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J D Geiger

Publications and source records attributed to J D Geiger.

At least 109 records · Page 6Linked to original sources
PubMed1988

Distinct adenosine deaminase-containing inputs to the substantia nigra from the striatum and tuberomammillary nucleus.

Immunohistochemical, neuroanatomical and lesion methods were used to investigate the projections of adenosine deaminase immunoreactive (ADA-IR) neurons in the striatum (caudate/putamen) and hypothalamus to the substantia nigra (SN). Striatal ADA-IR neurons were distributed within two zones; anteriorly in the medial and ventromedial extreme of the head and body of the striatum, and posteriorly in the tail of the striatum. The posterior hypothalamus contained ADA-positive neurons which were confined to the tuberomammillary nucleus (TM). The SN was devoid of ADA-positive neurons, but contained two distinct types of ADA-IR fiber terminations. One type was confined to bands located at the ventrolateral and dorsomedial borders of the pars reticulata and consisted of fine puncta. The other type was distributed throughout the SN and consisted of long, beaded fibers. Injections of the retrograde tracer Fluoro-gold (FG) into the SN gave rise to FG-labelling of significant numbers of ADA-IR neurons in both the striatum and TM. Medial SN injections preferentially labelled ADA-IR neurons in the anterior striatum and lateral SN injections labelled posterior ADA-IR striatal neurons. Kainic acid lesions of the anterior medial striatum selectively abolished the punctate ADA-IR band in the medial SN and left the long, ADA-IR nigral fibers in an apparently hypertrophied state. Despite depletion of ADA-IR neurons in the striatum by kainic acid, ADA activity increased significantly at striatal lesion sites. The results suggest that the SN receives two topographically segregated fine terminal fields from striatal ADA-IR neurons, and a substantial innervation from ADA-IR neurons in the TM as well. These findings add to the heterogeneous chemical composition of nigral afferents and are discussed in the context of adenosine neuromodulatory mechanisms in the striatonigral system.

Adenosine Deaminase↗
PubMed1988

Adenosine deaminase-'like' immunoreactivity in cerebellar Purkinje cells of rat.

The localization of adenosine deaminase (ADA) throughout the rat CNS was investigated immunohistochemically with 5 different affinity purified polyclonal antibody preparations against ADA. Except in the cerebellum, identical immunostaining patterns of ADA-immunoreactivity were observed with all 5 antibodies. In the cerebellum, Purkinje cells and presumptive swellings on their axons were immunostained by only one of the 5 antibodies. Preabsorption with purified ADA abolished immunostaining with all 5 antibodies. Biochemical tests showed that the Km for substrate, the specific activity of immunoprecipitable enzyme and the isozymic characteristics of cerebellar ADA was not different from ADA in whole brain or several other brain regions examined. The atypical immunohistochemical behavior of cerebellar ADA, despite its biochemical similarity to ADA elsewhere in the brain, suggests that the enzyme in the cerebellum has some unique features which must be taken into account when considering its possible role in regulating the neuromodulatory actions of adenosine in the cerebellar cortex.

Adenosine Deaminase↗
PubMed1988

Distribution, morphology and habenular projections of adenosine deaminase-containing neurons in the septal area of rat.

Adenosine deaminase (ADA) was localized within several types of neurons within the septum and in septal efferent projections to the habenula by immunohistochemical, biochemical, retrograde tracing and lesion methods. Numerous ADA-immunoreactive (ADA-IR) neurons were observed in the septofimbrial nucleus, the triangular septal nucleus and the bed nucleus of the anterior commissure, while considerably fewer numbers were seen in the lateral septal area. Based on their size, shape and dendritic features, 4 morphologically distinct types of ADA-IR neurons were recognized in these septal structures. In addition, fine, non-varicose, ADA-IR fibers appeared to emanate from the postcommissural cell groups and these coalesced within the stria medullaris, continued caudally within this fiber bundle, and gave rise to a dense field of very fine immunoreactive elements within a restricted zone of the dorsal half of the medial habenula. Comparisons of the habenular localization of ADA-IR and enkephalin-IR elements showed that fibers labelled for either ADA or enkephalin occupied distinct, non-overlapping regions within the dorsal half of the medial habenula. After injections of Fluoro-gold (FG) into the medial habenula, the majority of ADA-IR neurons in the septofimbrial nucleus, triangular septal nucleus, and the bed nucleus of the anterior commissure were retrogradely labelled with this fluorescent tracer, whereas no ADA-positive FG-labelled neurons were observed in the lateral septal region. Unilateral transections of the stria medullaris caused substantial depletions of ADA-immunoreactivity and reduced enzymatically determined ADA activity by up to 80% in the medial habenula on the lesioned compared with the contralateral control side. These results demonstrate that ADA-IR neurons in the septum are heterogeneously distributed and that populations of positive neurons within the postcommissural septal nuclei give rise to dense, focal projections to the medial habenula. These projections appear to be restricted to a portion of the medial habenula known to contain substance P-IR neurons and are subregionally segregated from enkephalin-positive septohabenular projections ending within this same portion. In addition to pointing out a unique capacity for adenosine catabolism within some septal neurons, possibly related to purinergic neuromodulation, the results indicate the utility of ADA-immunohistochemistry for the delineation of anatomical relationships between the septum and the medial habenula.

