TMTPOST--Nissan has revised its profit forecast for the full fiscal year downward, following a 73% drop in profit for the April-June quarter compared to the previous year.  The company's chief executive Makoto Uchida described the results as "very challenging," attributing the decline to increased sales incentives and marketing expenses due to fierce competition, particularly in the U.S. market. Following the earnings announcement, Nissan's stock price fell sharply on the Tokyo Stock Exchange, closing nearly 7% lower.