Persistent increase of blood lead level and suppression of δ-ALAD activity in northern bobwhite quail orally dosed with even a single 2-mm spent lead shot.

Birds that display grit ingestion behavior are potentially at risk of lead (Pb) poisoning from mistaken ingestion of spent Pb shot pellets. The majority of available studies designed to assess such risk have used unspent shot pellets rather than field-obtained spent shot, which is oxidized and otherwise changed by weathering. Available studies also often administered more or heavier shot pellets to a bird than it might be expected to ingest. The current study dosed northern bobwhite quail (Colinus virginianus) weighing 194.6 ± 23.1 g (female birds) and 199.3 ± 12.2 g (male birds) with one to three spent no. 9 Pb shot collected from a skeet range, with particular interest in the toxicity that may occur from ingestion of a single 2-mm, 50 mg shot. An 8 week post-dosing clinical observation period was employed, over which feed consumption, body weight, blood Pb levels, and a battery of blood physiological parameters were made. Weight loss occurred in the birds, including male birds dosed with one Pb pellet. Erythrocyte delta aminolevulinic acid dehydratase (δ-ALAD) levels were decreased for the duration of the study across exposures and to levels associated with injury in wild bird populations. Decreased ALAD was particularly severe in female birds dosed with one Pb pellet and was still 92 % decreased at 8 weeks after dosing. Together, these results suggest that inadvertent ingestion of a single no. 9 Pb shot pellet can adversely affect the health of northern bobwhite quail.

Poult performance as influenced by age of dam, genetic line, and dietary vitamin E.

An experiment was conducted to measure the effects of age of dam, genetic line, and dietary levels of vitamin E on growth and immunocompetence of poults. Age of dam was defined as younger (in early egg production) and older (past peak production); line consisted of a commercial sire and dam line; and dietary vitamin E was supplemented into the diet at 10 and 300 IU/kg of feed. Traits measured included body, liver, gizzard, and yolk sac weights at hatch; BW and feed conversion to 9, 28, and 42 d; response to SRBC, Phaseolus vulgaris agglutinin-P, and Escherichia coli administered at 28 d of age; and response to a cold stress on d 5 posthatch. Differences among genetic lines were evident with growth greater for poults from the sire than from the dam line. Performance of poults from older dams was generally superior to that of poults from younger dams. The higher level of vitamin E resulted in a greater than 7-fold increase in blood plasma vitamin E and reduced mortality. There were interactions among the main effects in which the fitness of poults from younger dams was enhanced by the higher level of vitamin E and the effect of breeder age differed among genetic lines.

Memory antibody responses of broiler and leghorn chickens as influenced by dietary vitamin E and route of sheep red blood cell administration.

Influences of dietary levels of vitamin E fed to hens and their progeny, and routes of SRBC inoculation on antibody responses of diverse populations of chickens were studied. Populations were a commercial broiler sire line (C), 2 commercial broiler dam lines (A and B), and Leghorn lines selected for high (H) or low (L) antibody response to SRBC. Dams from lines A and B were fed diets supplemented with either 10 or 300 IU/kg of vitamin E, whereas dams from lines H and L received only the diet with 10 IU of vitamin E/kg. Progeny from matings of C males with A and B females as well as H and L females mated to males from their respective lines were hatched on the same day and fed diets supplemented with either 10 or 300 IU/kg of vitamin E. Breeders were the same age and eggs were incubated in the same machine. Chicks were inoculated on d 14 intravenously with 0.1 mL of a 0.5% suspension of SRBC or intramuscularly with 0.1 mL of a 25% suspension of SRBC. Antibody response was measured 6 and 14 d later. Chicks received a booster i.m. inoculation of 0.1 mL of 25% SRBC on d 28. Titers were again measured 6 and 14 d later. Level of vitamin E fed to dams did not affect progeny BW or plasma vitamin E levels. Although titers were higher following i.v. than i.m. inoculation, the degree of difference varied among stocks. Dietary vitamin E level interacted with inoculation route with a greater response to the higher than lower level of vitamin E for i.v., but there was no difference for i.m. There were stock x level of vitamin E and stock x route of inoculation interactions for secondary responses to SRBC inoculation. Stock rankings after the first inoculation were not predictive of the rankings after the second inoculation. The 30-fold increase in dietary level of vitamin E resulted in >12-fold differences in plasma levels of vitamin E. Overall, there was a stock-dependent influence of dietary vitamin E on growth and humoral antibody response.

