal nociceptive threshold and intra-epidermal nerve fiber (IENF) density are also affected by THP, which interacts with GABA-A receptor. Because, a therapeutic approach with specific synthetic receptor ligands could avoid the typical side effects of steroids, future experiments will be devoted to evaluating the role of PR and GABA-A receptor in these protective effects.

Aging in peripheral nerves: regulation of myelin protein genes by steroid hormones.

The process of aging deeply influences morphological and functional parameters of the peripheral nerves. Interestingly, recent observations performed in our laboratory on the rat sciatic nerves have indicated that the deterioration of myelin occurring in the peripheral nerves during aging may be explained by the fall of the messenger levels of the major peripheral myelin proteins (glycoprotein Po, myelin basic protein and peripheral myelin protein 22). At least in the case of the Po, the low levels of its messengers and of the protein itself found in aged animals are increased by the treatment with a physiological progesterone derivative like dihydroprogesterone. It has also been found that in normal adult male rats the levels of the messengers for Po in the sciatic nerve are increased by progesterone, dihydroprogesterone and tetrahydroprogesterone; surprisingly, the gene expression of peripheral myelin protein 22 is stimulated only by tetrahydroprogesterone. These observations have been confirmed in parallel studies performed on Schwann cell cultures. Since tetrahydroprogesterone does not bind to the progesterone receptor but is a ligand for the GABAA receptor, the hypothesis has been put forward that part of the steroidal effects reported might occur not through the classical progesterone receptor, but rather via an interaction with the GABAA receptor. In other experiments it has been found that the gene expression of Po may be decreased by orchidectomy and restored by treatment with the androgen dihydrotestosterone. Altogether, these observations suggest the future use of physiological and/ or synthetic steroid hormones as a possible therapeutic approach for some pathological situations occurring in peripheral nerves during aging and demyelinating diseases.

Neuroactive steroids influence peripheral myelination: a promising opportunity for preventing or treating age-dependent dysfunctions of peripheral nerves.

The process of aging deeply influences morphological and functional parameters of peripheral nerves. The observations summarized here indicate that the deterioration of myelin occurring in the peripheral nerves during aging may be explained by the fall of the levels of the major peripheral myelin proteins [e.g., glycoprotein Po (Po) and peripheral myelin protein 22 (PMP22)]. Neuroactive steroids, such as progesterone (PROG), dihydroprogesterone (5alpha-DH PROG), and tetrahydroprogesterone (3alpha,5alpha-TH PROG), are able to stimulate the low expression of these two myelin proteins present in the sciatic nerve of aged male rats. Since Po and PMP22 play an important physiological role in the maintenance of the multilamellar structure of PNS myelin, we have evaluated the effect of PROG and its neuroactive derivatives, 5alpha-DH PROG and 3alpha,5alpha-TH PROG, on the morphological alterations of myelinated fibers in the sciatic nerve of 22-24-month-old male rats. Data obtained clearly indicate that neuroactive steroids are able to reduce aging-associated morphological abnormalities of myelin and aging-associated myelin fiber loss in the sciatic nerve.

Steroids and the reversal of age-associated changes in myelination and remyelination.

The myelin sheaths that surround all but the smallest diameter axons within the mammalian central nervous system (CNS) must maintain their structural integrity for many years. Like many tissues, however, this function is prone to the effects of ageing, and various structural anomalies become apparent in the aged CNS. Similarly, the regenerative process by which myelin sheaths, lost as a consequence of exposure to a demyelinating insult, are restored (remyelination) is also affected by age. As animals grow older, the efficiency of remyelination progressively declines. In this article, we review both phenomena and describe how both can be partially reversed by steroid hormones and their derivatives.

Tumor suppressor Nf2/merlin drives Schwann cell changes following electromagnetic field exposure through Hippo-dependent mechanisms.

Previous evidence showed mutations of the neurofibromin type 2 gene (Nf2), encoding the tumor suppressor protein merlin, in sporadic and vestibular schwannomas affecting Schwann cells (SCs). Accordingly, efforts have been addressed to identify possible factors, even environmental, that may regulate neurofibromas growth. In this context, we investigated the exposure of SC to an electromagnetic field (EMF), which is an environmental issue modulating biological processes. Here, we show that SC exposed to 50 Hz EMFs changes their morphology, proliferation, migration and myelinating capability. In these cells, merlin is downregulated, leading to activation of two intracellular signaling pathways, ERK/AKT and Hippo. Interestingly, SC changes their phenotype toward a proliferative/migrating state, which in principle may be pathologically relevant for schwannoma development.

