Biomedical subjects

H E Lowndes

Publications and source records attributed to H E Lowndes.

At least 19 recordsLinked to original sources

PubMed2005

Methylmercury alters Eph and ephrin expression during neuronal differentiation of P19 embryonal carcinoma cells.

Developmental exposure to methylmercury (MeHg) induces a spectrum of neurological impairment characterized by cognitive disturbance, sensory/motor deficit, and diffuse structural abnormalities of the brain. These alterations may arise from neural path-finding errors during brain development, resulting from disturbances in the function of morphoregulatory guidance molecules. The Eph family of tyrosine kinase receptors and their ligands, the ephrins, guide neuronal migration and neurite pathfinding mainly via repulsive intercellular interactions. The present study examined the effects of MeHg on mRNA and protein expression profiles of Ephs and ephrins in the P19 embryonal carcinoma (EC) cell line and its neuronal derivatives. Undifferentiated control P19 cells displayed low- to undetectable levels of mRNA for ephrins or Ephs, with the sole exception of EphA2 which was highly expressed. Upon differentiation into neurons, the ephrin expression increased progressively through day 10. Similarly, expression of the Ephs, including EphsA3, -A4, -A8, -B2, -B3, -B4, and -B6, increased significantly. In contrast, EphA2 expression decreased in day 2, 6 and 10 control neurons. Treatment with MeHg did not affect the expression of mRNA for ephrins or Ephs in undifferentiated P19 cells. However, treatment of differentiating neurons with MeHg for 24 h caused consistent increases in ligand mRNA expression, particularly ephrin-A5, -A6, -B1, and -B2. Similarly, MeHg induced variable increases in mRNA expression of receptors EphA2, -A3, -B3, and -B6. A trend toward a concentration-response relationship was observed for the alterations in Eph receptor mRNA expression although increases at the low and mid concentrations did not reach statistical significance. Immunoblots for ligand and receptor proteins mirrored the increases in the mRNA levels at the 0.5 and 1.5 microM MeHg concentrations but showed decreased protein levels compared to controls at the 3.0 microM concentration. Alterations in the Eph/ephrin family of repulsion molecules may represent an important mechanism in developmental MeHg neurotoxicity.

Cell Differentiation↗

PubMed1998

Distribution and induction of cytochrome P450 1A1 and 1A2 in rat brain.

Cytochromes P450 1A1 and 1A2 are involved in the oxidation of a wide spectrum of endogenous compounds and xenobiotics. Although their presence has been repeatedly confirmed in brain tissue, reports regarding their distribution in the brain are often contradictory. In the present study the possibility was examined that CYP1A1 and CYP1A2 are localized and inducible in the brain-CSF barrier and regions with a leaky blood brain barrier, where they may serve as a protective metabolic barrier. CYP1A1 and CYP1A2 levels were determined in subcellular fractions of multiple brain regions, as well as tissue homogenates of circumventricular organs, and the meninges by Western blotting and catalytic activity in control male rats and rats treated with the inducer beta-naphthoflavone (BNF). In control animals CYP1A1 immunoreactive protein was undetectable in regional brain microsomes or whole tissue homogenates of the arachnoid, dura mater, choroid plexus, pineal gland, median eminence, and pituitary. However, low levels of ethoxyresorufin O-deethylase (EROD) activity were observed in homogenates of the arachnoid, dura mater, choroid plexus, pineal gland, and pituitary. Western blotting revealed only low levels of CYP1A2 immunoreactive protein in brain microsomes from the cortex, cerebellum, brainstem, thalamus, hippocampus, and striatum from control animals. Following BNF treatment, EROD activity was induced 12-42-fold in the arachnoid, choroid plexus, dura mater, pineal gland, pituitary, and median eminence. Western blot analysis revealed CYP1A1 to be induced in the arachnoid, dura mater, choroid plexus, pineal gland, and pituitary, while CYP1A2 was undetectable. No induction of CYP1A1 or CYP1A2 protein was observed in brain microsomes from the olfactory bulb, cortex, striatum, hippocampus, cerebellum, or brainstem following BNF treatment, providing that the arachnoid membranes and choroid plexus had been carefully removed prior to brain dissection. Neither CYP1A1, 1A2 protein, nor EROD activity were detected in purified brain mitochondria, regardless of treatment or region. In conclusion, catalytically active CYP1A1 is located in the meninges as well as certain circumventricular organs, is inducible by BNF, and appears to be absent or expressed constitutively at very low levels in the majority of the brain parenchyma. The localization of CYP1A1 in the blood-CSF barrier and circumventricular tissues likely plays a role in protecting the brain from xenobiotics.

