Effect of corticosteroid hormones on electrical activity in rat hippocampus.

Pyramidal neurons in the rat CA1 hippocampal area contain both mineralocorticoid (MR) and glucocorticoid receptors (GR) which bind the endogenous adrenal steroid corticosterone with differential affinity. With intracellular electrophysiological recording techniques we have investigated how corticosterone affects the membrane properties of these cells. We observed that low doses (1 nM) of corticosterone or aldosterone can, through MR, reduce the spike frequency accommodation and afterhyperpolarization (AHP) evoked by a short depolarizing current in pyramidal neurons. As the accommodation/AHP can be considered as an intrinsic mechanism of CA1 neurons to attenuate transmission of excitatory input, the MR-mediated action might potentially enhance cellular excitability in the CA1 area. Higher doses of corticosterone or selective glucocorticoids were able to reverse the MR-mediated effect on accommodation/AHP, eventually increasing particularly the amplitude of the AHP. GR-mediated events may thus potentially suppress excitability in the hippocampal CA1 area. Not only current- but also transmitter-induced membrane effects were affected by the steroids. Firstly, GR-ligands were able to suppress a temporary noradrenaline-evoked decrease in accommodation/AHP. Secondly, membrane hyperpolarizations induced by serotonin were reduced by MR-agonists. We propose that cellular excitability in the hippocampus is at least partly under control of coordinative, antagonistic MR- and GR-mediated effects on electrical activity.     

Effect of methamphetamine on the locomotor activity in the 6-OHDA dorsal hippocampus lesioned rat

The present studies were carried out to examine a possible role of hippocampal dopamine in the hyperactivity induced by methamphetamine. For this purpose, 6-hydroxydopamine (6-OHDA) lesion of the dorsal hippocampus (D-HPC) was made in desmethylimipramine pretreated rats in order to specifically destroy dopamine neurons. D-HPC lesions produced a large (96%) and selective depletion of content of dopamine in the D-HPC. This lesion did not change spontaneous locomotion and rearing behavior. The 6-OHDA lesioned rat produced a blockade of the increase in locomotor activity induced by 1.0 and 2.0 mg/kg of methamphetamine. In contrast, the 6-OHDA lesion of the D-HPC failed to influence the methamphetamine-induced rearing activity. These results indicate that dopamine neurons in the D-HPC may have some role in methamphetamine-induced locomotion, but not in methamphetamine-induced rearing.     

Effect of temperature on the electrical activity of the rat epididymis in vitro

1. 1.|Regional differences in the frequency of electrical activity in rat epididymis were maintained at all temperatures below 39°C.

2. 2.|The change in frequency per deg C increased with temperature and was highest in the temperature region of 34–39°C and the Arrhenius plots of the frequency were linear and parallel in all parts of the epididymis.

3. 3.|The Q₁₀ of the frequency varied between 2.2.–4.3.

4. 4.|The conduction velocity at the cauda epididymis was highest (2.8 mm/s) at 37°C. The Q₁₀ of the conduction velocity was 2.3 in the temperature region of 24–37°C.

Effect of streptozotocin-induced diabetes on phosphodiesterase activity in rat luteal cells

The present studies were carried out to characterize the cAMP-phosphodiesterase enzyme (PDE) in luteal cells recovered from pseudopregnant rats with streptozotocin-induced diabetes. A significant increase in the specific activity of the enzyme was detected in luteal cells from diabetic rats (Group D) with respect to control rats (Group C). This increase could not be prevented by insulin therapy (Group I). Luteal cells from Groups C and D rats responded in vitro to insulin by increasing their PDE activity (% of stimulus of specific activity: C = 75%, D = 110%). However, in cells isolated from Group I, the hormone caused an inhibition of PDE activity (% of inhibition of specific activity: 48%). When cytosolic fractions from Groups C, D, and I were submitted to ion exchange chromatography, two PDE activity peaks could be observed and the activity of the different fractions was increased in the presence of Ca²⁺ and calmodulin. Nevertheless, the Ca²⁺—calmodulin effect was much lower in the extracts from Groups D and I than for controls. Kinetic studies of luteal PDE showed nonlinear Lineweaver-Burk graphs with two apparent ATP hydrolysis sites. Similar K_m values were found for PDE from groups C, D, and I, whereas the V_max2 for the enzyme was higher in Groups D and I. The endogenous concentration of cAMP, measured by RIA, showed no significant differences among Groups C, D, and I. On the basis of these results, we conclude that the specific activity of PDE is significantly increased in luteal cells from streptozotocin-induced diabetic animals, which could explain the previously described reduction in LH-stimulated progesterone production by luteal cells in diabetic rats. © 1996 Wiley-Liss, Inc.     

Spontaneous electrical activity of the rat epididymis in vitro

Smooth muscle electrical activity was recorded with suction electrodes from the partly or completely uncoiled epididymal duct of the rat in vitro. The electrical activity of the cauda epididymidis consisted of one or few spikes followed by a plateau of 1-2 sec. The frequency of electrical activity declined from the thicker-walled initial segment of the thin-walled initial segment, was increased to the level seen in the initial segment in the thicker, major portion of the caput epididymidis, declined in the corpus and fell steeply in the cauda epididymidis towards the vas deferens. Electrical activity spread over long distances in the distal cauda and epididymal vas. Elsewhere in the epididymis activity remained synchronous only for a short period in short segments.     

