Differentiated interaction of hypothalamic and bulbar mechanisms in regulating blood flow in skeletal muscles

Acute experiments on dogs anesthetized with chloralose and numbutal were made to examine the changes in the blood flow in the muscles of hind limbs in response to stimulation of different parts of the hypothalamus before and after elimination of the effects of the main reflexogenic zones. Vasodilatation in leg muscles evoked by stimulation of the anterior hypothalamus (supraoptic dorso- and ventro-medial nuclei) increased after elimination of baroceptor effects. Qualitatively, the same response evoked by stimulation of the mamillary nuclei diminished. A conclusion has been made about differential interaction of the hypothalamic and bulbar mechanisms in muscle circulation control. It is assumed that vasodilatation of the skeletal muscles evoked by stimulation of the posterior hypothalamus might be determined by reflex inhibition of the vascular tone.     

The role of the lateral and medial hypothalamus in reproducing food and escape instrumental reactions]

In experiments on two dogs it has been found that testing electric stimulation of the lateral hypothalamus reproduces instrumental movement in case of elaborated alimentary instrumental conditioned reflexes (CR) to a tone and does not reproduce it at elaborated acid-defensive instrumental CR. Under testing electric stimulation of the medial hypothalamus the instrumental movement practically is not reproduced neither in alimentary nor in defensive situation. Appearance of instrumental movement at LH electro-stimulation in alimentary situation is connected with activation of backward conditioned connection from motivation "alimentary" LH centre to representation of this movement in the motor cortex.     

Hypothalamic modulation of baroreceptor inhibition of the electrical activity in the renal nerve

Changes in the renal nerve sympathetic activity in response to electrical stimulation of posterior hypothalamus and vago-aortic nerve were studied in acute experiments on cats. It was shown that stimulation of certain points in hypothalamus defence area led to the suppression of baroreceptor reflex-mediated inhibition of the renal nerve sympathetic activity. Chloralosa depressed hypothalamic modulation of baroreceptor reflexes.     

Conditioned reflex reproduction of evoked potentials during reinforcement by electrostimulation of the hypothalamus]

Conditioned evoked potentials to stimulation of a limb, a light flash or a short tone were studied on rats in acute experiments with nembutal anaesthesia and in chronic experiments. Electrical stimulation of the hypothalamus was used as reinforcement. Following the pairings of conditioned and hypothalamic stimulation, the appearance of conditioned EP was recorded, as manifest in the period of the previously applied unconditioned signal after its omission. Their emergence was facilitated after high-frequency stimulation of the hypothalamus or administration of galantamine, an anticholinesteraze drug. Coagulation of the hypothalamus did not prevent any manifestation of conditioned evoked potentials.     

Maternal care effects on the development of a sexually dimorphic motor system: The role of spinal oxytocin

Maternal licking in rats affects the development of the spinal nucleus of the bulbocavernosus (SNB), a sexually dimorphic motor nucleus that controls penile reflexes involved with copulation. Reduced maternal licking results in decreased motoneuron number, size, and dendritic length in the adult SNB, as well as deficits in adult male copulatory behavior. Our previous findings that licking-like tactile stimulation influences SNB dendritic development and upregulates Fos expression in the lumbosacral spinal cord suggest that afferent signaling is changed by differences in maternal stimulation. Oxytocin afferents from the hypothalamus are a possible candidate, given previous research that has shown oxytocin is released following sensory stimulation, oxytocin modulates excitability in the spinal cord, and is a pro-erectile modulator of male sex behavior. In this experiment, we used immunofluorescence and immediate early gene analysis to assess whether licking-like tactile stimulation of the perineum activated parvocellular oxytocinergic neurons in the hypothalamus in neonates. We also used enzyme immunoassay to determine whether this same stroking stimulation produced an increase in spinal oxytocin levels. We found that stroking increased Fos immunolabeling in small oxytocin-positive cells in the paraventricular nucleus of the hypothalamus, in comparison to unstroked or handled control pups. In addition, 60 s of licking-like perineal stimulation produced a transient 89% increase in oxytocin levels in the lumbosacral spinal cord. Together, these results suggest that oxytocin afferent activity may contribute to the effects of early maternal care on the masculinization of the SNB and resultant male copulatory behavior.     