Animals↗

PubMed1998

Methamphetamine-induced modification of dopamine metabolism in cultured striatal astrocytes.

The role of striatal astrocytes in the metabolic processing (by deamination) of methamphetamine-released dopamine is not known. To investigate the relationship between methamphetamine and dopamine metabolism, we measured 6-hydroxydopamine, dopamine and, 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations following methamphetamine treatment of cultured striatal astrocytes prepared from 1-2 day-old rats. Addition of low concentrations of dopamine (5 x 10(-5) to 5 x 10(-4) M) to cultured astrocytes increased DOPAC levels in a dose-dependent fashion while higher concentrations (5 x 10(-3) to 10(-2) M) inhibited its metabolism and induced formation of 6-hydroxydopamine. Under the same experimental conditions, 10(-4) M dopamine in combination with methamphetamine (10(-5) to 10(-3) M) inhibited DOPAC formation and increased dopamine levels in a dose-dependent fashion, but the formation of intracellular 6-hydroxydopamine was not evident. Deprenyl (10(-5) or 10(-4) M), an inhibitor of monoamine oxidase B, and pargyline (10(-5) or 10(-4) M), a non-selective monoamine oxidase inhibitor, completely inhibited DOPAC formation and increased dopamine levels, while clorgyline (10(-5) or 10(-4) M), an inhibitor of monoamine oxidase-A, only partially inhibited DOPAC formation (42 or 45% of control, respectively). These results support the hypothesis that methamphetamine inhibits monoamine oxidase and causes increases in dopamine levels in cultured striatal astrocytes.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1995

Effects of pargyline and pyrogallol on the methamphetamine-induced dopamine depletion.

The formation of 6-hydroxydopamine (6-OHDA) from dopamine (DA) was investigated in the striatum of male Sprague-Dawley rats following a single administration of methamphetamine hydrochloride (100 mg/kg, sc). Rats were sacrificed 30, 60, and 90 min, and 1 wk after injection, and striatal 6-OHDA, DA, and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured by HPLC with electrochemical detection. Methamphetamine decreased striatal DA and DOPAC levels (to 65 and 50% at 90 min, respectively) in the time-course study and also resulted in a long-lasting dopamine depletion (34%) 1 wk after its administration. However, endogenous 6-OHDA formation proved difficult to detect after administration of the methamphetamine alone. Pretreatment with the monoamine oxidase (MAO) inhibitor pargyline (100 mg/kg, ip) and the catechol-O-methyltransferase (COMT) inhibitor pyrogallol (25 mg/kg, ip) resulted in the HPLC detection of a 6-OHDA-like substance 30 min after methamphetamine administration when the oxidizing potential was set at 0.5 V, but not when it was set at 0.2 V. Moreover, pargyline (25 mg/kg, ip) alone or in combination with pyrogallol exacerbated the long-lasting dopamine depletion induced by methamphetamine (50 mg/kg, sc). These results indicate that simultaneous inhibition of MAO and COMT provides a cellular environment that encourages the autoxidation of dopamine to a 6-OHDA-like substance.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1995

Glutathione S-transferases and gamma-glutamyl transpeptidase in the rat nervous systems: a basis for differential susceptibility to neurotoxicants.