Adenosine Deaminase↗
PubMed1988

Pharmacological characterization of rapidly accumulated adenosine by dissociated brain cells from adult rat.

Mechanically dissociated brain cells from adult rats were used to study biochemically and pharmacologically their capacity to accumulate rapidly [3H]adenosine. The assay, which used an inhibitor-stop method to prevent further uptake into cells, was characterized with respect to protein and optimal substrate concentrations, and incubation times that ranged from 5 to 180 s. The accumulation of [3H]adenosine using 15-s incubation periods, conditions under which less than 10% of accumulated [3H]adenosine was metabolized, was best described kinetically by a two-component system with Km and Vmax values for the high-affinity component of 0.8 microM and 6.2 pmol/mg protein/15 s and for the low-affinity component 259 microM and 2,217 pmol/mg protein/15 s, respectively. The potencies with which nucleosides, adenosine deaminase resistant adenosine receptor agonists, and nucleoside uptake inhibitors competed for these uptake components were determined. Of the nucleosides examined, adenosine was the "preferred" substrate for the uptake site. The Ki value of adenosine for the high-affinity component was 10.7 microM. Inosine and uridine competed for a single lower affinity uptake system: Ki values were 142 and 696 microM, respectively. Nucleoside uptake inhibitors--nitrobenzylthioinosine, dipyridamole, and dilazep--were the most potent inhibitors of [3H]adenosine accumulation tested: the Ki values for the high-affinity system were 0.11, 1.3, and 570 nM, respectively. The adenosine analogs S-phenylisopropyladenosine, R-phenylisopropyladenosine, and cyclohexyladenosine inhibited the high-affinity component with Ki values of 2.3, 9.3, and 14.5 microM, respectively. N-Ethylcarboxamidoadenosine competed for a single lower affinity uptake system: Ki, 292 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1987

Adenosine uptake and [3H]nitrobenzylthioinosine binding in developing rat brain.

The ontogenesis of adenosine transport sites as labelled with [3H]nitrobenzylthioinosine ([3H]NBI) was examined using radioligand binding and membrane preparations from whole brain and 4 brain regions of rats between the postnatal ages of one day through to adulthood. In whole brain, cerebral cortex and cerebellum, [3H]NBI binding was two-fold higher in 6-day-old than in 50-day-old rats. In contrast, [3H]NBI binding was higher in adults than in one-day-old rats by 4-fold in hypothalamus and 8-fold in superior colliculus. In cortex and hypothalamus, the levels of [3H]NBI binding in newborn and adult rats were reflected by changes in Bmax and not Kd values. As a measure of the utility of [3H]NBI as a probe for identifying functional adenosine transport sites, we examined [3H]NBI binding to and [3H]adenosine accumulation by intact brain cells prepared from adult and newborn rats. For [3H]NBI binding to brain cells from adult rats, the values of Kd were 0.092 nM and of Bmax were 274 fmol/mg protein. For newborns, slightly higher Kd and Bmax values were observed; 0.2 nM and 395 fmol/mg protein, respectively. [3H]Adenosine accumulation was higher in brain cells from one-day-old than from adult rat brains. Kinetically this uptake was best described by a two-component model: the Vmax values for the high- and low-affinity uptake, and the Km value for the high-affinity component in one-day-old rats were greater than in adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1987

Central effects of adenosine analogs on stress-induced gastric ulcer formation.

