d-serine regulation of the timing and architecture of the inspiratory burst in neonatal mice

d-serine, released from mouse medullary astrocytes in response to increased CO₂ levels, boosts the respiratory frequency to adapt breathing to physiological demands. We analyzed in mouse neonates, the influence of d-serine upon inspiratory/expiratory durations and the architecture of the inspiratory burst, assessed by pwelch's power spectrum density (PSD) and continuous wavelet transform (CWT) analyses. Suction electrode recordings were performed in slices from the ventral respiratory column (VRC), site of generation of the respiratory rhythm, and in brainstem-spinal cord (en bloc) preparations, from the C5 ventral roots, containing phrenic fibers that in vivo innervate and drive the diaphragm, the main inspiratory muscle. In en bloc and slice preparations, d-serine (100 μM) reduced the expiratory, but not the inspiratory duration, and increased the frequency and the regularity of the respiratory rhythm. In en bloc preparations, d-serine (100 μM) also increased slightly the amplitude of the integrated inspiratory burst and the area under the curve of the integrated inspiratory burst, suggesting a change in the recruitment or the firing pattern of neurons within the burst. Time-frequency analyses revealed that d-serine changed the burst architecture of phrenic roots, widening their frequency spectrum and shifting the position of the core of firing frequencies towards the onset of the inspiratory burst. At the VRC, no clear d-serine induced changes in the frequency-time domain could be established. Our results show that d-serine not only regulates the timing of the respiratory cycle, but also the recruitment strategy of phrenic motoneurons within the inspiratory burst.

D-serine released by astrocytes in brainstem regulates breathing response to CO2 levels

Central chemoreception is essential for adjusting breathing to physiological demands, and for maintaining CO₂ and pH homeostasis in the brain. CO₂-induced ATP release from brainstem astrocytes stimulates breathing. NMDA receptor (NMDAR) antagonism reduces the CO₂-induced hyperventilation by unknown mechanisms. Here we show that astrocytes in the mouse caudal medullary brainstem can synthesize, store, and release d-serine, an agonist for the glycine-binding site of the NMDAR, in response to elevated CO₂ levels. We show that systemic and raphe nucleus d-serine administration to awake, unrestrained mice increases the respiratory frequency. Application of d-serine to brainstem slices also increases respiratory frequency, which was prevented by NMDAR blockade. Inhibition of d-serine synthesis, enzymatic degradation of d-serine, or the sodium fluoroacetate-induced impairment of astrocyte functions decrease the basal respiratory frequency and the CO₂-induced respiratory response in vivo and in vitro. Our findings suggest that astrocytic release of d-serine may account for the glutamatergic contribution to central chemoreception.

Astrocytes are involved in chemoreception in brainstem areas that regulate breathing rhythm, and astrocytes are known to release d-serine. Here the authors show that astrocyte release of d-serine contributes to CO₂ sensing and breathing in brainstem slices, and in vivo in awake unrestrained mice.

Aβ potentiates inflammatory activation of glial cells induced by scavenger receptor ligands and inflammatory mediators in culture

Alzheimer disease (AD) is a neurodegenerative disorder characterized by the accumulation of β amyloid (Aβ) aggregates. Aβ induces the inflammatory activation of glia, inducing secretion of Interleukin 1β (IL1β), nitric oxide (NO) and superoxide radicals. The specific receptor responsible for the induction of inflammatory activation by Aβ, is still an open question. We propose that scavenger receptors (SR) participate in the activation of glia by Aβ. We assessed production of NO, synthesis of IL1β and activation of ERK, JNK and NF-κB signaling pathways by Western blot, in primary rat glial cultures exposed to SR ligands (fucoidan and Poly I), LPS + IFNγ (LI), and Aβ. Poly I but not fucoidan nor fibrillar Aβ increased threefold NO production by astrocytes in a time-dependent manner. Fucoidan and Poly I increased 5.5- and 3.5-fold NO production by microglia, and co-stimulation with Aβ increased an additional 60% NO induced by SR ligands. Potentiation by Aβ was observed later for astrocytes than for microglia. In astrocytes, co-stimulation with Aβ potentiated ERK and JNK activation in response to Fucoidan and Poly I, whereas it reduced induction of JNK activation by LI and left unaffected NF-κB activation induced by LI. Levels of pro-IL1β in astrocytes increased with Aβ, SR ligands and LI, and were potentiated by co-stimulation with Aβ. Our results suggest that SRs play a role on inflammatory activation, inducing production of NO and IL1β, and show potentiation by Aβ. Potentiation of the inflammatory response of Aβ could be meaningful for the activation of glia observed in AD.

