Multiple kainic acid seizures in the immature and adult brain: ictal manifestations and long-term effects on learning and memory

PURPOSE: While there is increasing evidence that the adverse effects of prolonged seizures are less pronounced in the immature than in the mature brain, there have been few investigations of the long-term effects of recurrent seizures during development. This study examined the effects of multiple administrations of the convulsant kainic acid (KA) on seizure characteristics and spatial learning as a function of brain development. METHODS: To determine the long-term effects of serial KA seizures during ontogeny, saline or convulsant doses of KA were given intraperitoneally 4 times, at 2-day intervals. Immature rats were given KA on P20, P22, P24 and P26; adult rats got KA on P60, P62, P64 and P66. Ictal characteristics and EEGs were recorded. To examine the effects of multiple KA seizures on the retention of spatial learning, water maze testing was performed before (immature group: from P16-19, adult group: from P56-P59) and after (immature: from P60-P63, adult: from P100-P103) KA injections. Finally, histology was performed to compare KA-induced damage at each age. RESULTS: In immature animals, serial KA administration resulted in seizures with a progressively longer onset latency and decreased severity. In contrast, KA serially administered to adult rats caused severe seizures after each of the 4 injections. In immature rats, epileptiform EEG changes were most prominent after the first KA injection, whereas in adults, prolonged paroxysmal EEG patterns were seen after all 4 KA injections. Before KA, both rat pups and adults acquired place learning in the water maze. One month after the final KA injection, there was no deficit in spatial learning retention in the immature group, whereas the adult group had profound impairment compared to age-matched, saline-injected controls. Histology revealed no lesions in immature rats treated multiple times with KA but profound cell loss in hippocampal fields CA4, CA3 and CA1 in rats treated serially with KA as adults. CONCLUSIONS: Previous studies have shown that a single KA injection causes prolonged status epilepticus (which persists for several hours), leading to severe histologic and behavioral sequelae in adult rats but not in pups. Our study extends those findings, demonstrating that immature rats are spared the cognitive and pathological sequelae of multiple injections of convulsant doses of KA as well.     

Travelling-wave erbium fibre ring laser with 60 kHz linewidth

Operation of an erbium-doped-phospho-alumino-silicate-fibre ring laser in a unidirectional travelling-wave configuration enables narrow linewidth, single frequency emission to be obtained at a wavelength of 1.555 mu m. A 60 kHz linewidth has been measured.<>     

Stress softening in natural rubber vulcanizates. Part V. The anomalous tensile behavior of natural rubber

Stress-strain cycling of natural rubber to high strains produces greater softening than amorphous rubbers, but only if the force on the sample is relaxed below a certain value during the cycle. This phenomenon, attributed to crystallization shows why nonrelaxing tests give a longer fatigue life than relaxing tests.     

Pyruvate carboxylase as a model for oligosubstituted enzyme-ligand conjugates in homogeneous enzyme immunoassays

Theoretical models suggest that the detection capabilities of homogeneous enzyme immunoassays can be improved by the use of oligosubstituted enzyme-ligand conjugates rather than the traditionally used multisubstituted ones. The natural form of pyruvate carboxylase contains four covalently bound biotins (one per subunit) and it can be considered as an oligosubstituted enzyme-biotin conjugate. The enzyme is nearly completely inhibited in the presence of the natural binder for biotin, avidin. When the enzyme is incubated with avidin and free biotin, a competition occurs between the free biotin and the prosthetic group of the enzyme for the avidin. Steep dose-response curves are obtained by relating the observed inhibition to the free biotin concentration. By variation of the amount of avidin or enzyme in the assay, the detection limits of the system can be altered allowing for sensitive determinations over a wide range of biotin concentrations. Such data from real sample analysis of several vitamin supplements are reported.     

Basophilic meningitis secondary to lymphoma

In this case report of basophilic meningitis, the patient was a 5-year-old girl under treatment for a diffuse lymphocytic lymphoma. She presented with headache and bilateral papilledema. Cerebrospinal fluid examination showed 60 percent basophils. Subsequent specimens showed a rare blast. It is postulated that after the lymphoma cells had spread to the meninges, a cell-mediated immune reaction was initiated with the appearance of basophils in the exudate.