ATP-induced in vivo neurotoxicity in the rat striatum via P2 receptors

Supersensitivity of P2X receptors in cerebrocortical cell cultures after in vitro ischemia

Neuronally enriched primary cerebrocortical cultures were exposed to glucose-free medium saturated with argon (in vitro ischemia) instead of oxygen (normoxia). Ischemia did not alter P2X7 receptor mRNA, although serum deprivation clearly increased it. Accordingly, P2X7 receptor immunoreactivity (IR) of microtubuline-associated protein 2 (MAP2)-IR neurons or of glial fibrillary acidic protein (GFAP)-IR astrocytes was not affected; serum deprivation augmented the P2X7 receptor IR only in the astrocytic, but not the neuronal cell population. However, ischemia markedly increased the ATP- and 2'-3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP)-induced release of previously incorporated [3H]GABA. Both Brilliant Blue G and oxidized ATP inhibited the release of [3H]GABA caused by ATP application; the Brilliant Blue G-sensitive, P2X7 receptor-mediated fraction, was much larger after ischemia than after normoxia. Whereas ischemic stimulation failed to alter the amplitude of ATP- and BzATP-induced small inward currents recorded from a subset of non-pyramidal neurons, BzATP caused a more pronounced increase in the frequency of miniature inhibitory postsynaptic currents (mIPSCs) after ischemia than after normoxia. Brilliant Blue G almost abolished the effect of BzATP in normoxic neurons. Since neither the amplitude of mIPSCs nor that of the muscimol-induced inward currents was affected by BzATP, it is assumed that BzATP acts at presynaptic P2X7 receptors. Finally, P2X7 receptors did not enhance the intracellular free Ca2+ concentration either in proximal dendrites or in astrocytes, irrespective of the normoxic or ischemic pre-incubation conditions. Hence, facilitatory P2X7 receptors may be situated at the axon terminals of GABAergic non-pyramidal neurons. When compared with normoxia, ischemia appears to markedly increase P2X7 receptor-mediated GABA release, which may limit the severity of the ischemic damage. At the same time we did not find an accompanying enhancement of P2X7 mRNA or protein expression, suggesting that receptors may become hypersensitive because of an increased efficiency of their transduction pathways.

Changes in purinergic signaling after cerebral injury -- involvement of glutamatergic mechanisms?

Extracellular purines act as neuromodulators on transmitter release and may exert toxic effects at higher concentrations. In microdialysis studies, endogenous ATP facilitated the extracellular concentration of glutamate in the nucleus accumbens (NAc) of rats. Additionally, P2 receptors are involved in astrogliosis in vivo after a stab wound injury in the same region, suggesting that these receptors, preferentially the metabotropic P2Y(1) receptor subtype, mediate also trophic responses. Two sets of experimental findings support the involvement of purinergic and glutamatergic mechanisms in the response of brain to mechanical damage. First, in the present studies, the initial time course of extracellular ATP and glutamate was analyzed after a mechanical injury. The concentration of ATP in microdialysates was elevated only in the first 15-min sample whereas glutamate returned to a basal concentration not before a 90-min period had elapsed. We suggest, that the acute injury-evoked stimulation of P2 receptors contributes to glutamate-mediated excitotoxicity. Second, the expression of P2Y(1) receptors and their possible relation to glutamatergic structures, identified by neuronal vesicular glutamate transporters (VGLUTs), were elucidated in non-treated and mechanically injured animals after 4 days. The number of P2Y(1)-positive cells was significantly increased after injury. Furthermore, P2Y(1) receptor-labeled cells do not exhibit immunoreactivity for VGLUT1 and VGLUT2 without and after injury. However, after injury, a co-expression of the P2Y(1) receptor on VGLUT3-immunopositive cells in the NAc was observed. No VGLUT1-, 2- and 3-immunoreactivity was found on P2Y(1)-positive glial fibrillary acidic protein-immunopositive astrocytes at both conditions. Our data suggest that the expression of P2Y(1) receptors at neurons and astrocytes is modulated in response to cerebral injury. It can be assumed, that the enhanced sensitivity of neurons to purinergic signaling may be related directly or indirectly to changes of the glutamatergic transmission.