Rats subjected to restraint stress developed gastric lesions that could be reduced by R-phenylisopropyladenosine (R-PIA) administered intracerebroventricularly. This protective effect was reversed by 8-sulfophenyltheophylline given centrally, and by peripherally administered 8-phenyltheophylline. These results suggest that central adenosine receptors mediate the effect. In subsequent studies it was found that if the absolute level of ulcer formation in control rats was low, R-PIA had no ulcer protective effect. Thus, although it appears that adenosine receptors are important in attenuating pathological gastric responses to stress, this attenuation seems to be dependent on the level of ulcer formation in control animals.

Adenosine↗
PubMed1987

Pharmacokinetics of 2'-deoxycoformycin, an inhibitor of adenosine deaminase, in the rat.

The distribution of the potent inhibitor of adenosine deaminase (ADA), 2'-deoxycoformycin (DCF), in the brain of the rat and its inhibition of ADA in brain and gut was determined. The accumulation of [3H]DCF in brain was maximal 2 hr after intraperitoneal injection and elimination was best described by a two compartment model having t1/2 phases of about 1-5 hr and 50 hr. The activity of ADA in gut exhibited dose-related inhibition at 1.9, 3.7 and 18.6 mumol/kg (i.p.) and returned to normal by 16 days. In brain, ADA was inhibited by about 95% at all three of these doses of DCF 2 hr after injection and activity returned to control levels by 30 days with the two smaller doses, but remained at 66% of control levels at 50 days with 18.6 mumol/kg. The t1/2 of the recovery of the activity of ADA in both brain and gut was found to be dose-dependent. The failure of the activity of ADA in brain to recover after treatment with 18.6 mumol/kg suggests either long-term down-regulation of the expression of ADA or irreversible damage to ADA-containing neurons.

Adenosine Deaminase↗
PubMed1987

Inhibitors of histidine decarboxylase decrease basal gastric acid secretion in the rat.

We examined the ability of two specific inhibitors of histidine decarboxylase, (s)-alpha-fluoromethylhistidine (FMHd) and (s)-alpha-fluoromethylhistamine (FMHm), to inhibit basal gastric acid secretion. The two highest doses of FMHd administered, 50 and 100 mg/kg, decreased basal gastric acid secretion and total secretion volume but did not affect intraluminal pH. FMHm decreased gastric acid secretion, raised intraluminal pH, and to a lesser degree decreased total secretion volume. Neither compound changed the severity of gastric ulcers produced by cold restraint stress.

Animals↗
PubMed1987

Subcellular, regional and immunohistochemical localization of adenosine deaminase in various species.

Immunohistochemical and subcellular fractionation techniques were employed to compare the cellular and subcellular localization of adenosine deaminase (ADA) in various brain regions of several mammalian species. A relatively restricted distribution of ADA-immunoreactive neurons in rat brain was previously reported. Mouse brain exhibited a pattern similar in many respects to rat and, in addition, contained intensely immunostained neurons in lateral habenula and hippocampus. Glial immunostaining was absent or very light in rat but evident in mouse. Prominent immunoreactive fibers and neurons were observed in hamster spinal cord and anterior hypothalamus, respectively. ADA-immunostaining in guinea-pig was localized to presumptive fibers in the superficial layers of spinal cord dorsal horn and to glial cells throughout the brain. Demonstration of specific immunostaining in rabbit was not possible. ADA activity was far more heterogeneously distributed in rat and most brain areas in guinea-pig and rabbit contained up to 5-fold and 10-fold higher levels of activity, respectively, compared with rat. Crude synaptosomal (P2) fractions of rat cortex contained a greater proportion of ADA activity than those of rabbit cortex. Within rat, relatively high activity was found in P2 fractions of whole hypothalamus, cerebellum, and hippocampus. ADA activity was greater in P2 fractions of rat anterior compared with whole hypothalamus and the greatest proportion of the enzyme in this fraction was localized to purified synaptosomes. The large variations in the activity and cellular location of ADA in the animals examined suggest species differences in mechanisms governing adenosine metabolism in brain and possible differences in the relationships between cellular metabolism, ADA and the neuroregulatory role of adenosine in the CNS.

Adenosine Deaminase↗
PubMed1987

Ontogenesis of adenosine deaminase activity in rat brain.

