Age-dependent changes in voltage-gated calcium channels and ATP-dependent potassium channels in Fischer 344 rats

Effects of age-related loss of P/Q-type calcium channels in a mice model of peripheral nerve injury

We analyzed the role of P/Q-type calcium channels in sciatic nerve regeneration after lesion induced by chronic constriction injury (CCI) in heterozygous null mutant mice lacking the CaV2.1α1 subunit of these channels (Cacna1a+/-). Compared with wild type, Cacna1a+/- mice showed an initial reduction of the CCI-induced allodynia, indicating a reduced pain perception, but they also evidenced a lack of recovery over time, with atrophy of the injured hindpaw still present 3 months after CCI when wild-type mice fully recovered. In parallel, Cacna1a+/- mice exhibited an early onset of age-dependent loss of P/Q-type channels, which can be responsible for the lack of functional recovery. Moreover, Cacna1a+/- mice showed an early age-dependent reduction of muscular strength, as well as of Schwann cells proliferation and sciatic nerve remyelination. This study demonstrates the important role played by P/Q-type channels in recovery from nerve injury and has important implications for the knowledge of age-related processes.

3,4-DAP-evoked transmitter release in hippocampal slices of aged rats with impaired memory

Based on a slice superfusion technique, this study investigated the release of acetylcholine, noradrenaline and serotonin in the hippocampus of aged rats (25-27 months) showing no or severe deficits in a spatial reference-memory task (water maze). Young adults (3-5 months) were used as controls. 3,4-diaminopyridine (3,4-DAP), a potassium channel antagonist which increases neuronal excitability, was used to evoke the overflow of the three neurotransmitters. The release of [3H]noradrenaline induced by stimulation of presynaptic nicotinic receptors was also assessed. The experiment compared the accumulation and 3,4-DAP-evoked (or nicotine-evoked) overflow of [3H] in hippocampal slices preincubated with [3H]choline, [3H]noradrenaline, or [3H]serotonin. In aged rats, only the accumulation of [3H]serotonin was reduced significantly (-17%). In percent of tissue-[3H], the 3,4-DAP-evoked overflow of [3H]serotonin was increased (+28%), and that of [3H]acetylcholine was reduced (-23%) in the aged rats. The nicotine-evoked overflow of [3H]noradrenaline was not altered in aged rats. There was a significant correlation of water-maze performance (distance to platform) and evoked overflow of [3H]serotonin. It is concluded that hippocampal cholinergic functions are more altered by aging than noradrenergic or serotonergic ones. Excessive excitability of serotonergic terminals, perhaps in addition to cholinergic dysfunction, might be a crucial factor accounting for age-related cognitive deficits in the present population of rats.

Age-related changes in the subtypes of voltage-dependent calcium channels in rat brain cortical synapses

Age-related changes in the relative contribution of voltage-dependent calcium channel (VDCC) subtypes to depolarization-induced Ca(2+) influx and in the density of VDCC subtypes in cortical synapses were investigated using synaptosomes and their membrane preparations from brain cortices of Wistar rats. The relative contribution of VDCC subtypes to Ca(2+) influx was determined by measuring the inhibition of depolarization-induced Ca(2+) influx with four VDCC subtype-specific peptide blockers. In adult rat synaptosomes, L-, N-, P- and Q-type channels accounted for 24, 32, 27 and 12% of the total Ca(2+) influx, respectively. Brain aging significantly reduced the relative contributions of N- and P-type channels and increased the contribution of the channels resistant to the four blockers used. The densities of VDCC subtypes, determined by binding experiments using radiolabeled PN200 -110, omega-conotoxin GVIA and omega-conotoxin MVIIC, were found to be significantly decreased in aged synaptic plasma membranes. On the contrary, the dissociation constants of the blockers were not changed except for PN200-110-sensitive L-type channels. These results suggest that aging alters the relative contributions of each VDCC subtype to depolarization-induced Ca(2+) influx and decreases the number of VDCCs in rat brain cortical synapses. These changes in VDCCs may lead to age-related hypofunction of synaptic neurotransmission in brain cortices.

