The basal ganglia are deep gray-matter brain nuclei which modulate the performance of motor tasks in series and in parallel with the cerebellum and motor cortex. Dysfunction of these structures is clinically associated with a specturm of neurological illnesses which include Huntington's disease (caudate), Parkinson's disease (substantia nigra), and the dystonias (putamen and globus pallidus). Neurochemical methods have advanced our understanding of transmitter systems which are concentrated in te basal ganglia, most notable dopamine (substantia nigra) and somatostatin (caudate). Evidence has recently accumulated that a group of heretofore uncharacterized neuron-specific phosphoproteins is highly restricted to the basal ganglia. Nine such proteins have been identified: except for a protein of apparent molecular weight of 32,000 (DARPP-32), the details of their structure and function is unknown. The likelihood of their importance may be implied by te critical roles known to be played by phosphoproteins in neurotransmittersynthesis and intracellular signal transduction. The study of the pohosphoproteins will certainly lead us to a better understanding of basal ganglionic structure, function, organization and disease. The prototype protein, DARPP-32, has been prepared and studied by an approach analogous to that outlined herein for another phosphoportein, called ARPP-40. The successful isolation and biochemical and physiological characterization of DARPP-32 attests to the potential for application of these techniques to ARPP-40. ARPP-40 will be purified to homogeneity from bovine caudate and extensively characterized by protein chemical tehcniques. Antibodies will be prepared against purified ARPP-40 and used for radioimmunossays as well as immunocytochemical studies. Immunolocalization of ARPP-40 will be compared with that of known neural antigens such as tyrosine hydroxylase, synapsin I, and glutamate decarboxylase. ARPP-40 holoprotein and peptide fragments will be examined for activity as a phosphatase inhibitor, a known feature of DARPP-32. Rat brain slices will be used to study the effects of depolarizing agents, neurotransmitter candidates and various drugs on ARPP-40 and its state of phosphorylation. The effect of supplementation of ARPP-40 on the physiological characteristics of medium spiny neurons will be examined by intracellular microinjection. Finally, the potential role of ARPP-40 in human disease will be examined by the preparation of profiles of ARPP-40 levels by radioimmunoassay of samples from the serum and spinal fluid of normals and patients suffering from neurological lesions, especially of the basal ganglia.