Glutathione and its related enzymes play a major role in the detoxification of toxic chemicals. In rat brain the pattern of distribution of reduced glutathione exhibits cellular heterogeneity, suggesting also the possibility of cellular differences in glutathione conjugating capacity. To understand the potential role of GSH in detoxification of neurotoxicants, the distributions of the glutathione conjugating and metabolizing enzymes, glutathione S-transferase (GST; alpha-, mu- and pi-classes) and gamma-glutamyl transpeptidase (gamma-GT) were determined immunohistochemically in brain, lumbar spinal cord and dorsal root ganglia (DRG) of adult Sprague-Dawley rats using polyclonal antibodies. The influence of tissue fixation on apparent distribution was also examined. Glial cells and neurons throughout the nervous system were only weakly positive with alpha-GST in frozen sections. No immunoreactivity for the alpha-class GSTs was observed in any of the paraformaldehyde-fixed neural specimens examined. In microwave-fixed frozen sections, immunoreactivity to mu-GST was found in astrocytes and neurons throughout the brain and spinal cord, and in the neurons and satellite cells of the DRG. Immunoreactivity for pi-GST was seen in oligodendrocytes but not in astrocytes in any region of the CNS examined. Similarly, satellite cells of the DRG were positive for pi-GST. Neuronal perikarya of the entire neopallium, hippocampus, cerebellum, brainstem, spinal cord and DRG were also positively stained for pi-GST. The differential staining of astrocytes and oligodendrocytes with pi- and mu-GST was unaltered in paraformaldehyde fixed tissues, but the neuronal immunostaining was lost. The ependyma, pia and choroid plexus stained positively with all three GST antibodies regardless of fixation. Gamma-Glutamyl transpeptidase-like immunoreactivity was confined to non-neuronal elements of both central and peripheral nervous systems. Ependymal cells throughout the central nervous systems stained intensely with antibodies directed against gamma-GT. Satellite and Schwann cells of the DRG and glial cells of the spinal cord and brain exhibited moderate to intense immunoreactivity for gamma-GT. The heterogeneous cellular distribution of glutathione and its metabolizing enzymes may reflect cellular differences in capacity for metabolic processing of both endogenous compound and xenobiotics.

3,3'-Diaminobenzidine↗

PubMed1995

Developmental changes in the cellular distribution of glutathione and glutathione S-transferases in the murine nervous system.

The distribution of glutathione (GSH) and glutathione S-transferases (GSTs) in the adult rat brain is cell-type specific, but their cellular distribution in the developing central nervous system is unknown. In the present study, GSH distribution in the mouse nervous system was visualized by mercury orange histochemistry and class-specific GSTs were localized by immunohistochemistry at ages E13 to PN30. Both neuronal and glial progenitor cells stain uniformly positive for GSH at E13. Spinal anterior horn neurons become GSH-negative by E17, at which time neurons and glia in other CNS regions are still GSH-positive. By PN5, most neurons have lost GSH staining and are surrounded by GSH-rich neuropil, ependyma, and vasculature. Olfactory mitral and granule cells, cerebellar granule cells, and dorsal root ganglion (DRG) neurons retain consistently high levels of GSH throughout development and into adulthood. Immunoreactivity to alpha-class GST antisera is not observed in the CNS until PN10, when very weak staining becomes apparent in the pia, ependyma, choroid plexus and neurons throughout the brain and spinal cord. Immunoreactivity to mu-GST is observed in neurons and astrocytes (but not oligodendrocytes), pia, ependyma, and choroid plexus throughout the brain by PN10. pi-GST immunoreactivity is observed in all cells of the embryonic nervous system. Postnatally, it is found in neurons and oligodendrocytes (but not astrocytes) in all regions of the brain and spinal cord as well as in pia, ependyma, and choroid plexus. The neurons and satellite cells of the DRG are immunoreactive to alpha-, mu-, and pi-GST antisera at all time points examined. The developmental changes in the cellular distribution of GSH and GSTs suggest that enzymatic conjugation and antioxidant activities may also be cell specific during brain development.

Animals↗

PubMed1994

Substrates for neural metabolism of xenobiotics in adult and developing brain.

