While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of AstraZeneca (NYSE:AZN) climbed 1.5% today, after Bank of America upgraded the drug giant from "underperform" to "neutral."

So what: Along with the upgrade, analyst Sachin Jain boosted his price target to $55.20 (from $48.82), representing about 5% worth of upside to yesterday's close. While Jain believes that AstraZeneca's valuation remains steep on long-term P/E basis, he believes that the stock has enough looming catalysts to prevent it from falling too far, too fast.

Now what: B of A doesn't expect EPS to bottom out until 2017, when Crestor is set to expire, but it offered two reasons for some possible short-term strength:

1. We believe the consensus EPS downgrade cycle is closer to the bottom, and

2. Pipeline newsflow (product launches, PIII and PII) picks up significantly into next year, particularly important given AZN has been devoid of product newsflow for years.

So while long-term value investors should keep away from AstraZeneca's seemingly lofty valuation, momentum investors might do well to ride the stock's recent surge into 2014. 

Fool contributor Brian Pacampara has no position in any of the stocks mentioned. The Motley Fool recommends and owns shares of Bank of America. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.