Article Type : Opinion Article
Authors : Bon EI, Otlivanchik NI and Narbutovich AP
Autonomic Functions
Autonomic
mechanisms of the spinal cord take part in the regulation of a number of
visceral functions. There is evidence, for example, of the participation of thermosensitive
neurons of the spinal cord in the maintenance of homeostasis of the organism.
Since maintenance of blood pressure constancy is one of the most important
manifestations of homeostasis of autonomic functions involving the spinal cord,
let us consider this issue in more detail. The functional state of sympathetic
preganglionic neurons (SPNs) of the spinal cord is of crucial importance in
maintaining blood pressure homeostasis and regulation of vascular tone and
cardiac activity. When studying the functional specialization of these neurons,
it was shown that on vasomotor neurons of sympathetic ganglia responding
antidromically to muscle nerve stimulation (sympathetic postganglionic fibers
oriented only to blood vessels pass in muscle nerves), axons of only B2 and
C-SPNs converge. The conclusion that B2 -SPNs are the main vasomotor output
from the spinal cord is confirmed by the data obtained when studying the
background activity of SPNs of the lateral horns [1]. Not only somato-visceral
afferentation but also descending influences converge to vasomotor SPNs.
Bulbo-spinal neurons of the lateral, reticular, small cell, paramedian, ventral
reticular, gigantocellular nuclei of the reticular formation, and the central
nucleus of the medulla oblongata participate in the descending transmission of
suprasegmental influences on the sympathetic mechanisms of the spinal cord.
According to Henry and Calaresu, at least five descending reticulo-spinal
systems of the medulla oblongata, of which two are sympatho-activating and
three sympathoinhibitory, are involved in the suprasynal regulation of
cardioacceleratory SPNs. In studying the influence of bulbospinal monoaminergic
pathways on sympathetic nerve activity, it has been shown that
catecholaminergic pathways pass in the dorsolateral canaliculus of the medulla
oblongata. Descending sympathoactivating pathways are also localized in this
region. According to Coote and McLeod, there are both noradrenergic and
serotonergic sympathoinhibitory pathways. The authors note the existence of
three descending inhibitory systems: the noradrenergic sympathoinhibitory
system of ventrolateral medulla oblongata neurons with axons in the
dorsolateral canaliculus of the spinal cord, the serotoninergic system of
suture nuclei neurons with axons in the dorso- and ventrolateral canaliculi of
the spinal cord, and the reticulo-spinal system of the ventromedial reticular
formation of the medulla oblongata. When the ventromedial reticular formation,
i.e., the classic depressor area of the medulla oblongata, is irritated,
inhibition of the SPN occurs with a latency period of 5-30 ms, whereas the
latency period of baroreflex inhibition of the sympathetic discharge of the
spinal cord when the sinus nerve is irritated is 150-300 ms. Therefore, it is
unlikely that the system of ventromedial reticular formation neurons with
fast-conducting axons participates in the baroreflex inhibition of SPN. When
dorso- and ventrolateral tubules are irritated in the area C3 -C4 of the spinal
cord and sympathetic discharge is registered at the level of thoracic segments
(distance of about 130 mm), inhibition of somatosympathetic discharge occurs
with a latency period of 130 ms. Taking into account the localization of
monoaminergic neurons of the medulla oblongata, whose axons form these
bulbospinal inhibitory pathways, we can think that baroreflex inhibition is
transmitted through descending channels from the ventrolateral reticular
formation of the medulla oblongata and the caudal nucleus of the suture, which
are characterized by a slow rate of conduction of inhibitory bulbospinal
impulsation[2,3]. The question of the level at which baroreflex inhibition of
spinal cord SPN occurs is of interest. There is data on both the bulbar and
spinal level of realization of baroreflex inhibition of SPN. The authors who
adhere to the viewpoint about the bulbar level of closing the reflex arc of
late somatosympathetic reflex responses, taking into account the
barosensitivity of these responses and the absence of a pronounced barosensitivity
of the early spinal response, believe that baroreceptor inhibition of
sympathetic activity occurs at the bulbar level. However, a number of data
contradicts the idea of the bulbar level of realization of baroreflex
inhibition of SPN activity and testifies to the existence of spinal mechanisms
of baroreceptor inhibition of sympathetic discharge. Thus, it was found that
irritation of descending pathways at the level of lateral canaliculi of the
spinal cord causes the same inhibition of sympathetic activity as baroreflex
inhibition. It is shown that not only early but also partially late
barosensitive components of somatosympathetic discharge are formed mainly at
the level of the spinal cord. The data on some barosensitivity of the early,
purely spinal component of somatosympathetic discharge are indicative of the
spinal, not only bulbar, level of realization of baroreflex inhibition.