Cellular heterogeneity and structural complexity of the nervous system, coupled with regional and cellular differences in the metabolic capabilities of neurons, glia and other non-neuronal elements, may underlie the selective cellular involvement following exposure to neurotoxicants. Determination of the role of biotransformation of xenobiotics in neural pathoclisis requires an understanding of the cellular distribution of both phase I and phase II enzyme systems in the brain. While ependyma, choroid plexus and endothelial linings of blood vessels throughout the nervous system appear to contain appreciable amounts of several isoforms of cytochrome P450 (CYP450), glia and neurons tend to be highly specific in which forms of CYP450 they express. Regional and cellular heterogeneity similarly characterize the distribution of glutathione (GSH) and the conjugating enzyme glutathione S-transferase (GST) in the brain. While all cells of the embryonic nervous system express high levels of GSH and pi-GST (with lesser amounts of alpha- and mu-class), by adulthood neurons and non-neuronal cells differ in the distribution of GSH and isoforms of GST. Neurons (except the dorsal root ganglia and the cerebellar granule cells) become GSH-negative but contain alpha-, mu-, and pi-GST. Glia, ependyma, choroid plexus and neurovascular cells are rich in GSH and variously express GSTs. The differences found in the cellular distribution of GSH and GSTs may contribute to changes in the vulnerability of the nervous system to neurotoxicants at different ages. A comprehensive understanding of the neurotoxicological and pharmacological consequences of the cellular heterogeneity in the localization the CYP450s and glutathione S-transferases pre- and postnatally will require systematic study of the distribution, substrate specificity, and inducibility of the various isoforms of these enzyme systems.

Animals↗

PubMed1993

Synergistic neurotoxic effects of styrene oxide and acrylamide: glutathione-independent necrosis of cerebellar granule cells.

Conjugation with glutathione (GSH) is a mechanism of detoxification of acrylamide (ACR); hence, prior depletion of GSH might be expected to exacerbate ACR's neurotoxicity. GSH levels in female rats were reduced by ip administration of styrene oxide (SO; 250 mg/kg), diethylmaleate (DEM; 0.5 ml/kg), or 2-vinylpyridine (VP; 100 mg/kg) 1.5 or 2 hr prior to a single dose of ACR (100 mg/kg). The time course of GSH depletion following treatment with SO/ACR, DEM/ACR, or VP/ACR showed that all three regimens were equally effective in reducing GSH in liver, cerebellum, cerebral cortex, and hippocampus. GSH levels in the liver were reduced to 4-22% of control levels between 2 and 4 hr after treatment and to 38-57% of control levels in all brain regions between 4 and 8 hr. ACR alone (100 mg/kg) reduced both brain and liver GSH to about 60% of normal. The administration of a second dose of ACR (also 100 mg/kg) 12 hr later further depleted brain and liver GSH to 33% of control. Brains were examined 2, 4, 7, 14, and 30 days after treatment by light and electron microscopy. The administration of SO plus ACR (in either order) produced lesions consisting of pyknotic granule cells confined to the anterior portions of the cerebellum and some of the small neurons of lamina II and III of the cerebral cortex. Electron microscopy revealed condensation of the granule cell chromatin and dissolution of the cytoplasm with the formation of large pericellular spaces. The granule cell lesion was not produced when the time between SO and ACR injections was either 4 or 24 hr. No pathology was observed following treatment with DEM/ACR, VP/ACR, ACR/ACR, vehicle (peanut oil), SO, or ACR alone. It appears that the neurotoxicity in animals treated with SO plus ACR is not directly the result of reduced cellular GSH levels per se, but may involve other detoxification pathways of ACR and SO.

Acrylamide↗

PubMed1993

The effect of glutathione depletion on methyl mercury-induced microtubule disassembly in cultured embryonal carcinoma cells.

