Distinct transcriptional responses of mouse sensory neurons in models of human chronic pain conditions

Background: Sensory neurons play an essential role in almost all pain conditions, and have recently been classified into distinct subsets on the basis of their transcriptomes. Here we have analysed alterations in dorsal root ganglia (DRG) gene expression using microarrays in mouse models related to human chronic pain. Methods: Six different pain models were studied in male C57BL/6J mice: (1) bone cancer pain using cancer cell injection in the intramedullary space of the femur; (2) neuropathic pain using partial sciatic nerve ligation; (3) osteoarthritis pain using mechanical joint loading; (4) chemotherapy-induced pain with oxaliplatin; (5) chronic muscle pain using hyperalgesic priming; and (6) inflammatory pain using intraplantar complete Freund's adjuvant. Microarray analyses were performed using RNA isolated from dorsal root ganglia and compared to sham/vehicle treated controls. Results: Differentially expressed genes (DEGs) were identified. Known and previously unreported genes were found to be dysregulated in each pain model. The transcriptomic profiles for each model were compared and expression profiles of DEGs within subsets of DRG neuronal populations were analysed to determine whether specific neuronal subsets could be linked to each of the pain models.  Conclusions: Each pain model exhibits a unique set of altered transcripts implying distinct cellular responses to different painful stimuli. No simple direct link between genetically distinct sets of neurons and particular pain models could be discerned.

Seasonal variation in bacterial pathogens isolated from stool samples in Karachi, Pakistan

OBJECTIVE

To determine the seasonal variation of the commonly isolated bacterial pathogens in stool samples.

MATERIAL AND METHODS

A retrospective descriptive study was undertaken of all the stool samples submitted from within Karachi to the Aga Khan University Hospital Laboratory over a period of five years (January 1997- December 2001) in order to determine the commonly isolated bacterial pathogens and to predict their seasonal variation.

RESULTS

A total of 16379 stool samples were included in this review. Bacterial isolates were found in 6670 stool samples (culture detection rate=40.7%). The mean age at the time of culture of each sub-group was < or = 1 year group (6.58 +/- 3.1 months), 1-5 years (2.13 +/- 0.94 years), 5-14 years (8.3 +/- 2.6 yrs) and adults (43.2 +/- 18.5 years). Male: Female ratio was 1.2:1. Vibrio cholera 01 Ogawa (32.8%), Campylobacter jejuni (17.3%), Enteropathogenic Escherichia coli (9.9%), Salmonella paratyphi b (6.6%) and Shigella flexneri (6.2%) were the most common organisms isolated. These organisms show a distinct seasonal variation with summer predilection.

CONCLUSION

In contrast to the previous studies from South Asia, which have identified E. coil, followed by Vibrio cholerae as the most common enteric isolates, we found Vibrio cholera 01 Ogawa followed by Campylobacter jejuni as the most common enteric pathogens isolated in an urban setting. It is important to consider seasonal variation when empirically treating diarrheal diseases in our region.

Pragmatic solutions for problems in the undergraduate medical programmes in Pakistan

Reforms in the Pakistani undergraduate medical education have remained elusive for decades. An attempt is made to highlight the importance of research-oriented education and problem-based learning to Pakistani medical schools. Possible causes are analyzed and implementable solutions are suggested with appropriate references from literature search. An innovative "Research Ladder" approach to implementing a research-oriented curriculum that culminates in attainment of a combined MBBS-BRS degree is also proposed. In the end, techniques for making existing lecture-based learning more interactive are suggested.