Analysis of the response of 128 reticulospinal neurons in the magnocellular and ventral reticular nuclei showed that 36.7% of these cells responded with short-latency (2-4 msec) action potentials and increased their tonic activity in response to electrical stimulation of the central parts of the hypothalamus, which evoked increases in hindlimb muscle tone in rats. These cells completely stopped producing action potentials during electrical stimulation and during chemical stimulation of the dorsolateral parts of the pons, which inhibited movement and muscle tone. A total of 23.4% of the cells produced only short-latency (1-4 msec) action potentials in response to stimulation of the inhibitory parts of the pons. A total of 3.9% of reticulospinal neurons increased their activity during stimulation of the hypothalamic zones and pontine areas of the brain. No responses were obtained from 35.9% of neurons. It is suggested that excitation of pontine structures inhibiting movement and muscle tone may prevent conduction in descending activatory systems from the rostral parts of the brain (which increase muscle tone) to the reticulospinal neurons of the medulla oblongata.
The reaction of 277 neurons located in the brain pons dorsolateral portion was analyzed in awake and narcotized rats during the immobility reflex induced by skin constriction on the neck dorsal surface. The following were excited: fast adaptive tactile neurons (n = 32), interneurons (n = 42), and cells forming monosynaptic inputs to the parts of the medulla oblongata, which inhibit the movements (n = 10). The following were inhibited: somatosensory (n = 42), nociceptive (n = 24), and unidentificated (n = 14) neurons. In some neurons the charge characteristics were stable or slightly modified, namely: respiratory neurons (n = 16), cell group having stable background firing (n = 72), and stimulating antidromicaUy spontaneously silent ponto-medullar neurons (n = 22).
The dependence of the dominant form of the defensive behavior of white male mongrel rats on the functional state of the brain stem inhibitory locomotor system has been studied in chronic experiments. It was established that the electrolytic destruction of the inhibitory zones of the cuneate nucleus of the midbrain, the medial parabrachial nucleus, the central and great nuclei of the raphé leads to the dominance of active defensive reactions in animals in confrontations with partners. The opposite effect is exerted by local injection of kainic acid into these regions of the brainstem. It is hypothesized that the functional state of the brain stem inhibitory locomotor system can exert a modulating influence on the formation of the defensive behavior of animals.
We have developed a conditioned defense reflex in chronic experiments with rats using electrodes implanted in the reticular oral pons nucleus, the corticomedial group of amygdalar nuclei, the ventromedial hypothalamic nucleus, and the central gray matter of the midbrain. We showed that the synchronization of the activity of neuronal groups of emotiogenic formations of the brain structures investigated was enhanced during formation of the conditioned reflex. We established a dependence of the correlation of the activity of limbic neuronal groups on the functional state of the reticular formation, and also neurochemical correlation mechanisms. We were able to show that an increase/decrease in the coefficients of mutual correlation of the activity of the neuronal aggregates of limbic structures is accompanied by a change in the parameters of the evoked potentials recorded in them.
The effect of electrical stimulation of the region of the medial parabrachial nucleus on the behavior of albino rats is studied in chronic experiments. Stimulation of this region is found to cause an increase in the rate of respiration and inhibition of natural behavioral reactions and reactions elicited by stimulation of the nuclei of the amygdala, lateral hypothalamus, and the zona incerta of the brain. Similar inhibitory effects are noted for stimulation of certain zones of the midbrain cuneate nucleus and regions of the pontine suture. The inhibitory influence of stimulation of the parabrachial nucleus on behavior is thought to be due to the switching-on of the central mechanisms of inhibition of motor activity in animals.
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