1. The effects of intraperitoneal injections of 10 mg/kg harmaline were tested in normal mice and three strains of cerebellar mutant mice with Purkinje cell degeneration. Ten normal (wild-type) mice (+/+), as well as five lurcher (lc/+), six nervous (nr/nr), and eight Purkinje cell degeneration (pcd/pcd) mutants were implanted with chronic electromyogram (EMG) electrodes in the hamstring and quadriceps muscle groups of the right hindlimb. 2. EMGs were recorded in each of the mice during spontaneous activity before and after intraperitoneal injections of 0.3 ml harmaline (10 mg/kg). Spectral analysis was used to quantify the amplitude and frequency of tremor found in the EMGs after harmaline administration. Normal mice responded to harmaline with strong, continuous 11- to 14-Hz tremor. Mutants from the pcd/pcd strain also reacted with continuous tremor, but of lower amplitude and frequency. In contrast, nr/nr mutants exhibited intermittent paroxysmal tremor lasting for only a few seconds, and lc/+ mutants showed no evidence of tremor whatsoever. 3. In order to detect covert tremor that was possibly not revealed by focal intramuscular EMG recordings, several mutant and normal mice were also tested on a suspended platform to which an accelerometer was attached. The results confirmed the findings from EMG recordings. 4. An incidental observation made during the course of this study was that harmaline tremor disappeared from the normal mouse during swimming and reappeared when the animal was withdrawn from the water. 5. Although Purkinje cells appeared to increase both the depth of modulation and the frequency of tremor, the inhibitory action of the cerebellar cortex does not seem to be essential for the generation of tremor. 6. Parasagittal cerebellar sections of the normal, wild-type mice and the three strains of cerebellar mutant mice of various ages were stained with cresyl violet and examined for Purkinje cell degeneration. Purkinje cell degeneration was found to be complete in the pcd/pcd and lc/+ strains. Although an initial examination of parasagittal sections of the nr/nr strain failed to find any surviving Purkinje cells, further examination of sections cut in the coronal plane revealed small clusters of Purkinje cells in the vermal area of the posterior lobe. 7. The retrograde transport of wheat-germ-agglutinin-conjugated horseradish peroxidase (WGA-HRP) pressure-injected into the cerebellar cortex was used to study the olivocerebellar projections in the wild-type mice and the three strains of cerebellar mutant mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Lithium diiodosalicylate (LIS) was used to selectively solubilize proteins from purified intestinal brush border membrane vesicles. Incubation of the vesicles with increasing concentrations of LIS resulted in the progressive release of proteins with total disruption of the membranes being obtained at 200 mM. Maximum selectivity was observed at 20-30 mM LIS which preferentially released actin and other non-glycosylated proteins while all the glycoproteins remained associated with the membrane. Electron micrographs showed that, after LIS treatment, brush border vesicles are partially disrupted and have lost their inner core of microfilaments. Sucrase, trehalase, leucylnaphthylamide hydrolase, gamma-glutamyl transpeptidase and alkaline phosphatase all retained more than 70% of their activities and remained associated with the membrane fraction after LIS solubilization (30 mM). The results indicate that lithium diiodosalicylate treatment provides an efficient method for the separation of cytoskeletal proteins from intrinsic membrane glycoproteins and should be very useful for the purification of microvilli proteins and for the study of membrane-protein interactions.