NEW YORK ( TheStreet) -- Shares of Orexigen Therapeutics ( OREX) were surging on higher volumes in Monday forenoon trading as the stock seeks to regain ground.

The stock has been extremely volatile over the past week. It sank 72% to $2.50 last Tuesday after U.S. regulators unexpectedly denied approval of its obesity drug Contrave.

Even savvy hedge fund trader Steven Cohen's SAC Capital Advisors, which picked up a 5% stake in the company a day ahead of the FDA decision, was caught by surprise. Buying, however, once again resumed in the stock starting Wednesday, with the share price rebounding to $3.61 on Friday. The stock was last up 8.7% at $3.94. Over 12 million shares were changing hands.

China MediaExpress ( CCME) was in the spotlight after CEO Zheng Cheng defended the company against what he said was an attack by short sellers. Shares were up 4.7% to $14.55 after the CEO wrote in a letter to shareholders that short sellers "timed and coordinated their efforts" in "reckless and baseless attacks" against the company. Earlier, the stock rose to as high as $15.94.

Last week, Muddy Waters Research accused China MediaExpress of "engaging in a massive 'pump-and-dump' scheme whereby it significantly inflates revenue and profits in order to enrich management through earn-outs and stock sales." Citron Research and Bronte Capital also released similarly bearish reports on China MediaExpress on Jan. 31 and Feb. 1, respectively.

The biggest gainer among small-cap stocks was surgical-equipment maker Emergent ( LZR). Shares were soaring 38% to $8.41 on volumes of about 300,000 shares after Universal Hospital said it will make a cash tender offer for the company at $8.76 per share after a customary 21-day go shop period. However Emergent is already being served with lawsuits for possible breaches of fiduciary duties by the board in connection to the sale.

Among the more actively-traded stocks (those with a volume of 1 million or more), uranium mining company Crosshair Exploration ( CXZ) was attracting interest. Shares were up 12% at $2.49. Denison Mines ( DNN - Get Report), another miner of uranium, saw its shares rise 5% at $4.16 respectively.

Shares of US Airways ( LCC) were rising 4.8% to $9.67 after Southwest Airlines ( LUV) reported strong traffic in January. Last week, US Airways reported a 7% growth in revenue per average seat mile.

Shares of KV Pharmaceutical ( KV-A) climbed another 9% on Monday to $4 after regulatory approval of its drug Makena, used to reduce the risk of preterm birth in pregnant women, sent shares up 130% on Friday.

Shares of real estate investment trust Gramercy Capital ( GKK), mobile data services provider Motricity ( MOTR) and fiber optics and photovoltaics player Emcore ( EMKR) were also up smartly on Monday's session.

--Written by Shanthi Bharatwaj in New York

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