Glycogen phosphorylase activity in the olfactory bulb of the young rat

Regional Distribution of Glycogen in the Mouse Brain Visualized by Immunohistochemistry

Considering that the brain constantly consumes a substantial amount of energy, the nature of its energy reserve is an important issue. Although the brain is rich in lipid content encompassing membranes, myelin sheath, and astrocytic lipid droplets, it is devoid of adipose tissue which serves as an energy reserve. Notably, glycogen represents the major energy store in the brain. While glycogen has been observed mainly in astrocytes for decades by electron microscopy, glycogen distribution in the brain has only been partially documented. The involvement of glycogen metabolism in memory consolidation, demonstrated by several research groups, has reiterated the functional significance of this macromolecule and the need for description of its comprehensive distribution in the brain. The combination of focused microwave-assisted brain fixation and glycogen immunohistochemistry permits assessment of glycogen distribution in the rodent brain. In this article, we describe glycogen distribution in the mouse brain using glycogen immunohistochemistry. We find heterogeneous glycogen storage patterns at multiple spatial scales. The heterogeneous glycogen distribution patterns may underlie local energy metabolism or synaptic activity, and its mechanistic understanding should extend our knowledge on brain metabolism in health and disease.

Mechanisms underlying early odor preference learning in rats

Early odor preference training in rat pups produces behavioral preferences that last from hours to lifetimes. Here, we discuss the molecular and circuitry changes we have observed in the olfactory bulb (OB) and in the anterior piriform cortex (aPC) following odor training. For normal preference learning, both structures are necessary, but learned behavior can be initiated by initiating local circuit change in either structure. Our evidence relates dynamic molecular and circuit changes to memory duration and storage localization. Results using this developmental model are consistent with biological memory theories implicating N-methyl-D-aspartate (NMDA) receptors and β-adrenoceptors, and their associated cascades, in memory induction and consolidation. Finally, our examination of the odor preference model reveals a primary role for increases in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor synaptic strength, and in network strength, in the creation and maintenance of preference memory in both olfactory structures.

Visualizing odor representation in the brain: a review of imaging techniques for the mapping of sensory activity in the olfactory glomeruli

The brain transforms clues from the external world, the sensory stimuli, into activities in neuroglial networks. These circuits are activated in specialized sensory cortices where specific functional modules are responsible for the spatiotemporal coding of the stimulus. A major challenge in the neuroscience field has been to image the spatial distribution and follow the temporal dynamics of the activation of such large populations in vivo. Functional imaging techniques developed in the last 30 years have enabled researchers to solve this critical issue, and are reviewed here. These techniques utilize sources of contrast of radioisotopic, magnetic and optical origins and exploit two major families of signals to image sensory activity: the first class uses sources linked to cellular energy metabolism and hemodynamics, while the second involves exogenous indicators of neuronal activity. The whole panel of imaging techniques has fostered the functional exploration of the olfactory bulb which is one of the most studied sensory structures. We summarize the major results obtained using these techniques that describe the spatial and temporal activity patterns in the olfactory glomeruli, the first relay of olfactory information processing in the main olfactory bulb. We conclude this review by describing promising technical developments in optical imaging and future directions in the study of olfactory spatiotemporal coding.

Expression and localization of insulin receptors in dissociated primary cultures of rat Schwann cells

The objective of the present study was to examine for the presence of the IRs (insulin receptors) in the primary dissociated culture preparation of SCs (Schwann cells). This was achieved using immunological techniques using a rabbit polyclonal anti-IR antibody and at molecular level by RT (reverse transcription)-PCR. Light microscopic immune cytochemistry revealed that almost all SCs in cluster and associated neuritis exhibited positive immune reaction with the antibody, confirming the presence of IRs in them. Immunoblotting detected a prominent protein band of 90 kDa, which is consistent with those reported by the manufacturer. Like the peripheral nerve, primary SC cultures showed a predominantly high affinity IR mRNA lacking exon 11. Ultrastructural immune localization confined the presence of the IRs in the basal lamina, plasma membrane and the cytoplasmic processes of the SCs.

Theta bursts in the olfactory nerve paired with beta-adrenoceptor activation induce calcium elevation in mitral cells: a mechanism for odor preference learning in the neonate rat

Odor preference learning in the neonate rat follows pairing of odor input and noradrenergic activation of beta-adrenoceptors. Odor learning is hypothesized to be supported by enhanced mitral cell activation. Here a mechanism for enhanced mitral cell signaling is described. Theta bursts in the olfactory nerve (ON) produce long-term potentiation (LTP) of glomerular excitatory postsynaptic potentials (EPSPs) and of excitatory postsynaptic currents (EPSCs) in the periglomerular (PG) and external tufted (ET) cells. Theta bursts paired with beta-adrenoceptor activation significantly elevate mitral cell (MC) calcium. Juxtaglomerular inhibitory network depression by beta-adrenoceptor activation appears to increase calcium in MCs in response to theta burst stimulation.

