The renin-angiotensin system in the rat brain. Immunocytochemical localization of angiotensinogen in glial cells and neurons

The distribution of angiotensinogen containing cells was determined in the brain of rats using immunocytochemistry. Specific angiotensinogen immunoreactivity is demonstrated both in glial cells and neurons throughout the brain, except the neocortical and cerebellar territories. Positive neurons are easily and invariably detected in female brains, and haphazardly in male brain (sex hormone dependent). Angiotensinogen immunoreactivity in male brain neurons can be induced by water deprivation or binephrectomy in some areas and particularly in paraventricular nuclei. Finally, the highest concentrations of positive neurons are found in the anterior and lateral hypothalamus, preoptic area, amygdala and some well known nuclei of the mesencephalon and the brainstem. Our results confirm the wide distribution of angiotensinogen mRNA in the brain reported recently by Lynch et al. (1987). Thus the demonstration of angiotensinogen in neurons and glial cells allows a greater understanding of the biochemical and physiological data in accordance with multiple brain renin angiotensin systems.     

Na(+)-K(+)-ATPase gene expression in the avian eggshell gland: distinct regulation in different cell types

In lactating rats, ANG II receptor binding in the arcuate nucleus (ARH) and median eminence is decreased. To further evaluate brain angiotensinergic activity during lactation, we assessed angiotensinogen (AON) mRNA by in situ hybridization in forebrains of day 10 or 11 postpartum lactating and diestrous rats. AON mRNA was abundantly expressed in the ARH, preoptic, suprachiasmatic, supraoptic, paraventricular, and dorsomedial hypothalamic nuclei, and other regions, similar to that reported in male rat brains. AON mRNA levels were decreased 27% in the midcaudal ARH of lactating rats but did not differ between lactating or diestrous rats in any of the other brain areas examined. Immunofluorescence for AON and glial fibrillary acidic protein or tyrosine hydroxylase confirmed that the AON immunoreactivity in the ARH was limited to astrocytes. Confocal microscopy revealed close appositions of AON-positive astrocytes to dopaminergic neurons in the ARH. The decrease in AON mRNA in the midcaudal ARH during lactation coupled with decreased ARH ANG II receptor binding suggests that lactating rats are less subject to ANG II-mediated inhibition of prolactin secretion.     

Neuronal and Glial Expression of the Multidrug Resistance Gene Product in an Experimental Epilepsy Model

1. Failure of anticonvulsive drugs to prevent seizures is a common complication of epilepsy treatment known as drug-refractory epilepsy but their causes are not well understood. It is hypothesized that the multidrug resistance P-glycoprotein (Pgp-170), the product of the MDR-1 gene that is normally expressed in several excretory tissues including the blood brain barrier, may be participating in the refractory epilepsy. 2. Using two monoclonal antibodies against Pgp-170, we investigated the expression and cellular distribution of this protein in the rat brain during experimentally induced epilepsy. Repeated seizures were induced in male Wistar rats by daily administration of 3-mercaptopropionic acid (MP) 45 mg/kg i.p. for either 4 days (MP-4) or 7 days (MP-7). Control rats received an equivalent volume of vehicle. One day after the last injection, rats were sacrificed and brains were processed for immunohistochemistry for Pgp-170. As it was previously described, Pgp-170 immunostaining was observed in some brain capillary endothelial cells of animals from control group. 3. Increased Pgp-170 immunoreactivity was detected in MP-treated animals. Besides the Pgp-170 expressed in blood vessels, neuronal, and glial immunostaining was detected in hippocampus, striatum, and cerebral cortex of MP-treated rats. Pgp-170 immunolabeled neurons and glial cells were observed in a nonhomogeneous distribution. MP-4 animals presented a very prominent Pgp-170 immunostaining in the capillary endothelium, surrounding astrocytes and some neighboring neurons while MP-7 group showed increased neuronal labeling. 4. Our results demonstrate a selective increase in Pgp-170 immunoreactivity in the brain capillary endothelial cells, astrocytes, and neurons during repetitive MP-induced seizures. 5. The role for this Pgp-170 overexpression in endothelium and astrocytes as a clearance mechanism in the refractory epilepsy, and the consequences of neuronal Pgp-170 expression remain to be disclosed.     