Oligodendrocytes express P2Y12 metabotropic receptor in adult rat brain

In the CNS, nucleotide receptors termed P2 receptors are identified on neurons and glial cells, mediating neuron-neuron, glia-glia and glia-neuron communication. In the present work, we qualify in vivo in the adult rat CNS the cellular/subcellular distribution of P2Y12 receptor protein in cerebral cortex, white matter and subcortical nuclei (striatum and substantia nigra), by means of immunofluorescence-confocal, electron microscopy and Western blot analysis. P2Y12 receptor immunoreactivity colocalizes neither with markers such as neuronal nuclei, neurofilament light chain, calbindin and tyrosine hydroxylase, nor with glial fibrillary acidic protein and isolectin B4, but with myelin basic protein and the oligodendrocyte marker RIP, in both cell bodies and processes, indicating therefore oligodendrocyte localization. Electron microscopy identifies P2Y12 receptors in both the perikaryon and under the plasmalemma of oligodendrocyte cell bodies and radiating processes, until the paranodal region of fibers. By Western blot analysis, P2Y12 receptor shows a specific band of 42-44 kDa, matching the molecular mass predicted from amino acid sequencing. Since in platelets P2Y12 receptor is known to regulate adhesion/activation and thrombus growth/stability, from our results we could speculate by analogy that, in oligodendrocytes, P2Y12 receptor signaling might contribute to the migration and adhesion of the glial processes to axons to be myelinated.

ATP extracellular concentrations are increased in the rat striatum during in vivo ischemia

Interest is growing in the role of adenosine triphosphate (ATP) on P2 receptors during hypoxic/ischemic events in the brain. However, there is no direct evidence of an increase in extracellular ATP levels during cerebral ischemia in vivo. The aim of the present study was to evaluate ATP outflow from the rat striatum by the microdialysis technique associated with focal cerebral ischemia in vivo by intraluminal occlusion of the right middle cerebral artery (MCA). Between 1 and 4h after ischemia, rats showed a clear turning behavior contralateral to the ischemic side. Twenty-four hour after MCA occlusion, ischemic rats had definite neurological deficit and striatal and cortical damage. The ATP concentration (mean+/-S.E.M.) in the striatum of normoxic rats (n = 8) was 3.10+/-0.34 nM. During 220 min after MCA occlusion, the extracellular ATP levels significantly increased two-fold, being 5.90+/-0.61 nM (p < 0.01 versus normoxic level). ATP outflow showed a tendency to increase over time during the 220 min of ischemia. Since extracellular ATP is rapidly metabolized to adenosine, we also assessed ATP outflow in the presence of the ecto-5'-nucleotidase inhibitor, alpha,beta-methylene-adenosine diphosphate (AOPCP, 1 mM) directly perfused into the striatum. The ATP concentration in normoxic rats (n = 8) was increased three-fold in the presence of the ecto-5'-nucleotidase inhibitor (9.57+/-0.26 nM). During 220 min of ischemia, extracellular ATP levels significantly increased 1.3-fold in AOPCP-treated rats (12.62+/-0.65 nM, p < 0.01 versus normoxic level). The present study confirms that ATP is continuously released in the brain and demonstrates for the first time that ATP outflow increases during ischemia in vivo. These results confirm that ATP may be an important mediator in brain ischemia.

Lesional accumulation of P2X4 receptor+ monocytes following experimental traumatic brain injury

P2X4 receptor (P2X4R) is an ATP-gated ion channel. ATP is an important messenger in traumatic brain injury. Here, we report expression of P2X4R in rat traumatic brain injury with focus on the early phase, most amenable to therapy. Accumulation of P2X4R+ cells was observed as early as 6 h after injury and continued to increase 4 days post-injury at the lesion and remote areas. Double staining revealed that most P2X4R+ cells co-expressed ED-1, a marker for reactive microglia/macrophages, but not nestin or W3/13. Our data suggest that P2X4R expression defines a subtype of activated microglia/macrophages involved in the early processes following traumatic brain injury.

Increase of adenine nucleotide hydrolysis in rat hippocampal slices after seizures induced by quinolinic acid

Quinolinic acid (QUIN), an endogenous convulsant compound, overstimulates the glutamatergic system stimulating N-methyl-D-aspartate receptors, enhancing glutamate release and inhibiting glutamate uptake. Glutamate releases the neuroprotector adenosine, which in turn reduces glutamate release and depresses the neuronal activity. Additionally, adenine nucleotides are an important source of adenosine, by action of ecto-nucleotidases. Here we evaluated the adenine nucleotide hydrolysis in hippocampal slices of adult rats in different times after seizures induced by QUIN. After 45 min, there was an increase of ATP and ADP hydrolysis. After 5 h, there was an increase of ATP, ADP and AMP hydrolysis. After 12 h, there was an increase only of ATP hydrolysis. After 24 h, all hydrolysis returned to control levels. As slice preparations maintain tissue integrity, this study indicates, more than previously observed with synaptosomal preparations, that the extracellular production of the neuroprotector adenosine may be involved in brain responses to seizures.