Recently, convincing data have been obtained showing that baroreflex
sympathoinhibitory influences are probably realized on the interneuronal
apparatus of the spinal cord [4-6]. Multichannel transmission of suprasegmental
influences on SPN is provided not only by the reticulospinal system of the
medulla oblongata, but also by a number of other descending projection pathways
(pontomesencephalic, hypothalamic, corticospinal), which are also important
components of the mechanisms of central control of autonomic functions that
maintain homeostasis of various physiological constants of the organism. The
data on convergence of extero- and interoceptive afferent inflow and
supraspinal modulating influences on SPN indicate some integration of
supraspinal cardiovascular reflexes at the spinal level. This view differs from
the classical concept of the organization of central mechanisms of regulation
of cardiovascular functions, according to which afferent and suprabulbar
activity is integrated in the medulla oblongata and transmitted to the spinal
cord through common excitatory and inhibitory pathways [7,8]. The question of
possible realization by the spinal cord of the reflex control of autonomic
functions has long been disputed by many authors. However, to date, a number of
convincing data on the contribution of spinal cord structures to the formation
of the neurogenic component of vascular tone maintenance, to the realization of
somatosympathetic reflexes and, ultimately, to the vasomotor regulation have
been accumulated. Thus, a number of studies have shown the possibility of
realization of reflex reactions of the cardiovascular system in spinal animals.
In early terms after high atraumatic transection of the spinal cord, performed
by ultrasound scalpel, a high level of blood pressure can be maintained and
pressor reactions can be induced. All these data were the basis for the assertion
that spinal cord mechanisms can maintain arterial pressure at values peculiar
to an animal with an intact central nervous system. A number of
electrophysiological studies have shown the existence of tonically active
sympathetic elements in the spinal cord even after chordotomy [9].
The
brainstem reticular formation is involved in the regulation of cardiac
activity, blood pressure and vascular tone, respiration, motor activity and
other vital functions of the organism. Data on the role of the brainstem in
providing homeostatic processes aimed at maintaining constant parameters of the
cardiovascular system function were obtained in the last century. Ovsyannikov
and Dittmar, studying changes in arterial pressure under irritation of
peripheral nerves in conditions of brain stem transection at different levels,
revealed the localization of the "vasomotor" center in the medulla
oblongata. Subsequently, by means of methods of local destruction and
electrical stimulation of various parts of the brainstem, numerous data
confirming the concept of localization of the main vasomotor center in the
medulla oblongata were obtained. The notion that the only structure that
tonically and reflexively activates the cardiovascular system is the medulla
oblongata center, and all other parts of the central nervous system play only
an auxiliary conductive role, proved to be untenable. It has been established
that the complex multilink system of central control of blood circulation
consists of a constellation of "centers" of different order, which
are in a certain hierarchical subordination, which is consistent with the
general principles of organization of mechanisms of central control of various
functional systems of the organism. Each link of the unified system of blood
circulation regulation is characterized by its specific regulation circuit.