Microtubule (MT) assembly and stability are thought to be dependent on intracellular glutathione for the maintenance of critical sulfhydryl groups. Since methyl mercury (MeHg) is a sulfhydryl-binding toxicant, it is possible that alteration of intracellular glutathione status might enhance the toxic effects of MeHg on microtubules. The influence of MeHg on the relationship between intracellular glutathione and the structural integrity of interphase microtubules was assessed in embryonal carcinoma cells by immunofluorescence microscopy, using antibodies to tyrosinated and acetylated alpha-tubulins. Intracellular glutathione concentrations were reduced by treatment with 10 microM buthionine sulfoximine (BSO; an inhibitor of gamma-glutamyl cysteine synthetase) for 18-24 hr. BSO-treated cells displayed little change in the pattern of microtubule staining, despite reduction of glutathione levels to less than 10% of control levels. Similarly, a combination of BSO and the nonspecific glutathione-depleting agent diethylmaleimide (DEM) had little effect on microtubule networks, except at the highest concentrations of DEM where nonspecific cytotoxicity was observed. The susceptibility of microtubules to MeHg-induced disassembly was determined in normal and glutathione-depleted cells incubated with 1.0 to 7.5 microM MeHg for 2 hr. MeHg treatment alone resulted in concentration-dependent disassembly of microtubules; depletion of glutathione with BSO prior to MeHg treatment did not enhance MT damage. Further, BSO-pretreated cells exposed to MeHg still showed substantial recovery of microtubule networks following removal of MeHg from culture media, even when glutathione levels remained less than 5% of control levels. These data indicate that the integrity of interphase microtubules is largely unaffected by reductions in glutathione concentration and that susceptibility of microtubules to MeHg-induced disassembly is not directly dependent on intracellular glutathione content.

Animals↗

PubMed1993

3-Acetylpyridine-induced degeneration in the dorsal root ganglia: involvement of small diameter neurons and influence of axotomy.

3-Acetylpyridine (3-AP), an analogue of nicotinamide, produces highly selective CNS lesions, the severity of which may be influenced by prior alterations in the metabolic activity of the affected neurons. The present study was undertaken to determine whether prior axotomy modified the response of dorsal root ganglia (DRG) and anterior horn (AH) neurons to 3-AP. A single administration (50 or 80 mg/kg i.p.) of 3-AP to adult rats resulted in degeneration of primarily small-dark DRG neurons by 24 h. The AH neurons were not affected by either dose of 3-AP. Light and electron microscopy of the DRG revealed a spectrum of damage ranging from loss of Nissl substance and cytoplasmic degradation to frank necrosis with neuronophagia. Frequently, injured neurons exhibited perinuclear aggregation of cytoplasmic organelles with dissolution of Nissl substance, clearing of the peripheral cytoplasm, and formation of large peripheral vacuoles. Occasionally, a second pattern of 3-AP injury was observed in which the nuclear chromatin of the neurons was condensed and there was formation of small vacuoles throughout the cytoplasm without peripheral clearing or perinuclear aggregation of cytoplasmic organelles. Axotomy induced typical axon reactions in both large-pale and small-dark DRG neurons. The combination of axotomy followed by 3-AP 4 days later produced morphological features characteristic of both axotomy and 3-AP exposure, but did not appear to alter the incidence of neuronal cell death. The almost exclusive vulnerability of the small dorsal root ganglion neurons to 3-AP neurotoxicity make this model potentially useful for the study of small fibre neuropathies.

Animals↗

PubMed1992

Motor unit function during evolution of proximal axonal swellings.