Widespread immunoreactivity for neuronal nuclei in cultured human and rodent astrocytes

The monoclonal antibody (mAb) neuronal nuclei (NeuN) labels the nuclei of mature neurons in vivo in vertebrates. NeuN has also been used to define post-mitotic neurons or differentiating neuronal precursors in vitro . In this study, we demonstrate that the NeuN mAb labels the nuclei of astrocytes cultured from fetal and adult human, newborn rat, and embryonic mouse brain tissue. A non-neuronal fibroblast cell line (3T3) also displayed NeuN immunoreactivity. We confirmed that NeuN labels neurons but not astrocytes in sections of P10 rat brain. Western blot analysis of NeuN immunoreactive species revealed a distribution of bands in nucleus-enriched fractions derived from the different cell lines that was similar, but not identical to adult rat brain homogenates. We then examined the hypothesis that the glial fibrillary acidic protein/NeuN-double positive population of cells might correspond to neuronal precursors. Although the NeuN-positive astrocytes were proliferating, no evidence of neurogenesis was detected. Furthermore, expression of additional neuronal precursor markers was not detected. Our results indicate that primary astrocytes derived from mouse, rat, and human brain express NeuN. Our findings are consistent with NeuN being a selective marker of neurons in vivo , but indicate that studies utilizing NeuN-immunoreactivity as a definitive marker of post-mitotic neurons in vitro should be interpreted with caution.     

NeuN immunoreactivity in the brain of Xenopus laevis

Neuronal nuclear antigen (NeuN), discovered in mice brain cell nuclei by Mullen et al. (1992), is used as an excellent marker of post-mitotic neurons in vertebrates. In this study, the expression pattern of NeuN was examined in the Xenopus brain to explore phylogenetic differences in NeuN expression. Anti-NeuN antibody showed selective staining in mouse and Xenopus brain extracts, but the number and molecular weight of the bands differed in Western blotting analysis. In immunostaining, anti-NeuN antibody showed selective staining of neurons, but not glial cells, in the Xenopus brain. Most neurons, including olfactory bulb mitral cells and cerebellar Purkinjie cells, which show no immunoreactivity in birds/mammals, showed NeuN immunoreactivity in Xenopus. This study revealed that anti-NeuN antibody is a useful marker of post-mitotic neurons in amphibians, but it also stains neurons that show no reactivity in more derived animals.     

Immunohistochemical Localization of Ca2+/Calmodulin-Dependent Protein Kinase II in Rat Brain and Various Tissues

Polyclonal antibodies against Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) of rat brain were prepared by immunizing rabbits and then purified by antigen-affinity column. The antibodies which recognized both subunits of the enzyme with Mrs 49K and 60K were used for the study on the distribution of CaM kinase II in formalin-fixed, paraffin-embedded tissues. In the brain, a light-microscopic study demonstrated strong immunoreactivity in neuronal somata and dendrites and weak immunoreactivity in nuclei. The densely stained regions included cerebral cortex, hippocampal formation, striatum, substantia nigra, and cerebellar cortex. In substantia nigra, neurites were stained, but not neuronal somata. Electron microscopy revealed that the immunoreactive product was highly concentrated at the postsynaptic densities. In addition to neurons, weak immunoreactivity was also demonstrated in glial cells, such as astrocytes and ependymal cells of ventricles and epithelial cells of choroid plexus. In other tissues, strong immunoreactivity was observed in the islet of pancreas and moderate immunoreactivity in skeletal muscle and kidney tubules. Immunoreactivity was demonstrated in all of the tissues tested. The results suggest that CaM kinase II is widely distributed in the tissues.     

胃伤害性刺激诱导大鼠脑干星形胶质细胞GFAP蛋白表达及其与神经元的关系

研究大鼠在福尔马林诱发胃伤害性刺激时脑干内星形胶质细胞及神经元的变化。应用免疫组织化学三重标记法在脑原位切片同时显示脑干内Fos蛋白,胶质原纤维酸性蛋白（GFAP）,酪氨酸羟化酶（TH）的表达,结果显示：1、在福尔马林诱发胃伤害性刺激后,脑干胶质细胞GFAP表达阳性,并表现出明显的核团或亚核定位特点,在延髓内脏带（MVZ0,中缝大核（RMg),蓝斑（LC）,臂旁外侧核（LPB）,中缝背核（DR）,中脑导水管周围灰质腹外侧区（vlPAG),上丘中灰层（IngSC)等脑区有较多的Fos阳性细胞,而且Fos阳性表达的分布与上述GFAP阳性分布基本一致;2、MVZ,LC,DR,vlPAG等部位有大量Fos及TH双标阳性神经元,周围有密集的GFAP阳性细胞;3、随着刺激后存活时间的变化,GFAP与Fos阳性细胞的反应均经历逐渐升高后又渐降低直至消失的变化。结果表明：上述核团的神经元和星形胶质细胞可能同时参与了内脏痛及其调节过程。     

