A comparison of the changes in the non‐neuronal cell populations of the superior cervical ganglia following decentralization and axotomy

Transecting the axons of neurons in the adult superior cervical ganglion (SCG; axotomy) results in the survival of most postganglionic neurons, the influx of circulating monocytes, proliferation of satellite cells, and changes in neuronal gene expression. In contrast, transecting the afferent input to the SCG (decentralization) results in nerve terminal degeneration and elicits a different pattern of gene expression. We examined the effects of decentralization on macrophages in the SCG and compared the results to those previously obtained after axotomy. Monoclonal antibodies were used to identify infiltrating (ED1+) and resident (ED2+) macrophages, as well as macrophages expressing MHC class II molecules (OX6+). Normal ganglia contained ED2+ cells and OX6+ cells, but few infiltrating macrophages. After decentralization, the number of infiltrating ED1+ cells increased in the SCG to a density about twofold greater than that previously seen after axotomy. Both the densities of ED2+ and OX6+ cells were essentially unchanged after decentralization, though a large increase in OX6+ cells occurred after axotomy. Proliferation among the ganglion's total non‐neuronal cell population was examined and found to increase about twofold after decentralization and about fourfold after axotomy. Double‐labeling experiments indicated that some of these proliferating cells were macrophages. After both surgical procedures, the percentage of proliferating ED2+ macrophages increased, while neither procedure altered the proliferation of ED1+ macrophages. Axotomy, though not decentralization, increased the proliferation of OX6+ cells. Future studies must address what role(s) infiltrating and/or resident macrophages play in regions of decentralized and axotomized neurons and, if both are involved, whether they play distinct roles. © 2002 Wiley Periodicals, Inc. J Neurobiol 53: 68–79, 2002     

A stochastic model for leukocyte random motility and chemotaxis based on receptor binding fluctuations

Two central features of polymorphonuclear leukocyte chemosensory movement behavior demand fundamental theoretical understanding. In uniform concentrations of chemoattractant, these cells exhibit a persistent random walk, with a characteristic "persistence time" between significant changes in direction. In chemoattractant concentration gradients, they demonstrate a biased random walk, with an "orientation bias" characterizing the fraction of cells moving up the gradient. A coherent picture of cell movement responses to chemoattractant requires that both the persistence time and the orientation bias be explained within a unifying framework. In this paper, we offer the possibility that "noise" in the cellular signal perception/response mechanism can simultaneously account for these two key phenomena. In particular, we develop a stochastic mathematical model for cell locomotion based on kinetic fluctuations in chemoattractant/receptor binding. This model can simulate cell paths similar to those observed experimentally, under conditions of uniform chemoattractant concentrations as well as chemoattractant concentration gradients. Furthermore, this model can quantitatively predict both cell persistence time and dependence of orientation bias on gradient size. Thus, the concept of signal "noise" can quantitatively unify the major characteristics of leukocyte random motility and chemotaxis. The same level of noise large enough to account for the observed frequency of turning in uniform environments is simultaneously small enough to allow for the observed degree of directional bias in gradients.     

Chemotactic peptide binding by rabbit polymorphonuclear leukocytes. Presence of two compartments having similar affinities but different kinetics

N-Formylnorleucylleucylphenylalanine (f-Nle-LeuPhe) bound to rabbit peritoneal polymorphonuclear leukocytes at 4 degrees C exists in at least two compartments that can be differentiated by their off rates. The off rate of one compartment is similar to that of the receptor characterized previously, about 0.4 min-1 (Aswanikumar, S., Corcoran, B., Schiffmann, E., Day, A. R., Freer, R. J., Showell, H. J., Becker, E. L., and Pert, C. B. (1977) Biochem. Biophys. Res. Commun. 74, 810-817; Sullivan, S. J., and Zigmond, S. H. (1980) J. Cell Biol. 85, 703-711); the off rate of the second compartment is about 0.005 min-1. Lysis of the cells at 4 degrees C with 1% Triton does not affect the peptide release from either compartment. Accumulation of peptide at 4 degrees C into the fast off-rate compartment is rapid, reaching a plateau in about 5 min, while peptide in the slow off-rate compartment continues to increase for up to 4 h. The rate of accumulation in the slow off-rate compartment is approximately proportional to the amount of peptide bound to the fast off-rate compartment. Cells lysed at 4 degrees C before binding are still able to accumulate peptide into both compartments. Three possible models to explain the data are presented.     

