Glucose protects DBA/2J mice from audiogenic seizures: correlation with brain glycogen levels

A Chromosome 13 locus is associated with male-specific mortality in mice

BACKGROUND AND AIM

Mortality is a highly complex trait influenced by a wide array of genetic factors.

METHODS

We examined a population of 1200 mice that were F2 generation offspring of a 4-way reciprocal cross between C57BL6/J and DBA2/J strains. Animals were sacrificed at age 200, 500, or 800 days and genotyped at 96 markers. The 800 days old cohort, which were the survivors of a much larger breeding group, were examined for enriched frequency of alleles that benefit survival and depletion of alleles that reduce survival.

RESULTS

Loci on Chr 13 in males and on Chr X in females were significantly distorted from Mendelian expectations, even after conservative correction for multiple testing. DBA2/J alleles between 35 and 80 Mb on Chr 13 were underrepresented in the age 800 male animals. D2 genotypes in this region were also associated with premature death during behavioral testing. Furthermore, confirmatory analysis showed BXD recombinant inbred strains carrying the D2 alleles in this region had shorter median survival. Exploration of available pathology data indicated that a syndrome involving dental malocclusions, pancreatic islet hypertrophy, and kidney lipidosis may have mediated the effects of DBA alleles on mortality specifically in male mice. The heterozygote advantage locus on the X Chr was not found to be associated with any pathology.

CONCLUSIONS

These results suggest a novel locus influencing survival in the B6/D2 genetic background, perhaps via a metabolic disorder that emerges by 200 days of age in male animals.

Role of brain glycogen in the response to hypoxia and in susceptibility to epilepsy

Although glycogen is the only carbohydrate reserve of the brain, its overall contribution to brain functions remains unclear. It has been proposed that glycogen participates in the preservation of such functions during hypoxia. Several reports also describe a relationship between brain glycogen and susceptibility to epilepsy. To address these issues, we used our brain-specific Glycogen Synthase knockout (GYS1^Nestin-KO) mouse to study the functional consequences of glycogen depletion in the brain under hypoxic conditions and susceptibility to epilepsy. GYS1^Nestin-KO mice presented significantly different power spectra of hippocampal local field potentials (LFPs) than controls under hypoxic conditions. In addition, they showed greater excitability than controls for paired-pulse facilitation evoked at the hippocampal CA3–CA1 synapse during experimentally induced hypoxia, thereby suggesting a compensatory switch to presynaptic mechanisms. Furthermore, GYS1^Nestin-KO mice showed greater susceptibility to hippocampal seizures and myoclonus following the administration of kainate and/or a brief train stimulation of Schaffer collaterals. We conclude that brain glycogen could play a protective role both in hypoxic situations and in the prevention of brain seizures.

Influences of hyperbaric oxygen on blood pressure, heart rate and blood glucose levels in patients with diabetes mellitus and hypertension

BACKGROUND

We investigated the influences of hyperbaric oxygen (HBO(2)) on systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR) and blood glucose level (BGL).

METHODS

Forty one patients with hypertension (HTN), diabetes mellitus (DM), HTN and DM and/or no HTN or DM underwent HBO(2) sessions (15-40 sessions for each patient). SBP, DBP, HR and BGL (for diabetics) were recorded before and after each session.

RESULTS

HBO(2) caused significant elevation in SBP (11%) and DBP (12%) and a decrease in HR (18%) (p <0.001). Patients with DM and HTN showed higher elevation in SBP and DBP. HBO(2) lowered BGL by 23% (p <0.001). When basal BGL was in the range of 120-170 mg/dl, it dropped to <100 mg/dl in 31/60 treatment sessions (52%). When basal BGL was <120 mg/dl it dropped to <70 mg/dl in 8/34 sessions. There was a possibility of lowered BGL when basal BGL was <170 mg/dl and a marked reduction in BGL occurred when basal BGL was <120 mg/dl. HBO(2) caused a marked elevation in SBP and DBP when basal SBP was >140 mmHg. Critical elevation was obtained when SBP was >160 mmHg. The use of beta blockers caused significant elevation of blood pressure while reducing HR.

