Spontaneously hypertensive rats are highly vulnerable to AMPA-induced brain lesions.

BACKGROUND AND PURPOSE: Whereas the effects of chronic arterial hypertension on the cerebral vasculature have been widely studied, its effects on brain tissue have been studied less so. Here we examined if spontaneously hypertensive rats (SHRs) or the normotensive control Wistar Kyoto rats (WKYs) made hypertensive by renal artery stenosis (R-WKYs) are vulnerable to an excitotoxic brain lesion provoked by an overactivation of glutamate receptors. METHODS: Lesion volumes were quantified by histology in WKYs and SHRs subjected to striatal administration of N-methyl-d-aspartate (NMDA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA). The expression of AMPA receptors subunits and calcium/calmodulin kinase-II alpha was analyzed by real-time polymerase chain reaction and Western blot. RESULTS: NMDA (50 and 75 nmol) induced similar lesions in both SHRs (10+/-2 mm(3) and 16+/-4 mm(3), respectively) and WKYs (11+/-2 mm(3) and 19+/-7 mm(3), respectively). However, AMPA-induced (2.5 and 5 nmol) lesions were significantly greater in 14-week-old SHRs (14+/-3 mm(3) and 20+/-5 mm(3), respectively) than WKYs (4+/-2 mm(3), P<0.05 and 7+/-4 mm(3), P<0.001, respectively). Furthermore, normotensive 7-week-old SHRs also displayed an aggravated AMPA-induced lesion compared with age-matched WKYs (10+/-3 mm(3) vs 6+/-3 mm(3); P<0.05). Neither NMDA nor AMPA produced increased lesion volumes in R-WKYs (12+/-3 mm(3) and 5+/-4 mm(3), respectively) compared with WKYs. Striatal levels of AMPA receptors subunits, GluR1 and GluR2, were not different between SHRs and WKYs. However, SHRs displayed an increase in phosphorylated form of GluR1 at Ser-831 (P<0.05), as well as in calcium/calmodulin kinase-II alpha (P<0.002). Selective inhibition of this kinase by KN-93 reduced AMPA-induced damage in SHRs (P<0.01 vs vehicle). CONCLUSIONS: These findings show that an increase in phosphorylated GluR1, which increases AMPA receptor conductance, may be involved in the vulnerability of SHRs to AMPA.

Involvement of the alpha 7 subunit of the nicotinic receptor in morphogenic and trophic effects of acetylcholine on embryonic rat spinal motoneurons in culture.

The morphogenic and trophic effects of acetylcholine (ACh) on embryonic cultured rat spinal cord motoneurons (MNs) through nicotinic alpha7 autoreceptors were assessed. Alpha7 Subunits of the nicotinic cholinergic receptor were detected in cultures of purified rat spinal embryonic MNs sampled at E15, by both immunocytochemistry and alpha-bungarotoxin binding. According to these two methods, alpha7 subunits are located mainly at somatic and axonal membrane. Functional involvement of the alpha7 subunit in survival and development of morphological properties of growing cultured MNs was tested using an antisense strategy. The antisense oligonucleotide significantly decreases the expression of the alpha7 protein compared with control and mismatch oligonucleotide-treated cultures. This decrease in the expression of the alpha7 protein leads to a significant increase in the number of axonal branches and in the length of the axon. The antisense treatment also induces, as early as the first day in culture, a decrease of MN survival, leading to total cell death at day 5. TUNEL staining revealed that the MNs are dying through apoptotic processes. Thus, our study shows that ACh is a morphogenic and trophic factor. These effects are directly linked to the membrane expression level of alpha7 protein. Indeed, the lower the alpha7 expression, the lower the inhibition of axonal growth (i.e., axonal elongation) and the lower the MN survival.