Effect of pentobarbital on neurones in the reticular formation of the brain stem: ionophoretic study in the rat

The effect of ionophoretically applied pentobarbital (PB) upon neurones in the nucleus reticularis gigantocellularis of the rat was studied. PB applied through a micropipette depressed the spontaneous activity of 81% of the neurones tested; the remaining neurones did not change their firing rates. Regardless of current intensities used for PB ejection (5-60 nA) there was no increase in the firing rate during PB administration. The depression was dependent upon both the control firing rate and the PB dose; a total depression of activity was observed at currents between 40 and 60 nA. EC50 (15.5 nA, about 5 X 10(-5) mol.l-1--the drug concentration was approximated theoretically) was assessed from the dose-response curve. Repeated application resulted in a shift of EC50 towards higher current values (desensitization). The Hill coefficient was calculated in conformity with the classical theory. From its value (1.4), it may be assumed that the occupation of only one subunit of the binding site is enough to give a response. Possible mechanisms of action of PB upon neurones are discussed.     

Effect of stimulation of the reticular formation on the motivational and reinforcing effects of the self stimulation zones

The influence was studied on the midbrain reticular formation (RF) on motivational and reinforcing effects of stimulation of the same selfstimulation zones (SS) of hypothalamic area. A current of gradually increasing intensity was used, by means of which three groups of functionally (behaviourally) specific reticular points were revealed: motivationaly neutral, positive and negative. The data obtained show that influences of RF on SS zones of hypothalamus differand depend on functional properties of various RF areas. Changes of motivational effects in SS zones reflex the specificity of reticular foci in a lesser degree than changes in reinforcing effects. It has been suggested that reinforcing effects of the SS hypothalamic zones possess their own activating mechanism specifically related to its "positive" link and differing from reticular mechanism of unspecific activation.     

Spectral characteristics of the EEG of the visual and motor cortices in the rabbit during stimulation of the reticular formation of the brain

Study of amplitude-frequency characteristics of dominating spectral maxima in the delta, theta and alpha-ranges of the rabbit visual and motor neocortical areas has shown that an increase of the midbrain reticular formation stimulation frequency from 60 to 1000 imp/s leads to an increase in both area of dominating rhythms frequencies in the theta and alpha-ranges, and to a decrease of the alpha-rhythm amplitude. The theta-rhythm amplitude in the visual area declines while in the motor area a slight increase is observed and then a decrease. Characteristics of the dominating frequency component in the delta-range are determined by three types of oscillations with different types of dependence on frequency of reticular formation stimulation. The most significant differences between areas are manifest in the spectrum amplitude characteristics. Qualitatively similar changes are also seen in correlation of power of spectral ranges in both areas but quantitatively they are more expressed in the motor area.     

Evoked potentials in the reticular formation of the rabbit midbrain during formation of a dominant focus in it

During creation of a dominant focus in the midbrain reticular formation (RF) by its multiple stimulation with a high-frequency current (stimulation frequency 200 Hz, pulse duration 0.1-0.5 ms, voltage 1-3 V, duration 5 s) a statistically significant increase of the amplitude of the evoked potential (EP) in RF to light flashes was revealed in comparison with background data. Significant increase of EP amplitude was also observed in RF in response to the same stimuli applied in successive experiments without RF stimulation, which pointed to the existence of a latent dominant focus in the CNS.     

Changes in collagen metabolism during the chronic electrical stimulation of the midbrain reticular formation

The content of 11-hydroxycorticosteroids, free and bound hydroxyproline in the peripheral blood, as well as the level of free and net hydroxyproline in the aortic wall and myocardium of rabbits were studied in chronic prolonged electrical stimulation of the mesencephalon reticular system. The experiments have shown that electrical stimulation leads to the activation of adrenal cortex function and is accompanied by alterations in collagen metabolism, accumulation of collagen in the aorta and decreased collagen level in the myocardium.     

Neurons of the rabbit midbrain reticular formation during a defensive conditioned reflex]

Analysis of unit activity of the midbrain reticular formation was carried out on alert rabbits during defensive conditioning. Most of the examined neurones exhibited phasic responses corresponding in time to the components of the evoked potential (EP) recorded in the cortical visual area in response to the "indifferent" stimulus, and to the conditioned stimulus and electric cutaneous reinforcement. The data obtained are considered from the standpoint of the Anokhin functional systems theory. A conclusion has been made regarding the participation of reticular units in providing all the basic mechanisms of the functional system of the behavioral act. Discharges of one and the same neurone may correspond to different components of the EPs to conditioned and unconditioned stimuli. In different behavioral acts a neurone may apparently participate in different systemic mechanisms.     

Reflex effect of skeletal muscle mechanoreceptor stimulation on the cardiovascular system

To determine the potential for mechanical stimulation of skeletal muscle to contribute to the reflex cardiovascular response to static contraction (exercise reflex), we examined the cardiovascular effects caused by either passive stretch or external pressure applied to the triceps surae muscles. First, the triceps surae were stretched to an average developed tension of 4.8 +/- 0.3 kg. This resulted in increases in mean arterial pressure (MAP) of 28 +/- 7 mmHg, dP/dt of 1,060 +/- 676 mmHg/s, and heart rate (HR) of 6 +/- 2 beats/min (P less than 0.05). Additionally, increments of 0.3, 0.5, 1.0, 2.0, 4.0, and 8.0 kg of tension produced by passive stretch elicited pressor responses of -6 +/- 1, 7 +/- 1, 16 +/- 3, 21 +/- 8, 28 +/- 6, and 54 +/- 9 mmHg, respectively. External pressure, applied with a cuff to the triceps surae to produce intramuscular pressures (125-300 mmHg) that were similar to those seen during static contraction, also elicited small increases in MAP (4 +/- 1 to 10 +/- 1 mmHg) but did not alter HR. Transection of dorsal roots L5-L7 and S1 abolished the responses to passive stretch and external pressure. Moreover, when the triceps surae were stretched passively to produce a pattern and amount of tension similar to that seen during static hindlimb contraction, a significant reflex cardiovascular response occurred. During this maneuver, the pressor response averaged 51% of that seen during contraction.(ABSTRACT TRUNCATED AT 250 WORDS)