Leonard L. Ross

Membrane-Bound γ-Glutamyl Transpeptidase

γ-Glutamyl transpeptidase is a membrane-bound enzyme that catalyzes the transfer of the γ-glutamyl moiety of glutathione (and of other γ-glutamyl compounds) to amino acid (and peptide) acceptors as indicated in reaction (1):

Central adrenergic receptor changes in the inherited noradrenergic hyperinnervated mutant mouse tottering

glutathione + a\min o\,acid \to \gamma - glutamyl\,a\min o\,acid + cysteinyl\,glycine

Effect of destruction of the postganglionic sympathetic neurons in neonatal rats on development of choline acetyltransferase and survival of preganglionic cholinergic neurons

(1) This reaction is the first step in a quantitatively significant pathway of glutathione metabolism, and it has been postulated that this or analogous reactions are involved in amino acid transport. Thus, γ-glutamyl transpeptidase mediates the translocation of the amino acid across the cell membrane by interacting with both extracellular amino acid and intracellular glutathione (or other compounds that contain the γ-glutamyl carrier); according to this idea, the amino acid enters the cell as a γ-glutamyl amino acid.

Thyroid hormone control of preganglionic innervation of the adrenal medulla and chromaffin cell development in the rat. An ultrastructural, morphometric and biochemical evaluation

The noradrenergic (NE) innervation to sympathetic preganglionic nuclei in the rat thoracic cord was studied by immunocytochemical localization of dopamine-beta-hydroxylase (DBH), a specific NE antigen. DBH antisera was prepared against DBH purified from bovine adrenal medulla. The most intense immunoreaction was observed within the intermediolateral cell column (IML) of the spinal cord, the major sympathetic preganglionic nucleus in mammals. DBH was also localized in both the central autonomic and intercalated nuclei, cell groups known to contain sympathetic preganglionic visceral motor neurons. Two weeks following a midthoracic spinal transection, DBH immunoreactivity was no longer observed caudal to the lesion. Thus, the cells of origin of these noradrenergic terminals are supraspinal. Following a midthoracic hemisection DBH, immunoreactivity was similarly reduced in both the ipsilateral and contralateral IML caudal to the lesion. Therefore, bulbospinal NE neurons project bilaterally to sympathetic preganglionic nuclei.

Alteration of antibody response to pneumococcal polysaccharide type III in rats by neonatal immobilization stress.

Adrenergic receptor binding characteristics were analyzed in the mutant mouse tottering (tg/tg), a single gene locus autosomal recessive mutation causing hyperinnervation by locus coeruleus neurons of their target regions, which results in epilepsy. Instead of the expected down-regulation of receptors due to the hyperinnervation, both [3H]prazosin (alpha 1-receptor) and [125I]iodopindolol (beta-receptor) binding were normal in the tg/tg hippocampus, spinal cord and slightly increased in the cerebellum. This lack of postsynaptic receptor modulation in the target cells, combined with increased levels of norepinephrine due to the aberrant axon growth, may the critical factors in the expression of the abnormal spike-wave absence seizures in the tg/tg mouse.

Development of β-adrenergic receptors and the in vitro accumulation of cyclic AMP in the chick spinal cord

