James A. Nathanson

The cellular Na+ pump as a site of action for carbon monoxide and glutamate: A mechanism for long-term modulation of cellular activity

Carbon monoxide (CO) induces a long-lasting alteration in cerebellar alpha 3-Na,K-ATPase independent of [Na+] but linked to cGMP synthesis and localized to Purkinje neurons. The action of CO is absent in Purkinje neuron-deficient mice, mimicked by 8-Br-cGMP, and blocked by inhibition of PKG. Glutamate (Glu) and metabotropic agonists mimic the action of CO, an effect that requires PKC and is associated with CO synthesis. These data suggest that CO regulates Na,K-ATPase through cGMP and PKG, and that Glu regulates CO through mGluRs. This system is also modulated by NMDA agonists and nitric oxide, possibly via Glu release, as well as by free radicals. These findings offer a mechanism by which CO, Glu, and free radicals can exert specific effects on synaptic transmission (relevant to long-term changes in cell excitability), as well as more general actions on energy metabolism (relevant to the pathophysiology of excitotoxicity).

Atrial natriuretic factor and salt wasting after aneurysmal subarachnoid hemorrhage.

Background and Purpose The causes of volume depletion and hyponatremia after subarachnoid hemorrhage are not fully understood but may be in part due to natriuresis or “cerebral salt wasting.” Because previous studies using infrequent hormone sampling have given inconsistent results, we determined if elevations in atrial natriuretic factor concentrations preceded negative sodium and fluid balances. Methods We measured diurnal atrial natriuretic factor and vasopressin concentrations and sodium balance for 5 days in 14 consecutive patients after aneurysmal subarachnoid hemorrhage. Results Plasma concentrations of atrial natriuretic factor on admission were elevated in subarachnoid hemorrhage patients (mean±SD 106 ±59 pg/ml) compared with acutely ill controls (39±30 pg/ml). In eight patients, high peak concentrations of atrial natriuretic factor, greater than 300 pg/ml or a twofold increase above baseline, were followed by natriuresis and a negative sodium balance. Three patients, two of whom became hyponatremic, developed cerebral infarcts after natriuresis. Vasopressin concentrations were slightly elevated just after hemorrhage but subsequently declined to normal values. Conclusions A markedly increased atrial natriuretic factor concentration precedes natriuresis in some patients and, with other abnormalities of water handling possibly including a relatively diminished vasopressin concentration, may cause volume depletion. Patients with natriuresis appear to be at increased risk for delayed cerebral infarction after subarachnoid hemorrhage.

Characterization of insect neuronal octopamine receptors (OA3 receptors)

Octopamine receptors in the nervous tissue of insects were investigated using a ligand-receptor assay with [3H]NC-5Z or [3H]octopamine as the radioligands. Both ligands recognized a homogenous class of binding sites with the properties of an octopamine receptor. This receptor has been characterized pharmacologically. Both high-affinity agonists (e.g. NC 7, K1=0.3 nM) and antagonists (e.g. maroxepine, K1=1.02 nM) were investigated. The neuronal octopamine receptor belongs to a receptor class that can easily be distinguished from peripheral octopamine receptors. Initial investigations of the localization of octopamine receptors within the insect nervous tissue show the greatest receptor density in the optic lobes.

Galanin stimulates rat pituitary growth hormone secretion in vitro

The effect of galanin on growth hormone (GH) secretion was investigated in monolayer cultures of rat anterior pituitary cells. Galanin caused a gradual increase in GH concentrations into the culture medium that was maximal at 90 minutes and sustained after 180 minutes. The ED50 for galanin-stimulated GH secretion was approximately 200 nM compared to an ED50 for rat GH-releasing factor (rGRF)-stimulated GH secretion of 10pM. Galanin and rGRF were additive in increasing GH release into the incubation medium. These data indicate that porcine-derived galanin has a direct effect on pituitary GH secretion in vitro.

Cerebral microvessels contain A β2-adrenergic receptor

Cerebral microvessels isolated from cat forebrain contain a specific β-adrenergic-sensitive adenylate cyclase. Among various compounds tested, the most potent activator of enzyme activity is isoproterenol (ka = 1.4 × 10−7M), followed in order by epinephrine (ka= 1.5 × 10−6M), norepinephrine (ka= 1.4 × 10−5M) and phenylephrine (ka> 3 × 10−4M). Isoproterenol-stimulated enzyme activity is blocked by propranolol (ki= 2.4 × 10−9M, IPS 339 (ki= 4 × 10−9M), H35/25 (ki = 1.2 × 10−7M), atenolol (ki= 5.9 × 10−6M) and practolol (ki= 1.8 × 10−5M). These agonist and antagonist properties are quite similar to those demonstrated by β2-adrenergic receptors and β2-stimulated adenylate cyclase present in other tissues and indicate that the majority of adenylate cyclase-associated adrenergic receptors in cerebral microvessels are β2. The findings are relevant to physiological studies of cerebral blood flow and vascular permeability.