[Adult attention-deficit/hyperactivity disorder: descriptive study in a Memory Unit]

INTRODUCTION

Attention-deficit/hyperactivity disorder (ADHD) is the main neurological diagnosis in Chilean children. Its profile and evolution in adults has not been appropriately studied, despise its personal and social impact.

AIM

To describe the characteristics of adults with ADHD evaluated in a memory unit, verifying the existence of differences depending on gender.

PATIENTS AND METHODS

A demographic and symptomatic evaluation protocol was applied to all patients diagnosed with ADHD who consulted at the Memory Unit of the Pontificia Universidad Católica de Chile, during the year 2004.

RESULTS

Eighty six patients were included. Average age was 37, being 53% male. Most patients were diagnosed for the first time in adulthood, corresponding to an ADHD of combined type. The main patients' complaints were forgetfulness and distraction. A stressing factor capable of worsening the symptoms was identified in 59% of patients. Depression was the principal comorbidity, with a significantly higher incidence in women.

CONCLUSIONS

The limitations of ADHD diagnostic criteria available for adult patients are discussed. Differences depending on gender were analyzed, describing a predominantly disruptive profile in men and depressive profile in women. There is a clear under-diagnosis of female children with ADHD, with a potential negative impact on their neuropsychological development. The differential diagnosis with mild cognitive impairment, in patients complaining of recent memory decline is discussed.

Modulation by astrocytes of microglial cell-mediated neuroinflammation: effect on the activation of microglial signaling pathways

The strong inflammatory response observed in neurodegenerative diseases can depend on the impairment of the endogenous control of microglial activation, triggering the release of potentially detrimental factors such as cytokines, nitric oxide (NO) and superoxide anion (O(2)(-)). Our aim was to study the activation of microglial cells and the transduction pathways involved in their modulation by IL-1beta and TNF-alpha. Microglial and mixed glial cell cultures from neonatal rats were exposed to IFN-gamma and/or IL-1beta and TNF-alpha. We analyzed NO secretion and the activation of ERK and STAT1. We found that astrocytes modulated microglial cell activation, decreasing production of NO. IFN-gamma induced an 18- to 25-fold increase in NO, associated to a 3- to 5-fold increase in ERK phosphorylation in microglial cultures. IL-1beta, but not TNF-alpha, inhibited IFN-gamma-induced production of NO in microglia by 87%. It also reduced IFN-gamma-induced phosphoERK (pERK) by 40%, without affecting phosphoSTAT1 (pSTAT1). In contrast, in microglial cultures exposed to media conditioned by astrocytes, IL-1beta did not inhibit pERK, whereas it reduced activation of STAT1. Inducible NO synthase expression induced by IFN-gamma in microglial cultures was reduced when the activation of ERK was prevented. We propose that IL-1beta modulates IFN-gamma-induced production of oxidative molecules through cross talk between STAT1 and MAPK pathways, regulating the amplitude and duration of microglial activation. Modulation of ERK was observed at 30 min, whereas inhibition of pSTAT was observed later (at 4 h), indicating that it was an early and transient phenomenon.

Development and pH sensitivity of the respiratory rhythm of fetal mice in vitro

In newborn and adult mammals, chemosensory drive exerted by CO(2) and H(+) provides an essential tonic input: without it the rhythm of respiration is abolished. It is not known, however, whether this chemosensory drive and the respiratory rhythm appear simultaneously during development. In isolated brainstem-spinal cord preparations from fetal mice, we determined at what stage of fetal life the respiratory rhythm appeared in third to fifth cervical ventral roots (phrenic motoneurons) and whether this fetal rhythm was sensitive to chemosensory inputs. A respiratory-like rhythm consisting of short duration bursts of discharges recurring at 2-16 min(-1) was detected in two of nine embryonic day 13 fetuses; it was abolished by transection of the spinal cord between the first to second cervical segments and was phase-related to rhythmic activity from medullary units of the ventral respiratory group. At embryonic day 13, it coexisted with a slow rhythm (0.1-2.0 min(-1)) of long duration bursts of action potentials which was generated by the spinal cord. At later fetal stages, the respiratory-like rhythm became more robust and of higher frequency, while the spinal cord rhythm became less obvious. At all fetal stages, acidification of the superfusion medium from pH 7.5-7.2 or 7.4-7.3 or 7.4 to 7.2 increased the frequency of both the respiratory-like and the spinal cord rhythms. In addition, acidification reduced the amplitude of the integrated burst activity of the spinal cord rhythm of embryonic day 13-embryonic day 16 fetuses and the respiratory-like rhythm of embryonic day 17 and older fetuses. Our results indicate that the rhythms transmitted by phrenic motoneurons during fetal development are chemosensitive from early fetal stages. Through its effects on induction and patterning of the rhythm, chemosensory drive may play a role in activity-dependent formation of respiratory neural networks.