Parkinson's disease: studies with an animal model

Parkinson' disease has been associated with degeneration of dopamine-containing neurons of the nigrostriatal bundle. Many neurological features of Parkinsonism can be produced in rats by selective destruction of central dopaminergic neurons using the neurotoxin 6-hydroxydopamine. In this review we discuss two aspects of Parkinson's disease that have been investigated in these animals. First, we consider why near-total degeneration of nigrostriatal bundle neurons is required before neurological symptoms emerge. It appears that the loss of dopaminergic neurons is accompanied by an exponential increase in the ratio of tyrosine hydroxylase activity to dopamine content. Thus, after the brain lesions there may be a compensatory increase in the capacity of residual dopaminergic neurons to synthesize and release transmitter. Second, we consider why stress produces severe neurological deficits in patients who are only mildly impaired otherwise. It appears that a variety of stressors produce an abrupt but transient increase in dopaminergic activity in the striatum of intact animals and that this increase is markedly attenuated by 6-hydroxydopamine treatment. Thus, stress-induced akinesia in animals with dopamine-depleting brain lesions and in Parkinsonian patients may result from the impaired ability of residual neurons to respond approximately to such stimuli.     

Increased Neostriatal Tyrosine Hydroxylation During Stress: Role of Extracellular Dopamine and Excitatory Amino Acids

Abstract: We examined the regulation of neostriatal tyrosine hydroxylation during acute stress, testing the hypothesis that excitatory amino acids (EAAs) contribute to the stress-evoked increase in dopamine (DA) synthesis. Dialysis probes implanted into neostriatum permitted delivery of drugs and sampling of extracellular fluid. Rats were exposed to 30 min of intermittent tail shock during infusion of an inhibitor of aromatic amino acid decarboxylase (AAAD), NSD-1015 (100 µM), and DOPA was measured in the dialysate. Tail shock was applied beginning either 15 min after the onset of NSD-1015 treatment (the initial rate of DOPA accumulation) or 75 min after the onset of treatment (when DOPA had approached steady state). Tail shock increased the steady-state levels of extracellular DOPA in neostriatum (+40%). However, there was no change in the initial rate of DOPA accumulation unless animals also received the D₂ receptor antagonist eticlopride (50 nM), in which case an increase was observed (+228%). The impact of tail shock on the steady-state level of DOPA was attenuated by the D₂ agonist quinpirole (100 µM), or by 2-amino-5-phosphonovalerate (APV) (100 µM) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (100 µM), EAA antagonists acting at NMDA or d ,l -α-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA) receptors, respectively. These data suggest that acute stress normally has little effect on tyrosine hydroxylation in neostriatum due to the inhibitory influence of DA in the extracellular fluid. However, when that influence is absent (e.g., during extended inhibition of DOPA decarboxylation or blockade of DA receptors), stress increases tyrosine hydroxylation via EAAs acting on NMDA and AMPA receptors. Thus, EAAs released from corticostriatal projections may stimulate DA synthesis and thereby restore dopaminergic activity under conditions in which the availability of DA for release has been compromised.     

Stress-Induced Sensitization of Dopamine and Norepinephrine Efflux in Medial Prefrontal Cortex of the Rat

Abstract: We examined whether prior exposure to chronic cold (17–28 days, 5°C) alters basal or stress-evoked (30-min tail shock) catecholamine release in medial prefrontal cortex, nucleus accumbens, and striatum, using in vivo microdialysis. Basal norepinephrine (NE) concentrations in medial prefrontal cortex did not differ between chronically cold-exposed rats and naive control rats (2.7 ± 0.3 vs. 2.5 ± 0.2 pg/20 µl, respectively). Basal dopamine (DA) efflux in any of the brain regions was not significantly different between chronically cold-exposed rats and naive rats. However, a trend for lower basal DA efflux in the cold-exposed relative to naive rats was observed in medial prefrontal cortex (1.5 ± 0.2 vs. 2.2 ± 0.3 pg/20 µl, respectively), nucleus accumbens (3.7 ± 0.8 vs. 5.4 ± 0.9 pg/20 µl, respectively), and striatum (4.4 ± 0.5 vs. 7.2 ± 1.5 pg/20 µl, respectively). In medial prefrontal cortex of rats previously exposed to cold, tail shock elicited a greater increase from baseline in both DA and NE efflux relative to that measured in naive rats (DA, 2.3 ± 0.3 vs. 1.2 ± 0.1 pg, respectively; NE, 3.8 ± 0.4 vs. 1.4 ± 0.2 pg, respectively). However, in nucleus accumbens or striatum of rats previously exposed to cold, the stress-induced increase in DA efflux was not significantly different from that of naive rats (nucleus accumbens, 1.8 ± 0.7 vs. 1.5 ± 0.3 pg, respectively; striatum, 1.9 ± 0.4 vs. 2.6 ± 0.7 pg, respectively). Thus, both cortical NE projections and cortically projecting DA neurons sensitize after chronic exposure to cold. In contrast, subcortical DA projections do not sensitize under these conditions.     