Sox1-deficient mice suffer from epilepsy associated with abnormal ventral forebrain development and olfactory cortex hyperexcitability.

Mutations in several classes of embryonically-expressed transcription factor genes are associated with behavioral disorders and epilepsies. However, there is little known about how such genetic and neurodevelopmental defects lead to brain dysfunction. Here we present the characterization of an epilepsy syndrome caused by the absence of the transcription factor SOX1 in mice. In vivo electroencephalographic recordings from SOX1 mutants established a correlation between behavioral changes and cortical output that was consistent with a seizure origin in the limbic forebrain. In vitro intracellular recordings from three major forebrain regions, neocortex, hippocampus and olfactory (piriform) cortex (OC) showed that only the OC exhibits abnormal enhanced synaptic excitability and spontaneous epileptiform discharges. Furthermore, the hyperexcitability of the OC neurons was present in mutants prior to the onset of seizures but was completely absent from both the hippocampus and neocortex of the same animals. The local inhibitory GABAergic neurotransmission remained normal in the OC of SOX1-deficient brains, but there was a severe developmental deficit of OC postsynaptic target neurons, mainly GABAergic projection neurons within the olfactory tubercle and the nucleus accumbens shell. Our data show that SOX1 is essential for ventral telencephalic development and suggest that the neurodevelopmental defect disrupts local neuronal circuits leading to epilepsy in the SOX1-deficient mice.

Performance of pureline broiler breeders fed two levels of vitamin E.

Reported in this paper is an experiment designed to evaluate responses of two commercial broiler dam purelines (A and B) continuously fed 10 or 300 IU of vitamin E/kg from 168 to 441 d of age. Prior to Day 168, all pullets were fed diets containing 10 IU of vitamin E/kg. During the early laying period, percentage hen-day ovulations and percentage hen-day normal egg production were similar for both lines and diets. During the latter part of the laying cycle, there were differences between lines for these traits (A > B), as well as for BW and egg weight for which line differences were reversed (A < B). Also during this period, percentage hen-day ovulations and percentage hen-day normal egg production differed between diets (300 > 10 IU/kg). These differences between diets were consistent with the greater number of females that entered lay and higher hen-housed egg production of the 300- than 10-IU/kg group. Although during the laying cycle all females received a fixed amount of feed, BW gains were greater for Line B than A and for the 300- than the 10-IU/kg level of vitamin E. Heterophil (H):lymphocyte (L) ratios, percentage livability, and relative asymmetries of shank length and diameter were similar among groups. Pullets from Line B and those fed the higher level of vitamin E exhibited more fear than their counterparts. Head shaking did not differ between vitamin E levels; however, there was a line-by-time of day interaction for this behavior. The 30-fold difference in dietary vitamin E was reflected by a 15-fold difference in plasma vitamin E levels in both lines. For vitamin E level in the yolk, however, there was a line-by-diet interaction. The interaction resulted from no difference between lines at the 10 IU/kg level and differences of 10- and 6+-fold in Lines B and A at the 300 IU/ kg level, respectively. Overall, responses to continuous feeding of vitamin E at these levels were influenced by genetic stock, age, duration of feeding, and measurement criteria.

Elevated levels of group-III metabotropic glutamate receptors in the inferior colliculus of genetically epilepsy-prone rats following intracollicular administration of L-serine-O-phosphate.