Microglia-astrocyte interaction in Alzheimer's disease: friends or foes for the nervous system?

Brain glial cells secrete several molecules that can modulate the survival of neurons after various types of damage to the CNS. Activated microglia and astrocytes closely associate to amyloid plaques in Alzheimer Disease (AD). They could have a role in the neurotoxicity observed in AD because of the inflammatory reaction they generate. There is controversy regarding the individual part played by the different glial cells, and the interrelationships between them. Both astrocytes and microglia produce several cytokines involved in the inflammatory reaction. Moreover, the same cytokines may have different effects, depending on their concentration and the type of cells in the vicinity. In turn, the events occurring in response to injury may lead to changes in the nature and relative concentration of the various factors involved. To learn about these putative glial interrelationships, we examined some effects of astrocytes on microglial activation.

Immobilized amyloid precursor protein constructs: a tool for the in vitro screening of glial cell reactivity

Astrocytes and microglia are closely associated with amyloid plaques in Alzheimer's disease (AD). Microglia constitute the first barrier surrounding plaques, although they seem to be unable to remove them efficiently. We evaluated the reaction of microglial cells from neonatal rats and mice to plaque mimetics. The C-terminal part of the amyloid precursor protein (APP) or amyloid peptide (A beta) was immobilized to either 60-microm or 2.8-microm beads and incubated with microglial cells. Beads of 60 microm, having approximately the size of senile plaques, were not phagocytosed, in contrast to 2.8-microm beads, which were phagocytosed by microglia but not by astrocytes. Once taken up by the cells, proteins immobilized to the beads were degraded rapidly, as confirmed by mass spectrometry and immunofluorescence with an antibody against beta-amyloid. On the other hand, no protein degradation was observed with 60-microm beads. Also, probably as a reaction to its incapability to phagocytose the beads, glia organized around the beads and started to proliferate. Cell proliferation was more pronounced when the beads contained the A beta epitope compared with the beads with an inert surface. This in vitro effect could be exploited to set up a screening assay for compounds that ameliorate the adverse reaction of microglia supposed to contribute to the pathogenesis of AD.

Expression of alpha(2)-macroglobulin receptor/low density lipoprotein receptor-related protein (LRP) in rat microglial cells

Low density lipoprotein receptor-related protein (LRP) participates in the uptake and degradation of several ligands implicated in neuronal pathophysiology including apolipoprotein E (apoE), activated alpha(2) -macroglobulin (alpha(2)M*) and beta-amyloid precursor protein (APP). The receptor is expressed in a variety of tissues. In the brain LRP is present in pyramidal-type neurons in cortical and hippocampal regions and in astrocytes that are activated as a result of injury or neoplasmic transformation. As LRP is expressed in the monocyte/macrophage cell system, we were interested in examining whether LRP is expressed in microglia. We isolated glial cells from the brain of neonatal rats and LRP was immunodetected both in microglial cells and in astrocytes expressing glial fibrillar acidic protein (GFAP). Microglial cells were able to bind and internalize LRP-specific ligand, alpha(2)M*. The internalization was inhibitable by RAP, with a Kd of 1.7 nM. The expression of LRP was up-regulated by dexamethasone, and down-regulated by lipopolysaccharide (LPS), gamma interferon (IFN-gamma) or a combination of both. LRP was less sensitive to dexamethasone in activated astrocytes than in microglia. We provided the first analysis of LRP expression and regulation in microglia. Our results open the possibility that microglial cells could be related to the participation of LRP and its ligands in different pathophysiological states in brain.