Adenylate cyclase activation is not sufficient to stimulate somatostatin release from dispersed cerebral cortical and diencephalic cells in glia-free cultures.

Under conditions in which vasoactive intestinal peptide (VIP) induces somatostatin release from cortical and diencephalic neuronal cultures, VIP causes large increases in intracellular cyclic AMP. Both the release of somatostatin and the increase in cyclic AMP elicited by VIP require exogenous calcium, can be blocked by cobalt ion, and can be qualitatively mimicked by depolarizating concentrations of exogenous potassium ion. Direct activation of adenylate cyclase by forskolin causes large increases in cyclic AMP content but does not induce somatostatin release. In the absence of VIP, the calcium ionophore, ionomycin, and the phorbol ester, phorbol 12-myristate-13-acetate, also stimulate somatostatin release. These results indicate that VIP-stimulation of cyclic AMP formation and VIP-stimulation of somatostatin release are calcium-dependent and that the two phenomena are dissociatable. Cyclic AMP formation is not a necessary condition for VIP-induced somatostatin release. Nucleotide formation may be a sufficient condition for release or, possibly in association with calcium influx, it may be an event unrelated to the release process.

EFFECTS OF A POTENT AND SPECIFIC β2‐ADRENOCEPTOR ANTAGONIST ON INTRAOCULAR PRESSURE

1 Physiological studies support the possibility of adrenergic regulation of aqueous humor secretion from the ciliary process, a tissue which has recently been shown to contain a predominance of β2‐adrenoceptors. 2 The present experiments examine the effects of a potent and highly specific β2‐antagonist (IPS 339) on intraocular pressure in the normal rabbit eye. 3 The observed decrease in pressure caused by IPS 339 suggests that highly specific β2‐antagonists may be useful in decreasing elevated intraocular pressure.

Adrenergic receptors in brain microvessels

Abstract The brain is isolated metabolically from the rest of the body by two major anatomical barrier systems. The first is the blood-brain barrier, consisting of capillary endothelium and astrocytic processes, which separates the systemic vasculature from the extracellular fluid compartment of the brain. The second is the blood-CSF barrier, consisting of the epithelial cells of the choroid plexus, which separates the choroidal (part of the systemic) vasculature from the cerebrospinal fluid. Recent anatomical, biochemical and physiological studies raise the possibility that the cellular components of these barrier systems may be subject to adrenergic regulation. This article will focus in particular on possible hormonal and neurogenic regulation of the blood-brain barrier and the cerebral microvasculature. The reader is referred to a recent review by Nathanson for a discussion of possible adrenergic regulation of the choroid plexus 15 .

Monoamine uptake in insect synaptosomal preparations.

Biochemical studies of mammalian synaptosomal nerve fractions indicate the existence of multiple transporter proteins important for the termination of synaptic transmission by each of several monoamines. In insects, however, data on monoamine uptake has been limited to the study of whole tissue preparations, making it unclear whether neuronal (as opposed to glial) uptake is a significant mechanism in the insect. The present experiments elucidate the difficulties that have limited the use of insect synaptosomal preparations for characterizing amine reuptake. Key procedural improvements, including the utilization of carrier protein for tracer separation and the use of receptor antagonists to decrease non-specific membrane binding are described. With these and other modifications, reproducible sodium-dependent and cocaine-inhibitable dopamine and octopamine uptake are described in synaptosomal-containing preparations from insect brain and ganglia. These studies therefore support the existence of specific Na(+)-dependent uptake mechanisms in insect neurons.

Morphine withdrawal causes subsensitivity of adrenergic receptor response

Abstract To determine whether the hyperactivity of noradrenergic neurons that occurs during opiate withdrawal might be associated with a reciprocal alteration in noradrenergic receptor response, isoproterenol-stimulated adenylate cyclase activity was examined in the cerebella of morphine-addicted monkeys at two time periods: a) prior to withdrawal, and b) during late withdrawal. Compared to controls, the chronically-addicted group showed a significant increase in maximal enzyme velocity, a finding consistent with the observed hypoactivity of noradrenergic neurons which occurs during opiate administration. In contrast, the morphine withdrawal group demonstrated a significant decrease in enzyme activity. Piperoxan, known to mimic the effects of withdrawal in causing noradrenergic hyperactivity, also decreased enzyme activity. In no group was there a change in Ka for isoproterenol. These findings, indicating that opiate withdrawal is associated with a subsensitivity of noradrenergic receptor response, suggest a possible etiology for certain of the physiological changes of noradrenergic hypoactivity seen during the secondary (or protracted) abstinence syndrome.