Neuropeptide Y Y5 receptors inhibit kindling acquisition in rats.

Neuropeptide Y inhibits neuronal excitability and seizures in various experimental models. This peptide delays kindling epileptogenesis but the receptors involved in this action are unknown. We have studied the role of Y5 receptors in kindling using the selective antagonist GW438014A (IC50=210 nM), a small heterocycle molecule that crosses the blood-brain barrier, and the selective peptide agonist Ala31Aib34 NPY (IC50=6.0 nM). Intraperitoneal injection of GW438014A (10 mg/kg), 30 min before the beginning of a rapid-kindling protocol, significantly accelerated the rate of kindling acquisition as compared to vehicle-injected rats. Thus, the number of electrical stimuli required to reach stages 3 and 4-5 of kindling were reduced by 50% and 25%, respectively. The average afterdischarge duration in the stimulated hippocampus was prolonged by 2-fold. Conversely, kindling rate was delayed by intracerebroventricular administration of 24 nmol Ala31Aib32 NPY. Thus, the number of stimuli necessary to reach stages 2 and 3 of kindling was increased by 3- and 4-fold, respectively. During the stimulation protocol (40 stimuli) none of the rats treated with the Y5 agonist showed stages 4-5 seizures. Twenty-four hours after the last kindling stimulation, thus during the re-test session, Y5 agonist- or antagonist-treated rats had stages 4-5 seizures as their controls. In rats treated with both the antagonist and the agonist, kindling rate was similar to vehicle-injected rats. These data indicate that Y5 receptors mediate inhibitory effects of NPY in kindling and display anticonvulsant rather then antiepileptogenic effects upon agonist stimulation.

Somatostatin receptor subtypes 2 and 4 affect seizure susceptibility and hippocampal excitatory neurotransmission in mice.

We have investigated the role of somatostatin receptor subtypes sst2 and sst4 in limbic seizures and glutamate-mediated neurotransmission in mouse hippocampus. As compared to wild-type littermates, homozygous mice lacking sst2 receptors showed a 52% reduction in EEG ictal activity induced by intrahippocampal injection of 30 ng kainic acid (P < 0.05). The number of behavioural tonic-clonic seizures was reduced by 50% (P < 0.01) and the time to onset of seizures was doubled on average (P < 0.05). Seizure-associated neurodegeneration was found in the injected hippocampus (CA1, CA3 and hilar interneurons) and sporadically in the ipsilateral latero-dorsal thalamus. This occurred to a similar extent in wild-type and sst2 knock-out mice. Intrahippocampal injection of three selective sst2 receptor agonists in wild-type mice (Octreotide, BIM 23120 and L-779976, 1.5-6.0 nmol) did not affect kainate seizures while the same compounds significantly reduced seizures in rats. L-803087 (5 nmol), a selective sst4 receptor agonist, doubled seizure activity in wild-type mice on average. Interestingly, this effect was blocked by 3 nmol octreotide. It was determined, in both radioligand binding and cAMP accumulation, that octreotide had no direct agonist or antagonist action at mouse sst4 receptors expressed in CCl39 cells, up to micromolar concentrations. In hippocampal slices from wild-type mice, octreotide (2 micro m) did not modify AMPA-mediated synaptic responses while facilitation occurred with L-803087 (2 micro m). Similarly to what was observed in seizures, the effect of L-803087 was reduced by octreotide. In hippocampal slices from sst2 knock-out mice, both octreotide and L-803087 were ineffective on synaptic responses. Our findings show that, unlike in rats, sst2 receptors in mice do not mediate anticonvulsant effects. Moreover, stimulation of sst4 receptors in the hippocampus of wild-type mice induced excitatory effects which appeared to depend on the presence of sst2 subtypes, suggesting these receptors are functionally coupled.

Seizure susceptibility and epileptogenesis are decreased in transgenic rats overexpressing neuropeptide Y.

Functional studies in epileptic tissue indicate that neuropeptide Y and some of its peptide analogs potently inhibit seizure activity. We investigated seizure susceptibility in transgenic rats overexpressing the rat neuropeptide Y gene under the control of its natural promoter. Seizures were induced in adult transgenic male rats and their wild-type littermates by i.c.v. injection of 0.3 microg kainic acid or by electrical kindling of the dorsal hippocampus. Transgenic rats showed a significant reduction in the number and duration of electroencephalographic seizures induced by kainate by 30% and 55% respectively (P<0.05 and 0.01). Transgenic rats were also less susceptible to epileptogenesis than wild-type littermates as demonstrated by a 65% increase in the number of electrical stimuli required to induce stage 5 seizures (P<0.01). This phenotype was associated with a strong and specific expression of neuropeptide Y mRNA in area CA1, a brain area involved in the seizure network. We conclude that endogenous neuropeptide Y overexpression in the rat hippocampus is associated with inhibition of seizures and epileptogenesis suggesting that this system may be a valuable target for developing novel antiepileptic treatments.

Powerful anticonvulsant action of IL-1 receptor antagonist on intracerebral injection and astrocytic overexpression in mice.

IL-1beta and its endogenous receptor antagonist (IL-1Ra) are rapidly induced by seizures in the rodent hippocampus. Exogenously applied IL-1beta prolongs seizures in an IL-1R type I-mediated manner. This effect depends on N-methyl-d-aspartate receptor activation. We report here that intrahippocampal application of recombinant IL-1Ra or its selective endogenous overexpression in astrocytes under the control of glial acidic fibrillary protein promoter potently inhibits motor and electroencephalographic seizures induced by bicuculline methiodide in mice. Accordingly, transgenic mice show a reduced seizure-related c-fos mRNA expression in various forebrain areas compared with their wild-type littermates. Recombinant IL-1Ra was ineffective in mice deficient in IL-1R type I, having per se a delayed onset to generalized convulsions. These results demonstrate that IL-1Ra mediates potent anticonvulsant effects acting on IL-1R type I and suggest that the balance between brain IL-1beta and IL-1Ra represents a crucial mechanism to control seizure generalization.