Regulation of vasoactive intestinal peptide expression in sympathetic neurons in culture and after axotomy: The role of cholinergic differentiation factor/leukemia inhibitory factor

Vasoactive intestinal peptide (VIP) expression increases in sympathetic neurons when they are grown in dissociated cell or explant cultures and when they are axotomized in vivo. In dissociated cell culture, the magnitude of the VIP increase was reduced when nonneuronal cells were removed and medium conditioned by ganglionic nonneuronal cells increased VIP in neuron-enriched cultures. Antiserum Against cholinergic differentiation factor (also leukemia inhibitory factor; CDF/LIF), but not against ciliary neurotrophic factor, immunoprecipitated this activity. Medium conditioned by sympathetic ganglion explants also contained a VIP-stimulatory molecule that was immunoprecipitated by CDF/LIF antiserum, and CDF/LIF antiserum partially blocked VIP induction in explants. CDF/LIF mRNA was increased in dissociated cell cultures, in ganglion explants and in vivo after axotomy. Our results suggest that CDF/LIF released from ganglionic nonneuronal cells plays an important role in regulating VIP after axotomy. 1994 John Wiley & Sons, Inc.     

TYROSINE HYDROXYLASE ACTIVITY IN NORADRENERGIC NEURONS OF THE LOCUS COERULEUS AFTER RESERPINE ADMINISTRATION: SEQUENTIAL INCREASE IN CELL BODIES AND NERVE TERMINALS

The effect of a single systemic injection of reserpine on tyrosine hydroxylase activity in the locus coeruleus, cerebellum, hypothalamus, and hippocampus was examined. Increases in enzyme activity were seen in all four brain areas; the time-course of the changes, however, was different in each case. In the locus coeruleus the maximum change in enzyme activity was seen 3 days after drug administration; in the cerebellum, 7-11 days; in the hypothalamus, 8-11 days; and in the hippocampus, 21 days. Since tyrosine hydroxylase in the cerebellum and hippocampus is present in terminals of neurons whose cell bodies are located in the locus coeruleus, the delayed increase in enzyme activity in cerebellum and hippocampus probably depends upon the slow rate of transport of TH molecules in these neurons.     

A radioenzymatic assay for catecholamines and dihydroxyphenylacetic acid.

Picogram quantities of the catecholamines, dopamine, norepinephrine, and epinephrine, and the dopamine metabolite, dihydroxyphenylacetic acid, can be measured in tissue or plasma samples utilizing a rapid radioenzymatic procedure. The catechols are converted to their ³H-methylated derivatives (3-methoxytyramine, normetanephrine, metanephrine and homovanillic acid, respectively) by the enzyme catechol-O-methyltransferase with ³H-S-adenosylmethionine serving as the ³H-methyl donor. Following the enzymatic reaction, unreacted ³H-S-Adenosylmethionine is removed by precipitation and the reaction products are separated by thin layer chromatography on silica plates. The areas corresponding to the ³H-methylated derivatives are scraped into scintillation vials, eluted with aqueous buffer, extracted into nonpolar scintillation cocktail, and counted by liquid scintillation spectrometry. Using the standard assay procedure described here, over 100 tubes can be assayed in a single day with a sensitivity of 15–25 pg for all compounds measured. With the application of additional procedures, as little as 1 pg norepinephrine and epinephrine and 5–10 pg dopamine and dihydroxyphenylacetic acid can be quantified in a single sample.