Monoclonal antibody against a neuronal antigen impairs formation of the axon scaffold in grasshopper central nervous system

The pathway a growing axon follows is determined by a number of cues, including differential adhesion to surface molecules on axons and the matrix of the fascicles along which they grow. We have characterized the differential expression of an extracellular antigen and the effects of a monoclonal antibody against this molecule on the development of the grasshopper central nervous system (CNS). The 5C1 monoclonal antibody was generated against ganglion chains of grasshopper embryos; it labels cell bodies of newly differentiated neurons and their axons as they extend. Electron microscopy of embryos at 42% of development reveals that 5C1 labels neuronal filopodia, axons and somata, and areas of glial membrane in apposition to neurite fascicles. After 70% of development, labeling is lost from axon bundles, but remains on cell bodies. 5C1 also cross-reacts with an epitope expressed in Drosophila CNS during embryonic development. Enzymatic digestion suggests that the antigen recognized by the antibody is likely to be a glycolipid. In embryos exposed to 5C1 during early stages of development of the CNS, at the time when the first axons begin to extend, the formation of axon pathways is blocked or greatly delayed. Our results suggest that the 5C1 antigen participates in the formation of the axon scaffold and may play a functional role in the initiation and maintenance of axon outgrowth during early development of the CNS.

Mannose receptor is present in a functional state in rat microglial cells

We studied the expression of the mannose receptor (ManR) in rat microglial cells. Microglial cells are the central nervous system resident macrophages, key participants of the innate immune response. ManR is a differentiation marker and a relevant glycoprotein for the phagocytic and endocytic function of macrophages. Because there is evidence suggesting that ManR could mediate some of the nonenzymatic effects of acetilcholinesterase (AchE) and the enzyme seems to be involved in Alzheimer's disease (AD), we looked for ManR in microglia, evaluating the functionality of the receptor. We isolated microglial cells from the brain of 2-day-old neonatal rats. Microglial cells, identified by their specific staining with the lectin Griffonia simplicifolia, expressed ManR, being detected by immunocytochemistry, Western blot, and immunoprecipitation. Microglial ManR was downregulated by lipopolysaccharide (LPS) and upregulated by dexamethasone, as described for peripheral macrophages. Microglial ManR was functional and able to internalize horseradish peroxidase (HRP), a known ManR ligand, in a mannan-inhibitable manner. The presence of a functional ManR in microglia opens the possibility that ManR could participate in multiple physiologic and pathologic conditions in the central nervous system (CNS), including inflammation, ischaemia, and neurodegenerative diseases such as AD.

Transformation of leech microglial cell morphology and properties following co-culture with injured central nervous system tissue

When the leech central nervous system (CNS) is injured, microglial cells migrate to the site of the lesion. It is possible that the injured CNS releases diffusible substances that alter the properties of microglial cells; to investigate this, microglial cells were cultured in the presence of injured or uninjured CNS tissue. Grown on Concanavalin A (Con-A), 75 % of microglial cells are rounded in shape and are avoided by growing neurites. However, when chains of leech ganglia with damaged connectives were cultured on Con-A next to microglial cells, many of the microglial cells changed their morphology. The number of rounded cells present decreased to 48 %, 4 % became spindle-shaped and 48 % had an intermediate form. In addition, the presence of crushed ganglionic chains allowed more growth of neurites across microglial cells than occurred under control conditions, although round-shaped microglia were still avoided by growing neurites. Similar changes in microglial cells were produced in cells plated on Con-A in the presence of conditioned medium from crushed ganglionic chains. Hence, a diffusible substance from injured CNS tissue caused the morphology of the microglial cells plated on Con-A to become more like that of microglia plated on laminin, on which only 22 % of the cells are rounded while the remainder are spindle-shaped and are readily crossed by neurites. Changes in morphology were not observed when microglial cells were cultured with frozen and crushed ganglionic chains or with uncrushed chains. These experiments demonstrate that substances released from damaged leech CNS cause microglial cells plated on Con-A to change their morphology and the way in which they interact with growing neurites.

