(ShareCast News) - The FTSE 250 showed a few green islands of buoyant investor sentiment, compared to the red sea of the FTSE, though the index was well in negative territory on Monday like all its counterparts around the globe.By 1600, London's the mid-cap index was down 3.44% at 16,295.98 points.Those islands in the storm included AO World, the top performer across the FTSE 350 on Monday. The stock is one of the index's perennially volatile seesaw shares.Clothing retailer N Brown bounced back after a sharp fall on Friday. It may have been slightly helped by a positive note from broker Singer which upgraded to 'buy'p fall. "We believe management strategy is on track with next news the interims on 14 October - no pre-close statement is expected. Given the phasing of costs and the bias of negative margin guidance to the first half, we forecast sales +4.1% and a 14.7% decline in first half profit before tax to £35.5m."The biggest fallers included several commodities stocks, with Premier Oil and Tullow Oil as oil prices traded as low as $38.13 for WTI, its lowest since the financial crisis.Poundland was another badly hit. On Tuesday the Competition and Markets Authority will announce the provisional findings report into Poundland's acquisition of rival 99p Stores. Earlier in August, broker Jefferies upgraded the shares to a 'buy' rating and said it expected the CMA's provisional findings statement will lead to a re-rating of Poundland's, predicting the FTSE 250 company will only be forced to divest at most 80 of the estate of 99p storesNMC Health was abother big faller, despite confirmation that it had opened another hospital in the United Arab Emirates. The company is due to publish interim results on Wednesday. FTSE 250 - RisersAO World (AO.) 125.90p +2.86%Brown (N.) Group (BWNG) 306.20p +2.65%Wetherspoon (J.D.) (JDW) 742.00p +0.82%Computacenter (CCC) 752.50p +0.47%Rank Group (RNK) 262.30p +0.19%FTSE 250 - FallersPremier Oil (PMO) 90.40p -12.40%Evraz (EVR) 76.80p -9.06%Tullow Oil (TLW) 185.20p -8.63%Poundland Group (PLND) 322.70p -7.67%Kaz Minerals (KAZ) 162.60p -7.61%Telecom Plus (TEP) 1,013.00p -7.49%Redefine International (RDI) 50.60p -7.33%Hunting (HTG) 392.10p -6.69%Genesis Emerging Markets Fund Ltd Ptg NPV (GSS) 401.50p -6.67%NMC Health (NMC) 708.50p -6.65%