The effects of chronic imidazoline drug treatment on glial fibrillary acidic protein concentrations in rat brain

Abstract

1 The concentration of the astrocytic marker, glial fibrillary acidic protein (GFAP) was quantitated by immunoblotting (western blotting) in the rat brain after treatment with various imidazoline drugs and other agents. 2 Chronic (7 days) but not acute (1 day) treatment with the imidazoline drugs, cirazoline (1 mg kg-', i.p.) and idazoxan (1Omg kg', i.p.), but not with the structurally related a2-adrenoceptor antagonists, RX821002 (2-methoxy idazoxan) (1Omg kg', i.p.) and efaroxan (1O mg kg', i.p.), markedly increased (45%) GFAP immunoreactivity in the rat cerebral cortex. Chronic treatment (7 days) with yohimbine (10mg kg-', i.p.), a non-imidazoline a2-adrenoceptor antagonist, did not significantly modify GFAP immunoreactivity in the cerebral cortex. 3 Chronic treatment (7 days) with cirazoline and idazoxan did not alter the density of brain monoamine oxidase (MAO)-B sites labelled by [3H]-Ro 19-6327 (lazabemide), another relevant astroglial marker. Moreover, these imidazoline drug treatments did not modify the levels of a-tubulin in the cerebral cortex. These negative results reinforced the specificity of the effects of imidazoline drugs on GFAP. 4 Irreversible inactivation of brain x2-adrenoceptors (and other neurotransmitters receptors) after treatment with an optimal dose of the peptide-coupling agent EEDQ (1.6 mg kg-', i.p., for 6-24 h) did not alter GFAP immunoreactivity in the cerebral cortex. These results further disproved the involvement of these receptors on astroglial cells in the tonic control of GFAP levels. 5 The binding of [3H]-idazoxan in the presence of 10-6 M (-)-adrenaline was used to quantitate in parallel 12-imidazoline preferring sites in the rat brain after the same treatments. Chronic treatment (7 days) with cirazoline and idazoxan, but not with RX821002, efaroxan or yohimbine, significantly increased (25%) the density of I2-sites in the cerebral cortex. The up-regulation of I2-sites induced by cirazoline was not observed in the liver, a tissue that also expresses 12-sites but lacks glial cells. 6 A strong correlation (r = 0.97) was found when the mean percentage changes in GFAP immunoreactivity were related to the mean percentage changes in 12 imidazoline sites after the various drug treatments. 7 Together the results suggest a direct physiological function of glial I2-imidazoline preferring sites in the regulation of GFAP levels.

Interactions between the NO-Citrulline Cycle and Brain-derived Neurotrophic Factor in Differentiation of Neural Stem Cells

“…Moreover, it has been shown that agmatine increases neurogenesis by recruiting NSC in the hippocampus of adult mice because of blockade of NMDA receptors (50). Furthermore, treatment with drugs with marked affinity to imidazoline-binding sites led to increased levels of GFAP immunostaining together with increased density of imidazoline-binding sites in rat brain (51). Thus, L-arginine, even without altering NO concentration, increased GFAP and ␤3-tubulin expression, possibly because of induction of polyamine synthesis, such as agmatine.…”

“…Having in mind that NO-induced effects depend on the dose and local of production of this gaseous messenger (7,42), the incapability of L-citrulline in promoting neurogenesis can be explained by the lack of NO production in most of the cells of the heterogeneous population of differentiating NSC. Consequently, NO is only produced in a subset of cells expressing L-citrulline transporters (51), by yet unknown mechanisms FIGURE 10. BDNF restores neural differentiation inhibited by lack of nitric oxide.…”

Attenuation of tolerance to opioid‐induced antinociception and protection against morphine‐induced decrease of neurofilament proteins by idazoxan and other I2‐imidazoline ligands

“…before morphine administration. These drugs were used at doses known to interact with the dierent target receptors (Ernsberger et al, 1993;Olmos et al, 1994;Alemany et al, 1995;Lalies & Nutt, 1995;Kolesnikov et al, 1996;Ventayol et al, 1997).…”

“…Immunoblotting of neuro®lament proteins of low (68 kDa) molecular weight (NF-L) was done as previously described for other cytoskeletal proteins (Olmos et al, 1994) with minor modi®cations (GarcõÂ a-Sevilla et al, 1997). After 13 days of chronic drug treatments and 24 h of drug washout the rats were decapitated and brains rapidly removed under ice.…”

“…According to dierences in their pharmacological pro®les, tissue and subcellular distributions, imidazoline receptors have been classi®ed into two main types: I 1 -and I 2 -imidazoline receptors (Michel & Insel, 1989;Ernsberger, 1992). The I 2 -imidazoline receptors are widely distributed and in the brain are expressed on neurones, but mainly on glial cells (Regunathan et al, 1993;Olmos et al, 1994;Ruggiero et al, 1998). The amine agmatine (decarboxylated arginine) has been proposed as an endogenous agonist at imidazoline receptors (Li et al, 1994) and to act as a neurotransmitter or neuromodulator for some members of this receptor family (Li et al, 1994;Piletz et al, 1995).…”