Anesthetic and postanesthetic effects of isoflurane on neuronal activity in the rat hippocampus

In this study, we explored anesthetic and postanesthetic effects of isoflurane on GABA-ergic and glutamatergic systems in the rat hippocampus. Our results demonstrate that different neuronal targets affected by isoflurane recover from anesthesia at dissimilar rates. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 371–373, July–October, 2007.     

Effect of electrical stimulation of the hippocampus and neocortex on cingulate cortical neurons in rabbits

Extracellular unit activity of the anterior and posterior zones of the cingulate cortex and also of the anterior and posterior cortical association areas was analyzed in unanesthetized rabbits. In the posterior zone considerably more cells (60%) responded to hippocampal stimulation than in the anterior zone (18%). In 43% of these cells in the posterior zone but only in 5% in the anterior zone, the responses followed the frequency of stimulation. Unit responses in the posterior zone could be divided into two discrete groups: those with short (12.3 ± 6.5 msec) and those with long (50.2 ± 10.0 msec) latent periods. Inhibitory phenomena also were well marked during hippocampal stimulation. More than one-third of cells of the cingulate cortex responded to stimulation of the posterior association zones by spikes which followed the stimulus, and by subsequent inhibition. Responses of this kind to stimulation of the anterior association zones were found in only a few cells in the anterior zone of the cingulate cortex. The results are discussed in the light of data from morphological investigations relating to connections between these structures.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 270–277, May–June, 1982.     

Alteration of membrane electrical activity in rat myocardial cells following selective laser microbeam irradiation

Laser microirradiation of neonatal rat (1 to 2-day-old) ventricular cells in tissue culture results in overt changes in contractility. The intracellular study of their ongoing electrical activity prior to, during, and after laser microirradiation demonstrates that definite membrane alteration occurs concomitantly with induced contractile responses. Although all ventricular cells are depolarized by laser microirradiation, the ultimate response elicited seems to differ according to the type of myocardial cell impaled. Typical fibrillation potentials were induced mainly in pacemaker cells.     

Effect of cannabinoids on glycine-activated currents in pyramidal neurons of the rat hippocampus

Using electrophysiological techniques (a patch-clamp technique in the whole-cell configuration and intracellular perfusion of neurons), we studied the effect of cannabinoids on the characteristics of glycine-activated currents in freshly isolated pyramidal neurons of the rat hippocampus. We found that endocannabinoids (anandamide and 2-arachidonoyl glycerol), as well as a synthetic cannabinoid, WIN 55,212-2, when applied in physiological concentrations, decreased the amplitude of glycine-activated currents. The agents under study accelerated the kinetics of activation and desensitization of glycine-induced Cl⁻ currents. The characteristics of the currents recovered after washout from cannabinoids. Changes in the kinetics of desensitization of glycine-activated currents depended noticeably on the holding potential; at positive potentials the sensitivity to cannabinoids was higher. These effects of cannabinoids were also observed in the presence of antagonists of CB1/CB3 receptors and an inhibitor of G proteins, GDPβS. These data indicate that under our experimental conditions cannabinoids exerted direct effects on glycine receptors. Neirofiziologiya/Neurophysiology, Vol. 39, No. 1, pp. 15–21, January–February, 2007.     

Effect of the catalytic subunit of cAMP-dependent protein kinase on the electrical activity of the rat heart in isadrine myocarditis

The content of cAMP in the rat heart under neoepinephrine myocarditis does not differ from the control values and less increases relative to the control at the adrenalin concentrations of 5 X 10(-5) and 5 X 10(-4) M in the in vitro experiments (control: myocardium of healthy animals). Under these conditions dissociation of holoenzyme of cAMP-dependent protein kinase is disturbed in the presence of endogene-developed nucleotide and the phosphorylating activity decreases, respectively. The injection of the catalytic subunit of cAMP-dependent protein kinase encapsulated into neutral liposomes increases the duration of the myocarditis action potential for animals with the metabolic myocardial insufficiency.     

Effect of amyloid beta peptide on poly(ADP-ribose) polymerase activity in adult and aged rat hippocampus

It is suggested that the fibrillar amyloid beta peptide (A beta) in brain plays a direct role in neurodegeneration in Alzheimer's disease, probably through activation of reactive oxygen species formation. Free radicals and numerous neurotoxins elicit DNA damage that subsequently activates poly(ADP-ribose) polymerase (PARP, EC 2.4.2.30). In this study the effect of neurotoxic fragment (25-35) of full length A beta peptide on PARP activity in adult and aged rat hippocampus was investigated. In adult (4 month old) rat hippocampus the A beta 25-35 peptide significantly enhanced PARP activity by about 80% but had no effect on PARP activity in cerebral cortex and in hippocampus from aged (24-27 month old) rats. The effect of A beta peptide was reduced by half by the nitric oxide synthase inhibitor N-nitro-L-arginine. Stimulation of glutamate receptor(s) itself enhanced PARP activity by about 80% in adult hippocampus. However, A beta 25-35 did not exert any additional stimulatory effect. These results indicate that A beta, through NO and probably other free radicals, induces activation of DNA bound PARP activity exclusively in adult but not in aged hippocampus.