Interlimb Reflexes Induced by Electrical Stimulation of Cutaneous Nerves after Spinal Cord Injury

Whether interlimb reflexes emerge only after a severe insult to the human spinal cord is controversial. Here the aim was to examine interlimb reflexes at rest in participants with chronic (>1 year) spinal cord injury (SCI, n = 17) and able-bodied control participants (n = 5). Cutaneous reflexes were evoked by delivering up to 30 trains of stimuli to either the superficial peroneal nerve on the dorsum of the foot or the radial nerve at the wrist (5 pulses, 300 Hz, approximately every 30 s). Participants were instructed to relax the test muscles prior to the delivery of the stimuli. Electromyographic activity was recorded bilaterally in proximal and distal arm and leg muscles. Superficial peroneal nerve stimulation evoked interlimb reflexes in ipsilateral and contralateral arm and contralateral leg muscles of SCI and control participants. Radial nerve stimulation evoked interlimb reflexes in the ipsilateral leg and contralateral arm muscles of control and SCI participants but only contralateral leg muscles of control participants. Interlimb reflexes evoked by superficial peroneal nerve stimulation were longer in latency and duration, and larger in magnitude in SCI participants. Interlimb reflex properties were similar for both SCI and control groups for radial nerve stimulation. Ascending interlimb reflexes tended to occur with a higher incidence in participants with SCI, while descending interlimb reflexes occurred with a higher incidence in able-bodied participants. However, the overall incidence of interlimb reflexes in SCI and neurologically intact participants was similar which suggests that the neural circuitry underlying these reflexes does not necessarily develop after central nervous system injury.     

The role of the lateral and medial hypothalamus in reproducing a motor reaction as the signal during the acquisition of classical conditioned reflexes]

In experiments on three dogs there was shown that testing electrostimulation of the lateral hypothalamus reproduced the motor reaction which is a signal stimulus at elaboration of classic alimentary conditioned reflexes (CRs) and did not reproduce it at elaboration of classic defensive CR. Testing electrostimulation of medial parts of the hypothalamus reproduced, as LH electrostimulation the "signal" motor reaction, but in less percentage of cases, during elaboration of classic alimentary CRs and did not reproduce it at elaboration of classic defensive CRs. The reproduction of the signal motor reaction at LH electrostimulation is connected with activation of backward conditioned connection from motivation structures of the hypothalamus to representation of the signal stimulus in the motor cortex.     

Generalization of an instrumental defensive conditioned reflex elaborated to electric stimulation of the hypothalamus in dogs

Generalization of defensive conditioned reflexes elaborated to electrical stimulation of the lateral hypothalamus (LH) was studied in four dogs with electrodes implanted in various structures of the limbic system. Electrocutaneous stimulation was switched off when the dog lifted the foreleg to a definite level. Generalization of the conditioned reflex was manifested in different degrees when testing different formations of the limbic system, or testing one and the same structure, but at different stages of conditioning. Two types of generalization were found: the first one--a well pronounced motor reaction, by its latency, level and duration of lifting the foreleg similar to movements appearing in response to the conditioned stimulus; and the second one--low amplitude or short-term movements differing from conditioned ones. The first type of generalization was observed in response to stimulation of LH, contralateral to the point of signal stimulation, of the ventromedial hypothalamic nucleus, the mammillary bodies and the basal, lateral and to a lesser degree, the central nucleus of the amygdaloid complex; the second type--in response to stimulation of the ventral hippocampus, the medial and lateral septum nuclei.     

The organization of the network characteristics of the cells in local and distributed neuronal networks of the cat brain]

In cats with elaborated alimentary instrumental reflexes to light net characteristics of neurones of visual, motor cortex and the hypothalamus lateral nucleus were studied on the basis of revealed interneuronal interactions by means of cross-correlation method of analysis. Different organization of net properties of the cortical neurones in organization of local and distributed neuronal networks was shown, namely: predominance of the divergent characteristics over the convergent ones for cells in local networks and levelling of these relations in distributed nets. Neurones of the lateral hypothalamus nucleus had equal presentation of divergent and convergent properties in organization of local and distributed networks. Net characteristics of neurones of the cortical and subcortical structures were manifested in the background after the elaboration and the extinction of conditioned reflexes. Only small cells of the visual cortex were functionally dependent and changed correlation of net characteristics in local networks at CR extinction.     

Effect of activating the putamen on alimentary conditioned reflexes in dogs

The influence was studied of the near-threshold high- and low-frequency stimulation of the putamen on achievement of alimentary conditioned reflexes in dogs. Both low- and high-frequency activation of the examined structure significantly changes the parameters of intermediate secretion, of the salivary conditioned reflexes, without influencing unconditioned ones. Unilateral stimulation disturbs the achievement of positive and inhibitory conditioned reflexes to a greater extent than bilateral one. Difference between the effects of low- and high-frequency stimulation has been revealed.     