The selective group-III metabotropic glutamate receptor agonist, L-serine-O-phosphate (L-SOP), when injected bilaterally into the inferior colliculus of the sound sensitive genetically epilepsy-prone (GEP) rats produces a short proconvulsant excitation followed by a long phase of protection against sound-induced seizures lasting for 2-4 days. We have studied this prolonged suppression of audiogenic seizures using pharmacological and molecular biological approaches including semiquantitative RT-PCR and western blotting. The intracerebroventricular injection of the protein synthesis inhibitor cycloheximide (120 microg) 30 min beforehand significantly reduces the proconvulsant seizure activity and the prolonged anticonvulsant effect of intracollicular L-SOP (500 nmol/side). The sensitive semiquantitative RT-PCR revealed a significant up-regulation in mGlu(4) and mGlu(7) mRNA levels in the inferior colliculus at 2 days (maximum suppression of audiogenic seizures) after intracollicular L-SOP injection compared with the non-injected, 2-day post-vehicle treated and 7-day (return to expressing audiogenic seizures) post-drug or vehicle-treated groups. No significant changes were observed in mGlu(6) or mGlu(8) mRNA expression levels in drug-treated compared with control groups. Examination of mGlu(4a) and mGlu(7a) protein levels using western blotting showed a significant increase in mGlu(7a) but no significant change in mGlu(4a) protein levels 2 days after L-SOP treatment compared with the control groups (non-injected and 2-day vehicle-injected group). These results suggest that up-regulation of mGlu(7) receptors is involved in the prolonged anticonvulsant effect of L-SOP against sound-induced seizures in GEP rats. The potential use of mGlu(7) agonists as novel anti-epileptic agents merits investigation.

Anticonvulsant activity of a mGlu(4alpha) receptor selective agonist, (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid.

The metabotropic Group III agonist, (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid (ACPT-1), selective for the mGlu(4alpha) receptor, suppresses sound-induced seizures in DBA/2 mice following its intracerebroventricular (i.c.v.) administration (ED(50) 5.6 [2.9-10.7], nmol i.c.v., 15 min, clonic phase) and in genetically epilepsy-prone (GEP) rats following focal administration into the inferior colliculus (ED(50) 0.08 [0.01-0.50], nmol, 60 min, clonic phase). ACPT-1 also protects against clonic seizures induced in DBA/2 mice by the Group I agonist, (RS)-3,5-dihydroxyphenylglycine (3,5-DHPG) (ED(50) 0.60 [0.29-1.2], nmol i.c.v.) and by the Group III antagonist, (RS)-alpha-methylserine-O-phosphate (MSOP) (ED(50) 49.3 [37.9-64.1], nmol i.c.v.). Another Group III agonist, (RS)-4-phosphonophenyl-glycine (PPG), preferentially activating the mGlu(8) receptor, previously shown to protect against sound-induced seizures in DBA/2 mice and GEP rats, also protects against seizures induced in DBA/2 by 3,5-DHPG (ED(50) 3.7 [2.4-5.7], nmol i.c.v.) and by the Group III antagonist, MSOP (ED(50) 40.2 [21.0-77.0], nmol i.c.v.). At very high doses (500 nmol i.c.v. and above), Group III antagonists have pro-convulsant and convulsant activity. The anticonvulsant protection against sound-induced seizures in DBA/2 mice provided by a fully protective dose (20 nmol, i.c.v.) of the mGlu(4) receptor agonist ACPT-1, is partially reversed by the co-administration of the Group III antagonists, MSOP, (RS)-alpha-methyl-4-phosphonophenylglycine (MPPG) or (S)-2-amino-2-methyl-4-phosphonobutanoic acid (MAP4), in the 20-50 nmol dose range. At doses of 50-200 nmol, MPPG and MAP4 cause further reversal of the ACPT-1 anticonvulsant protection, while the MSOP effect on ACPT-1 protection is abolished at higher doses. In contrast, the anticonvulsant protection against sound-induced seizures in DBA/2 mice provided by a fully protective dose (20 nmol, i.c.v.) of the mGlu(8) receptor agonist PPG, is not significantly affected by the co-administration of the same Group III antagonists, MSOP, MPPG or MAP4. We conclude that activation of either mGlu(4alpha) or mGlu(8) receptors confer anticonvulsant protection in DBA/2 mice. Furthermore, the metabotropic Group III receptor antagonists, MSOP, MPPG, and MAP4 appear to be functionally selective for the mGlu(4) receptor in this system.

Anti-epileptic activity of group II metabotropic glutamate receptor agonists (--)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268) and (--)-2-thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY389795).