Involvement of P2 receptors in the growth and survival of neurons in the CNS

Extracellular adenosine 5'-triphosphate (ATP) has been recognized as a ubiquitous, unstable signalling molecule, acting as a fast neurotransmitter and modulator of transmitter release and neuronal excitability. Recent findings have demonstrated that ATP is a growth factor participating in differentiation, cell proliferation, and survival, as well as a toxic agent that mediates cellular degeneration and death. Potential sources of extracellular purines in the nervous system include neurons, glia, endothelium, and blood. A complex family of ectoenzymes rapidly hydrolyzes or interconverts extracellular nucleotides, thereby either terminating their signalling action or producing an active metabolite of altered purinoceptor selectivity. Most effects are mediated through the 2 main subclasses of specific cell surface receptors, P2X and P2Y. Members of these P2X/Y receptor families are widely expressed in the central nervous system (CNS) and are involved in glia-glia and glia-neuron communications, whereby they play important physiological and pathophysiological roles in a variety of biological processes. After different kinds of "acute" CNS injury (e.g., ischemia, hypoxia, mechanical stress, axotomy), extracellular ATP can reach high concentrations, up to the millimolar range, flowing out from cells into the extracellular space, exocytotically, via transmembrane transport, or as a result of cell damage. In this review, P2 receptor activation as a cause or a consequence of neuronal cell activation or death and/or glial activation is described. The involvement of P2 receptors is also described under different "chronic" pathological conditions, such as pain, epilepsia, toxic influence of ethanol or amphetamine, retinal diseases, Alzheimer's disease (AD), and possibly, Parkinson's disease. The relationship between changes in P2 receptor expression and the specific response of different cell types to injury is extremely complex and can be related to detrimental and/or beneficial effects. The present review therefore considers ATP acting via P2 receptors as a potent regulator of normal physiological and pathological processes in the brain, with a focus on pathophysiological implications of P2 receptor functions.

Increased resistance of glioma cell lines to extracellular ATP cytotoxicity

Glioblastomas are the most common form of primary tumors of the central nervous system (CNS) and despite treatment, patients with these tumors have a very poor prognosis. ATP and other nucleotides and nucleosides are very important signaling molecule in physiological and pathological conditions in the CNS. ATP is degraded very slowly by gliomas when compared to astrocytes, potentially resulting in the accumulation of extracellular ATP around gliomas. Cell lysis caused by excitotoxic death or by tumor resection may liberate intracellular ATP, a known mitotic factor for glioma cells. The aim of this study is to examine the effects on cytotoxicity induced by extracellular ATP in U138-MG human glioma cell line and C6 rat glioma cell line compared to hippocampal organotypic cell cultures. The cytotoxicity of ATP (0.1, 0.5, 5 mM) was measured using propidium iodide and LDH assays. Caspases assay was performed to identify apoptotic cell death. Results showed that the glioma cells present resistance to death induced by ATP when compared with a normal tissue. High ATP concentrations (5 mM) induced cell death after 24 h in organotypic cell cultures but not in glioma cell lines. Our data indicate that ATP released in these situations can induce cell death of the normal tissue surrounding the tumor, potentially opening space to the fast growth and invasion of the tumor.

Hypo-and hyperthyroidism affect the ATP, ADP and AMP hydrolysis in rat hippocampal and cortical slices

