In vivo microdialysis and gas chromatography/mass spectrometry for studies on release of N-acetylaspartlyglutamate and N-acetylaspartate in rat brain hypothalamus

Microdialysis and gas chromatography/mass spectrometry was used for the measurement of extracellular N-acetylaspartate (NAA) and N-acetylaspartylglutamate (NAAG) in rat hypothalamus. The sensitivity of the method for each of these compounds was approximately 5 pmol/30 microliters of dialysate. Baseline NAA concentrations in dialysate were estimated to be approximately 25 pmol/36 microliters, while that for NAAG was at or below the detection limit of 5 pmol/ 36 microliters. In vivo and in vitro calibrations of microdialysis probes showed that the recovery for NAA was approximately 10 percent. For NAAG, the in vitro recovery was 6.3%, and in vivo recovery, 11%. Depolarization stimulation using 100 mM KCl in the microdialysis perfusate was employed to measure extracellular NAA and NAAG concentrations. Extracellular NAA was elevated to approximately 70 pmol/36 microliters dialysate following depolarization. No significant elevation of NAAG was observed. By infusing known amounts of stable isotopically labeled NAAG-d3 via the microdialysis probe and measuring the isotopically labeled catabolic product, NAA-d3, in collected microdialysate, we were able to confirm the existence of one or more hydrolytic enzymes active towards NAAG in the hypothalamus. This finding suggest the possible involvement of active metabolic processes in the relationship between NAAG and NAA releases.     

Patterns of psoriatic arthritis in Orientals

OBJECTIVE: To determine the clinical features of psoriatic arthritis (PsA) in a multiethnic Oriental population and to study the effect of ethnicity on disease patterns. METHODS: A retrospective study of 80 patients with PsA seen at either a rheumatology or dermatology referral center. Patients and case records were reviewed and data abstracted according to a standard protocol. Eighty consecutive patients with psoriasis without PsA seen at the dermatology center were recruited as controls. RESULTS: Asymmetric polyarthritis developing in the 4th decade with an equal male to female ratio was the commonest pattern of arthritis among Chinese, Indians, and Malays. Clinically apparent lumbar spondylitis was significantly more common in Indians than Chinese (10/11 vs 11/20, respectively; p = 0.046), although the prevalence of lumbar spondylitis was similar in all ethnic groups. Eighty-nine percent of subjects required nonsteroidal antiinflammatory drugs and 51% required disease modifying antirheumatic drugs at some time for control of joint disease. PsA was significantly more common among Indians compared to the ethnic distribution of the Singapore population (p < 0.000001). Multiple logistic regression identified Indian ethnicity as a risk factor for the development of PsA (OR 2.39, 95% confidence interval 1.02 to 5.60). CONCLUSION: The commonest pattern of PsA in all ethnic groups was asymmetric polyarthritis. Ethnicity affected the development and presentation of PsA in our series: Indians with psoriasis had double the risk of developing PsA compared to Chinese with psoriasis, and lumbar spondylitis when present in Chinese subjects was asymptomatic in 45%, being detectable only on radiological examination.