Fine structure of the neural sheath,glia and neurons in the brain of the housefly,Musca domestica

Summary The fine structure of the neural sheath, glial cells and nerve cells in the brain of adult male houseflies is described. The neural sheath is composed of neural lamella and perineurium. The neural lamella consists of an external lamina and collagen-like fibrils which are embedded in an amorphous matrix. The perineurial cells form a continuous layer around the brain. On their inner surface, perineurial cells form junctional complexes with glial cell processes. A cortical cellular layer composed of neurons and glial cells surrounds the centrally located neuropil. Three types of glial cells are identified. Glial cells differ in size and in relative development and distribution of organelles. Thin processes of glioplasm completely surround the cell bodies of the neurons. Five types of neurons are described. Most of the neurons are monopolar, a few are bipolar.Supported by a grant from the National Science Foundation     

Presence of Calmodulin and Calmodulin-Binding Proteins in the Nuclei of Brain Cells

The nuclear calmodulin levels have been measured in rat neurons and glial cells. The values are 1.0 and 1.1 γg/ mg of protein, respectively. These levels are about threefold higher than those in the nuclei of rat liver cells. We have also investigated the presence of several calmodulin-binding proteins in the nuclei of both brain cellular types. As similarly observed in the nuclei of liver cells, we detected the presence of a-spectrin and a 62-kDa calmodulin-binding protein (p62) in the nuclei of neurons and glial cells by irnmunoblotting and immunocytochemical methods. Both proteins are enriched in the purified nuclear matrix samples from both cellular types. In contrast to that occurring in rat hepatocytes, we have not been able to detect, by irnmunoblotting methods, caldesmon in the nuclear matrices of neurons and glial cells. The immunocytochemical studies suggest, however, that caldesmon can be present in the nuclei but in a fraction distinct from the nuclear matrices.     

Evidence that endogenous thymosin alpha-1 is present in the rat central nervous system

We have previously reported that administration of Thymosin alpha 1 (T-1) can enhance the level of the Nerve Growth Factor and the distribution of its receptor in the developing Central Nervous System (CNS) of rat. To further explore the role of T-1 and verify its presence in cells of rat CNS, we carried out an immunohistochemical study using a polyclonal antibody against T-1. T-1 immunoreactivity was found mainly in neurons of the hippocampus and spinal cord and in several small cells, resembling glial cells, of specific regions of the brain. Moreover, to study whether cerebral cells were receptive to T-1, we injected iodinated T-1 (¹²⁵I-T-1) icv. ¹²⁵I-T-1 labelled neurons were observed in the hypothalamus and septal nuclei. Our results indicate that specific neuronal populations in the rat CNS are able to express and respond to T-1.     

Differential distribution of immunoreactive angiotensinogen in the hind-brain and spinal cord of neonatal and adult rats

The present communication deals with the cytochemical localization of angiotensinogen (ATG) immunoactivity in the hind-brain and spinal cord of neonatal (1-day-old) and adult (3-month-old pregnant) female rats. In the neonatal hind-brain, the immunoreactive cells were more numerous than in that of adult rats. In the adult rat hind-brain, the number of ATG-positive cells was quite limited in each nucleus. Further, in some nuclei, only neurons or neuroglia were positive, while in others the immunoactivity was observed in both the components. Spinal cords of neonatal rats showed a few undifferentiated ATG-positive cells in the grey matter. Contrary to this, the spinal cord of adult animals contained numerous immunoreactive glial cells in the grey matter, fasciculus cuneatus and fasciculus gracilis. Immunoactivity in the neurons was localized in the Nissl bodies.     