beta,beta'-Iminodipropionitrile (IDPN) impairs axonal transport of neurofilaments; their accumulation leads to the formation of proximal swellings in motor axons. Similar proximal swellings are a feature of some cases of motor neuron disease such as amyotrophic lateral sclerosis (ALS). Motor units in IDPN-treated animals were assessed to determine their relative susceptibilities to impaired function and whether the functional changes resulting from proximal axonal swellings share certain electromyographic features with ALS. Intrinsic properties of medial gastrocnemius motoneurones (MN) and contractile responses of their motor units were examined during the evolution of proximal axonal swellings in cats administered IDPN (50 mg/kg once weekly) for 7, 14 or 35 days. While conduction velocities were significantly decreased in all motor unit types by 35 days, the conduction slowing was greater in fast fatigable (types FF and FI) motor units than in fatigue resistant (types FR and S) motor units. Normal correlations between axonal conduction velocity and MN input resistance (Rin) and the inverse relationship between Rin and rheobase were lost with progression of the neuropathy. Twitch and maximum tetanic tension developed by fast-fatigable motor units declined early in the neuropathy, whereas fatigue-resistant units did not show similar changes until later stages of the intoxication. In some motor units, irregular and abnormal tetanic tensions were elicited by repetitive MN discharge. At 14 and 35 days, a novel, intermediate motor unit response classified as slow and fatigable (SF) was observed. Conduction block, characterized by repetitive MN firing without a corresponding contractile response, was observed in some type FF and S units by 35 days. Morphometric analysis of muscle fiber types showed significant atrophy, particularly in the type I fibers at 14-35 days; the atrophy reversed following cessation of IDPN administration. The influence of proximal axonal swellings on motor unit function in IDPN neuropathy is discussed in terms of reported electrophysiological alterations in motoneurone disease.

Action Potentials↗

PubMed1992

Ectopic impulse generation in dorsal root ganglion neurons during methylmercury intoxication: an electrophysiological and morphological study.

Electrophysiological function and morphology of dorsal root ganglion (DRG) neurons were investigated in female Wistar rats following administration of methylmercury (5 mg/kg/day for 10 days). Neurons were classified according to the conduction velocities of their peripheral axons and perikaryal action potential characteristics as types A alpha, A beta A delta and C. In methylmercury-treated rats, the majority of DRG neuron action potential characteristics were not significantly altered. However, axonal conduction velocities were slowed in all type A ganglion cells, leading to significant delays in action potential onset in types A beta and A delta neurons. An initial complex-soma inflection was observed on the rising phase of the action potential of some cells. These inflection potentials had longer conduction times and lower amplitudes in treated animals. Repetitive discharge, characterized by 3-5 action potentials upon single peripheral nerve stimulation, was observed in 8 of 38 cells recorded in treated animals, predominantly in type A beta (4/8) and A beta (3/12) neurons; direct current injection into repetitively discharging cells via the recording electrode elicited only single action potentials. Extracellular recordings from dorsal root filaments confirmed that the repetitive action potentials arising in the DRG were conducted to the spinal cord. Morphological examination of DRG revealed damage in up to 10% of neurons, consisting of loss of Nissl staining, cytoplasmic vacuolization, and proliferation of satellite cells. Large, pale neurons appeared preferentially involved. Rarely, neuronophagia was observed. Further microscopic examination of proximal and distal sections of sciatic and tibial nerves revealed only occasional degeneration of myelinated axons. While morphological alterations did not appear to offer a structural basis for the multiple firing, it is speculated that repetitive action potential discharge may contribute to the paresthesias associated with MeHg intoxication.

Action Potentials↗

PubMed1991

Cellular and regional distribution of reduced glutathione in the nervous system of the rat: histochemical localization by mercury orange and o-phthaldialdehyde-induced histofluorescence.

Differences in the cellular distribution of antioxidant defense mechanisms in heterogeneous tissue such as the nervous system are likely critical determinants of differential sensitivity to toxicants. Regional and cellular localization of reduced glutathione (GSH) in central and peripheral nervous tissue was determined from the pattern of fluorescence observed in tissue sections stained with mercury orange; localization was confirmed using a novel histofluorochromatic staining method, o-phthaldialdehyde (OPT). Excellent concordance between the distribution of fluorescence obtained with mercury orange and OPT staining was observed. Depletion of GSH by treatment with diethyl maleate resulted in a diminution in both mercury orange and OPT histofluorescence. Generally, strong staining of the CNS neuropil was seen with little or no observable fluorescence in neuronal somata. The cerebellar granular cells were an exception, exhibiting fluorescence with both mercury orange and OPT. Cerebellar Purkinje cells exhibited nonuniform fluorescence with mercury orange but generally uniform staining with OPT. In contrast to the patterns observed in the CNS, the sciatic nerve and the sensory cell bodies of the lumbar dorsal root ganglia exhibited prominent fluorescence with both mercury orange and OPT. Reduced glutathione in the central nervous system appears primarily localized in the neuropil and white matter tracts; with a few exceptions, the neuronal somata do not appear to contain appreciable amounts of GSH. The heterogeneous distribution of GSH and enzymes involved in the detoxification and/or excretion of xenobiotics in the nervous system may form a basis for selective cellular and/or regional expression of neurotoxicity.

