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D W Hoffman

Publications and source records attributed to D W Hoffman.

65 records · Page 4Linked to original sources
PubMed1980

Characteristics of norepinephrine uptake in developing peripheral nerve terminals.

In the chick the various characteristics of [3H]norepinephrine (NE) uptake do not appear simultaneously during the development of the iris. Na+-dependence and ouabain sensitivity are both first seen at a significant level at 10 days of incubation (d.i.). Na+-dependence achieves its peak value at 14 d.i. and is unchanged at 3 months after hatching (a.h.). Ouabain sensitivity increases after its initial appearance to 14 days a.h. and then slowly declines. Temperature sensitivity develops only at hatching and is modified subsequently. Both desmethylimipramine (DMI) and cocaine inhibition develop at 10 d.i. and follow the same developmental pattern; however, DMI appears to be a more effective inhibitor than cocaine. Metanephrine, an inhibtor of extraneuronal uptake, first inhibits NE uptake to a significant degree at hatching. These changes may be related to changes in membrane structure and metabolic function in the developing neuronal membrane. No evidence of [3H]NE uptake is seen at 7 d.i. After this age the Km values tend to fall into two groups, the first 1.3--1.9 X 10(-5) M, up to one month a.h., the second, 3.5--5.0 X 10(-6) M, after one month a.h. There is a large increase in Vmax from 10 to 14 d.i., a period of rapid growth of sympathetic innervation of the iris. Our study suggests that Na+-dependent uptake is a more reliable and constant index of innervation in development than temperature-dependent uptake. It also indicates that in longitudinal developmental studies it is necessary to determine the characteristrics of the transport process of each stage, as characteristics such as N1+-, drug- and temperature-sensitivity may all have unique developmental profiles.

Aging↗
PubMed1980

Age dependent changes in choline uptake of the chick iris.

The kinetics of the uptake of choline, the rate-limiting substrate in the in vivo synthesis of acetylcholine, were studied during the period 1--7 years in the iris of the chick. These changes were correlated to the endogenous levels of acetylcholine and choline in the same organ. Vmax values per iris decrease significantly at 5 years and continue to decrease at 7 years, to 64% and 37% of the one year value, respectively. If the variation in Vmax is calculaed per protein the decline is 34% between 1 and 5 years. Km does not change significantly during the period 1--7 years. Total acetylcholine and choline levels follow a similar trend, decreasing progressively from 1 to 7 years. Sensitivity to hemicholinium (5.5 X 10(-5) M) decreases significantly between 5 days of incubation (d.i.) and 5 years. Inhibition by ouabain (10(-4) M) shows an opposite trend, increasing significantly from 20% at 5 d.i. to 52% at 3 months. At 5 years sensitivity to ouabain is the same as at 3 months. Nardependence decreases significantly between 5 d.i. and 5 years but no significant changes are seen between 5 d.i. and 3 months. Uptake at 27 degrees C decreases from 59% of control at 5 d.i. to 45% at 3 months, and is not changed at 5 years. Our observations suggest that the effect of aging on peripheral cholinergic neurons is not generalized, but is specifically directed toward the neuronal periphery (terminals) as opposed to cell bodies.

Acetylcholine↗
PubMed1980

Norepinephrine uptake in aging adrenergic nerve terminals.

Norepinephrine (NE) uptake has been studied in the adult (3-6 months) and aging (5 yr) chick iris, in which there is a discrete population of norepinephrine containing nerve terminals. although total accumulation of 3H-NE in the iris does not change with age, there is a decline in Na+-dependence, temperature-sensitivity, ouabain-and inhibitor -sensitivity of uptake. The results indicate either a loss of active, carrier-mediated NE uptake during aging, or a change in the biochemical and pharmacological characteristics of this uptake. changes in the composition of the organ and in the sites of accumulation of NE are considered.

Aging↗
PubMed1980

Development and aging of cholinergic synapses. III. Choline uptake in the developing iris of the chick.

Choline (Ch) uptake in the iris of the chick has been characterized from 4 1/2 days of incubation to 1 year of age, in conjunction with an electron microscopic ultrastructural study of the innervation of the iris. Uptake has been shown to constitute an early and reliable biochemical marker for the presence of innervation in target organs. The characteristics of Ch uptake, including Na+ and temperature dependence and inhibitor sensitivity, change during development, and the Vmax increases steadily while the Km does not vary significantly during the period of study. The relationships among uptake and other cholinergic functions also change with development of the iris. Acetylcholine (ACh) and Ch uptake but not Ch levels appear to develop together, while cholinergic enzyme activities follow a developmental course more closely related to neurotransmission. The significance of these findings in relation to proposed regulatory relationships in cholinergic biosynthetic mechanisms in discussed.