Modulation of olfactory learning in young rats through intrabulbar GABA(B) receptors

After training with an odour paired with foot shock on postnatal day 11, rat pups show an aversion to the odour in testing on postnatal day 12. The mechanisms underlying this aversive olfactory learning involve disinhibition of mitral/tufted cells in the olfactory bulb by the somatosensory stimulation-induced activation of centrifugal noradrenergic fibres originating in the locus coeruleus. The activity of mitral/tufted cells is regulated through gamma-aminobutyric acidA (GABA(A)) receptors in the external plexiform layer and GABA(B) receptors in the glomerular layer. We have previously presented that aversive olfactory learning in young rats is modulated through GABA(A) receptors in the olfactory bulb. In the present study we examined the consequence of manipulating GABA(B) receptors in the olfactory bulb during training. Baclofen, a GABA(B) receptor agonist when infused into the olfactory bulb during the pairing of an odour with foot shock, prevented aversive olfactory learning in a dose-dependent manner. Infusion of saclofen, a GABA(B) receptor antagonist, during training with a citral odour in the absence of foot shock produced aversive responses not only to the odour, but also to strange odours (benzaldehyde and vanillin) not previously presented. Such olfactory aversions were observed even if saclofen was infused without odour exposure. These results suggest that olfactory learning in young rats is modulated through GABA(B) receptors in the olfactory bulb.

Glycogen phosphorylase reactivity in the amygdala and bed nucleus of the stria terminalis

The present study examines the reactivity of the glial metabolic enzyme, glycogen phosphorylase, within the amygdala and bed nucleus of the stria terminalis. Reactivity for phosphorylase a, the active form of glycogen phosphorylase, was higher in all parts of the medial amygdaloid nucleus, in the medial division of the central amygdaloid nucleus, in the anterior amygdaloid area and in the bed nucleus of stria terminalis than in all parts of the lateral amygdaloid nucleus, the anterior cortical amygdaloid nucleus, the posteromedial and posterolateral cortical amygdaloid nuclei, the intercalated nucleus of the amygdala, main part and the intercalated nuclei. A greater degree of phosphorylase a reactivity was also observed in the basolateral amygdaloid nucleus, anterior and posterior parts, and in the basomedial amygdaloid nucleus, anterior part, while other parts of these nuclei were less reactive. Reactivity attributed to total glycogen phosphorylase enzyme, phosphorylase a+phosphorylase b activated by AMP, was higher and homogeneous across the amygdala. Phosphorylase a patterns are likely to reflect differences in the contribution of glycogenolysis to the metabolic support of cells in the amygdala and bed nucleus of the stria terminalis. Possible relationships to local neuronal activity and to differences in glycogenolytic neuromodulatory input are discussed.

Distribution of glycogen phosphorylase and cytochrome oxidase in the central nervous system of the turtle Trachemys dorbigni

Glycogen phosphorylase (GP) and cytochrome oxidase (CO) activities were mapped histochemically in the brain of the turtle Trachemys dorbigni. In the telencephalon, both activities occurred in the olfactory bulb, in all cortical areas, in the dorsal ventricular ridge, striatum, primordium hippocampi and olfactory tubercle. In the diencephalon, they were identified in some areas of the hypothalamus, and in rotundus and geniculate nuclei. Both reactions were detected in the oculomotor, trochlear, mesencephalic trigeminal nuclei, the nucleus of the posterior commissure, torus semicircularis, substantia nigra and ruber and isthmic nuclei of the mesencephalon. In all layers of the optic tectum GP activity was found, but CO only labelled the stratum griseum centrale. In the medulla oblonga both enzymes appear in the reticular, raphe and vestibular nuclei, locus coeruleus and nuclei of cranial nerves. In the cerebellum, the granular and molecular layers, and the deep cerebellar nuclei were positive for both enzymes. The Purkinje cells were only reactive for CO. In the spinal cord, motor and commissural neurones exhibited a positive reaction for the two enzymes. However, CO also occurred in the marginal nucleus and in the lateral funiculus. These results may be useful as a basis for subsequent studies on turtle brain metabolism.

