Alterations in activity at dopamine synapses have been implicated in the development of: A. anxiety. B. schizophrenia. C. Alzheimer's disease. D. nicotine addiction.

Dopamine is a neurotransmitter that plays an important role in the brain, particularly in the reward, motivation, and motor control systems. Alterations in dopamine activity can lead to various psychological and neurological disorders.

A. Anxiety - Anxiety is mainly associated with alterations in the levels of other neurotransmitters, such as serotonin, norepinephrine, and GABA. Dopamine may play a role, but it's not the primary factor in anxiety development. B. Schizophrenia - Schizophrenia is closely associated with dopamine dysregulation, as increased dopamine activity is linked to the positive symptoms of the disorder (hallucinations, delusions, etc.), and decreased dopamine activity to the negative symptoms (lack of motivation, social withdrawal, etc.). C. Alzheimer's disease - Alzheimer's disease primarily involves the degeneration of brain cells and the accumulation of amyloid plaques and neurofibrillary tangles. Although dopamine may be involved in the cognitive decline associated with Alzheimer's, it is not the main neurotransmitter implicated in the disease's development. Instead, the main neurotransmitters implicated are acetylcholine and glutamate. D. Nicotine addiction - Nicotine addiction is partly related to dopamine, as the substance increases dopamine release in the brain's reward pathways. However, other neurotransmitters, such as acetylcholine and glutamate, also play a role in nicotine addiction.

Out of the four given options, the condition most closely related to alterations in dopamine activity is schizophrenia (Option B). This is because irregularities in dopamine functioning are directly related to the positive and negative symptoms of schizophrenia, making it the best answer choice.