Neuron/glia relationships observed over intervals of several months in living mice

Identified neurons and glial cells in a parasympathetic ganglion were observed in situ with video-enhanced microscopy at intervals of up to 130 d in adult mice. Whereas the number and position of glial cells associated with particular neurons did not change over several hours, progressive differences were evident over intervals of weeks to months. These changes involved differences in the location of glial nuclei on the neuronal surface, differences in the apparent number of glial nuclei associated with each neuron, and often both. When we examined the arrangement of neurons and glial cells in the electron microscope, we also found that presynaptic nerve terminals are more prevalent in the vicinity of glial nuclei than elsewhere on the neuronal surface. The fact that glial nuclei are associated with preganglionic endings, together with the finding that the position and number of glial nuclei associated with identified neurons gradually changes, is in accord with the recent observation that synapses on these neurons are normally subject to ongoing rearrangement (Purves, D., J. T. Voyvodic, L. Magrassi, and H. Yawo. 1987. Science (Wash. DC). 238:1122-1126). By the same token, the present results suggest that glial cells are involved in synaptic remodeling.     

Expression of vitamin D receptors in the superior cervical ganglia of rats

We investigated the role of vitamin D in the sympathetic nervous system including the distribution of vitamin D receptors (VDR), 1α-hydroxylase and 24-hydroxylase (CYP24) in neuronal subpopulations and satellite glia in the superior cervical ganglia (SCGs) of rats using immunohistochemistry. VDR immunoreactivity was observed in the cytoplasm and nucleus of nearly all neurons in the SCG. Intensity of VDR fluorescence was significantly greater in the cytoplasm of neuropeptide Y (NPY) negative somata compared to NPY positive neurons. Immunoreactivity for 1α-hydroxylase also was observed in the cytoplasm of all neurons of the SCG, but the intensity of fluorescence was less in the nuclei. To the contrary, the immunoreactivity for CYP24 was stronger in the nuclei, although it was present at lower intensity also in the cytoplasm of neurons. VDR and 1α-hydroxylase immunofluorescence was observed in many non-neuron cells, except satellite glial cells, which exhibited weak CYP24 immunofluorescence. Expression of VDRs and key metabolizing enzymes indicated the importance of vitamin D in the autonomic nervous system and the ability of sympathetic neurons to activate and deactivate vitamin D for its autocrine and paracrine roles.     

Testosterone metabolism in brain cells and membranes

The central nervous system (CNS) is considered a target structure for the action of all the classes of hormonal steroids produced by the organism. Well-characterized genomic and less well-understood membrane mechanisms of action are probably involved in the steroid modulation of brain activities. Moreover, some classes of steroids need to be converted into “active” metabolites before interacting with their effector systems. In particular, testosterone (T) exerts many of its effects after conversion to 5-dihydrotestosterone (DHT) and estrogens. The CNS possesses both the 5-reductase, the enzyme which produces DHT and the aromatase which transforms T into estrogens; however, the relative role and distribution of these enzymes in the various structural components of the CNS has not been clarified so far. The 5-reductase has been found to be present in high concentrations in brain white matter structures because these are particularly rich in myelin membranes, to which the enzymatic activity appears to be associated. This membrane localization might suggest a possible involvement of steroidal 5-reduced metabolites in membrane-mediated events in the CNS. Moreover, the distribution of 5-reductase was studied in neurons, astrocytes and oligodendrocytes isolated from the brain of male rats by density gradient ultracentrifugation, as well as in neurons and glial cells grown in culture. The aromatase activity was also evaluated in neurons and glial cells grown in culture and in isolated oligodendrocytes. Among the three cell types isolated, neurons appear to be more active than oligodendrocytes and astrocytes, respectively, in converting T into DHT. Also, in cell culture experiments, neurons are more active in forming DHT than glial cells. Only neurons possess aromatase activity, while glial cells are apparently unable to aromatize T.     

Biosynthesis of Angiotensinogen and Angiotensins by Brain Cells in Primary Culture

This study focuses on the ability of primary rat brain cells in culture to synthesize angiotensinogen, angiotensin I, and angiotensin II. HPLC in combination with radioimmunoassay was used to characterize these compounds. Following incubation with 3H-labeled isoleucine, radioactively labeled angiotensinogen with an approximate molecular weight of 25,000 was identified in both glial and neuronal cells. Other molecular weight forms of angiotensinogen with molecular weights of about 300 and 160,000 were present in both cell types. In addition to angiotensinogen, radioactively labeled angiotensin I and angiotensin II were also synthesized by neuronal and glial cells. These results suggest that glial and neuronal cells can synthesize angiotensinogen, angiotensin I, and angiotensin II in a similar manner shown for the peripheral renin angiotensin system.     

