Hydrogen Sulfide Mediating both Excitatory and Inhibitory Effects in a Rat Model of Meningeal Nociception and Headache Generation

Background/purpose

Hydrogen sulfide (H₂S) is a neuromodulator acting through nitroxyl (HNO) when it reacts with nitric oxide (NO). HNO activates transient receptor potential channels of the ankyrin type 1 (TRPA1) causing release of calcitonin gene-related peptide from primary afferents. Activation of meningeal nociceptors projecting to the human spinal trigeminal nucleus (STN) may lead to headaches. In a rat model of meningeal nociception, the activity of spinal trigeminal neurons was used as read-out for the interaction between H₂S and NO.

Methods

In anesthetized rats extracellular recordings from single neurons in the STN were made. Sodium sulfide (Na₂S) producing H₂S in the tissue and the NO donor diethylamine-NONOate (DEA-NONOate) were infused intravenously. H₂S was also locally applied onto the exposed cranial dura mater or the medulla. Endogenous production of H₂S was inhibited by oxamic acid, and NO production was inhibited by nitro-l-arginine methyl ester hydrochloride (l-NAME) to manipulate endogenous HNO formation.

Key results

Systemic administration of Na₂S was followed either by increased ongoing activity (in 73%) or decreased activity (in 27% of units). Topical application of Na₂S onto the cranial dura mater caused a short-lasting activation followed by a long-lasting decrease in activity in the majority of units (70%). Systemic administration of DEA-NONOate increased neuronal activity, subsequent infusion of Na₂S added to this effect, whereas DEA-NONOate did not augment the activity after Na₂S. The stimulating effect of DEA-NONOate was inhibited by oxamic acid in 75% of units, and l-NAME following Na₂S administration returned the activity to baseline.

Conclusion

Individual spinal trigeminal neurons may be activated or (less frequently) inhibited by the TRPA1 agonist HNO, presumably formed by H₂S and NO in the STN, whereby endogenous H₂S production seems to be rate-limiting. Activation of meningeal afferents by HNO may induce decreased spinal trigeminal activity, consistent with the elevation of the electrical threshold caused by TRPA1 activation in afferent fibers. Thus, the effects of H₂S–NO–TRPA1 signaling depend on the site of action and the type of central neurons. The role of H₂S–NO–TRPA1 in headache generation seems to be ambiguous.

Overexpression of wild-type presenilin 2 or its familial Alzheimer's disease-associated mutant does not induce or increase susceptibility to apoptosis in different cell lines

Programmed cell death, or apoptosis, has been implicated in Alzheimer's disease. Mutations in the presenilin (PS) genes, PS1 and PS2, are a major cause of early-onset familial Alzheimer's disease (FAD). Previous studies have suggested that the PS play a role in apoptosis. However, the mechanisms whereby presenilins affect apoptosis and the relationship of FAD-associated presenilin mutants to the apoptotic effect have not been elucidated. In the present study, in an attempt to further explore the effect of PS2 on apoptosis we examined whether overexpression of wild-type or mutant PS2 can directly induce apoptosis or increase cell susceptibility to apoptosis in various cell lines, such as N2a, CHO, and HEK 293T. Wild-type or mutant PS2 was transiently transfected into these cell lines and the viability of the transfected cells was evaluated by their morphology, DNA fragmentation and condensation, appearance of sub-G(1/0) cells, and caspase activation. We also examined the susceptibility of the PS2-transfected cells to apoptosis induced by the apoptotic inducers staurosporine and H(2)O(2). Our results showed that overexpression of either wild type or mutant PS2 in these cell lines did not directly induce apoptosis or increase the susceptibility to apoptosis induced by staurosporine or H(2)O(2). Taken together, these results suggest that overexpression of PS2 does not cause pro-apoptotic effects, at least not in the cellular systems and conditions employed in this study, and therefore it seems unlikely that apoptosis plays a prominent role in the neuropathological effects of PS2 in Alzheimer's disease.

[Follow-up of psychiatric disorders and specific developmental delay disorders in special education students]

In a prospective longitudinal study 72 children who were attending a special school for children with learning disabilities in Erlangen were examined in 1990 and again in 1992/93. At the first examination the children's mean age was 7 years 1 month and at the second 8 years 10 months. The sample contained many more boys than girls. Reported here are the findings on the course of the psychiatric disorders and the specific developmental disorders of speech and language and motor function. There was a marked decrease in the prevalence of psychiatric disorders. Of the 17 children with a psychiatric disorder at follow-up, 13 (76%) also had a disorder at the start of the study and of the 23 with a psychiatric disorder at the start 13 (57%) still had a disorder at follow-up. Children with enuresis and those with disturbances of activity or attention had the best prognosis. The special school had a positive effect on conduct. The prevalence of specific developmental disorders also decreased over the two-year period. As expected, specific speech articulation disorders had the best prognosis. All other disorders had a poor prognosis. Increases in prevalence were mainly the result of different cutoff points for a given diagnosis at different ages. The high number of specific disorders of motor function at both time points is especially noteworthy.

[Intelligence and language performance of special education children at 7 and 9 years of age]

Prospective longitudinal data from children at a school for learning disabled were obtained. Intelligence and language scores were assessed at first grade and two years later. The results of two samples from Erlangen and München showed a high stability of the intelligence scores but less stability of the language scores. There were remarkable improvements in language comprehension. Expressive language had a constant lag compared with the test-standard of children of the same age; the articulation did improve as expected. The children from this special school still had problems with verbal short term memory.