Age-induced decrease of glycoprotein Po and myelin basic protein gene expression in the rat sciatic nerve. Repair by steroid derivatives.

The data here reported show that the gene expression of the glycoprotein Po and of the myelin basic protein, the major components of myelin in the peripheral nervous system, dramatically decreases with ageing in the sciatic nerve of normal male rats. A one-month treatment with dihydroprogesterone, the 5alpha-reduced derivative of progesterone, is able to partially restore the fall in Po gene expression occurring in the sciatic nerve of aged male rats, without significantly modifying the gene expression of the myelin basic protein. In cultures of neonatal Schwann cells (the peripheral nervous system elements involved in the synthesis of myelin), the addition of progesterone and of dihydroprogesterone significantly increases Po gene expression; the 3alpha-reduced metabolite of dihydroprogesterone, tetrahydroprogesterone proved to be even more effective. These data suggest that the effect of progesterone is linked to its conversion into dihydroprogesterone and especially into tetrahydroprogesterone, since Schwann cells possess the 5alpha-reductase-3alpha-hydroxysteroid dehydrogenase system. The data provide the first demonstration that ageing decreases the gene expression of two major components of the peripheral myelin in the sciatic nerve; they also show that this phenomenon may be partially reversed by progesterone derivatives, which might act by stimulating Po gene expression in the Schwann cells.

Effects of steroid hormones on gene expression of glial markers in the central and peripheral nervous system: variations induced by aging.

The present article summarizes our data regarding: (a) the effect of sex steroids on the expression of a specific astrocytic marker in glial cell cultures (GFAP); (b) the effects of aging on two markers of the peripheral myelin (glycoprotein Po and the myelin basic protein, MBP); (c) the possible modification of the damaging effects of aging on these two markers by the in vivo administration of progesterone and its derivatives; and, finally, (d) the effect of progesterone derivatives on the gene expression of Po in cultures of rat Schwann cells. The data obtained have indicated that progesterone and its 5 alpha-reduced metabolites may play an important role in the control of gene expression of GFAP and Po, respectively, in type 1 astrocytes and Schwann cells. It has also been found that the gene expression of Po and MBP is dramatically decreased in the myelin of the sciatic nerve of aged male rats and that the aged-linked decrease of the gene expression of Po is partially reversible with steroid treatment.

Corticosteroids regulate the gene expression of FGF-1 and FGF-2 in cultured rat astrocytes.

The present data show that the gene expression of FGF-1 and FGF-2 is regulated by corticosteroids in rat type 1 astrocytes. In particular, the gene expression of FGF-1 is modulated by corticosteroids acting both on type I (minerocorticoid) and type II (glucocorticoid) receptors. In fact, at short times of exposure (2 h) a slight decrease in FGF-1 mRNA levels is induced by deoxycorticosterone, a steroid able to interact with the type I receptors; a similar effect is observed at 6 h following exposure to corticosterone or its 5alpha-reduced metabolite, dihydrocorticosterone. Conversely, at longer times of exposure (24 h) corticosterone is able to strongly increase FGF-1 mRNA levels. Both effects of corticosterone (inhibition and stimulation) were duplicated by dexamethasone, indicating that both effects occur via the type II receptors. Interestingly, the 5alpha-3alpha-reduced metabolite of deoxycorticosterone, tetrahydrodeoxycorticosterone, which does not interact with either corticosteroid receptors, is able to stimulate (at 6 and 24 h of exposure) the gene expression of FGF-1. It is possible that this effect might be induced via the GABA(A) receptor, since muscimol, an agonist of this receptor, exerts a similar effect. The situation is different in the case of FGF-2. The mRNA levels of this growth factor are only stimulated by steroids interacting with type II receptors. Altogether, these observations indicate that corticosteroids modulate the levels of FGF-1 and FGF-2 gene expression in astroglial cells by interaction with classical (type I and II) or nonclassical (GABA(A) receptor) steroid receptors.

Po gene expression is modulated by androgens in the sciatic nerve of adult male rats.