Responses induced by tacrine in neuronal and non-neuronal cell lines

Alzheimer's disease (AD) is associated with a reduction in cholinergic activity as a result of specific neuronal loss. Current potential treatments for the disease include both cholinomimetic drugs and anticholinesterase inhibitors. One of the drugs approved by the FDA is tacrine (9-amine-1,2,3,4 tetrahydroacridine; THA), a strong acetylcholinesterase (AChE) inhibitor. We have studied the effects of tacrine on glial and neuronal cells in culture assessing cell survival and viability and morphology. Lactate dehydrogenase (LDH) activity and methylthiazol-diphenyl-tetrazolium (MTT) reduction were used as toxicity indicators. We found that tacrine toxicity on rat B12 glial cells and mouse Neuro 2A cells was strongly dependent on its concentration (up to 500 microM) and time of exposure. The toxic effect was not prevented by serum factors nor by bovine serum albumin. Fluorescein-conjugated phalloidin was used to examine the arrangement of actin filaments at substrate adhesion regions and cell-cell contacts. Primary events following exposure to tacrine included changes in cell morphology, disappearance of actin filament bundles, and disruption of focal adhesion contacts. At concentrations between 10 and 50 microM, tacrine induced neurite outgrowth in Neuro 2A cells, an effect that was not observed in B12 cells, suggesting that certain tacrine effects could be specific for neuronal cells. Although similar trends of response were observed for both cell types, some differences between undifferentiated and differentiated cells were apparent.

Toxic effects of acetylcholinesterase on neuronal and glial-like cells in vitro

Acetylcholinesterase (AChE), the enzyme involved in the hydrolysis of the neurotransmitter acetylcholine, has been implicated in non-cholinergic actions which may play a role in neurodegenerative diseases such as Alzheimer's disease. To study the potential cytotoxicity of brain AChE, the effects of affinity purified AChE were analyzed on neuronal (Neuro 2a) and glial-like (B12) cells. LDH release and MTT reduction assays showed that AChE was toxic; the toxicity was dependent on the enzyme concentration, time of incubation and cellular density. The toxic effect of AChE was not related to its catalytic activity, since the anti-cholinesterase drug BW284C51 and heat inactivation were unable to block the effects of the enzyme. When cells were incubated at 4 degrees C, toxicity was completely blocked, in contrast to cells incubated at 37 degrees C. The presence of serum in the culture medium inhibited the toxic effects of AChE. Cytoplasmic shrinkage, condensation and fragmentation of nucleus as well as DNA strand breaks detected with the TUNEL technique indicated that apoptotic cell death is involved in the effect of AChE. Considering that we have previously shown that AChE promotes the assembly of beta-amyloid peptide into neurotoxic amyloid fibrils, it is conceivable that the neurotoxicity of AChE shown here may play a role in the neuronal degeneration observed in Alzheimer's disease.

Contact between identified leech neurones in culture prevents retraction of neurites following electrical activity

Neurites of individual leech neurones in culture retract in response to electrical stimulation or K+ depolarisation. The aim of these experiments was to assess whether retraction of neurites is prevented by the establishment of cell-cell contacts. Retzius and anterior pagoda (AP) cells were isolated from leech ganglia and plated either as single cells or in pairs. A profusion of well-developed neurites was observed after 5-9 days in culture on laminin-rich leech extracellular matrix extract. Brief trains of action potentials in single cells caused neurites to retract reversibly by approximately 26% of their average length, confirming and extending and earlier results. In contrast, retraction after stimulation was significantly decreased in cultures of paired cells that had formed synapses or contacts between their processes. Even free neurites that had not made contact failed to retract; many neurites continued to elongate during and after electrical stimulation. These results indicate that the retraction of neurites induced by electrical stimulation is prevented by the establishment of intercellular contacts. By stabilising the neurites of neurones contacting potential target cells, the search for additional targets and the strengthening of connections that are being made can continue in the presence of electrical activity.

Repair of the central nervous system: lessons from lesions in leeches

In contrast to the limited repair observed in the mammalian central nervous system (CNS), injured neurons in the leech reliably regenerate synapses and restore function with remarkable accuracy at the level of individual neurons. New and recent results reveal important roles for microglial cells and extracellular matrix components, including laminin, in repair. Tissue culture experiments have permitted isolation of neurons and manipulation of their environment, providing insights into the influence of substrate, electrical activity, and other cells, including microglia, on axon growth and synapse formation. The results account for distinctive features of successful repair in the adult leech, where axonal sprouting and target selection can be influenced by unequal competition between neurons. Differences between the formation of connections during embryonic development and repair in the adult include dissimilarities in the roles of glia and microglia in adults and embryos, suggesting that axon growth during regeneration in the CNS is not simply a recapitulation of processes observed during embryonic development. It may be possible in the future to improve mammalian CNS regeneration by recruiting cells whose counterparts in the leech have been identified as instrumental in repair.