Aging↗
PubMed1980

Development and aging of cholinergic synapses. IV. Acetylcholinesterase and choline acetyltransferase activities in autonomic ganglia and iris of the chick.

Age-related changes in the activities of choline acetyltransferase an acetylcholinesterase in avian sympathetic ganglia, ciliary ganglia and iris have been determined throughout the posthatching life span. Kinetic characteristics of these enzymes have been analyzed in the nerve terminals in the iris from early embryonic stages to the latest periods of life. Enzyme activities and kinetics have been related to each other and also to the endogenous levels of acetylcholine. The regulation of the biosynthetic mechanism for acetylcholine through choline uptake and choline acetyltransferase activity in the developing nerve terminal have been examined. The activities of both enzymes in all tissue are reduced at later ages, which is referred to declines in Vmax, as the Km values do not vary significantly at any age. Declines with age are most pronounced in the iris, both in choline acetyltransferase activity and Vmax and in acetylcholine levels, supporting our view of the peripheral autonomic nerve terminal as a major locus for the effects of aging on the peripheral nervous system.

Acetylcholinesterase↗
PubMed1979

Biochemical characterization of [3H]norepinephrine uptake in dissociated brain cell cultures from chick embryos.

The uptake of [3H]norepinephrine ([3H]NE) was studied in dissociated brain cell cultures prepared from 8-day-old chick embryos using the whole brain (minus optic lobes). Uptake [3H]NE, 5 x 10(-9) m, 10 min incubation, in freshly dissociated noncultured embryonic chick brain cells, was detected in 6-day-old embryos; it was temperature and drug (cocaine, metanephrine) sensitive and increased with brain development. In cultured cells, which were assayed at various days in culture, the increase in [3H]NE accumulation per culture was less than that seen in freshly dissociated noncultured embryonic cells. When [H]NE uptake was expressed per mg protein, a decrease with days in culture was observed. reflecting perhaps a dilution of growth or proliferation of cells not accumulating NE. Metanephrine, 5 X 10(-6) M, an inhibitor of extraneuronal uptake, inhibited [3H]NE in 5-day-old cultures whereas desmethylimipramine, an inhibitor of neuronal uptake, inhibited [3H]NE uptake in 15- and 20-day-old cultures. Cocaine, another neuronal inhibitor, inhibited [3N]NE at 10 and 15 days only. We interpret these findings to suggest that during early growth in culture most neuroblasts accumulate NE nonspecifically and, as neuronal maturation proceeds, NE accumulation becomes specific.

Animals↗
PubMedDate not supplied

Neurotransmitters of the cochlea and cochlear nucleus: immunocytochemical evidence.

Many neurotransmitter candidates have been identified in the cochlea and cochlear nucleus with the use of immunocytochemical techniques. Choline acetyltransferase immunoreactivity suggests acetylcholine as a transmitter of medial and lateral efferent systems in the cochlea. Immunoreactivities to enkephalins, dynorphins, calcitonin gene-related peptide, and tyrosine hydroxylase (a marker for dopamine) are also found in lateral efferents. Choline acetyltransferase, enkephalin, and dynorphin immunoreactivities are co-contained in neurons of the lateral system. In the anteroventral cochlear nucleus, the inhibitory amino acid transmitters, gamma aminobutyric acid (GABA), and glycine, as well as the presumed excitatory amino acid transmitter of the auditory nerve, have been directly or indirectly localized, immunocytochemically, to discrete populations of terminals on spherical cells with distinct morphologic characteristics.

Acetylcholine↗
PubMedDate not supplied

Potentiation of ototoxicity by glutathione depletion.

