Postoperative cognitive dysfunction (POCD) and postoperative delirium occurs mainly in aged patients. POCD and POD may increase the mortality and morbidity. However, the mechanism of POCD is not clear yet and no effective therapy method was proved. According to previous study, the neuroinflammation is the main reason both for POCD and POD. Minocycline is a tetracycline derivative. Due to it's lipophilic structure, it is easy to pass through blood brain barrier and attenuate neuroinflammation. It's neuroprotective effects has been proven in many experimental animal models such as Alzheimer's disease, Huntington's disease and Parkinson's syndrome. In present study, the investigators hypothesized that minocycline would attenuate the incidence of POCD and POD in the aged patients.

For the placebo and minocycline group;

Inclusion Criteria:

1. Elder than 65 years old
2. Speak Chinese Mandarin
3. Those who will undergo major general surgery like colorectal cancer excision, major urinary surgery like radical prostatectomy and radical nephrectomy
4. Signed the inform consent
5. American Society of Anesthesiologists classification I to III

Exclusion Criteria:

1. Existing cerebral disease, or have a history of neurological and psychiatric diseases including Alzheimer Disease, stroke, epilepsy and psychosis;
2. Existing cognitive impairment as evidenced by Mini-Mental State Examination scores below 24;
3. Severe audition or vision disorder;
4. Unwillingness to comply with the protocol or procedures.
5. Cannot communicated with Chinese Mandarin
6. With severe skin disease
7. Serious heart or liver or renal insufficiency patients
8. Had surgery in the past 30 days
9. Allergy to tetracycline or minocycline

For the health volunteers;

Inclusion Criteria:

1. Elder than 65 years old
2. Speak Chinese Mandarin
3. Signed the inform consent
4. No major disease health people

Exclusion Criteria:

1. Existing cerebral disease, or have a history of neurological and psychiatric diseases including Alzheimer Disease, stroke, epilepsy and psychosis;
2. Existing cognitive impairment as evidenced by Mini-Mental State Examination scores below 24;
3. Severe audition or vision disorder;
4. Unwillingness to comply with the protocol or procedures.
5. Cannot communicated with Chinese Mandarin
6. Drug abuse, alcoholism
7. Serious heart or liver or renal insufficiency patients
8. Had surgery in the past 30 days
9. Plan to undergo surgery in the following 3 months.