Crucial supportive evidence for the theory was given by studies showing that classical degenerative brain changes were largely absent, by the presence of microscopic brain changes indicative of abnormal brain development, and by the absence of clear evidence for progressive ventricular dilatation among schizophrenia subjects. It is possible that the microscopic neuropathological changes described in schizophrenia may be vulnerable factors for schizophrenia. Alternatively, they could be an intrinsic component or a consequence of illness. Neuropathological studies cannot tell which interpretation is correct. However, there are some important similarities in the neuropathology of schizophrenia, major depressive disorder (MDD) and bipolar disorder (BPD), which suggest that a common process of change is involved in each disorder. There are several lines of investigation that support the view that glucocorticoid-related neurotoxicity may be implicated in depression and schizophrenia. The glial deficit found in these disorders may also relate to glucocorticoid effects.