The cerebellar cortex has a fundamental parasagittal organization that is apparent in the physiological response properties of Purkinje cells (PCs) and the expression of several molecular markers such as zebrin II (ZII). ZII is heterogeneously expressed in PCs such that there are sagittal stripes of high expression [ZII immunopositive (ZII+)] interdigitated with stripes of little or no expression [ZII immunonegative (ZII−)]. Several studies in rodents have suggested that climbing fiber (CF) afferents from an individual subnucleus in the inferior olive project to either ZII+ or ZII− stripes but not both. In this report, we show that this is not the case in the pigeon flocculus. The flocculus (the lateral half of folia IXcd and X) receives visual-optokinetic information and is important for generating compensatory eye movements to facilitate gaze stabilization. Previous electrophysiological studies from our lab have shown that the pigeon flocculus consists of four parasagittal zones: 0, 1, 2, and 3. PC complex spike activity (CSA), which reflects CF input, in zones 0 and 2 responds best to rotational optokinetic stimuli about the vertical axis (VA zones), whereas CSA in zones 1 and 3 responds best to rotational optokinetic stimuli about the horizontal axis (HA zones). In addition, folium IXcd consists of seven pairs of ZII+/− stripes. Here, we recorded CSA of floccular PCs to optokinetic stimuli, marked recording locations, and subsequently visualized ZII expression in the flocculus. VA neurons were localized to the P4+/− and P6+/− stripes and HA neurons were localized to the P5+/− and P7− stripes. This is the first study showing that a series of adjacent ZII+/− stripes are tied to specific physiological functions as measured in the responses of PCs to natural stimulation. Moreover, this study shows that the functional zone in the pigeon flocculus spans a ZII+/− stripe pair, which is contrary to the scheme proposed from rodent research.

Glycolysis, the process responsible for the conversion of monosaccharides to pyruvic acid, is a ubiquitous feature of cellular metabolism and was the first major biochemical pathway to be well characterized. Although the majority of glycolytic enzymes are common to all organisms, the past quarter of a century has revealed that glycolysis in higher plants possesses numerous distinctive features. Research in the nineteenth century established convincingly that plants carry out alcoholic fermentation under anaerobic conditions. In 1878, Wilhelm Pfeffer asserted that a non-oxygen-requiring ‘intramolecular respiration’ was involved in the aerobic respiration of plants. Between 1900 and 1950 it was demonstrated that plants metabolize sugar and starch by a glycolytic pathway broadly similar to that of yeasts and muscle tissue. In 1948, the first purification and characterization of a plant glycolytic enzyme, aldolase, was published by Paul Stumpf. By 1960 the presence of each of the 10 enzymes of glycolysis, presumed at the time to be located in the cytosol, had been confirmed in higher plants. Shortly after 1960 it was shown that the mechanism of glycolytic regulation in plants had features in common with that of animals and yeasts, especially as regards the important role played by the enzyme phosphofructokinase; but important regulatory properties peculiar to plants were soon demonstrated. In the last 30 years, higher-plant glycolysis has been found to exhibit a number of additional characteristics peculiar to plant systems. One conspicuous feature of plant glycolysis, discovered in the 1970s, is the presence of a complete or nearly complete sequence of glycolytic enzymes in plastids, distinct and spatially separated from the glycolytic enzymes located in the cytosol. Plastidic and cytosolic isoenzymes of glycolysis have been shown to differ in their kinetic and regulatory properties, suggesting that the two pathways are independently regulated. Since about 1980 it has become increasingly clear that the cytosolic glycolysis of plants may make use of several enzymes other than the conventional ones found in yeasts, muscle tissue and plant plastids: these enzymes include a pyrophosphate-dependent phosphofructokinase, a non-reversible and nonphosphorylating glyceraldehyde-3-phosphate dehydrogenase, a phosphoenolpyruvate phosphatase (vacuolar location) and a three-enzyme sequence able to produce pyruvate from phosphoenolpyruvate avoiding the pyruvate-kinase step. These non-conventional enzymes may catalyze glycolysis in the plant cytosol especially under conditions of metabolic stress. Experiments on transgenic plants possessing significantly elevated or reduced (reduced to virtually nil in some cases) levels of glycolytic enzymes are currently playing an important part in improving our understanding of the regulation of plant glycolysis; such experiments illustrate an impressive degree of flexibility in the pathway's operation. Plant cells are able to make use of enzymes bypassing or substituting for several of the conventional enzymic steps in the glycolytic pathway; the extent and conditions under which these bypasses operate are the subject of current research. The duplication of the glycolytic pathway in plants and the flexible nature of the pathway have possibly evolved in relation to the crucial biosynthetic role played by plant glycolysis beyond its function in energy generation; both functions must proceed if a plant is to survive under varying and often stressful environmental or nutritional conditions.

The mechanism by which the type Iα regulatory subunit (RIα) of cAMP-dependent protein kinase is localized to cell membranes is unknown. To determine if structural modification of RIα is important for membrane association, both beef skeletal muscle cytosolic RI and beef heart membrane-associated RI were characterized by electrospray ionization mass spectrometry. Total sequence coverage was 98% for both the membrane-associated and cytosolic forms of RI after digestion with AspN protease or trypsin. Sequence data indicated that membrane-associated and cytosolic forms of RI were the same RIα gene product. A single RIα phosphorylation site was identified at Ser81 located near the autoinhibitory domain of both membrane-associated and cytosolic RIα. Because both R subunit preparations were 30–40% phosphorylated, this post-translational modification could not be responsible for the membrane compartmentation of the majority of RIα. Mass spectrometry also indicated that membrane-associated RIα had a higher extent of disulfide bond formation in the amino-terminal dimerization domain. No other structural differences between cytosolic and membrane-associated RIα were detected. Consistent with these data, masses of the intact proteins were identical by LCQ mass spectrometry. Lack of detectable structural differences between membrane-associated and cytosolic RIα strongly suggests an interaction between RIα and anchoring proteins or membrane lipids as more likely mechanisms for explaining RIα membrane association in the heart.