The selective group II metabotropic glutamate receptor (mGlu(2/3)) agonists (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268) and (-)-2-thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY389795) have been evaluated as anti-epileptic drugs in dilute brown agouti (DBA/2) mice, lethargic (lh/lh) mice, genetically epilepsy-prone-9 (GEP) rats and amygdala-kindled rats. Sound-induced clonic seizures in DBA/2 mice were transiently inhibited by both agonists intracerebroventricularly (i.c.v.), LY379268 ED(50)=0.08 [0.02-0.33]nmol and LY389795 ED(50)=0.82 [0.27-3.24]nmol or intraperitoneally (i.p.), LY379268 ED(50)=2.9 [0.9-9.6]mg/kg and LY389795 ED(50)=3.4 [1.0-11.7]mg/kg. Both mGlu(2/3) agonists inhibited seizures induced by the group I mGlu receptor agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG), where LY379268, i.c.v. ED(50)=0.3 [0.02-5.0]pmol and LY389795, i.c.v. ED(50)=0.03 [0.05-0.19]nmol. The spike and wave discharge (SWD) duration of absence seizures in lh/lh mice was significantly reduced by both agonists at 1 and 10nmol (i.c.v.) up to 90min following infusion. The electrically induced seizure score and afterdischarge duration of amygdala-kindled rats was partially inhibited by the agonists 30min after i.p. injection of 10mg/kg. The agonists did not inhibit sound-induced seizures in GEP rats (0.1-1mg/kg, 30min 1h, i.p.), but were proconvulsant following sound stimulus (> or =0.1mg/kg). These findings identify a potential role for mGlu(2/3) agonists in the amelioration of generalised and partial epileptic seizures.

Neuroprotective effect of aminoguanidine on transient focal ischaemia in the rat brain.

Using serial magnetic resonance imaging we have evaluated the effectiveness of aminoguanidine (AG) as a neuroprotective agent in a rat model of transient middle cerebral artery occlusion (MCAO). Because aminoguanidine's neuroprotective properties have primarily been ascribed to its action as iNOS inhibitor, we also performed a biochemical analysis of nitric oxide metabolites and NOS isoforms in our model of ischaemia. Daily injections of AG (100 mg/kg) or saline, were started at 6 h after the occlusion and the effects of this treatment on lesion progression monitored by T(2)-weighted MRI at 6 (pre-treatment scan), 24 and 72 h. Measurements of lesion volumes showed that between 6 and 72 h post-MCAO, lesion growth was slower in AG-treated rats than in control rats. This difference was most pronounced between 24 and 72 h post-MCAO when AG halted the lesion volume expansion observed in control rats. Measurements of plasma NOx (nitrite plus nitrate) at 0, 24, 48 and 72 h after MCAO, showed that NO levels did not differ significantly between the AG- and saline-treated groups at any time-point. Moreover, NOS activity assays revealed that no iNOS activity was present in any of the brains tested and that constitutive neuronal NOS activity was similar across the two hemispheres between both groups. The absence of iNOS protein in the ischaemic and contralateral hemispheres at 48 and 72 h after MCAO (control group only) was confirmed by Western blot analysis. These results suggest that AG treatment reduces the rate of growth of ischaemic lesions, perhaps preserving the functioning of perifocal neurons. Our observations contradict suggestions that high levels of NO generated by iNOS are partially responsible for exacerbating the neuronal damage in the postischaemic phase of MCAO. Although this does not rule out a role for AG as a neuroprotective agent via its ability to inhibit iNOS, these findings indicate that neuroprotective actions of AG may also be mediated via other cellular targets.

Anticonvulsant activity of 3,4-dicarboxyphenylglycines in DBA/2 mice.

The 3,4-dicarboxyphenylglycines (3,4-DCPG) inhibit sound-induced seizures in DBA/2 mice with the racemate being notably more potent than either isomer (ED(50) (nmol, i.c.v.)): (RS)-3,4-DCPG (0.004; 86 mg/kg, i.p.)>>the mGlu(8) agonist (S)-3,4-DCPG (0.11)>the AMPA antagonist (R)-3,4-DCPG (0.38). A potentiation of anticonvulsant activity between AMPA and mGlu(8) receptors was confirmed by combining (R)-3,4-DCPG with the mGlu(8) agonist (RS)-4-phosphonophenylglycine. This potentiating mechanism provides a novel strategy for the treatment of epileptic seizures.