What is the specific role of the bulbar level of the "cardiovascular
center" in the regulation of the cardiovascular system? In a number of
works it has been shown that cardiovascular responses arising from the
excitation of "cardiovascular" neurons of the medulla oblongata are
components of integrative reactions of adaptive behavior, in the manifestation
of which a number of functional systems are involved. It is shown that the
functioning of the bulbar "cardiovascular center" is inseparably
connected with the regulation of respiration, and one of the biological values
of the bulbar reticular formation is the conjugation of the functions of blood
circulation and respiration. When studying the bulbar structures of homeostatic
regulation of cardiovascular functions, the question of diffuse or zonal
selective organization of the processes of regulation of the tone of various
regional vessels deserves special attention. When studying the morphofunctional
organization of the mechanisms of central regulation of regional blood
circulation, it was found that bulbar vasomotor centers are built according to
the type of zonal representation, which provides selective changes in the tone
of vessels of different regions of blood circulation. There is data on zonal
regulation of vascular tone irrespective of changes in heart rhythm and cardiac
output. When studying the effect of electrical and chemical stimulation of the
brainstem on the main hemodynamic parameters (systemic arterial pressure,
cardiac output, heart work, total peripheral vascular resistance, tissue blood
flow), it was revealed that when different medulla oblongata formations are
irritated, there is a significant difference in the hemodynamic structure of
cardiovascular responses, which indicates heterogeneity and mosaicism of the
bulbar level of regulation of the cardiovascular system. Of great interest is
the question of whether there are specialized bulbar systems of descending
modulation of individual functionally differentiated output neurons of the
spinal cord (sympathetic preganglionic neurons, respiratory motoneurons,
motoneurons of somatic reflex arcs, and parasympathetic neurons). When studying
conduction velocities along descending reticulospinal sympathoactivating fibers
of the dorsolateral canal, calculated at rostrocaudal displacement of the
stimulus point, as well as the difference of latency periods of responses in T3
and T10 white connective twigs, caused by irritation of the dorsolateral
canaliculus at the level C5 of the spinal cord, it is shown that descending
fibers activating B2 -sympathetic preganglionic neurons are characterized by
conduction velocity from 4 to 8. 9 m/s.9 m/s. It was found that in experiments
with rostro-caudal movement of the irritation point of the dorsolateral
canaliculus the minimum conduction velocities of descending activating
influences oriented to respiratory, somatic and parasympathetic motoneurons,
calculated by the shift of the posterior front of electrical responses of
diaphragmatic, T3 -segmental and pelvic nerves, are equal to 17.0, 10.1 and
15.9 m/s, respectively. Based on these data, the authors concluded that specialization
of suprasegmental efferent neurons exists. The presence of independent
descending channels does not exclude the interaction and integration of
different functional systems at the bulbar level. Maintenance of blood pressure
homeostasis is carried out by the interaction of two antagonistic mechanisms:
in case of blood pressure increase the depressor influence increases and, on
the contrary, in case of blood pressure decrease the central pressor mechanisms
are activated. To study the localization of depressor and pressor areas of the
brain, the stereotactic technique of detailed scanning of deep brain structures
with an irritating electrode has been used in numerous studies. The obtained
data indicate a complex heterogeneous character of morphofunctional
organization of vasomotor structures of the brainstem [10]. Homeostatic
mechanisms of maintaining a constant level of blood pressure are associated
with the activity of baro- and chemoreceptors. Information about parameters
vital for the whole organism (gas composition and pH of the blood, pumping
function of the heart, blood pressure level) is received by the central nervous
system via afferent fibers of the vagus and uvula nerves. Specific
cardiovascular afferentation from reflexogenic zones of the heart and vessels
by negative feedback mechanism regulates the optimal level of activity of the
spinal cord SPN. It is known that each pulse push is accompanied by powerful
activation of baroreceptors and a volley of excitation of afferents of aortic
depressor and carotid nerves is transmitted to neurons in the area of the
nucleus of the solitary tract. According to some authors, baro- and
chemoreceptor afferents monosynaptically excite also neurons of the depressor
area of the paramedian reticular nucleus. When the sinus nerve is irritated,
polysynaptic activation of neurons of the gigantocellular, small cell nuclei,
central nucleus of the medulla oblongata, nuclei of the pontine suture, and
medulla oblongata occurs. Intracellular recording indicates monosynaptic
activation of these neurons. In the studies of Biscoe and Sampson it is shown
that during electrical stimulation of nerves containing baro- and chemoreceptor
afferents, evoked potentials and evoked discharges of individual neurons are
registered in the gigantocellular, small cell, and lateral reticular nuclei.
The data of some other authors concerning the sinus nerve projection testify to
baroafferent monosynaptic activation of only neurons of the nucleus of the
solitary tract. Only when this nucleus is irritated, antidromic potentials in
the sinus nerve are registered. This probably explains the fact that, with the
exception of the narrowly defined area of the solitary complex, an
insignificant number of neurons discharging in the heart rhythm was detected in
the other brainstem regions. Obviously, baroreflex inhibition of sympathetic
nerve activity, synchronous with pulse fluctuations of arterial pressure, is
realized mainly at the spinal level. This is also evidenced by Lebedev's data
on the absence of inhibition of background evoked activity of
antidromnoid-identified reticulo-spinal sympathoactivating neurons of the
medulla oblongata on irritation of the aortic and sinus nerves [10,11].