The activity of adenosine deaminase (ADA) was determined in whole brain of rats at the embryonic age of 15 days through to adulthood and in nine brain regions in rats 1 day old through to adulthood. In 1-day-old rats, the highest activity was seen in olfactory bulbs (550 +/- 15 nmol/mg protein/30 min) and this was 4.5-fold higher than that in the pons, which was the lowest. In adult animals, olfactory bulb still contained the greatest activity, which was about eightfold higher than hippocampus, which had the lowest. Except for hypothalamus, where ADA activity increased nearly twofold in rats between the ages of 1 and 50 days, significant decreases of as much as fivefold were found in whole brain, superior colliculus, cortex, hippocampus, cerebellum, olfactory bulbs, and olfactory nucleus. In contrast, ADA activity in pons and subcortex remained relatively constant throughout the developmental period. The Km values for ADA in whole brain at 18 days gestation (48 +/- 5 microM) were not significantly different from that observed in adult rats (38 +/- 7 microM), whereas the Vmax values decreased significantly from 339 +/- 9 to 108 +/- 8 nmol/mg protein/30 min. Taken together, the developmental patterns observed in the various brain regions appear not to correspond to any one particular process such as periods of rapid cell proliferation, cell death, synaptogenesis, or myelination. Nor do they correspond to known developmental profiles of transmitters, their receptors, or their metabolic enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Deaminase↗
PubMed1987

Modulation of gastric acid secretion by adenosine in conscious rats.

Basal (nonstimulated) gastric acid output was determined in conscious rats fitted with indwelling gastric cannulae. The adenosine deaminase resistant analog of adenosine, R-phenylisopropyladenosine, elevated intraluminal pH beyond 7.0 and decreased gastric acid secretion when given at doses of 0.10 or 1.0 mg/kg, while S-phenylisopropyladenosine at similar doses did not affect either gastric acid output or pH. The potent adenosine receptor antagonist, 8-phenyltheophylline, given at doses of 0.1, 1.0, and 2.5 mg/kg augmented gastric acid output and, at doses of 0.01, 0.1, 1.0, and 2.5 mg/kg, blocked the acid-reducing effect of R-phenylisopropyladenosine (0.1 mg/kg). These data suggest that adenosine systems may be important regulators of gastric function.

Adenosine↗
PubMed1986

Lack of adenosine deaminase deficiency in the mutant mouse wasted.

The possibility that the mutant mouse wasted (wst/wst) may serve as an animal model for studies of severe combined immunodeficiency disease (SCID) and the role of adenosine deaminase (ADA, EC 3.5.4.4) in adenosine metabolism were investigated. The specific activity of ADA in wst/wst compared with control mice was significantly lower by 26% in thymus, but significantly higher by 18% in spleen and 32% in cerebellum. Vmax values of ADA in spleens were 43% higher in wst/wst mice and no changes were observed in Km values. In contrast, the Vmax of ADA was unchanged in erythrocytes from wst/wst mice, but the Km for adenosine was significantly elevated. Thus, based on ADA measurements alone, it may be premature to consider wst/wst mice as a model for ADA deficiency and SCID in humans.

Adenosine Deaminase↗
PubMed1986

Localization of [3H]cyclohexyladenosine and [3H]nitrobenzylthioinosine binding sites in rat striatum and superior colliculus.

The localization of adenosine receptors labelled with [3H]cyclohexyladenosine ([3H]CHA) and adenosine transport sites labelled with [3H]nitrobenzylthioinosine ([3H]NBI) was examined in striatum and superior colliculus (SC) using radioligand binding and lesioning methods. Striatal kainic acid lesions significantly reduced the number (Bmax) of a single class of high affinity binding sites for [3H]CHA by 50% and that for [3H]NBI by 15% without altering Kd values for either ligand. In SC, enucleations significantly reduced both high and low affinity [3H]CHA binding sites by about 60% while levels of [3H]NBI binding were unaffected. Thus, adenosine receptors are present on striatal interneurons and retinal projections to the SC and some [3H]NBI binding sites are located on striatal interneurons.

Adenosine↗
PubMed1986

Distribution of adenosine deaminase activity in rat brain and spinal cord.