The mGlu(2/3) agonist 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate, is anti- and proconvulsant in DBA/2 mice.

The anticonvulsant activity of the selective group II metabotropic glutamate receptor (mGlu) agonist 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC) has been evaluated in chemoconvulsant and sound-induced models of epileptic seizures in DBA/2 mice. 2R,4R-APDC (> or =10 nmol, intracerebroventricularly (i.c.v.), -15 min) transiently reduced sound-induced seizure activity including clonic seizures to 40% of vehicle at 20 nmol (i.c.v.) and 30% of vehicle at 100 mg/kg (intraperitoneally (i.p.), -15 min). 2R,4R-APDC inhibited clonic seizures induced by the group III mGlu antagonist (R,S)-alpha-methylserine-O-phosphate (2.5 micromol, i.c.v.) when co-injected at 20-40 nmol and inhibited limbic seizure activity induced by the mGlu(1/5) agonist (R,S)-3,5-dihydroxyphenylglycine (1.5 micromol, i.c.v.) when co-injected at 10-40 nmol. A reversal of the anticonvulsant activity of 2R,4R-APDC was observed at (>20 nmol) in each of the chemoconvulsant and sound-induced models of epileptic seizures. 2R,4R-APDC (0.1-1 micromol, i.c.v.) induced stimulus-independent, rapid and dose-dependent clonic seizures. Selective mGlu(2/3) agonists represent a novel class of potential anti-epileptic drugs, however due to the proconvulsant activity observed here, 2R,4R-APDC is obviously limited in this regard.

Anticonvulsant activity of two metabotropic glutamate group I antagonists selective for the mGlu5 receptor: 2-methyl-6-(phenylethynyl)-pyridine (MPEP), and (E)-6-methyl-2-styryl-pyridine (SIB 1893).

The selective mGlu5 antagonists, MPEP, 2-methyl-6-phenylethynyl-pyridine, and SIB1893, (E)-6-methyl-2-styryl-pyridine, have been evaluated as antiepileptic drugs in DBA/2 mice and lethargic mice. Clonic seizures induced by the selective mGlu5 agonist, (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG), 3 micromol intracerebroventricularly (i.c.v.), are potently suppressed by both compounds (MPEP, ED(50)=0.42 [0.28-0.62] mg/kg intraperitoneally (i.p.); SIB 1893 ED(50)=0.19 [0.11-0.33] mg/kg i.p. ). Clonic seizures induced by the mGlu1,5 agonist, 3, 5-dihydroxyphenylglycine (DHPG), 1.5 micromol i.c.v., are less potently suppressed by both compounds (MPEP, ED(50)=22 [13-38] mg/kg i.p., 110 [67-180] nmol i.c.v.; SIB1893, ED(50)=31 [18-54] mg/kg i.p. , 95 [82-110] nmol i.c.v.). Sound-induced seizures in DBA/2 mice are suppressed at 15 min by MPEP and SIB 1893 (MPEP ED(50) clonic seizures=18 [10-32] mg/kg i.p., 93 [69-125] nmol i.c.v.; tonic seizures=6.1 [4.5-8.3] mg/kg i.p., 46 [26-80] nmol i.c.v.; SIB 1893 ED(50) clonic seizures=27 [17-44] mg/kg i.p., 825 [615-1108] nmol i. c.v., tonic seizures=5.4 [3.4-8.6] mg/kg i.p., 194 [113-332] nmol i. c.v.). The ED(50) for MPEP for impaired rotarod performance is 128 [83-193] mg/kg i.p., at 15 min, i.e. a therapeutic index for sound-induced seizures of 5-20. In lethargic mice (lh/lh), a genetic absence model, MPEP, 50 mg/kg i.p., caused a marked reduction in the incidence of spontaneous spike-and-wave discharges. These selective antagonists of mGlu5 block seizures due to activation of mGlu5 at very low systemic doses. At rather higher doses they block convulsive and non-convulsive primary generalised seizures.