The presence of severe neurological symptoms in thyroid diseases has highlighted the importance of thyroid hormones in the normal functioning of the mature brain. Since, ATP is an important excitatory neurotransmitter and adenosine acts as a neuromodulatory structure inhibiting neurotransmitters release in the central nervous system (CNS), the ectonucleotidase cascade that hydrolyzes ATP to adenosine, is also involved in the control of brain functions. Thus, we investigated the influence of hyper-and hypothyroidism on the ATP, ADP and AMP hydrolysis in hippocampal and cortical slices from adult rats. Hyperthyroidism was induced by daily injections of l-thyroxine (T4) 25 microg/100 g body weight, for 14 days. Hypothyroidism was induced by thyroidectomy and methimazole (0.05%) added to their drinking water for 14 days. Hypothyroid rats were hormonally replaced by daily injections of T4 (5 microg/100 g body weight, i.p.) for 5 days. Hyperthyroidism significantly inhibited the ATP, ADP and AMP hydrolysis in hippocampal slices. In brain cortical slices, hyperthyroidism inhibited the AMP hydrolysis. In contrast, hypothyroidism increased the ATP, ADP and AMP hydrolysis in both hippocampal and cortical slices and these effects were reverted by T4 replacement. Furthermore, hypothyroidism increased the expression of NTPDase1 and 5'-nucleotidase, whereas hyperthyroidism decreased the expression of 5'-nucleotidase in hippocampus of adult rats. These findings demonstrate that thyroid disorders may influence the enzymes involved in the complete degradation of ATP to adenosine and possibly affects the responses mediated by adenine nucleotides in the CNS of adult rats.

P2X2 and P2Y1 immunofluorescence in rat neostriatal medium-spiny projection neurones and cholinergic interneurones is not linked to respective purinergic receptor function

1. The presence of ionotropic P2X receptors, targets of ATP in fast synaptic transmission, as well as metabotropic P2Y receptors, known to activate K(+) currents in cultured neostriatal neurones, was investigated in medium-spiny neurones and cholinergic interneurones contained in neostriatal brain slices from 5-26-day-old rats. 2. In these cells, adenosine-5'-triphosphate (ATP) (100-1000 microm), 2-methylthioadenosine-5'-triphosphate (2MeSATP), alpha,beta-methyleneadenosine-5'-triphosphate (alpha,betameATP, 30-300 microm, each) and adenosine-5'-O-(3-thiotriphosphate (ATPgammaS) (100 microm) failed to evoke P2X receptor currents even when 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microm), apyrase (10 U ml(-1)) or intracellular Cs(+) was used to prevent occluding effects of the ATP breakdown product adenosine, desensitisation of P2X receptors by endogenous ATP and an interference with the activation of K(+) channels, respectively. P2X receptor agonists were also ineffective in outside-out patches withdrawn from the brain slice tissue. Muscimol (10 microm) evoked GABA(A) receptor-mediated currents under all these conditions. 3. When used as a control, locus coeruleus neurones responded with P2X receptor-mediated currents to ATP (300 microm), 2MeSATP and alpha,betameATP (100 microm, each). 4. ATP and adenosine-5'-diphosphate (ADP) (100 microm, each) did not activate K(+) currents in the neostriatal neurones. 5. Despite the observed lack of function, P2X(2) and P2Y(1) immunofluorescence was found in roughly 50% of the medium-spiny neurones and cholinergic interneurones. 6. A role of ATP in synaptic transmission to striatal medium-spiny neurones and cholinergic interneurones appears unlikely, however, the otherwise silent P2X and P2Y receptors may gain functionality under certain yet unknown conditions.

Acute effects of pulsed microwaves and 3-nitropropionic acid on neuronal ultrastructure in the rat caudate-putamen

Ultrastructure of the medium sized "spiny" neuron in rat dorsal-lateral caudate-putamen was assessed after administration of 3-nitropropionic acid (3-NP) and exposure to pulsed microwaves. Sprague-Dawley male rats were given two daily intraperitoneal doses of 0 or 10 mg/kg 3-NP and 1.5 h after each dose were exposed to microwave radiation at a whole body averaged specific absorption rate (SAR) of 0 (sham exposure), 0.6, or 6 W/kg for 30 min. Microwave exposure consisted of 1.25 GHz radiation delivered as 5.9 micros pulses with repetition frequency 10 Hz. Tissue samples taken 2-3 h after the second sham or microwave exposure showed no injury with light microscope methods. Blinded qualitative assessment of ultrastructure of randomly selected neurons from the same samples did reveal differences. Subsequent detailed, quantitative measurements showed that, when followed by sham exposure, administration of 3-NP significantly increased endoplasmic reticulum (ER) intracisternal width, ER area density, and nuclear envelope thickness. Microwave exposure at 6 W/kg alone also significantly increased these measures. Exposure of 3-NP treated animals at 6 W/kg significantly increased effects of 3-NP on ultrastructure. Although exposure at 0.6 W/kg alone did not affect ultrastructure measures, exposure of 3-NP treated animals at 0.6 W/kg reduced the effects of 3-NP. We concluded that 3-NP changed neuronal ultrastructure and that the microwave exposures used here changed neuronal ultrastructure in ways that depended on microwave SAR and neuron metabolic status. The apparent cancellation of 3-NP induced changes by exposure to pulsed microwaves at 0.6 W/kg indicated the possibility that such exposure can protect against the effects of mitochondrial toxins on the nervous system.