The
complex of the bulbar vasomotor center includes a system of vasoconstrictor,
sympathoactivating neurons localized in the pressor "points" of the
medulla oblongata. Some of these neurons are output reticulospinal neurons, the
axons of which form descending sympathoactivating pathways of the dorsolateral
canaliculus of the spinal cord.
The
depressor mechanisms of the bulbar vasomotor center are associated with the
activity of two types of inhibitory systems. The source of one of them is the
central structures of baroreflex inhibition of sympathetic activity, depressor
zone "A", according to Scherrer. These structures, according to Coote
and McLeod, include noradrenergic and serotonergic elements of the
ventrolateral reticular formation of the medulla oblongata and the suture
nuclei area. Neural elements of the second inhibitory system are localized in
the classical depressor zone of the ventromedial reticular formation of the
medulla oblongata. It is the bulbar link of the inhibitory pathway that starts
from the sympathoinhibitory zone of the anterior hypothalamus. Depressor
effects during irritation of various structures of the medulla oblongata may
result from the interaction of both different types of inhibitory neurons with
pressor neurons at the bulbar level and inhibitory descending influences on
cardiovascular sympathetic preganglionic neurons at the spinal level. Only the
first steps are being made in the study of neural mechanisms of interactions
between activating and inhibitory brainstem systems involved in the formation
of both tonic and phasic influences of the medulla oblongata on sympathetic
neurons of the spinal cord. Cardioinhibitory neurons of the vagus nuclei system
play an important role in the bulbar regulation of the cardiovascular system.
The system of vagus motor nuclei forms the basis of the central apparatus of
cardiac regulation. Reflex regulation during excitation of cardiovascular
afferents is realized both by changes in the activity of sympathetic neurons of
the spinal cord and through cardioinhibitory neurons of the medulla oblongata.
In a number of morphophysiologic studies it has been shown that in cats the
source of cardioinhibitory influences are neurons of the reciprocal nucleus of
the vagus rather than the dorsal nucleus. Using the criterion of antidromic
identification taking into account latent periods of antidromic discharges
corresponding to conduction velocity along thin myelinated B? -fibers of
cardiac branches of vagus (conduction velocity 8.0-14.5 m/s), it is shown that
in pigeons cardioinhibitory influences are transmitted along axons of dorsal
motor nucleus of vagus nerve. Data on the localization of cardioinhibitory
neurons in the dorsal nucleus were also obtained in rabbits. Udelnov's studies
have shown that efferent neurons of the "cardiac parasympathetic
center" localized both in the region of the dorsal and vagus nucleus play
an important role in the adaptive regulation of heart activity in accordance
with the general needs of the organism and with the state of intracardiac
hemodynamics. The authors have established that in the implementation of
adaptive self-regulation of the heart, the "cardiac parasympathetic
center" of the medulla oblongata has the ability to exert multidirectional
effects on cardiac activity, which can both enhance and inhibit cardiac
function. Based on experimental data not only on inhibitory but also active
accelerating influences of parasympathetic innervation on the heart, the
authors believe that the central nervous system uses quantitative variations of
nerve influences in the organization of reflex influences of the
parasympathetic nervous system on the heart [11, 12]. A number of studies point
to the participation of midbrain formations in vasomotor reactions. Irritation
of the midbrain reticular formation area most often causes a pressor reaction,
heart rate increase and strengthening of myocardial contractile force. Tetanic
irritation of the mesencephalic reticular formation along with a pronounced
pressor reaction causes a generalized increase in tonic activity of the lower
cardiac, vertebral and renal postganglionary sympathetic nerves. Obviously, the
structures of the mesencephalic reticular formation itself form a massive
activation of homeostatic mechanisms and provide generalized excitation of the
sympathetic nervous system. Morphological studies have shown that hypothalamic
pressor pathways pass in the area of the medial longitudinal fascicle, central
gray matter as part of the longitudinal fascicle of Schütz and in the area of
the reticular formation of the midbrain, giving collaterals to its own neurons
of the reticular formation. The descending pathway of the sympathetic
cholinergic muscle vasodilation system also passes through the midbrain region.
When studying the role of the midbrain in the realization of somato-sympathetic
reflexes, its depressing influence on the structures of the pontobulbar region
of the brainstem was shown, tonically inhibiting reflex discharges of
vasoconstrictor neurons caused by impulses of A- and C-afferents. These data
elucidating the mechanisms of reversion of pressor reflexes to depressor
reflexes during decerebration and anesthesia testify to the important role of
tonic influences of suprabulbar brainstem sections for normal activity of
bulbospinal mechanisms of blood circulation regulation.