The present results show that androgens are able to modulate the Po gene expression in different models. In particular, we have shown that: (1) the messenger for the androgen receptor (AR) is present in the rat sciatic nerve but not in cultured Schwann cells; (2) castration induces a decrease of Po mRNA levels in the sciatic nerve of male rats, which is counteract by the subsequent treatment with dihydrotestosterone (DHT), the 5alpha-reduced metabolite of testosterone; (3) castration is also able to significantly decrease in the sciatic nerve the activity of the enzyme 5alpha-reductase (which converts testosterone into DHT); and (4) DHT is able to stimulate Po gene expression in cultured Schwann cells. These observations seem to indicate that androgens may exert their effect on Po gene expression via indirect mechanisms; modulation of neuronal influences reaching the Schwann cells through the binding of the androgen to the AR present in neurons may be postulated. However, alternative mechanisms may also be taken in consideration. The data presented suggest indeed that androgens might act on Schwann cells via the progesterone receptor (PR) rather than the AR. It has been observed that: (1) the messenger for PR is present in Schwann cells; (2) DHT may activate the transcriptional activity of a PR-responsive gene by binding to the PR; and (3) putative steroid responsive elements have been described in this paper to be present in the Po promoter region.

Hypothalamic transforming growth factor beta1 and basic fibroblast growth factor mRNA expression is modified during the rat oestrous cycle.

The present observations show that the mRNA levels of two growth factors, previously described to be involved in the control of neurones synthesizing the luteinizing hormone releasing hormone (LHRH) [i.e. transforming growth factor beta1 (TGFbeta1) and basic fibroblast growth factor (bFGF)], fluctuate in the hypothalamus of adult female rats during the oestrous cycle. In particular, the expression of TGFbeta1-mRNA shows a peak on the morning of the day of proestrus, which precedes the increased secretion of the two gonadotrophins that occurs on that day. In the case of bFGF, the peak is evident in the evening of the same day and is concomitant with that of the gonadotrophins. We evaluated the effects of ovariectomy and of exogenous oestrogens on the mRNA levels of these two growth factors in the hypothalamus. The data indicate that 3 weeks of ovariectomy are not able to change the hypothalamic messenger levels of the two growth factors considered, which remain at the levels found in diestrus 1, and that 17beta-oestradiol is able to induce a significant increase of both TGFbeta1- and of bFGF-mRNA levels in the hypothalamus of the ovariectomized rat. The present in vivo observations support the concept, previously proposed on the basis of in vitro data, that growth factors, such as TGFbeta1 and bFGF, play a role in the hypothalamic control of reproduction, and suggest that the control of LHRH dynamics involves a strict cooperation between gonadal steroids and growth factors.

Corticosteroid effects on gene expression of myelin basic protein in oligodendrocytes and of glial fibrillary acidic protein in type 1 astrocytes.

The paper describes the effects of corticosterone and deoxycorticosterone (DOC), used in their native or in their 5 alpha-reduced molecular forms (dihydrocorticosterone, DHC; dihydrodeoxycorticosterone, DHDOC; and tetrahydrodeoxycorticosterone, THDOC) on the gene expression of the myelin basic protein (MBP) and of the glial fibrillary acidic protein (GFAP) in pure cultures, respectively, of oligodendrocytes and type 1 astrocytes obtained from the neonatal rat brain. Among the different steroids tested (corticosterone, DHC, DOC, DHDOC and THDOC), only DHDOC was effective on the gene expression of MBP in the oligodendrocyte cultures; the mRNA levels of this typical oligodendrocyte marker were decreased following exposure to this steroid for 24 h. In the case of the astrocytic marker GFAP, its gene expression was increased by the exposure to corticosterone for 6 and 24 h, while DHC was ineffective; the mineralocorticoid DOC was also ineffective, while its 5 alpha-reduced derivative, DHDOC, strongly inhibited GFAP gene expression, starting at 6 h after beginning of the treatment. In conclusion, the present data show that: (1) adrenal steroids possessing gluco- and mineralocorticoid activities may influence the gene expression of the astrocytic marker GFAP; (2) the 5 alpha-reduced metabolite of DOC, DHDOC is able to influence the gene expression not only of GFAP but also that of MBP, which are, respectively, typical markers of the astrocytes and the oligodendrocytes; (3) the metabolic conversion of hormonal steroids into their 5 alpha-reduced metabolites, which also occurs in the glia, could be implicated in the biochemical control of oligodendrocyte and astrocyte functions.

Metabolism of steroids in pure cultures of neurons and glial cells: role of intracellular signalling.

In the brain, the 5 alpha-reductase converting testosterone (T) is present both in neurons and in glial cells, even if it prevails in neurons; the 3 alpha-hydroxysteroid-dehydrogenase (3 alpha-HSD), the enzyme converting dihydrotestosterone (DHT) into 3 alpha-diol, is particularly concentrated in type 1 astrocytes. In glial cells, since the 5 alpha-reductase is activated by a cAMP analogue, PKA seems to be involved in the control of this enzyme, postulating that nervous inputs utilizing cAMP as the second messenger might modify the activity of this enzyme in glial cells. Moreover, the results indicate that, in type 1 astrocytes, both the 5 alpha-reductase and the 3 alpha-HSD are stimulated by the co-culture with neurons and by the addition of neuron-conditioned medium, suggesting that secretory products released by neurons might intervene in the control of glial cell function.