Neuroprotective effects of inhibiting N-methyl-d-aspartate receptors, P2X receptors and the mitogen-activated protein kinase cascade: A quantitative analysis in organotypical hippocampal slice cultures subjected to oxygen and glucose deprivation

Cell death was assessed by quantitative analysis of propidium iodide uptake in rat hippocampal slice cultures transiently exposed to oxygen and glucose deprivation, an in vitro model of brain ischemia. The hippocampal subfields CA1 and CA3, and fascia dentata were analyzed at different stages from 0 to 48 h after the insult. Cell death appeared at 3 h and increased steeply toward 12 h. Only a slight additional increase in propidium iodide uptake was seen at later intervals. The mitogen-activated protein kinases extracellular signal-regulated kinase 1 and extracellular signal-regulated kinase 2 were activated immediately after oxygen and glucose deprivation both in CA1 and in CA3/fascia dentata. Inhibition of the specific mitogen-activated protein kinase activator mitogen-activated protein kinase kinase by PD98059 or U0126 offered partial protection against oxygen and glucose deprivation-induced cell damage. The non-selective P2X receptor antagonist suramin gave neuroprotection of the same magnitude as the N-methyl-D-aspartate channel blocker MK-801 (approximately 70%). Neuroprotection was also observed with the P2 receptor blocker PPADS. Immunogold data indicated that hippocampal slice cultures (like intact hippocampi) express several isoforms of P2X receptors at the synaptic level, consistent with the idea that the effects of suramin and PPADS are mediated by P2X receptors. Virtually complete neuroprotection was obtained by combined blockade of N-methyl-D-aspartate receptors, P2X receptors, and mitogen-activated protein kinase kinase. Both P2X receptors and N-methyl-D-aspartate receptors mediate influx of calcium. Our results suggest that inhibition of P2X receptors has a neuroprotective potential similar to that of inhibition of N-methyl-D-aspartate receptors. In contrast, our comparative analysis shows that only partial protection can be achieved by inhibiting the extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase cascade, one of the downstream pathways activated by intracellular calcium overload.

ATP-induced inhibition of gap junctional communication is enhanced by interleukin-1 beta treatment in cultured astrocytes

Nucleotides are signaling molecules involved in variety of interactions between neurons, between glial cells as well as between neurons and glial cells. In addition, ATP and other nucleotides are massively released following brain insults, including inflammation, and may thereby be involved in mechanisms of cerebral injury. Recent concepts have shown that in astrocytes intercellular communication through gap junctions may play an important role in neuroprotection. Therefore, we have studied the effects of nucleotides on gap junction communication in astrocytes. Based on measurement of intercellular dye coupling and recording of junctional currents, the present study shows that ATP (10-100 microM) induces a rapid and a concentration-dependent inhibition of gap junction communication in cultured cortical astrocytes from newborn mice. Effects of agonists and antagonists of purinergic receptors indicate that the inhibition of gap junctional communication by ATP mainly involves the stimulation of metabotropic purinergic 1 (P2Y(1)) receptors. Pretreatment with the pro-inflammatory cytokine interleukin-1beta (10 ng/ml, 24 h), which has no effect by itself on gap junctional communication, increases the inhibitory effect of ATP and astrocytes become sensitive to uridine 5'-triphosphate (UTP). As indicated by the enhanced expression of P2Y(2) receptor mRNA, P2Y(2) receptors are responsible for the increased responses evoked by ATP and UTP in interleukin-1beta-treated cells. In addition, the effect of endothelin-1, a well-known inhibitor of gap junctional communication in astrocytes was also exacerbated following interleukin-1beta treatment. We conclude that ATP decreases intercellular communication through gap junctions in astrocytes and that the increased sensitivity of gap junction channels to nucleotides and endothelin-1 is a characteristic feature of astrocytes exposed to pro-inflammatory treatments.