Adequate
supply of tissues with oxygen and removal of carbon dioxide from the body are
realized by coordinated activity of stem mechanisms of blood circulation and
respiration regulation. In case of various metabolic disorders and
environmental changes, there are significant shifts in the intensity of tissue
respiration, which are provided by corresponding changes in lung ventilation,
cardiac output and regional blood flow. In this complex of adaptive reactions,
the main importance of external respiration is to maintain an optimal, almost
constant level of blood gas composition, partial pressure of oxygen (Rao) and
carbon dioxide (Rao) in arterial blood. For more than a hundred years, the
regulation of respiration, aimed at ensuring homeostasis of blood gas
composition, is associated with the region of the rhomboid brain, where the
so-called "bulbar respiratory center" is located. The topography of
the respiratory center was established by Mislavsky as early as 1885. The use
of stereotactic method of local electrical stimulation with immersed needle
electrodes allowed to limit the zone of the respiratory center more precisely.
According to Pitts et al. data, the zone, irritation of which causes
inspiratory reactions, is located in the ventromedial and caudal parts of the
bulbar reticular formation in the area of the gigantocellular, ventral and
partly lateral reticular nuclei, while the expiratory zone is located in the
dorsal and rostral parts of the gigantocellular reticular nucleus. Micro-electrophysiological
studies of the localization and properties of respiratory neurons identified by
discharge synchronous with respiratory phases contributed to further deepening
of our understanding of the neural organization of the respiratory center [13].
A major role in the activity of the respiratory center is played by afferent
impulses from mechanoreceptors of the lungs, which are transmitted to the
bulbar respiratory center via afferent fibers of the vagus nerve. Three types
of mechanoreceptors have been described both in the lungs and in large parts of
the extrapulmonary bronchi and trachea: slowly adapting stretch receptors,
rapidly adapting stretch receptors, and spasm receptors. When they are excited,
there are respectively three types of reflex reactions of the respiratory
center: inhibition of inspiratory activity when lung volume increases and
increase in respiratory rate and force of contraction of inspiratory muscles
when lung volume decreases. During natural breathing, the receptors of the
vagus nerve are irritated only when the lungs are distended. Inspiratory
inhibition during lung volume expansion was first described by Gehring and
Breuer, who found that increasing lung volume inhibited contraction of the
inspiratory muscles. After transection of the vagus nerves, as a result of the
elimination of vagal inhibition of inspiration, breathing becomes slowed and
deep. The inhibitory reflex of Gehring-Breyer is one of the main mechanisms of
reflex self-regulation of breathing. With each breath impulses of vagus
afferents excite expiratory neurons of the respiratory center, which entails
the emergence of exhalation. Lung mechanoreceptors with afferent fibers of the
vagus nerve represent the main feedback of the respiratory periphery to the
respiratory center, and afferentation of this system maintains the periodic
activity of the respiratory center. After destruction of the pneumotaxis of the
weighty mechanism of the variolian bridge vagotomy leads to respiratory arrest
on inspiration or severe lengthening of breaths (apneic breathing) [14]. In
addition to mechanoreceptors of the lungs, proprioreceptors of the diaphragm,
intercostal muscles and abdominal wall muscles participate in the regulation of
respiration. Detailed information on the importance of reflexes from receptors
of the lungs, respiratory muscles and upper respiratory tract in the regulation
of respiration is given in the reviews by Glebowski and Felberbaum. In addition
to mechanoreceptors of the lungs, airways and proprioreceptors of respiratory
muscles, respiratory reflexes from peripheral and central chemoreceptors play
an important role in the regulation of breathing. The main function of
respiratory chemoreceptors is to ensure a constant gas composition and
acid-base balance of the internal environment of the body. At any deviations of
blood gas composition chemoreceptor reflexes due to changes in alveolar
ventilation provide elimination of these deviations. Increase of Rao and
decrease of Rao, exciting chemoreceptors, cause a reflex increase in the minute
volume of respiration, leading to a decrease in possible deviations in the
blood gas composition. The mechanism of blood gas composition homeostasis
maintenance in this case is realized by the principle of regulation by
deviation by means of feedback. Deviation of regulated parameters (Rao, and
Raco), acting reflexively on the respiratory center, and changes in external
respiration contributes to the restoration of the optimal level of Rao, and
Raco, at any level of tissue metabolism. The data of numerous experiments show
that along with regulation by deviation, the mechanism of regulation by
perturbation is widely used in the respiration control system. The importance
of the principle of regulation by perturbation for maintaining homeostasis of
blood gas composition is clearly revealed in the study of respiration under
conditions of muscular activity in the transient mode. In this case, at the
beginning of muscular work, the work of respiratory muscles is intensified and
the minute volume of respiration is increased due to proprioceptive signals
about the perturbation before the appearance of deviation in Raco, Rao, and pH.