Glutamate as a neurotransmitter in the brain: review of physiology and pathology.

Glutamate is the principal excitatory neurotransmitter in brain. Our knowledge of the glutamatergic synapse has advanced enormously in the last 10 years, primarily through application of molecular biological techniques to the study of glutamate receptors and transporters. There are three families of ionotropic receptors with intrinsic cation permeable channels [N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate]. There are three groups of metabotropic, G protein-coupled glutamate receptors (mGluR) that modify neuronal and glial excitability through G protein subunits acting on membrane ion channels and second messengers such as diacylglycerol and cAMP. There are also two glial glutamate transporters and three neuronal transporters in the brain. Glutamate is the most abundant amino acid in the diet. There is no evidence for brain damage in humans resulting from dietary glutamate. A kainate analog, domoate, is sometimes ingested accidentally in blue mussels; this potent toxin causes limbic seizures, which can lead to hippocampal and related pathology and amnesia. Endogenous glutamate, by activating NMDA, AMPA or mGluR1 receptors, may contribute to the brain damage occurring acutely after status epilepticus, cerebral ischemia or traumatic brain injury. It may also contribute to chronic neurodegeneration in such disorders as amyotrophic lateral sclerosis and Huntington's chorea. In animal models of cerebral ischemia and traumatic brain injury, NMDA and AMPA receptor antagonists protect against acute brain damage and delayed behavioral deficits. Such compounds are undergoing testing in humans, but therapeutic efficacy has yet to be established. Other clinical conditions that may respond to drugs acting on glutamatergic transmission include epilepsy, amnesia, anxiety, hyperalgesia and psychosis.

Factors influencing the frequency of fluorescence transients as markers of peri-infarct depolarizations in focal cerebral ischemia.

BACKGROUND AND PURPOSE: Peri-infarct depolarizations (PIDs) that occur in ischemic boundary zones of the cerebral cortex of experimental animals have been shown to promote rather than simply to indicate the evolution of the lesion and are especially prominent in the rat. To study the influence of one factor, species, on PID incidence, we compared the frequency of PIDs in a primate species, the squirrel monkey, with that in the cat after middle cerebral artery occlusion. Plasma glucose was reviewed as a possible cause of interexperiment variability in the cat experiments. METHODS: In open-skull experiments under chloralose anesthesia, changes in cortical fluorescence believed to indicate NADH/NAD(+) redox state, as markers of PIDs, were recorded by serial imaging of the cortical surface in vivo for 4 hours after middle cerebral artery occlusion. RESULTS: Fluorescence transients occurred in squirrel monkeys at a frequency (mean+/-SD) of 0.7+/-0.8 hours(-1) (n=5), which was not significantly less than in that observed in cats (1.3+/-1.6 hours(-1), n=8). Data from the cat experiments indicated a relationship between number of transients (dependent) and plasma glucose, with a striking increase in PID frequency in association with values of mean postocclusion plasma glucose <4.1 mmol/L (Mann-Whitney U=15.0, P=0.034); this observation agrees well with other published findings. CONCLUSIONS: Transient changes in fluorescence strongly suggestive of peri-infarct depolarizations, either transient or terminal, occur and propagate in the ischemic cerebral cortex of a nonhuman primate. The results also suggest that the relationship of frequency of peri-infarct depolarizations with plasma glucose requires further examination, to confirm the finding and to determine a safe lower limit for a target range for control of plasma glucose if insulin is used in the management of patients with cerebral ischemia.

Basic mechanisms of gabitril (tiagabine) and future potential developments.

Gabitril (tiagabine) is a potent selective inhibitor of the principal neuronal gamma-aminobutyric acid (GABA) transporter (GAT-1) in the cortex and hippocampus. By slowing the reuptake of synaptically-released GABA, it prolongs inhibitory postsynaptic potentials. In animal models of epilepsy, tiagabine is particularly effective against kindled (limbic) seizures and against reflexly-induced generalized convulsive seizures. These data are predictive of its efficacy in complex partial seizures in humans. Possible clinical applications outside the field of epilepsy include bipolar disorder and pain.

