Study of lever-holding phenomenon during the escape reaction in rats

A "preparatory" hypothesis according to which the bar-holding develops as a preparatory response placing an animal in an advantageous position for the reaction on the subsequent action of the electric current has been experimentally examined. Comparing the avoidance training under the condition allowing the bar-holding until the next conditioned and unconditioned stimuli, and under conditions excepting such long holding it has been established that in first case the number of bar-holding responses is more and the avoidance responses are less than in the second one. It contradicts the "preparatory" hypothesis. It has been shown that the dynamics of inter-trail and the bar-holding responses results from stimulus generalization and discrimination.     

The kinetics of S-transnitrosation--a reversible second-order reaction.

Transnitrosation between thiols and S-nitrosothiols has been suggested to be a mechanism of signal transduction. This kinetics of such reactions fit well to a reversible second-order model. Parameters derived from this model give both the forward and reverse rate constants and the equilibrium position at physiological temperature and pH. In addition, methods are shown for calculating the equilibrium distribution of the nitrosyl function group in mixtures of up to three thiols.     

Substance P in the central mechanisms of the escape reaction

The role of substance P in the central mechanisms of escape reaction elicited by electrical stimulation of the ventromedial hypothalamus was investigated in chronic experiments on rabbits. Intravenous injection of substance P (30 micrograms/kg) led to a short-term (less than 10 min) increase in the threshold of stimulation of the ventromedial hypothalamus and to more stable (up to 1.5 h) disorders of the hippocampal-hypothalamic relations. After substance P injection the inhibitory effects of the dorsal hippocampus but not the facilitating influences of the midbrain reticular formation on excitability of the hypothalamic motivation center were found to be lacking. Disorders of the central mechanisms of escape reaction after substance P injection correlated with new patterns of the main EEG rhythms in different areas of the brain cortex in response to the ascending excitations of the limbic-midbrain structures. Interpreting the mechanisms of substance P involvement in escape reaction the authors point to the ability of the given peptide to interact with different transmitter systems of the brain and opiate receptors and to alter the brain blood circulation.     

On the time course of the reversible Michaelis-Menten reaction

The methods of Padé approximants and Euler transformation are used to construct approximate solutions for the time course of the reversible Michaelis-Menten reaction. The solutions are found to describe the concentrations of the various species quite accurately throughout and beyond the transient phase. To illustrate the results, the ratio of the reverse bi-molecular rate constant to the forward bi-molecular rate constant, k2/k1, is varied from 0.1 to 5, and the initial enzyme-to-substrate concentration ratio is changed from 0.01 to 5. Only when k-2/k1 is less than one, the concentration of the intermediate complex, y(t), undergoes a maximum (steady state); for all other values of this ratio, y(t) increases monotonically with time t, to the equilibrium value, i.e. no maximum is attained. The present methods are particularly useful when the total enzyme concentration is comparable to, or greater than the initial substrate concentration, a situation commonly found under in vivo conditions.     

"Despair" and "escape" behavioral tests in the evaluation of antidepressant activity

Antidepressants pyrazidol (pirlindole), incazan, imipramine, nialamide, nomifensine, mianserin were shown to reduce the duration of immobilization in mice in "despair" tests and increase the number of rotations in water "escape" tests.     

Some characteristics of the insulin-induced potentiation to anaphylactoid reaction in Sprague-Dawley rats.

The insulin-induced sensitization to generalized and local anaphylactoid reaction evoked by dextran was studied in Sprague-Dawley CFY rats. The generalized reaction was shown to be potentiated by insulin given subcutaneously in a dose-related manner. The minimum effective dose was as low as 0.04 U/kg. When this dose was injected intravenously, a marked but short-lived potentiation was observed. The insulin response could be elicited throughout the whole year. The local oedema induced by subplantar injection of dextran was found to be much less sensitive to insulin. Potentiation was observed during the period from March to October, while in the intermediate months, no such effect could be seen. The seasonal refractory state to insulin was abolished by bilateral adrenalectomy, and daily pretreatment of the rats with insulin for several days. Actinomycin D prevented the restorative effect of insulin pretreatment. Sensitization by a single insulin dose to both systemic and local dextran was suppressed in rats older than 6 months, and the refractoriness was in part reversed by adrenalectomy.