The biphasic effects of locus coeruleus noradrenergic activation on dendrodendritic inhibition in the rat olfactory bulb

Some forms of olfactory learning require intact noradrenergic terminals in the olfactory bulb that originate from the locus coeruleus. To clarify the action of noradrenergic inputs on the dendrodendritic interaction between mitral and granule cells in the rat olfactory bulb, we analyzed field potentials in the granule cell layer of the olfactory bulb evoked by paired-pulse stimulation of the lateral olfactory tract before and after the activation of the locus coeruleus. Locus coeruleus activation by glutamate injection in the vicinity of the nucleus changed only the test response without any effect on conditioning response. Paired-pulse inhibition measured from the ratio of test response amplitude to conditioning response amplitude was significantly depressed immediately after locus coeruleus activation. Conversely, 2 min later, paired-pulse inhibition was significantly potentiated. The significant potentiation of inhibition lasted for several minutes. The depression-potentiation sequence of paired-pulse inhibition was blocked by infusion of timolol, a beta-antagonist, into the olfactory bulb, in a dose-dependent manner, but not by infusion of phentolamine, an alpha-antagonist. Infusion of isoproterenol, a beta-agonist, into the bulb mimicked the depression of paired-pulse inhibition by locus coeruleus activation. These results suggest that glutamate activation of the locus coeruleus produces a depression-potentiation sequence in granule cell-mediated feedback inhibition onto mitral cells in the olfactory bulb through beta-adrenergic receptors.

Medial forebrain bundle stimulation in rats activates glycogen phosphorylase in layers 4, 5b and 6 of ipsilateral granular neocortex

Functional activation in human brain produces an increase in glycolytic metabolism. Animal studies suggest activation-induced glycolysis is coupled to brain glycogenolysis. Medial forebrain bundle (MFB) stimulation activates the release of neurotransmitters which promote neocortical glycogenolysis in vitro. In the present study, active glycogen phosphorylase (GP), an index of glycogenolysis, is assessed histochemically in rat brain after 15 min of MFB self-stimulation. Active GP increased significantly in layers 4, 5b and 6 of granular neocortex ipsilateral to MFB self-stimulation. Restriction of increased glycogenolysis to granular neocortex suggests an important functional interaction between sensory neocortical processing and ascending MFB systems.

Olfactory bulb glycogen metabolism: noradrenergic modulation in the young rat

The olfactory bulb exhibits high glycogen phosphorylase activity, the rate-limiting enzyme in the mobilization of glycogen. The bulb also receives dense noradrenergic innervation and noradrenaline is known to stimulate glycogen breakdown. We determined the levels of glycogen in the bulb over the course of development and then determined the ability of noradrenaline to mobilize bulb glycogen. At birth, olfactory bulbs have very high levels of glycogen, with levels declining as the pups develop. Picomolar levels of noradrenaline mobilize glycogen in the bulb,. Initially, beta-adrenergic receptors mediate teh glycogenolysis and subsequently, the alpha-noradrenergic receptors in the bulb stimulate the breakdown of glycogen. Carnosine is involved in the repletion of bulb glycogen levels. The stimulation of glycogen breakdown by noradrenaline may play a role in allowing the increased activity that accompanies early olfactory stimulation.

Daily variation in active glycogen phosphorylase patches in the molecular layer of rat dentate gyrus

A larger number of discrete patches of active glycogen phosphorylase (alpha GP) were found in the molecular layer of the hippocampal dentate gyrus in rats sacrificed during the daily dark phase (mean = 28.7/section) than during the light phase (mean = 7.8/section). Light-dark differences in the patterns of alpha GP may reflect circadian differences in metabolic demand in the hippocampus. Patch sizes were consistent with increased activation of single astrocytes or perisynaptic astrocyte clusters by focal input at night.

Neuroethology of olfactory preference development

Young mammals come to approach the odor of their mother, a response that facilitates their survival during early life. Young rats induce a cascade of events in their mother to induce the emission of her odor. The pups increase circulating prolactin levels, which increases food intake and the emission of large quantities of cecotrophe containing the maternal odor. This odor is synthesized by the action of cecal microorganisms and changes with maternal diet. The diet-dependence of the odor requires the pups to acquire their attraction to the odor postnatally. The acquisition of this preference occurs when an odor is paired with the tactile stimulation that pups receive during maternal care. The action of the tactile stimulation appears to be mediated by noradrenaline. The development of this type of olfactory attraction is accompanied by changes in the regions of the olfactory bulb that are responsive to the attractive odor. Metabolic, anatomical, and neurophysiological changes in response to the attractive odor emerge in such regions of the bulb after early olfactory preference training.