Anticonvulsant activity of a metabotropic glutamate receptor 8 preferential agonist, (R,S)-4-phosphonophenylglycine.

Agonists at group III glutamate metabotropic receptors, such as L-serine-O-phosphate, have pro- and anti-convulsant activities in rodent models. We have used intracerebroventricular administration to test a novel group III agonist, (R,S)-4-phosphonophenylglycine (PPG), that is preferential for mglu(8), against sound-induced seizures in DBA/2 mice. Tonic and clonic seizures are abolished at 15 min (ED(50s) 0.14 [0.04-0.4] nmol, and 3.4 [2.1-5.6] nmol, respectively). The protection against tonic and clonic seizures by 20 nmol PPG is complete for 4 h, diminished by 6 h, and absent by 10 h. In contrast, L-Serine-O-phosphate gives only partial protection against sound-induced clonic seizures for 15-30 min (ED(50) 79 [45-139] nmol) in DBA/2 mice. In genetically epilepsy prone rats sound-induced seizures were blocked 5-60 min after the bilateral administration of PPG, 5-10 nmol, into the inferior colliculus. These data suggest that the mglu(8) receptor is a potential target for novel antiepileptic drugs.

Glutamate receptors and transporters in genetic and acquired models of epilepsy.

Glutamate, the principal excitatory neurotransmitter in the brain, acts on three families of ionotropic receptor--AMPA (alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid), kainate and NMDA (N-methyl-D-aspartate) receptors and three families of metabotropic receptor (Group I: mGlu1 and mGlu5; Group II: mGlu2 and mGlu3; Group III: mGlu4, mGlu6, mGlu7 and mGlu8). Glutamate is removed from the synaptic cleft and the extracellular space by Na+-dependent transporters (GLAST/EAAT1, GLT/EAAT2, EAAC/EAAT3, EAAT4, EAAT5). In rodents, genetic manipulations relating to the expression or function of glutamate receptor proteins can induce epilepsy syndromes or raise seizure threshold. Decreased expression of glutamate transporters (EAAC knockdown, GLT knockout) can lead to seizures. In acquired epilepsy syndromes, a wide variety of changes in receptors and transporters have been described. Electrically-induced kindling in the rat is associated with functional potentiation of NMDA receptor-mediated responses at various limbic sites. Group I metabotropic responses are enhanced in the amygdala. To date, no genetic epilepsy in man has been identified in which the primary genetic defect involves glutamate receptors or transporters. Changes are found in some acquired syndromes, including enhanced NMDA receptor responses in dentate granule cells in patients with hippocampal sclerosis.

Decreased sensitivity to Group III mGluR agonists in the lateral perforant path following kindling.

The ability of the selective Group III mGluR agonist L-serine-O-phosphate (L-SOP) to inhibit lateral perforant path (LPP) evoked responses in the dentate gyrus was tested in hippocampal slices from commissurally-kindled rats 1-2 days after the last seizure, implanted controls, and fully-kindled rats rested for 28 days without stimulated seizures (28 days post-seizure, 28 dps). L-SOP was more potent in controls than kindled or 28 dps animals, decreasing the fEPSP slope with IC50s of 2.4 microM, 18.7 microM and 10.5 microM, respectively. Paired pulse facilitation (PPF, 50 ms) was comparable in control and kindled rats, but was markedly reduced in 28 dps rats, indicating increased release probability. Inhibition of the field excitatory postsynaptic potentials (fEPSP) by L-SOP was correlated with enhanced PPF in all groups, affirming a presynaptic site of action. At moderate levels of L-SOP-induced inhibition (20-60%), PPF showed significantly greater enhancement in 28 dps than in the other two groups. These results are interpreted as showing a functional reduction of the presynaptic inhibitory Group III mGluR (probably mGluR8) response in the LPP after kindling. Furthermore, PPF changes indicate that the kindled state may be associated with a long-lasting increase in the probability of release from LPP terminals, which may be temporarily masked or counterbalanced by recent seizures.