Animals↗

PubMed1991

Enhanced resolution of histochemical distribution of glucose-6-phosphate dehydrogenase activity in rat neural tissue by use of a semipermeable membrane.

We examined the histochemical distribution of glucose-6-phosphate dehydrogenase (G6PD) activity in neural tissue using different diffusion barriers. Although polyvinyl alcohol and agar overlays permitted regional localization of G6PD, a semipermeable membrane revealed cellular differences in G6PD activity within populations of neurons. Distribution of G6PD activity in selected regions of the nervous system was examined using the membrane technique. White matter usually exhibited strong G6PD activity. The neuronal somata of the dorsal root ganglia (L4-L6) and anterior horns of the spinal lumbar enlargement demonstrated a variation in activity which was independent of somal size. Satellite cells showed intense activity when the membrane technique was used. Hippocampal pyramidal and granular cells of the dentate gyrus exhibited moderate, uniform G6PD activity, but only weak activity was seen in hippocampal and dentate molecular layers. High levels of activity were observed in the vascular endothelial cells of the brain, spinal cord, and choroid plexus, and in the ependymal cells of the spinal central canal and ventricles of the brain. The superior vestibular nucleus appeared to have little G6PD activity in either the neuron cell bodies or the surrounding parenchyma. The use of a semipermeable membrane for localization of G6PD activity in neural tissues permits enhanced resolution of neuron elements and may provide a more accurate assessment of G6PD activity in histological preparations.

Animals↗

PubMed1990

Synaptic terminal degeneration and remodeling at the rat neuromuscular junction resulting from a single exposure to acrylamide.

Repetitive exposure to low doses of acrylamide results in extensive pathological changes at the neuromuscular junction (NMJ), but it remains undetermined if a single exposure to a larger dose will produce a similar neuropathological outcome. In the present study, morphometric and ultrastructural analyses of rat soleus NMJ were performed to determine early pathological effects of an intraperitoneal injection of 100 mg/kg acrylamide. Widespread nerve terminal degeneration, terminal sprouting, and endplate lengthening were evident as early as 4 days after injection. Degenerating terminal branches were swollen and exhibited enhanced argyrophilia. Ultrastructurally, the majority of terminals exhibited axolemmal abnormalities, neurofilament accumulations, and a paucity of synaptic vesicles; occasional swollen terminals lacked neurofilaments but contained increased numbers of tubulovesicular profiles. This early morphological pattern of nerve terminal changes suggests that acrylamide may disrupt both synaptic vesicle recycling and neurofilament degradation. These findings indicate that a single high dose of acrylamide triggers pathological lesions and remodeling in motor nerve terminals virtually identical to those resulting from multiple low doses.

Acrylamide↗

PubMed1990

Early degeneration and sprouting at the rat neuromuscular junction following acrylamide administration.

