Basically:

Life events involving goal-attainment (accepted to grad school), but not general positive events, can induce mania, but they are unrelated to changes in depression.

Negative life events (eg. death of close relative) can increase depression, but do not appear to induce mania.

Johnson, S. L., Sandrow, D., Meyer, B., Winters, R., Miller, I., Solomon, D., & Keitner, G. (2000). Increases in manic symptoms after life events involving goal attainment. Journal of Abnormal Psychology, 109(4), 721.

Johnson, S. L. (2005). Life events in bipolar disorder: towards more specific models. Clinical psychology review, 25(8), 1008-1027.