Interactions between type 1 astrocytes and LHRH-secreting neurons (GT1-1 cells): modification of steroid metabolism and possible role of TGFbeta1.

The hypothesis that type 1 astrocytes (A1) might modify the activities of the enzymes 5alpha-reductase (5alpha-R) and 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) present in the GT1-1 cells has been tested. The data obtained indicate that, utilizing a co-culture technique, A1 are able to: (1) decrease the formation of dihydrotestosterone (DHT) from testosterone (T); (2) increase the formation of dihydroprogesterone (DHP) from progesterone (P); (3) decrease the conversion of DHP into tetrahydroprogesterone (THP) in GT1-1 cells. Moreover, GT1-1 cells are able to increase the formation of DHP in A1; that of DHT was unchanged. The present data might suggest the possible existence of a third isoform of the enzyme 5alpha-R; details on this hypothesis are provided in the text. Interestingly, the inhibitory effect exerted by A1 on the formation of DHT in GT1-1 cells can be mimicked by transforming growth factor beta1 (TGFbeta1). Since TGFbeta1 had been previously shown to be directly involved in the stimulatory control of LHRH secretion by GT1-1 cells, acting both on LHRH release [R.C. Melcangi, M. Galbiati, E. Messi, F. Piva, L. Martini, M. Motta, Type 1 astrocytes influence luteinizing hormone-releasing hormone release from the hypothalamic cell line GT1-1: is transforming growth factor-beta the principle involved? Endocrinology 136 (1995) 679-686.] and gene expression [M. Galbiati, M. Zanisi, E. Messi, I. Cavarretta, L. Martini, R.C. Melcangi, Transforming growth factor-beta and astrocytic conditioned medium influence LHRH gene expression in the hypothalamic cell line GT1, Endocrinology 137 (1996) 5605-5609], the present data also show that TGFbeta1 might intervene in modulating feedback signals reaching hypothalamic LHRH producing neurons. The present findings underline once more the importance of the physiological cross-talk between A1 and neurons.

The 5alpha-reductase in the central nervous system: expression and modes of control.

The present paper will summarize two important aspects of the interactions between steroids and the brain, which have recently been studied in the authors' laboratory. In particular the paper will consider data on: (1) the significance of the two isoforms of the 5alpha-R during brain ontogenesis and development, and (2) the cross-talk between glial and neuronal elements, particularly in relation to the metabolism of sex hormones. (1) The data obtained have shown that the 5alpha-R type 1 enzyme is constitutively expressed in the rat CNS at all stages of brain development. Moreover, the expression of the 5alpha-R type 1 is similar in males and in females, and does not appear to be controlled by androgens. The gene expression of the 5alpha-R type 2 is totally different. This isoform appears to be expressed in the rat brain almost exclusively in the late fetal/early post-natal life and is controlled by testosterone. (2) The present data show that two cell lines derived respectively from a rat glioma (C6 cell line) and from a human astrocytoma (1321N1 cell line) are able to convert testosterone and progesterone into their corresponding 5alpha-reduced metabolites dihydrotestosterone and dihydroprogesterone. The possibility that secretory products of normal and tumoral brain cells might be able to influence steroid metabolism occurring in the two glial cell lines previously mentioned has been considered.

Effects of neuroactive steroids on myelin of peripheral nervous system.

Peripheral nervous system (PNS) possess both classical (e.g. progesterone receptor, PR, androgen receptor, AR) and non-classical (e.g. GABA(A) receptor) steroid receptors and consequently may represent a target for the action of neuroactive steroids. Our data have indicated that neuroactive steroids, like for instance, progesterone, dihydroprogesterone, tetrahydroprogesterone, dihydrotestosterone and 3alpha-diol, stimulate both in vivo and in vitro (Schwann cell cultures), the expression of two important proteins of the myelin of peripheral nerves, the glycoprotein Po (Po) and the peripheral myelin protein 22 (PMP22). It is important to highlight that the mechanisms by which neuroactive steroids exert their effects on the expression of Po and PMP22 involve different kind of receptors depending on the steroid and on the myelin protein considered. In particular, at least in culture of Schwann cells, the expression of Po seems to be under the control of PR, while that of PMP22 needs the GABA(A) receptor. Because Po and PMP22 play an important physiological role for the maintenance of the multilamellar structure of the myelin of the PNS, the present observations might suggest the utilization of neuroactive steroids as new therapeutically approaches for the rebuilding of the peripheral myelin.