CONCLUSIONS

HBO(2) causes elevation of blood pressure and lowering of HR and BGL, which were augmented in the presence of HTN, DM, or beta blocker. The use of beta blockers for the management of HTN should be avoided during HBO(2) therapy.

Effects of some quinolones on imipenem-induced seizures in DBA/2 mice

1. The behavioural and convulsant effects of imipenem, a carbapenem derivative, were studied after i.p. administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures and in Swiss mice. 2. It was found that DBA/2 mice were more susceptible to seizures induced by imipenem than Swiss mice. 3. The proconvulsant effects of some quinolones were also evaluated in DBA/2 mice on seizures evoked by means of i.p. administration of imipenem. The present study demonstrated that the order of proconvulsant activity in our epileptic model was pefloxacin > enoxacin > ofloxacin > nalidixic acid > rufloxacin > norfloxacin > ciprofloxacin > cinoxacin > temafloxacin. 4. The relationship between the chemical structure and the proconvulsant activity of quinolone derivatives was studied. The relationship between the lipophilicity and the proconvulsant activity was also investigated. 5. Although the main mechanism for seizure potentiation cannot be easily determined potential drug interactions exist. It has been reported that imipenem and quinolones are all believed to increase excitation of the central nervous system by inhibition of GABA binding to receptors. 6. A slow clearance from the central nervous system and from the kidney may also occur following the concomitant administration of some quinolones and imipenem.

Quinolones potentiate cefazolin-induced seizures in DBA/2 mice

The behavioral and convulsant effects of cefazolin, a beta-lactam derivative, were studied after intraperitoneal administration to DBA/2 mice, a strain genetically susceptible to sound-induced seizures, and Swiss mice. DBA/2 mice were more susceptible to seizures induced by cefazolin than were Swiss mice. The proconvulsant effects of some quinolones on seizures evoked by intraperitoneal administration of cefazolin were also evaluated in DBA/2 mice. Our study also demonstrated that the order of proconvulsant activity in our epileptic model was pefloxacin > enoxacin > ofloxacin > rufloxacin > norfloxacin > cinoxacin > ciprofloxacin > nalidixic acid. The relationships between the chemical structures and proconvulsant activities of quinolone derivatives were studied. The relationship between lipophilicity and proconvulsant activity was also investigated.

Audiogenic seizure susceptibility: inhibitory effect of glucose injection is counteracted by prior glucose

Audiogenic seizure susceptibility was examined in SJL/J mice injected with glucose 15-30 min before priming and/or subsequent tests. The obtained results confirm previous reports that glucose will inhibit seizure activity if given shortly before a test. In addition, it was found that glucose give 2-4 days previously would counteract the inhibitory effect of glucose injected shortly before testing.

Differential prostaglandin formation induced by convulsions in the brain of mice susceptible (DBA/2J) and resistant (CFLP) to acoustic stimulation

Endogenous cerebral prostanoids possess anticonvulsant properties. This study investigates possible age-dependent anomalies of prostanoid synthesis in the brain of seizure-prone DBA/2J (DBA2) mice as compared to sound stimulus-resistant CFLP mice. Irrespective of the age of the animals, a large increase of prostaglandin (PG) D2 and E2 in the brain of CFLP mice was observed in response to pentylenetetrazol (PTZ)-, or electroshock (ES)-induced seizures. Significantly less PGD2 and PGE2 was formed in the brain of DBA2 mice at day 21 after birth when subjected to PTZ or ES convulsions. At 42 days of age, however, this deficit of cerebral PGD2 synthesis in DBA2 mice disappeared concomitantly with the age-related decrease in audiogenic seizure (AS) susceptibility, whereas the deficit of PGE2 formation persisted. These results suggest that a deficiency of cerebral PGD2 synthesis may be one of the factors responsible for the AS susceptibility of the DBA2 mice. In contrast to PTZ or ES convulsions, acoustically induced seizures of the DBA2 mice were not accompanied by cerebral prostanoid synthesis. This supports the view that the pathways involved in AS are different from those involved in PTZ or ES models of epilepsy.