The activity of adenosine deaminase (ADA) was measured in 62 discrete regions of the CNS, and in some autonomic and sensory ganglia, peripheral nerves, and peripheral tissues of the rat using an automated high-pressure liquid chromatography (HPLC) method. The formation of inosine and hypoxanthine as a measure of ADA activity in homogenates of brain was optimal at pH 7.0, linear for up to 60 min at 37 degrees C using 500 microM adenosine as substrate, and linear with protein concentrations ranging from 0.05 to 0.8 mg. The Km and Vmax values for ADA activity in homogenates of whole brain were 47 microM and 107 nmol/mg protein/30 min, respectively. Among the CNS regions examined, the highest activity was found in posterior hypothalamic magnocellular nuclei and the lowest in hippocampus. In general, spinal cord contained relatively low levels of ADA activity, with that in dorsal cord approximately 40% higher than ventral cord. In the periphery, parasympathetic ganglia contained higher levels of ADA than sensory ganglia and brain. Most peripheral tissues--including adrenal gland, lung, liver, and anterior and posterior pituitary--exhibited activity comparable to levels in the posterior hypothalamus. ADA activity in thymus was about 10 times higher than any other tissue examined. The uneven distribution of ADA activity in the rat CNS corresponds well with the immunohistochemical localization of this enzyme in discrete neural systems of this species. Structures that contain high ADA activity exhibit intense ADA immunostaining of neuronal perikarya and/or fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Deaminase↗
PubMed1985

Localization of [3H]nitrobenzylthioinosine binding sites in rat spinal cord and primary afferent neurons.

The distribution of [3H]nitrobenzylthioinosine ([3H]NBI) binding to nucleoside transport sites in rat spinal cord and spinal roots was examined using membrane binding and autoradiographic techniques. A single class of high affinity binding sites having dissociation constants (KD) between 0.42 +/- 0.05 and 0.088 +/- 0.012 nM was observed in dorsal and ventral spinal cord and their associated roots. The maximal number of binding sites (Bmax) in dorsal and ventral spinal cord was 110.1 +/- 7.1 and 73.6 +/- 7.5 fmol/mg protein, respectively. The highest levels of [3H]NBI binding were found in the dorsal grey matter of the cervical and lumbar enlargements. Autoradiographic studies showed that [3H]NBI sites were especially concentrated in the substantia gelatinosa of the dorsal spinal cord and the nucleus caudalis of the spinal trigeminal nucleus. The level of these binding sites in dorsal roots was nearly 4 times that observed in ventral roots; 98.5 and 23.0 fmol/mg protein, respectively. Adult animals depleted of unmyelinated sensory fibers by neonatal capsaicin treatment showed significantly reduced numbers of [3H]NBI sites (35%) in dorsal roots but not ventral roots, while KD values were unaffected. These results indicate that [3H]NBI sites are enriched in areas of the spinal cord and brainstem which subserve sensory functions and that these sites are located, in part, on unmyelinated primary afferent fibers.

Adenosine Deaminase↗
PubMed1985

Adenosine receptor activation in brain reduces stress-induced ulcer formation.

Rats restrained in a cold environment for 3 h developed a high incidence of gastric ulcers. Administration of adenosine receptor agonists prior to a restraint period significantly reduced ulcer formation and severity, and lowered plasma corticosterone levels. This protective effect was blocked by 8-phenyltheophylline, a methylxanthine type adenosine receptor antagonist able to permeate the blood-brain barrier. This finding together with the absolute and relative order of potencies with which adenosine receptor agonists produced their effects suggests that CNS adenosine A1 receptors are involved in blocking and methylxanthines in exacerbating stress-induced gastric pathology.

Animals↗
PubMed1985

Adenosine uptake sites in rat brain: identification using [3H]nitrobenzylthioinosine and co-localization with adenosine deaminase.

The binding characteristics of [3H]nitrobenzylthioinosine ([3H]NBI) to rat brain membrane preparations was examined, and the autoradiographic distribution of this ligand in brain sections was compared with the immunohistochemical localization of adenosine deaminase (ADA). It was found that [3H]NBI labels sites for which adenosine has far higher affinity than do other nucleosides, that these sites are heterogeneously distributed and that there is an exact correspondence between areas containing [3H]NBI sites and ADA-immunoreactive neurons. Our results indicate that [3H]NBI and ADA are potential markers for revealing anatomical sites at which actions of adenosine may be expressed.

Adenosine↗