Age-related alteration of intracellular ATP maintenance in the cell suspensions of mice cerebral cortex

Neurological alteration in the aging brain has been suggested to be due to, in part, a declined cellular energy metabolism. In order to understand age-related alteration of intracellular ATP maintenance, the present in vitro study measured change of intracellular adenosine triphosphate (ATP) content in cell suspensions of cerebral cortex isolated from male ICR mice aged 2 days (infant), 8 weeks (young adult) and 12 months (aged) under several different conditions, using the chemiluminescence technique. Among the three different ages, significant decrease of intracellular ATP content by oxygen deprivation for 15 min was observed in the cell suspensions of cerebral cortex from 12-month-old mice (P < 0.05). When cell suspensions of 8-week cerebral cortex were incubated with or without glucose (0-60 min), intracellular ATP content decreased in a time-dependent manner under both conditions, but depletion rate was significantly high in the glucose-free condition. This decrease was maximally restored by adding 1 mM glucose as tested. In addition, the ability for intracellular ATP maintenance in the presence or absence of glucose was age-dependently different. The rank order of difference of intracellular ATP content between with and without glucose was 3 months > 12 months > 2 days. The highest decrease of intracellular ATP content by incubation without glucose was observed in the 12-month samples. Sodium cyanide (100 microM) produced a gradual ATP depletion in cerebral cortex suspended from 2-day-old mice, but rapid change in both 8-week and 12-month samples. Combination of cyanide and iodoacetate (3.5 mM) rapidly depleted the intracellular ATP content in all age groups tested. These results suggest that the aging process in the cerebral cortex of mice is accompanied by alteration of maintenance of intracellular ATP homeostasis under a given condition, and this may be associated with pathological change of overall mechanisms involved in the development of neuronal disease in the senescent brain.

Regulation of intracellular Ca2+ concentration by interleukin-1beta in rat cortical synaptosomes: an age-related study

The pro-inflammatory cytokine interleukin-1beta (IL-1beta) is released by cells during injury and stress, and increased neuronal expression of IL-1beta is a feature of age-related neurodegeneration. We have recently reported that IL-1beta has a biphasic effect on the K+-induced rise in intracellular Ca2+ concentration ([Ca2+]i) in cortical synaptosomes, exerting an inhibitory effect on the K+-induced rise in [Ca2+]i at lower (3.5 ng/mL) concentrations and a stimulatory effect on the K+-induced rise in [Ca2+]i at higher (100 ng/mL) concentrations. In the present study, we observed that the K+-induced rise in [Ca2+]i was inhibited to a similar extent by the lower concentration of IL-1beta in cortical synaptosomes prepared from young (3-month-old), middle-aged (12-month-old) and aged (24-month-old) rats. In contrast, cortical synaptosomes prepared from the aged rats exhibited an increased susceptibility to the higher concentration of IL-1beta, resulting in a marked elevation in [Ca2+]i. We propose that the age-related increase in neuronal concentration of IL-1beta promotes a dramatic elevation in [Ca2+]i following membrane depolarization, thereby altering Ca2+ homeostasis and exacerbating neuronal vulnerability to excitotoxicity.

Modulation of acetylcholine release in human cortical slices: possible implications for Alzheimer's disease

Superfused slices of human neocortex, prepared from surgically removed tissue (to gain access to subcortical tumors) and prelabelled with [3H]choline, were stimulated electrically to evoke action potential-induced, exocytotic [3H]acetylcholine release. For comparison, rat cortex slices were also used. [3H]ACh release decreased with the age of the patients and was modulated by muscarinic autoreceptors and by 5-hydroxytryptamine1F, neurokinin1, and kappa-opioid receptors located on cholinergic terminals. In addition, 5-hydroxytryptamine2 and delta-opioid receptors located on interneurons were also involved in the modulation of [3H]ACh release. The present findings might help to explain pathological conditions in Alzheimer's disease.