Evaluation of a modified infraorbital approach for a maxillary nerve block for rhinoscopy with nasal biopsy of dogs.

OBJECTIVE To determine whether a maxillary nerve block via a modified infraorbital approach, applied before rhinoscopy and nasal biopsy of dogs, would decrease procedural nociception, minimize cardiorespiratory anesthetic effects, and improve recovery quality. ANIMALS 8 healthy adult hound-type dogs PROCEDURES In a crossover study, dogs received 0.5% bupivacaine (0.1 mL/kg) or an equivalent volume of saline (0.9% NaCl) solution as a maxillary nerve block via a modified infraorbital approach. A 5-cm, 20-gauge over-the-needle catheter was placed retrograde within each infraorbital canal, and bupivacaine or saline solution was administered into each pterygopalatine region. Rhinoscopy and nasal biopsy were performed. Variables monitored included heart rate, systolic arterial blood pressure (SAP), mean arterial blood pressure (MAP), diastolic arterial blood pressure (DAP), plasma cortisol and norepinephrine concentrations, purposeful movement, and pain scores. After a 14-day washout period, the other treatment was administered on the contralateral side, and rhinoscopy and nasal biopsy were repeated. RESULTS SAP, MAP, and DAP were significantly higher for the saline solution treatment than for the bupivacaine treatment, irrespective of the time point. Plasma cortisol concentrations after saline solution treatment were significantly higher 5 minutes after nasal biopsy than at biopsy. Heart rate, norepinephrine concentration, purposeful movement, and pain score were not significantly different between treatments. CONCLUSIONS AND CLINICAL RELEVANCE Maxillary nerve block via a modified infraorbital approach prior to rhinoscopy and nasal biopsy reduced procedural nociception as determined on the basis of blood pressures and plasma cortisol concentrations during anesthesia. These findings warrant further evaluation in dogs with nasal disease.

Tumor necrosis factor-alpha-elicited stimulation of gamma-secretase is mediated by c-Jun N-terminal kinase-dependent phosphorylation of presenilin and nicastrin.

Gamma-secretase is a multiprotein complex composed of presenilin (PS), nicastrin (NCT), Aph-1, and Pen-2, and it catalyzes the final proteolytic step in the processing of amyloid precursor protein to generate amyloid-beta. Our previous results showed that tumor necrosis factor-alpha (TNF-alpha) can potently stimulate gamma-secretase activity through a c-Jun N-terminal kinase (JNK)-dependent pathway. Here, we demonstrate that TNF-alpha triggers JNK-dependent serine/threonine phosphorylation of PS1 and NCT to stimulate gamma-secretase activity. Blocking of JNK activity with a potent JNK inhibitor (SP600125) reduces TNF-alpha-triggered phosphorylation of PS1 and NCT. Consistent with this, we show that activated JNKs can be copurified with gamma-secretase complexes and that active recombinant JNK2 can promote the phosphorylation of PS1 and NCT in vitro. Using site-directed mutagenesis and a synthetic peptide, we clearly show that the Ser(319)Thr(320) motif in PS1 is an important JNK phosphorylation site that is critical for the TNF-alpha-elicited regulation of gamma-secretase. This JNK phosphorylation of PS1 at Ser(319)Thr(320) enhances the stability of the PS1 C-terminal fragment that is necessary for gamma-secretase activity. Together, our findings strongly suggest that JNK is a critical intracellular mediator of TNF-alpha-elicited regulation of gamma-secretase and governs the pivotal step in the assembly of functional gamma-secretase.

Tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma stimulate gamma-secretase-mediated cleavage of amyloid precursor protein through a JNK-dependent MAPK pathway.

The deposition of the amyloid beta (Abeta) peptide in neuritic plaques plays a critical role in the pathogenesis of Alzheimer's disease (AD). Abeta is generated through the proteolysis of amyloid precursor protein (APP) by the sequential actions of beta- and gamma-secretases. Although recent evidence has unveiled much about the biochemical identity and characteristics of gamma-secretase, the mechanism regulating endogenous gamma-secretase activity remains elusive. To identify possible extracellular signals and associated signaling cascades that could regulate APP proteolysis by gamma-secretase activity, we have developed a cell-based reporter gene assay by stably cotransfecting HEK293 cells with the Gal4-driven luciferase reporter gene and the Gal4/VP16-tagged C-terminal fragment of APP (C99-GV), the immediate substrate of gamma-secretase. The cleavage of C99-GV by gamma-secretase releases the transcription factor that activates luciferase expression, providing a quantitative measurement of gamma-secretase activity. Using this reporter assay, we have demonstrated that interferon-gamma, interleukin-1beta, and tumor necrosis factor-alpha can specifically stimulate gamma-secretase activity, concomitant with increased production of Abeta and the intracellular domain of APP (AICD). The gamma-secretase-dependent cleavage of Notch is also enhanced upon the stimulation of these cytokines. The cytokine-enhanced gamma-secretase activity can be suppressed by a potent inhibitor of c-Jun N-terminal kinase (JNK). Furthermore, cells transfected with dominant-positive MEKK1, one of the most potent activators of the JNK cascade, exhibit increased gamma-secretase activity, suggesting that the JNK-dependent mitogen-activated protein kinase pathway could mediate the cytokine-elicited regulation of gamma-secretase. Our studies provide direct evidence that cytokine-elicited signaling cascades control Abeta production by modulating gamma-secretase activity.