Aging of neurons in the mollusc Lymnaea stagnalis small parietal ganglion: a morpho-functional comparison in the same neuron.

The aim of this study was to compare the functional and structural changes in similarly identified neurons of the small parietal ganglion in 56 molluscs (Lymnaea stagnalis) of two age groups: adult (10-12 months) and old (20-22 months). No age changes were found in the values of membrane potential, resistance of the neuronal membrane, amplitude, duration, or rate of increase of the anterior action potential front. With aging, the thresholds of direct stimulation were significantly increased, the rate of action potential repolarization decreased, and the amplitude of trace hyperpolarization decreased. The most marked age-dependent changes were observed in the frequency of neuronal spontaneous activity. A clear relationship was established between the frequency of action potentials of the neuron and its structure in adult and old individuals alike. In the molluscs of both age groups, the neurons with a high frequency of action potential displayed ultrastructural features of high activity in the organelles involved in protein biosynthesis. The cytoplasm of these neurons was filled with numerous ribosomes and had a well-developed rough endoplasmic reticulum. The structure of cells with low spontaneous activity in old molluscs differed considerably from that of the corresponding neurons of the adult individuals. The former had significantly marked morphological signs of reduction of the protein-synthesizing processes, as well as of destructive and dystrophic changes. A decrease in the lability of neurons may be an important mechanism of aging.

Potential-dependent Ca channels of neurons in the mollusc Lymnaea stagnalis in aging: effect of norepinephrine.

During aging changes occur in the function of potential-dependent Ca channels of plasmic membrane of identified neurons in the mollusc Lymnaea stagnalis, i.e. the value of Ca inward current of neurons in old vs. adult molluscs was much higher at holding potential -50 - -30 mV. When held at -20 mV, the amplitude of Ca current decreased in the neurons of old molluscs, but continued to increase in those of adult molluscs. Various populations of potential-dependent Ca channels are assumed to have irregular age-related changes. The norepinephrine-induced inhibition of Ca current was more significant in old vs. adult molluscan neurons.

[Potential-dependent calcium channels of neurons of mollusks of various ages]. / Potentsialzavisimye kal'tsievye kanaly neironov molliuskov raznogo vozrasta.

It is shown that with the holding potentials (Eh) ranging from -50 to -30 mV the amplitudes of the inward Ca current of identified neurons are significantly higher in old (20-24 months) Lymnaea stagnalis molluscs than in adult ones.

[Effect of the endogenous peptide factor and vasopressin on the neurons of mollusks of different ages]. / Vliianie éndogennogo peptidnogo faktora i vazopressina na neirony prudovikov raznogo vozrasta.

Electric reactions of the identified neurons in adult (10-12 months) and old (22-24 months) molluscs Lymnaea stagnalis to endogenous peptide isolated from the water soluble fraction of the Helix Pomatia brain homogenate as well as to vasopressin are studied. The endogenous peptide causes a significant activation of the burst both in adult and old neurons of the molluscs. No significant age-related differences in the pronouncement of the above shifts of the molluscan neurons are found. There is an increased sensitivity to the identified peptide, vasopressin, in the old individuals. A non-uniform change in the sensitivity of mollusk neurons to various neuropeptides may affect the synaptic conduction in old age.

Age-related changes in the function of somatic membrane potassium channels of neurons in the mollusc Lymnaea stagnalis.

The function of the membrane potassium channels of the identified neurons of the small parietal ganglion was investigated in the adult (10-12-month) and old (22-24-month) molluscs Lymnaea stagnalis. Old molluscan neurons showed a decrease in maximal amplitude of fast and delayed potassium currents, in maximal potassium conductance, and in kinetics of inactivation of the delayed outward current. These features may be conditioned by the age changes in phospholipid composition of the membranes, rather than by the shifts of neuronal surface area during aging. Age dynamics in the function of potassium channels is thought to cause changes in the neuronal function.

[Functional characteristics of potassium channels in the somatic membrane of neurons of Lymnaea stagnalis of various ages]. / Funktsional'nye kharakteristiki kalievykh kanalov somaticheskoi membrany neironov prudovikov raznogo vozrasta.

It has been found that in old Lymnaea stagnalis neurons the maximal amplitude of the delayed potassium current and the maximal potassium conductance decreases and the kinetics of inactivation of the delayed outward current slows down. It is suggested that these changes may be associated with the age peculiarities of the phospholipid composition of membranes and not related to shifts in the surface area of the nerve cell during aging. The age dependence of the function of potassium channels may underlie the changes in the neuronal function during aging.

[Effect of estradiol dipropionate on cell membrane electrical properties and their electrolyte makeup in animals of different ages]. / Vliianie éstradiola dipropionata na élektricheskie svoistva membrany kletok i ikh élektrolitnyi sostav u zhivotnykh raznogo vozrasta.

Intraperitoneal administration of estradiol dipropionate (EDDP) leads to membrane hyperpolarization, the growth of its resistance, reduction of cell excitation and potassium and sodium ions redistribution on both sides of the membrane. In old animals the shift of the membrane potential occurred in response to half estrogen doses (50 microgram) in comparison with that in adults, this pointing to greater sensitivity of the muscle cells of old rats to EDDP. The protein biosynthesis inhibitors prevented development of hyperpolarization, changes of electrical properties of the membrane and ionic shifts usually following estrogen administration. Elimination of the EDDP effect in old animals was reached with lesser doses of the protein biosynthesis inhibitors.

Aging of the neuromuscular apparatus.

With age marked changes in metabolism and function of muscle fibers appear: electroexcitability thresholds rise, critical polarization level and membrane resistance decrease, time of action potential increases and its amplitude decreases, lability is reduced. The level of intracellular sodium increases and that of potassium decreases. Shifts in ionic asymmetry of muscle fibers are connected with changes in their membrane permeability and a modified function of the sodium-potassium pump. Along with the impairment of nervous influences on muscle fibers in old age, their sensitivity to many hormonal factors increases. Loading levels all age differences in the regulation of skeletal muscle vascular tone. The relationships between the activity of the genetic apparatus and electrical properties of the cell are altered.