The combination of 10 mg/kg ethacrynic acid (ETA) and 100 mg/kg kanamycin (KA) caused neither morphologic damage to the cochlea nor change in the auditory brain stem response of the chinchilla. However, after pretreatment with a single dose of buthionine sulfoximine (BSO; 800 mg/kg intraperitoneally) to reduce intracellular glutathione (gamma-glutamylcysteinylglycine; GSH) levels, the above single administration of ETA and KA resulted in complete deafness and severe morphologic damage. The kidney, which has a rapid GSH turnover and is therefore especially susceptible to GSH depletion by BSO, also demonstrated severe damage after this treatment. A similar rapid turnover of GSH and resulting limited capacity to detoxify reactive metabolites and free radicals may determine cochlear and renal vulnerability to this toxicity. These findings may explain the clinical observations of enhanced ototoxicity in patients administered amino-glycoside antibiotics concomitantly with loop diuretics.

Animals↗
PubMedDate not supplied

Infiltration and adsorption of dissolved atrazine and atrazine metabolites in buffalograss filter strips.

Vegetated filter strips (VFS) potentially reduce the off-site movement of herbicides from adjacent agricultural fields by increasing herbicide mass infiltrated (Minf) and mass adsorbed (Mas) compared with bare field soil. However, there are conflicting reports in the literature concerning the contribution of Mas to the VFS herbicide trapping efficiency (TE). Moreover, no study has evaluated TE among atrazine (6-chloro-N-ethyl-N'-isopropyl-[1,3,5]triazine-2,4-diamine) and atrazine metabolites. This study was conducted to compare TE, Minf, and Mas among atrazine, diaminoatrazine (DA, 6-chloro[1,3,5]triazine-2,4-diamine), deisopropylatrazine (DIA, 6-chloro-N-ethyl-[1,3,5]triazine-2,4-diamine), desethylatrazine (DEA, 6-chloro-N-isopropyl-[1,3,5]triazine-2,4-diamine), and hydroxyatrazine (HA, 6-hydroxy-N-ethyl-N'-isopropyl-[1,3,5]triazine-2,4-diamine) in a buffalograss VFS. Runoff was applied as a point source upslope of a 1- x 3-m microwatershed plot at a rate of 750 L h(-1). The point source was fortified at 0.1 microg mL(-1) atrazine, DA, DIA, DEA, and HA. After crossing the length of the plot, water samples were collected at 5-min intervals. Water samples were extracted by solid phase extraction and analyzed by high performance liquid chromatography (HPLC) photodiode array detection. During the 60-min simulation, TE was significantly greater for atrazine (22.2%) compared with atrazine metabolites (19.0%). Approximately 67 and 33% of the TE was attributed to Minf and Mas, respectively. These results demonstrate that herbicide adsorption to the VFS grass, grass thatch, and/or soil surface is an important retention mechanism, especially under saturated conditions. Values for Mas were significantly higher for atrazine compared with atrazine's metabolites. The Mas data indicate that atrazine was preferentially retained by the VFS grass, grass thatch, and/or soil surface compared with atrazine's metabolites.

Adsorption↗
PubMedDate not supplied

Adsorption and desorption of metolachlor and metolachlor metabolites in vegetated filter strip and cultivated soil.

Previous studies have indicated that dissolved-phase metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(methoxy-1-methylethyl) acetamide] transported in surface runoff is retained by vegetative filter strips to a greater degree than either metolachlor oxanilic acid 12-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl)amino]-2-oxo-acetic acid] (OA) or metolachlor ethanesulfonic acid [2-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl-1)amino]-2-oxoethanesul-fonic acid] (ESA), two primary metabolites of metolachlor. Adsorption-desorption of ESA and OA in vegetated filter strip soil (VFSS) has not been evaluated, yet these data are required to assess the mobility of these compounds in VFSS. The objective of this experiment was to compare metolachlor, ESA, and OA adsorption and desorption parameters between VFSS and cultivated soil (CS). Adsorption and desorption isotherms were determined using the batch equilibrium procedure. With the exception of a 1.7-fold increase in organic carbon content in the VFSS, the evaluated chemical and physical properties of the soils were similar. Sorption coefficients for metolachlor were 88% higher in VFSS than in CS. In contrast, sorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, sorption coefficients for ESA and OA were at least 79% lower in both soils. Metolachlor desorption coefficients were 59% higher in the VFSS than in the CS. Desorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, desorption coefficients for ESA and OA were at least 66% lower in both soils. These data indicate that the mobility of ESA and OA will be greater than metolachlor in both soils. However, higher organic carbon content in VFSS relative to CS may limit the subsequent transport of metolachlor from the vegetated filter strip.

Acetamides↗