Plasticity of purine release during cerebral ischemia: clinical implications?

Adenosine is a powerful modulator of neuronal function in the mammalian central nervous system. During a variety of insults to the brain, adenosine is released in large quantities and exerts a neuroprotective influence largely via the A(1) receptor, which inhibits glutamate release and neuronal activity. Using novel enzyme-based adenosine sensors, which allow high spatial and temporal resolution recordings of adenosine release in real time, we have investigated the release of adenosine during hypoxia/ischemia in the in vitro hippocampus. Our data reveal that during the early stages of hypoxia adenosine is likely released per se and not as a precursor such as cAMP or an adenine nucleotide. In addition, repeated hypoxia results in reduced production of extracellular adenosine and this may underlie the increased vulnerability of the mammalian brain to repetitive or secondary hypoxia/ischemia.

2-ClATP exerts anti-tumoural actions not mediated by P2 receptors in neuronal and glial cell lines

We investigated the effects of the ATP analogue and P2 receptor agonist 2-ClATP on growth and survival of different neuronal (PC12, PC12nnr5 and SH-SY5Y) and glial (U87 and U373) cell lines, by the use of direct count of intact nuclei, fluorescence microscopy, fluorescence-activated cell sorter analysis (FACS) and high pressure liquid chromatography (HPLC). 2-ClATP lowered the number of cultured PC12nnr5, SH-SY5Y, U87 and U373 cells to almost 5%, and of PC12 cells to about 35% after 3-4 days of treatment. EC(50) was in the 5-25 microM range, with 2-ClATP behaving as a cytotoxic or cytostatic agent. Analysis of the biological mechanisms demonstrated that pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (P2 receptor antagonist and nucleotidases inhibitor), but not Caffeine or CGS-15493 (P1 receptor antagonists) effectively prevented 2-ClATP-induced toxicity. 2-ClATP metabolic products (2-ClADP, 2-ClAMP, 2-Cladenosine) and new synthesis derivatives (2-CldAMP, 2-Cldadenosine-3',5'-bisphosphate and 2-CldATP) exerted similar cytotoxic actions. Inhibition of both serum nucleotidases and purine nucleoside transporters strongly reduced 2-ClATP-induced cell death, which was conversely increased by the nucleotide hydrolyzing enzyme apyrase. The adenosine kinase inhibitor 5-iodotubericidin totally prevented 2-ClATP or 2-Cladenosine-induced toxicity. In summary, our findings indicate that 2-ClATP exerts either cell cycle arrest or cell death, acting neither on P2 nor on P1 receptors, but being extracellularly metabolized into 2-Cladenosine, intracellularly transported and re-phosphorylated.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Axotomy dependent purinergic and nitrergic co-expression

Different lines of evidence indicate that ATP and nitric oxide (NO) play key roles in mediating neuronal responses after cell damage. Purinergic and nitrergic interactions have been proposed in non neural tissues physiological functions and, in different experimental models of brain injury, both purinergic and nitrergic activations have been reported. The present study was planned to ascertain possible relations of these two systems after brain damage. Variations in the expression of the nitric oxide synthase neuronal isoform (nNOS) enzyme, and of two subunits of purinergic ionotrophic receptors (P2X) namely P2X(1) and P2X(2) in precerebellar stations after cerebellar lesion in rats were analyzed and compared. After the lesion nNOS positive cells presented a clear increment followed by a decrement. Conversely, nNOS negative cells presented a rapid decrement in the first postlesional weeks that continued less pronounced afterward. Postlesional nNOS activation was related with time course of P2X(1) and P2X(2) activations. The capacity of the same cells to express both nNOS and P2X markers was investigated immunocytochemically. Confocal microscopy of double immunofluorescence showed a high percentage of co-localization among P2X(1)/nNOS, P2X(2)/nNOS and P2X(1)/P2X(2) in olivary and pontine neurons. In addition, NeuN/P2X(1) and NeuN/P2X(2) double immunofluorescence showed P2X(1) expressed only in neurons while P2X(2) expressed by both neurons and glia. Present data demonstrate that after cerebellar lesion nitrergic and purinergic systems are activated with similar time courses in precerebellar stations. Further, time differences in the relation between nNOS expression and cell survival suggest a multifarious role of NO in mediating cell reaction to axotomy. The tight cellular co-localization and temporal co-activation of purinergic and nitrergic markers indicate possible interactions between these two systems also in the CNS.