Dermatan sulfate and de-sulfated heparin solubilized collagen-tailed acetylcholinesterase from the rat neuromuscular junction

We are interested in the study of the interactions involved in the attachment of collagen-tailed acetylcholinesterase (AChE) to the synaptic basal lamina. The fact that AChE occupies less than 0.1% of the muscle basal lamina, suggests that there is a very high specificity in the interaction that defines its distribution. We have previously found that asymmetric AChE is bound to the neuromuscular junction via heparan sulfate proteoglycans. Sulfated glycosaminoglycans as heparan sulfate and heparin extracted the asymmetric AChE from the synaptic basal lamina. Here we show that dermatan sulfate as well as de-sulfated heparin, are also able to extract collagen-tailed AChE. Taking into account that the solubilization of the asymmetric AChE is concomitant with the liberation of a dermatan sulfate proteoglycan from the rat neuromuscular junction, the present results open the possibility that the collagen-tailed AChE is also anchored to dermatan sulfate proteoglycans at the synaptic basal lamina.

Round-headed spermatozoa: a model to study the role of the acrosome in early events of gamete interaction

Gamete interactions in mouse involves at least two steps: the first is the interaction of a spermatozoa receptor located in the plasma membrane and ZP3, a zona pellucida (ZP) glycoprotein. ZP3 also can induce the acrosome reaction, making possible the second step: a closer interaction between ZP2 and an inner acrosomal membrane receptor. Our aim was to study gamete interaction in round-headed spermatozoa to determine at which functional level fertility is impaired. These spermatozoa are predominant in some infertile male and are characterized by the absence of acrosome; they also present an abnormal pattern of chromatin condensation. Human ZP and zona free hamster oocytes were used to study gamete interaction. No binding to ZP was observed either with light or electron microscopy. Our findings suggest that the presence of the acrosome could be necessary for the sorting and right organization of plasma membrane proteins. Round-headed spermatozoa could also present a general alteration of membrane protein synthesis. The lack of fusion with zona-free hamster oocytes may be explained by an altered reorganization of plasma membrane proteins in the post acrosomal region as a result of the absence of the acrosome reaction in round headed spermatozoa.

Carrageenans solubilize asymmetric acetylcholinesterase from nicotinic cholinergic synapses

1. Acetylcholinesterase (AChE) catalyzes the hydrolysis of acetylcholine at cholinergic synapses in both vertebrate and invertebrates organisms. 2. The asymmetric synaptic AChE is attached to the extracellular matrix (ECM) of the neuromuscular junction through heparin sulphate proteoglycans (HSPGs). 3. It has been shown previously that heparin-like glycosaminoglycans (GAGs) can solubilize this enzyme from the cholinergic synapses. 4. The present paper describes the solubilization of asymmetric AChE by different marine macroalgal polysaccharides, called carrageenans. 5. Important differences were found among all the carrageenans tested; they released 15-50% of the total AChE activity normally solubilized by heparin. 6. Carrageenans extracted from tetrasporic stages of Iridaea ciliata and I. membranacea were always better extracting agents than those from the cystocarpic stages of these algae, suggesting that lambda-like carrageenans are involved. 7. This hypothesis was confirmed by extracting AChE with purified carrageenans.

Is the supply of axoplasmic proteins a burden for the cell body? Morphometry of sensory neurons and amino acid incorporation into their cell bodies

Since the perikaryon is considered to be the source of all axoplasmic proteins, we estimated the amount of protein synthesized in cell bodies and axoplasmic volumes of sensory neurons of two anuran species (Xenopus and Caudiverbera) to detect a correlation between these variables. The range of cell body volumes was 1:28 and 1:38 in Xenopus and Caudiverbera, respectively, while that of axoplasmic volumes was 1:5000-6000. The protein synthesis in glial and neuronal cell bodies was assessed with pulses of labeled amino acids followed by radioautography. No obvious correlation was found between axoplasmic volume and either rate or amount of amino acid incorporated into cell bodies. The rate of amino acid incorporation into glial and neuronal cell bodies was of the same order of magnitude. Results suggest that the maintenance of the axoplasm does not seem to be a burden for the perikaryon.