The change in external respiration at the very beginning of motor activity
prevents the occurrence of a deviation in arterial blood gas composition.
Considering the mechanisms of homeostasis regulation in this case, Marshak
notes that this is a typical example of regulation not by deviation, but by
perturbation.
Receptors
perceiving the gas composition of arterial blood are located in two areas: in
the region of the aortic arch and in the carotid sinus. Afferent fibers of
these receptors of the aortic and sinus nerves, respectively, enter the nucleus
of the solitary tract, and from here chemoreceptor impulses are transmitted to
respiratory neurons. Not only arterial chemoreceptors, the respiratory center
itself, but also specialized chemosensitive areas of the brainstem are
sensitive to changes in Pso, and pH. Discussing the role of various
chemoreceptors in the system of respiratory regulation, Breslav believes that
central chemosensitive zones located on the ventrolateral surface of the
medulla oblongata act as sensitive sensors signaling the concentration of
hydrogen ions and C02 tension in the cerebrospinal fluid. The author believes
that aortic chemoreceptors located at the "gate" of the entire
arterial system and sinocarotid chemoreceptors located at the "gate"
of the cerebral vascular system serve as sensors responding to changes in C02
tension and blood pH. Integration and interaction of chemo- and mechanoreceptor
impulses in neurons of the respiratory center contribute to the formation of
rhythmic activity of respiratory neurons [15]. Impulsation from baroreceptor
afferents also plays a role in the regulation of respiratory neuron activity.
According to Richter and Seller, baroreceptor afferentation causes
hyperpolarization of the membrane of inspiratory neurons either as a result of
their direct inhibition or as a result of dysfasciculation due to baroreceptor
inhibition of nonrespiratory neurons of the activating reticular formation
causing tonic activation of respiratory neurons. Baroreflex depolarization of
the membrane of expiratory neurons, occurring only during the period of
spontaneous membrane hyperpolarization, may be the result of disinhibition
during baroreflex hyperpolarization of inspiratory neurons. The bulbar
respiratory center is always under the influence of impulsation coming to it
from the higher parts of the brainstem. According to Monnier, the rhythmic
activity of inspiratory neurons is formed under the influence of three
inhibitory systems: the pneumotactic center of the Variolius Bridge, the
expiratory center of the dorsolateral reticular formation of the medulla
oblongata, and the inhibitory component of the reflex system of the vagus
nerve. Destruction of the anterior pontine region, especially after bilateral
vagotomy, leads to inspiratory apnea, apneic breathing. Inspiratory apnea after
transection of the varicose bridge anterior to the apneic center is eliminated
by rhythmic irritation of the vagus nerve or inflating the lungs, i.e.,
prolonged discharge of mechanoreceptors of lung stretching. Neurons of the
expiratory center, activated by the pneumotactic center or afferent vagus
impulses, exert an inhibitory influence on the inspiratory neurons. Excitation
of vagus afferents suppresses the inspiratory effect of the apneic center of
the varicose bridge and the inspiratory center of the medulla oblongata. The
activity of the pontobulbar structures of the respiratory center is influenced
by the midbrain reticular formation. According to Hori's data, irritation of
the medial region of the mesencephalic reticular formation results in
nonreciprocal facilitation of the activity of inspiratory and expiratory
neurons, while irritation of the lateral region results in nonreciprocal
inhibition of their activity [16].
The
brainstem reticular formation is also involved in the regulation of other
autonomic functions. There are numerous data on the role of the brainstem
reticular formation in the regulation of motor and secretory activity of the
digestive and excretory organs, and in the realization of neuroendocrine
functions. The brainstem reticular formation participates in the regulation and
maintenance of homeostasis in the organism as a system integrating
autonomic-endocrine-somatic functions, and the integrative activity of the
brainstem reticular formation is carried out in interaction with the
integrative mechanisms of the hypothalamus.