Immunocytochemical localization of acyl-CoA oxidase in the rat central nervous system

Peroxisomal β-oxidation, consisting of four steps catalysed by an acyl-CoA oxidase, a multifunctional protein and a thiolase, is responsible for the shortening of a variety of lipid compounds. The first reaction of this pathway is catalysed by a FAD-containing acyl-CoA oxidase, three isotypes of which have been so far recognised. Among these, straight-chain acyl-CoA oxidase (ACOX) acts on long and very long chain fatty acids, prostaglandins and some xenobiotics. We investigated ACOX localisation by means of a sensitive, tyramide based, immunocytochemical technique, thus obtaining a complete distribution atlas of the enzyme in adult rat CNS. Granular immunoreaction product was found in the cytoplasm of neuronal and glial cells, both in the perikarya and in the cell processes. ACOX immunoreactive neurons were present to variable extent, in either forebrain or hindbrain areas. Specifically, the strongest signal was detected in the pallidum, septum, red nucleus, reticular formation, nuclei of the cranial nerves, and motoneurons of the spinal cord. We then compared the ACOX immunoreactivity pattern with our previous distribution maps of other peroxisomal enzymes in the adult rat brain. While ACOX appeared to colocalise with catalase in the majority of cerebral regions, some differences with respect to d-amino acid oxidase were noted. These observations support the hypothesis of heterogeneous peroxisomal populations in the nervous tissue. The wide distribution of the enzyme in the brain is consistent with the severe and generalised neurological alterations characterising the peroxisomal disorder caused by ACOX deficiency (pseudo-neonatal adrenoleukodystrophy).     

Cytologie du lobe anterieur de l'hypophyse du chien

Summary Detailed histochemical studies have been made on the distribution of various enzymes such as phosphatases, cholinesterases, glycolytic enzymes and respiratory enzymes in various components of the hypothalamus with special reference to the supraoptic and paraventricular nuclei of the Squirrel Monkey. Cytological studies have also been made by the McManus, Einarson, Gomori and Bargmann methods.A few neurons of these nuclei showed scanty Gomori-positive material in the cytoplasm for the Gomori and Bargmann methods. Nissl granules were located in the peripheral cytoplasm of most neurons. No glycogen granules were observed in these neurons. For these reasons, the Squirrel Monkey, like the rat, may not be a suitable species for the study of neurosecretory phenomena.The axons of these neurons were negative for the specific cholinesterase test, though the perikaryon and some parts of the processes gave a moderately positive reaction. These neurons may be non-cholinergic and the cholinergic fibers from an unknown nucleus may end in synapses on their cell bodies. Blood vessels and glial cells in the neurosecretory nuclei showed non-specific cholinesterase activity. This enzyme may hydrolyze the acetylcholine which has escaped splitting by specific cholinesterase. Alkaline phosphatase and acid phosphatase in these neurons may be involved in the metabolism concerned with the production of neurosecretory material. The neurons may be physicochemical receptors and may get enough energy and raw material to synthesize the neurosecretory material from the rich blood supply. Neurons of the supraoptic and paraventricular nuclei as well as other hypothalamic neurons, like neurons of other regions of the brain, are well equipped with the enzymes of the glycolytic pathways and the tricarboxylic acid cycle. Since the glial cells of these nuclei have amylophosphorylase activity and glycolytic pathways, they may work as energy donators to the neurons of the neurosecretory nuclei. T. R. Shanthaveerappa in previous publications.     

Aortic coarctation hypertension induces fibroblast growth factor-2 immunoreactivity in the stimulated nucleus tractus solitarii