Corticosteroids protect oligodendrocytes from cytokine-induced cell death.

The present data show that the simultaneous exposure to tumor necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma) induces cell death with characteristics of apoptosis in cultured rat oligodendrocytes; TNFalpha alone was ineffective. We have also demonstrated that different corticosteroids (aldosterone, deoxycorticosterone, dexamethasone and corticosterone) protect rat oligodendrocytes in culture from apoptosis induced by TNFalpha plus IFNgamma. This effect seems to be exerted via the interaction with both type I and type II corticosteroid receptors since all steroids considered are effective. Since oligodendrocyte apoptosis represents an important event in multiple sclerosis and in several demyelinating diseases, the present observations might be considered an interesting background for further researches directed to the possibility of controlling in vivo the death of these cells.

Effect of progesterone, testosterone and their 5 alpha-reduced metabolites on GFAP gene expression in type 1 astrocytes.

Astrocytes possess steroid receptors as well as several enzymes typical of steroid target cells, such as 5 alpha-reductase, which converts testosterone (T) and progesterone (P) into their respective 5 alpha-reduced metabolites, and the 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD). Because of this, it was deemed of interest to analyze whether the original hormones P and T, and their 5 alpha-reduced metabolites dihydrotestosterone (DHT), 5 alpha-androstan-3 alpha, 17 beta-diol (3 alpha-diol), dihydroprogesterone (DHP) and 5 alpha-pregnan-3 alpha-ol-20-one (THP), might exert some effects on the expression of the most typical astrocytic marker, i.e. the glial fibrillary acidic protein (GFAP). Cultures of rat type 1 astrocytes were exposed to the various steroids for 2, 6, and 24 h, and the variations of GFAP mRNA were measured by Northern blot analysis. A significant elevation of GFAP mRNA levels was observed after exposure to either P or DHP; the effect of DHP appeared more promptly (at 2 h) than that of P (at 6 h). This result suggests that the effect of P might be linked to its conversion into DHP; this hypothesis has been confirmed by showing that the addition of finasteride (a specific blocker of the 5 alpha-reductase) is able to completely abolish the effect of P. After exposure to DHP or THP, a decrease of GFAP gene expression was observed at later intervals (24 h). In the case of androgens, T and 3 alpha-diol did not change GFAP expression at any time of exposure, while DHT produced a significant decrease of GFAP mRNA only after 24 h of exposure. Taken together, the data indicate that the 5 alpha-reduced metabolites of P and T may modulate the expression of GFAP in type 1 rat astrocytes.

Testosterone metabolites in patients reduce the levels of very long chain fatty acids accumulated in X-adrenoleukodystrophic fibroblasts.

Testosterone metabolites (dihydrotestosterone, DHT) and 5 alpha-androstan-3 alpha,17 beta-diol (3 alpha-diol), but not testosterone itself, were shown to reduce the levels of very long chain fatty acids which accumulate in cultured skin fibroblasts from X-adrenoleukodystrophic patients (X-ALD). In addition, in X-ALD fibroblasts, testosterone is less actively converted into DHT vs. controls (skin fibroblasts retrieved from normal subjects) whereas the additional conversion of DHT to the final product 3 alpha-diol is enhanced. This is the first report of altered testosterone metabolism in X-ALD fibroblasts and of the effects of androgens in lowering the abnormal accumulation of very long chain fatty acids in this type of cells.

Transforming growth factor beta2 is able to modify mRNA levels and release of luteinizing hormone-releasing hormone in a immortalized hypothalamic cell line (GT1-1).

On the basis of our previous observations which indicated that transforming growth factor beta1 (TGFbeta1) affects the gene expression and the release of luteinizing hormone-releasing hormone (LHRH) in GT1-1 cells, we have presently evaluated whether also TGFbeta2 might be effective on these parameters. The data here reported show that also TGFbeta2 is able to affect LHRH dynamics, and that this action presents a different kinetics than that reported by TGFbeta1. In particular TGFbeta2 is able to facilitate LHRH release and to decrease the mRNA levels of this decapeptide. The present data have also shown that, GT1-1 cells express the messengers for the two most important receptors of the TGFbeta family, namely TGFbetaRI and TGFbetaRII and consequently represent a target for the action of the different isoforms of TGFbeta. Since the two isoforms of TGFbeta are produced and released from astrocytes, the present data add new support to the hypothesis that astrocytes participate in the control of LHRH secretion in a paracrine fashion.