Prolonged acrylamide administration produces motor nerve-terminal branch degeneration and impairs axonal outgrowth following nerve crush. It is unclear how early terminal branch degeneration is initiated and whether there is a compensatory regenerative response at the neuromuscular junction (NMJ). A modified Pestronk and Drachman silver-acetylcholinesterase strain was used to carry out a detailed morphometric analysis of the NMJ in soleus and lumbrical muscles. Rats were given 3, 5, or 10 doses of acrylamide, 35 mg/kg/day, by intraperitoneal injection, 5 days/week, and killed 4, 7, or 14 days after the first dose, respectively. Degenerating terminal branches were evident in soleus NMJ after only three doses of acrylamide. Diminished synaptic vesicle content, neurofilament accumulations and tubulo-vesicular profiles were evident after three doses. At later time points, degenerating terminals contained few synaptic vesicles and were engorged with neurofilaments. Endplate lengthening, indicative of denervation supersensitivity, accompanied degeneration. Terminal sprouting proliferated after 3 and 5 doses but was less prominent after 10 doses. Although similar changes occurred in the lumbrical muscle, they were not initiated until after 5 doses. These experiments reveal that pathological changes in terminal branches commence earlier and after a lower cumulative dose of acrylamide than previously reported and suggest that acrylamide exerts a primary effect at motor nerve-terminal branches. Early, vigorous terminal sprouting indicates that acrylamide does not prevent the initiation of regeneration, but with prolonged treatment does cause degeneration of maturing sprouts.

Acrylamide↗

PubMed1989

Axotomy-like electrophysiological alterations in spinal motoneurons in beta,beta'-iminodipropionitrile neuropathy.

Motoneurons (MNs) exhibit characteristic electrophysiological alterations following axotomy which are concomitants of perikaryal remodeling induced by the axonal injury. beta,beta'-Iminodipropionitrile (IDPN) neurotoxicity, which produces proximal axonal swellings in the first internodes of motor fibers, was studied as a model of perikaryal electrophysiological properties in axonal pathologies without axonal degeneration. Similarities between parameters of MN excitability (delayed depolarizations, repetitive discharge, and the afterhyperpolarization potential, AHP) known to occur in axotomized MN and those in IDPN neuropathy were examined in type-identified spinal MN of cats during the evolution (7 to 35 days) of proximal axonal swellings. Delayed depolarization potentials were observed frequently in fast MN types throughout the neuropathy but only at 35 days in slow MN types. Similarly, repetitive firing occurred most prominently in fast MNs early in the neuropathy. Concomitantly, AHP duration decreased as early as 7 days in all MN types and was significantly shortened in types FF, FR, and S motoneurons. AHP peak amplitude and current declined continuously from 7 to 35 days of the neuropathy and were significantly (p less than 0.05) decreased at 35 days in types FF and S MNs. These results suggest that not only are fast MN types vulnerable early in IDPN neuropathy, but also that all MN types exhibit electrophysiological changes strikingly similar to those following mechanical axotomy. The possibility is raised that IDPN may initiate electrophysiological changes, analogous to perikaryal remodeling, by mechanism(s) unrelated to axonal degeneration.

Action Potentials↗

PubMed1989

Influence of proximal axonal swellings on rhythmic motoneuron firing.

Previous studies of electrophysiological function of motoneurons (MNs) in animals with beta, beta'-iminodipropionitrile (IDPN) neuropathy revealed alterations in action potential discharge indicative of enhanced MN excitability. These changes, particularly manifested in increased numbers of delayed depolarizations and repetitive firing upon single stimulation, are strikingly similar to those observed in axotomized MNs. The present study extends the parallels between axotomized and neuropathic conditions by assessing rhythmic firing responses of MNs to direct current injection in cats treated with IDPN (50 mg/kg/week for 5 weeks). Changes in excitability and frequency-current relationships were studied on Day 35 of IDPN intoxication and compared to those reported for axotomized (chromatolytic) MNs. In treated animals, lumbar MNs had increased thresholds for sustained discharge, tended to achieve higher maximum discharge frequencies, and adapted less to continuous current injection. In untreated cats 74% of MNs exhibited firing in both primary and secondary ranges, whereas only 39% of those in treated animals made the transition to secondary range firing. Most fired monotonically in the primary range with unchanged slope of the frequency-current relationships. When achieved, secondary range slopes were one-third of normal. MN afterhyperpolarization peak amplitude, duration, and conductance were reduced while input resistance was increased. The findings are discussed in terms of altered MN and dendritic excitability induced by the neuropathy, and similarities to electrophysiological changes in axotomized MNs.

Action Potentials↗