A comparison of glycogen phosphorylase a and cytochrome oxidase histochemical staining in rat brain

The utility of metabolic markers that index functional neuronal circuits is widely appreciated. The present study asks whether patterns of the metabolic enzyme, active glycogen phosphorylase, parallel those of the neuronal marker, cytochrome oxidase. Fresh frozen rat brain sections (30 microns) were processed for either active glycogen phosphorylase or cytochrome oxidase at each of ten levels of the neuraxis. Although these metabolic markers predominate in different cellular compartments--glycogen phosphorylase in the astrocytic compartment and cytochrome oxidase in the neuronal compartment--the patterns of high, moderate, and low levels of activity for both enzymes were generally parallel. These similarities extended to detailed patterns of heterogeneous staining within structures, in particular, to laminated and modular distribution within cerebral and cerebellar cortical structures. The modular distribution was evident in barrel structures in the cerebral cortex and in parasagittal compartments in the vermis of the cerebellum. Conspicuous differences between the two patterns occurred in white matter, in subcortical grey matter regions such as the nucleus accumbens, diagonal band, amygdala, and globus pallidus, and in the superior olivary nuclei of the brainstem as well as in nonneural structures such as the choroid plexus and ependyma. Discrete patchiness was characteristic of active glycogen phosphorylase distribution in the limbic neuropil of the dentate gyrus and entorhinal cortex. The strong parallels between active glycogen phosphorylase and cytochrome oxidase distribution support the view that glycogen phosphorylase, despite its glial localization, can reflect neuronal metabolic demands.

Increase in a focal population of juxtaglomerular cells in the olfactory bulb associated with early learning

Young rats learn to approach an odor that had been experienced in the presence of reinforcing tactile stimulation. Subsequent presentation of the conditioned odor also evokes an enhanced focal uptake of 2-deoxyglucose (2-DG) in the glomerular layer of the olfactory bulb, and the glomerular-layer width of such foci increases in conditioned pups. In the present study, we determined whether an increase in the glomerular-layer cell population contributes to this structural and functional change. We therefore counted and measured glomerular-layer cells in Nissl-stained sections from focal regions of radiolabeled 2-DG uptake. While cell size did not differ between groups, conditioned pups had a 19% increase in the number of glomerular-layer cells associated with the 2-DG foci compared to controls. The increase in cell number may contribute to the enhanced 2-DG uptake in glomerular-layer foci.

Glucose-6-phosphate dehydrogenase activity in the olfactory system of the young rat: an enzyme histochemical study using computerized image analysis

An understanding of olfactory system glucose metabolism is necessary for the interpretation of radiolabeled 2-deoxyglucose studies of odor processing since the relationship between glucose uptake and neural activity is based on assumptions regarding cellular glucose utilization. As part of an ongoing study examining divergent pathways of glucose metabolism in the olfactory system, the relative activity of glucose-6-phosphate dehydrogenase, the rate-limiting enzyme of the hexose monophosphate shunt, was examined among cells of the rat olfactory bulb and anterior olfactory nucleus, by using enzyme histochemistry on fresh frozen tissue. Optical density measurement of formazan reaction product in stained tissue were quantified by computerized image analysis. To aid in the identification of histochemically stained neurons, alternate sections were Nissl-stained. The highest olfactory bulb dehydrogenase levels were found in the olfactory nerve and glomerular layers. Individual mitral and tufted cells also showed high dehydrogenase activity. In most stained neurons, formazan reaction product filled the cytoplasm and sometimes extended into the proximal part of dendrites and axons. The external plexiform and granule cell layers had low enzyme activity. High activity also was seen in pyramidal cells of pars dorsalis and pars lateralis of the anterior olfactory nucleus, one of the first, and most rostral of the olfactory bulb projection sites. High glucose-6-phosphate dehydrogenase activity in the olfactory system indicates that a significant amount of glucose can be channeled through the hexose monophosphate shunt in these neurons, with a concomitant production of NADPH. This may reflect high activity of cellular detoxification enzymes that rely on NADPH for reducing power. Such detoxification processes may be engaged in response to the potential entry and transsynaptic movement of airborne chemicals into the brain via the olfactory system.

Are glial cells targets of the central noradrenergic system? A review of the evidence

It has been suggested by a number of investigators that glial cells as well as neurons are targets of the central noradrenergic system. This important hypothesis, however, has not been presented previously in a systematic and unified manner. The present review was therefore undertaken to accomplish this. The evidence supporting noradrenergic action on glia consists primarily of findings that beta-adrenoceptors, norepinephrine (NE)-stimulated cyclic AMP (cAMP) responses and glycogen are localized preferentially in glial cells and that beta-receptor density and glycogen hydrolysis are under the control of neuronally released NE. While there is some disagreement as to the extent to which beta-receptors are preferentially localized in glia, there is a consensus that most glycogen in the forebrain is localized in this cellular compartment. The presumed function of the noradrenergic action on glia appears to be the release of glucose for production of energy, the synthesis of neurotrophic factors such as nerve growth factor, and the release of substances which may affect local neurotransmission including taurine, cAMP and its metabolites. These glial responses may be intimately related to the electrophysiological actions of NE on neurons.