The actions of neurotrophic factors i.e. basic fibroblast growth factor (bFGF, FGF-2) to neurons are related not only to neuronal development and maintenance but also to synaptic plasticity regarding neurotransmission. We analyzed here the levels of FGF-2 immunoreactivity in the nucleus tractus solitarii (NTS) of Wistar Kyoto rats in response to alterations of neuronal activity promoted by the stimulation of the baroreceptor reflex following an aortic coarctation-induced-hypertension. The FGF-2 immunoreactivity (IR) was found in the cytoplasm of the neurons and in the nuclei of the glial cells in the NTS. A large number of NTS neurons expressed FOS immunoreactivity 4 h after coarctation, as an indication of neuronal activity. Stereological methods showed an increased number of FGF-2 immunoreactive (ir) neuronal profiles (90%) and glial profiles (149%) in the NTS of the 72 h aortic coarctated rats. 1-week later, FGF-2 ir neurons were still increased (54%) but no change was found in the number of FGF-2 ir glial profiles. The double immunoperoxidase method revealed that the majority of the FGF-2 ir glial cells was glial fibrillary acidic protein (GFAP) positive astrocytes. GFAP immunohistochemistry showed an astroglial reaction at 72 h time-interval (55%) but not 1 week after stimulation. The number of the cresyl violet positive neurons and OX42 ir profiles (marker of activated microglia) in the NTS of coarctated rats were not different from control by 1 week and 1 month after the surgery, indicating a lack of NTS injury in this period following coarctation hypertension. FGF-2 may be an important neurotrophic factor in areas involved in the control of blood pressure. The increased FGF-2 IR in the NTS cells following neuronal stimulation may represent trophic and plastic adaptive responses in this nucleus in an autocrine/paracrine fashion.     

Plasticity of Congo red staining displayed by subpopulations of neurons within the rat central nervous system

We document the presence of subpopulations of neurons within the rat central nervous system that are labelled with a new Congo red staining technique. These neurons (CR neurons) show shrunken somata, and smaller and darker nuclei than Congo red-negative cells (non-CR cells). With the Bielschowsky and the cresyl violet Nissl staining methods, two comparable subpopulations of cells can be distinguished by the same morphometrical criteria as those used for CR and non-CR cells. CR neurons are located preferentially in some brain regions while in others they are virtually absent. Their distribution and proportion varied greatly from animal to animal and after particular treatments. Injections of water that damaged the hippocampal dentate gyrus, cortical lesions or eye enucleation decreased the number of CR-cells in the CA1 subfield, reflected in a shift from the CR-staining subclass to the non-CR subclass. Treatment with 200 mg/kg of CDP-choline also significantly reduced the number of CR cells observed in CA1. In the red nucleus, CR neurons showed a characteristic distribution of β-amyloid precursor protein (APP) immunoreactivity. The population of dendrites immunolabelled for microtubule-associated protein 2 was markedly decreased in the areas of the hippocampus with high numbers of CR cells. Therefore, it is proposed that neurons labelled with the present Congo red technique might be in a reversible degenerative state or represent a particular physiological state in some areas of the central nervous system. Received: 12 December 1997 / Accepted: 1 February 1998     

Immunocytochemical localization of glycogen phosphorylase kinase in rat brain sections and in glial and neuronal primary cultures

Summary. The physiological function of brain glycogen and the role of phosphorylase kinase as a regulatory enzyme in the cascade of reactions associated with glycogenolysis in the brain have not been fully elucidated. As a first step toward elucidating such a function, we studied the localization of phosphorylase kinase in glial and neuronal primary cell cultures, and in adult rat brain slices, using a rabbit polyclonal antibody against skeletal muscle glycogen phosphorylase kinase. Immunocytochemical examination of rat astroglia-rich primary cultures revealed that a large number of cells were positive for glycogen phosphorylase kinase immunoreactivity. These cells were also positive for vimentin, a marker for immature glia, while they were negative for glial fibrillary acidic protein, a marker for mature astroglia, and for galactocerebroside, an oligodendroglial marker. Neurons in rat neuron-rich primary cultures did not show any kinase-positive staining. In paraformaldehyde-fixed adult rat brain sections, phosphorylase kinase immunoreactivity was detected in glial-like cells throughout the brain, with relatively high staining found in the cerebral cortex, the cerebellum, and the medulla oblongata. Phosphorylase kinase immunoreactivity could not be detected in neurons, with the exception of a group of large neurons in the brain stem, most likely belonging to the mesencephalic trigeminal nucleus. Phosphorylase kinase was also localized in the choroid plexus and to a lesser degree in the ependymal cells lining the ventricles. Phosphorylase kinase thus appears to have the same cellular distribution in nervous tissue as its substrates, i.e. glycogen phosphorylase and glycogen, which suggests that the physiological role of brain phosphorylase kinase is the mobilization of glycogen stores to fuel the increased metabolic demands of neurons and astrocytes.