Effect of tyramine on the spinal cord afferent link of pressor reflexes

In anesthetized cats, tyramine application on the dorsal surface of C6-TI spinal cord segments suppressed the pressor components of blood pressure reflexes evoked by radial nerve A sigma or A + C afferent stimulation. Tyramine application on L4-SI spinal cord segments suppressed pressor reflexes to tibial nerve stimulation. Both the degree and the rate of reflex suppression increased with the rise in tyramine concentration from I to 4%. Along with these local effects "distant" tyramine action was demonstrated: pressor reflexes to radial nerve stimulation increased when tyramine was applied on L4-SI segments, but after its application on C6-TI segments pressor reflexes to tibial nerve stimulation increased in some cats, decreased in the other ones, or remained practically unchanged.     

Inhibitory effects of dorsal horn and excitant effects of ventral horn intraspinal microinjections of norepinephrine and serotonin in the cat

Norepinephrine and serotonin microinjections (10 μg) into the dorsal spinal gray matter depressed C-fiber reflexes induced by electrical stimulation of the superficial peroneal nerve or radiant heat stimulation of the footpad. Microinjection of norepinephrine or serotonin into the ventral gray matter facilitated C-fiber reflexes. These studies lend support to the suggestion that dorsal horn projections of neuronal systems which utilized norepinephrine or serotonin as neurotransmitters inhibit nociceptive spinal reflexes, and ventral horn projections facilitate spinal reflexes.     

The effect of direct stimulation of the dog lateral hypothalamus on transformation of a passive-defensive situational reflex into an alimentary one]

The behavioral effect of electrical stimulation of the lateral hypothalamus with a current of equal parameters in chronic experiments on dogs depended on the signal significance of the surroundings. Stimulation of the lateral hypothalamus against the background of a defensive situational reflex in dogs which were in an experimental situation for the first time, far from evoking orientation to food and the act of feeding, enhanced the background fear reaction. After transformation of the defensive signal significance of the situation into an alimentary one, stimulation of the lateral hypothalamus began to activate the alimentary instrumental reflex and the act of feeding. However, at first the former was manifested irregularly. Combinations of stimulation of the lateral hypothalamus and achievement of the alimentary instrumental reflex with subsequent reinforcement stabilized and enhanced the alimentary instrumental reflex to the stimulation of the lateral hypothalamus.     

Features of the formation of conditioned secretory reflexes in response to the stimulation of different areas of the caudate nucleus of the dog

Properties were studied of elaboration of conditioned alimentary secretory reflexes to threshold electric stimulation of the caudate nucleus in dogs. The rate of formation of such a reflex and its magnitude were considerably lower than in reflexes elaborated to distant stimuli. Latencies were longer; dynamics of conditioned and unconditioned secretory reactions was similar to that of reflexes to a weak stimulus--light. The motor component of the conditioned alimentary reaction, as a rule, was absent. Characteristics were revealed of formation of alimentary reflexes to stimulation of the dorsal and ventral parts of the head and body of the caudate nucleus.     

Reflex control of posterior shoulder muscles from arm afferents in healthy people

In order to position the hand during functional tasks, control of the shoulder is required. Heteronymous reflexes from the upper limb to shoulder muscles are used to assist in this control. To investigate this further, the radial and ulnar nerves were stimulated at elbow level whilst surface electromyographic activity of posterior deltoid, infraspinatus and latissimus dorsi muscles were recorded. In addition, the cutaneous branch of the radial nerve and the skin of the fifth digit were stimulated in order to investigate any cutaneous contribution to reflex activity. Reflexes were evoked in all three of these shoulder muscles from hand and/or forearm afferents. However, the reflexes differed; whereas both excitatory and inhibitory reflexes were evoked in posterior deltoid and infraspinatus, the reflexes in latissimus dorsi were mainly excitatory. Cutaneomuscular reflexes were seldom evoked here, but when they were present they were generally evoked at longer latencies than the reflexes evoked by mixed nerve stimulation. The results suggest a role for reflexes originating from the forearm and/or hand in the control of the shoulder.     

Opposite modulating effects of the hypothalamic region on cardiac reflexes of Gadus morhua cod and Rana temporaria frogs

The effects of hypothalamic stimulation on cardiac reflexes have been investigated in the cod Gadus morhua and frog Rana temporaria. Cardiac reflexes were elicited by electrical stimulation of the medullar vagal lobes in fishes and central end of cardiac vagal branch in frogs. During simultaneous or successive stimulation of the hypothalamic region and vagal structures, modulation of the reflexes was observed. Reflex bradycardia was either augmented or inhibited, indicating the corresponding pattern of hypothalamic influences. No correlation was found between the parameters of stimulation, reflex intensity, hypothalamic region and the pattern of modulating influences. The data obtained suggest the existence of opposite modulating influences of the hypotalamic region upon parasympathetic reflexes in the heart of fishes and frogs.     