The sympathetic preganglionic neurons in the spinal cord receive dense serotonergic (5-HT) and catecholaminergic (CA) afferent inputs from the descending supraspinal pathways. In the rat spinal cord, the levels of these biogenic amines and their receptors are low at birth, but undergo rapid ontogenetic increases in the ensuing 2-3 postnatal weeks until the adult levels are reached. In many systems it has been shown that denervation of presynaptic neurons leads to an up-regulation of the number of postsynaptic receptors. To determine whether the 5-HT and CA receptors in the developing spinal cord are also subject to such transsynaptic regulation, we examined the ontogeny of serotonergic receptors and alpha- and beta-adrenergic receptors in thoracolumbar spinal cord of rats given neurotoxins which destroy serotonergic (5,7-dihydroxytryptamine (5,7-DHT)) or noradrenergic (6-hydroxydopamine (6-OHDA)) nerve terminals. Intracisternal administration of 5,7-DHT or 6-OHDA at 1 and 6 days of age prevented, respectively, the development of 5-HT and CA levels in the spinal cord. Rats lesioned with 5,7-DHT displayed a marked elevation of 5-HT receptors with a binding of 50% greater than controls at 1 week and a continuing increase to twice normal by 4 weeks. A similar pattern of up-regulation was also detected with the alpha-adrenergic receptor, as rats lesioned with 6-OHDA exhibited persistent increases in receptor concentration. However, in these same animals ontogeny of the beta-adrenergic receptor in the spinal cord remained virtually unaffected by the chemical lesion. In several other parts of the nervous system, it has been demonstrated that the beta-adrenergic sensitivity can be modulated by hormonal signals, particularly that of the thyroid hormones. This phenomenon was examined in the spinal cord and in confirmation with previous studies neonatal treatment of triiodothyronine (0.1 mg/kg, s.c. daily) was capable of evoking persistent increases in beta-adrenergic receptor binding. These results suggest that: (a) development of the postjunctional serotonergic and alpha-adrenergic receptors in the rat spinal cord can occur in the absence of the prejunctional nerve terminals and are subject to transsynaptic modulation; (b) beta-adrenergic receptors in the spinal cord also can develop after prejunctional lesions but are regulated by hormonal rather than neuronal factors.

An epinephrine-containing pathway in avian spinal cord: Development and localization

Neuronal death due to a lack of peripheral field is a widely observed phenomenon in vertebrates, although relatively little information is available in mammals. The objective of this study was to determine the effect of the postganglionic sympathetic neuron on the development and survival of the preganglionic cholinergic neuron arising from the intermediolateral nucleus of the spinal cord. The peripheral sympathetic nervous system of neonatal rats was destroyed by administering guanethidine (50 mg/kg/day, 5 days/week for 3 weeks). The tyrosine hydroxylase activity in the superior cervical ganglion was reduced to undetectable levels within 10 days of starting treatment. Light microscopic examination of the ganglia showed almost complete cell loss by 10 days. Choline acetyltransferase in the superior cervical ganglia of treated animals failed to attain normal adult values, but rather remained at the level of 10-day-old animals. Adrenal choline acetyltransferase, on the other hand, developed normally in sympathectomized animals (the adrenal medulla is not destroyed by guanethidine). Accompanying the failure of normal development of choline acetyltransferase activity in the ganglia is a loss of cells in the intermediolateral nucleus of the thoracic spinal cord. Cell counts in this nucleus at the thoracic segment (T1) showed a 24% decrease (P < 0.025) in animals 10 weeks of age and a 23% decrease (P < 0.001) in animals 7 months of age. Cell counts of the parasympathetic centers of the sacral spinal cord revealed no differences from control animals. These data support the hypothesis that during the developmental phase the survival of the preganglionic neuron is dependent upon the presence of its end-organ, the postganglionic neuron, and hence offers the potential for the development of a system in the postnatal mammal in which to study mechanisms involved in the maintenance of neurons during development.

The -glutamyl cycle in the choroid plexus: its possible function in amino acid transport.

In the rat, functional connections between the splanchnic nerve and the adrenal medulla are immature at birth and do not become fully competent until the first postnatal week. Neonatal administration of triiodothyronine (T3) accelerates this process, and the present study was undertaken to elucidate the underlying mechanisms. Rats were given T3 (0.1 mg/kg, s.c.) daily for 9 days beginning 1 day after birth. Preganglionic innervation of the adrenal medulla was examined by retrograde axonal transport of horseradish peroxidase (HRP). At 10 days of age, there was an increased number of labeled perikarya in the spinal cord of the hyperthyroid pups. Ultrastructural examination revealed a corresponding increase in synaptic density in the adrenal medulla and in the activity of choline acetyltransferase, a marker for preganglionic cholinergic nerve terminals. These effects were attenuated by 25 days of age, whereupon deficits in HRP-labeled neurons and adrenomedullary synapses were noted. Similarly, replication of chromaffin cells was enhanced transiently in the T3 group during the initial stage of hyperthyroidism, but subsequent long-lasting deficits in cell numbers were noted, along with a corresponding retardation of ontogeny of adrenal catecholamine biosynthesis and storage. Thus, neonatal hyperthyroidism accelerates synaptic development in the sympatho-adrenal axis but suppresses maturation of the target chromaffin cells, ultimately leading to impaired adrenomedullary function.