mental depression is caused by diminished activity of :

Options

A. Histamine
B. Norepinephrine
C. Dopamine
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Mental Depression**:
- Mental depression is a mental disorder characterized by a persistent low mood, loss of interest in daily activities, and feelings of sadness and dullness.

2. **Role of Neurotransmitters**:
- Neurotransmitters are chemicals in the brain that transmit signals between neurons. They play a crucial role in regulating mood and emotional responses.

3. **Key Neurotransmitters Involved**:
- The main neurotransmitters associated with mental depression include serotonin, norepinephrine, and dopamine. A decrease in the activity of these neurotransmitters can lead to symptoms of depression.

4. **Histamine's Role**:
- Histamine is known to stimulate the release and activity of neurotransmitters such as serotonin, norepinephrine, and dopamine. If histamine levels are low, it can lead to diminished activity of these neurotransmitters.

5. **Analyzing the Options**:
- **Option 1: Histamine** - While histamine itself stimulates neurotransmitters, it is not the primary cause of depression.
- **Option 2: Norepinephrine** - Diminished activity of norepinephrine is directly linked to depression.
- **Option 3: Dopamine** - Similar to norepinephrine, decreased dopamine activity is also associated with depression.
- **Option 4: All of the above** - Since both norepinephrine and dopamine are implicated in depression, and histamine affects their activity, this option is correct.

6. **Conclusion**:
- The correct answer to the question "mental depression is caused by diminished activity of" is **Option 4: All of the above**.