R.A. Rius

Age-related reduced affinity in [3H]nitrendipine labeling of brain voltage-dependent calcium channels

Literature data indicate a reduced calcium uptake in synaptosomes prepared from old rat brains. On this line, the present paper investigates the binding of ([3H]NDP) to brain synaptic membranes prepared from rats at different ages from birth up to 24 months of age. The binding is undetectable at birth but reaches within 9-18 day the values observed in adults [3H]NDP binding affinity and sensitivity to calcium were decreased in old rats (24 months). Tritiated dihydropyridines are believed to label voltage-dependent calcium channels (VDC). The observed age-related reduction in binding suggests that the characteristics of VDC in the aged brain may change.

Age-dependent increase in [3H]verapamil binding to rat cortical membranes.

[3H]Nitrendipine bound to cerebral cortex membranes is displaced more efficiently by verapamil in old rats (24 months old) compared to young ones (3 months old). In addition, [3H]verapamil binding was studied in detail in 3-, 12- and 24-month-old rats. Aging increases the Bmax of [3H]verapamil, leaving the affinity unchanged. These observations further indicate that aging may affect calcium channels leading to a derangement of calcium movements which in turn alter neuronal activity.

Acute ethanol effect on calcium antagonist binding in rat brain

We investigated the effect of acute ethanol administration on voltage-sensitive calcium channels (VSCC) by measuring [3H]nitrendipine ([3H]NTP) binding to crude synaptosomal membrane preparations from different rat brain areas, i.e. cerebral cortex, hippocampus and striatum. Ethanol enhances the number of binding sites shortly after the administration (40 min), then Bmax returns towards control values while the binding affinity increases. Kd decreased peaks 8 h after the oral administration and returns within the range of control values at 36 h. The in vitro addition of ethanol has no effect on [3H]NTP binding at various concentrations up to 600 mM. These results suggest that acute ethanol treatment modifies VSCC supporting the concept that the short-term neurochemical alterations induced by in vivo ethanol administration involve calcium channels.

Developmental changes in Gs and Golf proteins and adenylyl cyclases in mouse brain membranes

Guanine nucleotide-binding (G) proteins, Gs and G(olf) mediate the increase in cAMP formation through the activation of adenylyl cyclases. The developmental profiles of Gs, G(olf) and adenylyl were determined in mouse striatum and whole brain using immunobloting with specific antisera. Gs and the 115 kDa and 150 kDa adenylyl cyclases were present at the earliest age tested, embryonic day (E) 14.5 G(olf) and the 160 kDa adenylyl cyclase emerged in parallel, postnatally; during this period the increase in the relative abundance of the 150 kDa was observed. Gpp[NH]p activated Gs/G(olf) in a dose dependent manner, with a smaller response observed in embryos compared to adults. Mn2+ and forskolin activated the adenylyl cyclases and this activation increased during development. At E 14.5, maximal activation with Mn2+ and forskolin elicited a similar increase in cAMP levels, but from postnatal day 1, a nearly two fold higher response was obtained with forskolin compared to Mn2+; at the same time the 160 kDa adenylyl cyclase was detected. These data suggest that the appearance of certain forms of stimulatory G proteins was developmentally correlated with the expression of specific adenylyl cyclases.

Chronic ethanol changes opiate receptor function in rat striatum

Ethanol produces supersensitivity of striatal delta-opiate receptor sites labeled by [3H]DADLE and [3H]etorphine. The impairment may be ascribed to the diminished enkephalin release detected in rat striatum after chronic ethanol consumption. On the contrary, a lower affinity of striatal mu-opiate receptors results after same ethanol exposure. In fact, the Kd values of [3H]Met-enkephalin and [3H]DHM are enhanced when measured in striata of ethanol-dependent rats. The diverse sensitivity of the various classes of opiate receptors to ethanol may be ascribed to different ethanol effects on enkephalinergic transmission.

Acute ethanol and acetaldehyde administration produce similar effects on L-type calcium channels in rat brain

The present study investigates the effect of acute ethanol and acetaldehyde administration on neuronal L-type calcium channels by measuring the binding of 3H-nitrendipine (3H-NTP). Acute ethanol (3 g/kg orally) transiently increases (+40% at 40 min) 3H-NTP binding. Acetaldehyde has a similar effect, but the onset of action is shorter; in fact the binding increase peaks 15 min following administration and is completely reversible within 2 hours. Disulfiram pretreatment does not modify the effect produced by acute ethanol on 3H-NTP binding. The results indicate that acetaldehyde may participate in mediating the action of ethanol on voltage sensitive L-type calcium channels with consequent alterations of neuronal excitability.

Cyclic AMP-dependent protein phosphorylation is reduced in rat striatum after chronic ethanol treatment

Endogenous protein phosphorylation by cyclic AMP-dependent protein kinase was found reduced in striatal membranes obtained from chronic ethanol-treated rats. Experiments using an exogenous substrate show that the decreased response is due to a deficiency in the phosphorylating activity of the cyclic AMP-dependent protein kinase and not to a lack of endogenous substrate for phosphorylation.

In vivo chronic lead exposure alters [3H]nitrendipine binding in rat striatum

The effect of lead as a neurotoxic agent has been associated with alterations in calcium metabolism. On this line, the present study shows that lead alters the characteristics of [3H]nitrendipine ([ 3H]NDP) binding to rat striatal membranes. In vitro, lead shares the action of calcium in enhancing [3H]NDP binding although it is more potent on a molar basis. In vivo, lead exposure through drinking water enhances [3H]NDP binding to crude synaptosomal membrane preparations. This effect is lost when membranes are washed with EDTA-EGTA, indicating that the increased binding is due to the persistence of lead in the brain of treated rats.

The Central Dopaminergic System: Susceptibility to Risk Factors for Accelerated Aging

The synaptic deficit of brain dopaminergic activity involves a complex pattern of changes both at presynaptic and at postsynaptic level. The aged dopaminergic nuclei present a reduced number of dopamine terminals, a decreased ability to synthesize and reuptake dopamine and defective recognition sites both in terms of absolute number of D2 receptors and of transducing mechanisms linked to D1 receptors. These changes suggest that the dopaminergic system may be particularly sensitive during aging to environmental, iatrogenic and toxic factors, which may easily make the elderly develop symptoms of central dopamine deficiency.

Regional modification of brain calcium antagonist binding after in vivo chronic lead exposure

Lead toxicity in the central nervous system seems to be partially related to specific effects of the metal on calcium metabolism and in particular on calcium transport. On this line, the present study investigates the characteristics of [3H]nitrendipine binding to several rat brain regions after in vitro lead addition or after in vivo chronic exposure to this metal. In vivo a lead induced increase in [3H]nitrendipine binding, Bmax, is observed in cerebral cortex and striatum while the binding is unmodified in hippocampus. The in vitro studies are in agreement with in vivo data; lead addition stimulates the binding in synaptic membranes prepared from cortex and striatum but not from hippocampus where the binding is slightly inhibited. The data suggest that lead interferes with neuronal calcium channels in an area-selective manner.