guanylyl-imidodiphosphate and Seizures

Adenosine is an inhibitory modulator of neuronal activity and its possible involvement in seizures is of interest. We have examined changes in adenosine, its metabolites and receptors in brains of hippocampus-kindled rats, a model of partial epilepsy. Purine levels were measured by in vivo microdialysis and showed a small increase in adenosine and a dramatic increase in its metabolites after kindled seizures. Adenosine A1 receptor binding using [H]DPCPX was unaltered after seizures, whereas A1 agonist stimulated binding of GTP[gamma-S] and A1 mRNA expression increased in the CA3 and other regions. Striatal adenosine A2A mRNA and receptor binding with [H]SCH-58261 decreased. These findings indicate that kindled seizures increase adenosine release and metabolism and induces adaptive changes in adenosine receptors.

Topics: Animals; Autoradiography; Binding Sites; Brain Chemistry; Carrier Proteins; Corpus Striatum; Disease Models, Animal; Gene Expression Regulation; Guanosine 5'-O-(3-Thiotriphosphate); Guanylyl Imidodiphosphate; Hippocampus; In Situ Hybridization; Kindling, Neurologic; Male; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Purines; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A2A; Receptors, Purinergic P1; Seizures; Sulfur Isotopes; Tritium; Xanthines

In order to assess long-lasting consequences of recurrent seizures during development, the effects of repeated seizures in developing rats were investigated on brain adenosine A1 and A2A receptors. The characteristics of A1 and A2A receptors were analyzed by measuring the binding of the selective agonists [3H]CHA (N6-cyclohexyladenosine) and [3H]CGS 21680 (2-[p-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamido adenosine), respectively, on cerebral membrane preparations, whereas receptor coupling to G-proteins was examined by using a GTP analogue (Gpp(NH)p; guanylyl-5'-imidodiphosphate). Seizures were induced by bicuculline once a day at two different developmental stages: either from postnatal day 5 to postnatal day 7 (P5-P7) or from P15 to P17. Adenosine receptors were then studied at P15, P25 and P60. P5-P7 seizures led to an increase in A1 receptor density at P60 and to a decrease in their coupling to G-proteins at P15, but they did not affect A2A receptors. P15-P17 seizures decreased the coupling of A1 receptors to G-proteins at P25 and P60, reduced the density of A2A receptors at P25 and increased their affinity at P60. These results depict a persistent sensitivity of both A1 and A2A brain adenosine receptors to repeated seizures, with selective receptor alterations according to the cerebral maturational stage when seizures occur. In respect to the neuromodulatory and anticonvulsant properties of adenosine, such changes might be implicated in long-term functional brain reorganization after early seizures and future susceptibility to convulsive disorders.

Topics: Adenosine; Animals; Animals, Newborn; Bicuculline; Brain Chemistry; Convulsants; Female; Guanylyl Imidodiphosphate; In Vitro Techniques; Kinetics; Membranes; Phenethylamines; Pregnancy; Purinergic P1 Receptor Agonists; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A2A; Receptors, Purinergic P1; Seizures

In the central nervous system, adenosine has been shown to be a major regulator of neuronal activity in convulsive disorders, mainly via the A1 receptor subtype. In a previous work, we have shown that seizures lead to an age-dependent upregulation of cerebral adenosine A1 sites measured in isolated rat cerebral membranes. However, information concerning regional changes in the receptor density was so far lacking. In the present study, the effects of bicuculline-induced seizures were investigated by quantitative autoradiography of central adenosine A1 receptors in developing rats and in adults. Animals were sacrificed 30 min after an intraperitoneal injection of either saline or a convulsive dose of bicuculline. Adenosine A1 receptors in brain sections were labeled by [3H]N6-cyclohexyladenosine (CHA), a potent receptor agonist. Generalized seizures induced a widespread increase in CHA-specific binding, with a marked enhancement in structures that mediate seizure activity, such as substantia nigra, amygdala, septum and hippocampus. Moreover, the addition of guanylyl-5'-imidodiphosphate, a GTP analogue, to the incubation medium reduced CHA binding by the same order of magnitude whether rats were given saline or bicuculline, suggesting that additional adenosine A1 receptors are also functionally linked to G proteins. The age-related postictal increase in adenosine receptors might contribute to facilitate adenosine anticonvulsant effect, especially in newborns.

Topics: Adenosine; Animals; Autoradiography; Bicuculline; Brain; Brain Chemistry; Female; GTP-Binding Proteins; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Male; Rats; Rats, Inbred Strains; Receptors, Purinergic; Seizures