The effects of mating stimulation on c-Fos immunoreactivity in the female hamster medial amygdala are region and context dependent

During mating in hamsters, both tactile and nontactile sensory stimulation experienced by the female affect sexual behavior and progestational neuroendocrine reflexes. To test the interactions of these types of mating stimulation, c-Fos immunohistochemistry measured brain cellular activity during sexual behavior under conditions that included combinations of tactile and nontactile mating stimulation. Test groups received: (1) mating stimulation from a male, females being either fully mated or mated while wearing a vaginal mask, or (2) experimenter applied manual vaginocervical stimulation (VCS)-with or without males present, or (3) handling similar to VCS but without insertions-with or without males present. Numbers of c-Fos immunoreactive cells were counted in specific subdivisions of the posterior medial amygdala (MeP) and ventromedial hypothalamus (VMH). The medial amygdala dorsal and ventral subdivisions responded differentially to components of mating stimulation. The posterodorsal Me (MePD) cellular activation was greatest during mating conditions that included VCS and/or males present. However, the posteroventral Me (MePV) was sensitive to male exposure and not to VCS. Also, MePV and VMH shell responses mirrored each other, both being primarily sensitive to male exposure. In separate tests, manual VCS induced pseudopregnancy, though the procedure was most effective with additional nontactile stimulation from males present. In summary, contextual cues provided by nontactile male stimulation enhance the effect of vaginocervical and other tactile stimulation on reproductive processes. Furthermore, c-Fos expression in the female hamster medial amygdala is region and context dependent.     

Effects of tetanic stimulation on monosynaptic and dorsal root reflexes in kittens.

The effects of tetanic stimulation of peripheral afferents were examined on monosynaptic reflexes and dorsal root reflexes in kittens of various ages. Concomitantly recorded monosynaptic and dorsal root reflexes resulting from the stimulation of muscle nerves showed similar post-tetanic changes, namely, predominantly post-tetanic depression in neonates and post-tetanic potentiation in older kittens or adults. However, the changes in post-tetanic responses expressed as a percentage of control in dorsal root reflexes were much smaller than those in monosynaptic reflexes. When dorsal root reflexes originating from muscle and cutaneous afferents were compared, dorsal root reflexes from the latter behaved quite differently. For all ages, post-tetanic effects on dorsal root reflexes arising from cutaneous afferents were either insignificant or very small. The possible mechanisms underlying differences in post-tetanic effects from muscle and cutaneous afferents in adults and neonates are discussed.     

Neuromedin U is involved in nociceptive reflexes and adaptation to environmental stimuli in mice

Following our recent observations of inactivity and slowed movement in neuromedin U knockout (NMU KO) mice, we compared nociceptive reflexes and environmental adaptation in NMU KO and wild-type mice. Hot plate and formalin tests revealed that reflexes to heat and pain were significantly decreased in NMU KO mice. Conversely, intracerebroventricular injection of NMU into wild-type mice stimulated nociceptive reflexes in a dose-dependent manner. After NMU injection, increased c-Fos expression was observed in a wide range of locations in hypothalamus, brainstem, and spinal cord. NMU mRNA expression increased in the spinal cord, but not in the hypothalamus, 2 and 4 h after formalin injection. When their light-dark cycle was advanced or retarded by 5 h, NMU KO mice required a longer time to re-entrain into the new light-dark cycle than did wild-type mice. Wild-type mice displayed increased blood pressure after their environmental temperature was changed from 23 to 37 degrees C, whereas no such increase was observed in NMU KO mice. Blood corticosterone levels were significantly increased after 10 min of immobilization stress in wild-type mice, but not in NMU KO mice. These results suggest that endogenous NMU may be involved in reflexes and adaptation to environmental stimuli.     

Effect of electric stimulation of different portions of the amygdala on the formation of alimentary conditioned reflexes in the dog

In dogs with previous learning experience, a low-frequency (1 imp/s), weak (20-50 mcA) amygdala stimulation produces dissimilar influences on formation rate and value of conditioned alimentary reflexes in dependence on stimulation localization. At stimulation of amygdala basolateral part, the reflexes formation proceeds 2-3 times slower than normally. Their value is significantly reduced, the triggering of the secretory reaction is delayed. Dorsomedial part stimulation accelerates the process of conditioning, intensifies the secretion but delays the start of secretory reaction. The elaboration of differentiation inhibition is facilitated by basolateral part stimulation and is impeded by dorsomedial amygdala activation.