Conditioned reactions to time of hypothalamic neurons. The perifornical nucleus]

In 40% of the 52 neurones of the hypothalamic perifornical nucleus in alert rabbits conditioned trace reactions of the activational (52%) and inhibitory (48%) type were recorded in the course of elaboration of a conditioned motor reflex to time. The sign and pattern of the trace responses were determined by the nature of cell reactions to actual paired stimuli. After 50 to 70 pairings, the unit trace conditioned reaction to time persisted for a period of 10 to 15 successive omissions. Trace responses were observed most frequently in the 5th of 8th omissions. In some cases conditioned enhancement of cell activity coincided with the conditioned motor response to time. This fact together with the maximal development of a summery trace cellular response at the moment of formation of conditioned motor reactions attests the participation of neurones of the perifornical nucleus in maintaining conditioned motor activity.     

Effect of fenamin and haloperidol on conditioned activity of neurons of the motor cortex and striopallidal system

The activity of neurones in the motor cortex, caudate nucleus, putamen and globus pallidus was studied during elaboration of motor conditioned reflexes to time in rabbits, treated with 1-amphetamine and haloperidol. Mechanisms of reproduction of cells trace activity in the reflex to time at the omission of trials, reacted to 1-amphetamine by increasing the intensity of reactions in the motor cortex and inactivation in putamen cells. The curve of dynamics of intensity changes of trace discharges in the course of a series of trials omissions remained unaltered only in motor cortex; in the other structures it significantly differed from the norm of intact animals. Haloperidol depressed the mechanisms of reproduction of trace reactions of the globus pallidus cells, and made them almost fully inactive in the motor cortex; the putamen neurones reacted to haloperidol by an increase of trace reactions intensity. Against the background of the animal chronic 1-amphetamine intoxication, haloperidol normalized the dynamics and intensity of trace activity. "Therapeutic" effect of haloperidol was most distinctly expressed in the motor cortex and putamen cells, less--in the caudate nucleus and was completely absent in the globus pallidus.     

Octopaminergic modulation of locust motor neurones

The effect of octopamine on the fast extensor and the flexor tibiae motor neurones in the locust (Schistocerca gregaria) metathoracic ganglion, and also on synaptic transmission from the fast extensor to the flexor motor neurones, was examined. Bath application or ionophoresis of octopamine depolarized and increased the excitability of the flexor tibiae motor neurones. 1 mM octopamine reduced the amplitude of the fast extensor-evoked EPSP in the slow but not the fast flexor motor neurones, whereas 10 mM octopamine could reduce the EPSP amplitude in both. Octopamine broadened the fast extensor action potential and reduced the amplitude of the afterhyperpolarization, the modulation requiring feedback resulting from movement of the tibia. Octopamine also increased the frequency of synaptic inputs onto the tibial motor neurones, and could cause rhythmic activity in the flexor motor neurones, and reciprocal activity in flexor and extensor motor neurones. Octopamine also increased the frequency of spontaneous spiking in the octopaminergic dorsal unpaired median neurones. Repetitive stimulation of unidentified dorsal unpaired median neurones could mimic some of the effects of octopamine. However, no synaptic connections were found between dorsal unpaired median neurones and the tibial motor neurones. The diverse effects of octopamine support its role in mediating arousal.     

Electrophysiological Evidence for Oxytocin Receptors on Neurones Located in the Dorsal Motor Nucleus of the Vagus Nerve in the Rat Brainstem

Abstract

Intracellular recordings were obtained from vagal neurones and their response to oxytocin was investigated in slices from the rat brainstem. Following recording, Lucifer Yellow was injected into the cells in order to verify their localization within the dorsal motor nucleus of the vagus nerve. Virtually all neurones throughout the rostro-caudal extent of the nucleus increased their rate of firing in the presence of 10-1000 nM oxytocin and their membrane depolarized in a reversible, concentration-dependent manner. This excitation was probably exerted directly on the impaled cells rather than being synaptically mediated, since it persisted in a low calcium-high magnesium medium or in the presence of tetrodotoxin. These data provide evidence for a direct membrane effect of oxytocin on a defined population of neurones in the rat brain.     

Tracing of sensory neurones and spinal motoneurones of the pigeon by injection of fluorescent dyes into peripheral nerves

The projection of peripheral sensory and motor nerves was investigated in the pigeon (Columba livia) by means of retrogradely transported fluorescent dyes. Two combinations of fluorescent tracers were used that could be identified within the same cell when excited by light of 405 nm: 1) Propidium iodide and Bisbenzimide, which label the cytoplasm orange and the nucleus blue, respectively; 2) Fast Blue, which labels the cytoplasm blue, and Nuclear Yellow, which labels the nucleus (especially the nucleolar ring) yellow. The presence of the tracers in a given cell was confirmed microspectrophotometrically. Following injection of the tracers into peripheral nerves, labelled sensory neurones were seen in the dorsal root ganglia and motoneurones of the spinal cord. The peroneal and tibial nerves projected to L2-L5 and L2-L7, respectively, whereas the median and ulnar nerves projected to C12-Th2 and C13-Th1. Double-labelled sensory neurones were observed when both peroneal and tibial, or median and ulnar nerves were injected with different tracers. This indicates that some sensory neurones possess peripheral processes that dichotomize to pass down two different peripheral nerves. Double labelling was never seen in motoneurones, or in sensory neurones after tracer injection into the sciatic and femoral nerves.     

Regenerative Capacity of Visceral Preganglionic Neurones

IT seems to have been widely assumed that autonomic neurones respond to axonal damage much as do somatic motoneurones. From an extensive series of experiments on the albino rat, however, we have obtained evidence that autonomic preganglionic neurones are much more seriously affected. Thus, when the cervical vagus on one side was either crushed or cut, we consistently found in more than 100 animals that changes in the cells of the dorsal motor nucleus of the vagus were more severe and more protracted than in those of the hypoglossal nucleus when its nerve was similarly treated. The changes are seen particularly well in histochemical preparations designed to show the distribution of various metabolic enzymes. In the work described here attention was concentrated on alterations in the cholinesterases and in acid phosphatase.     

Conditioned reactions of hippocampal neurons during amphetamine poisoning and its counteraction with haloperidol

Activity of 144 neurones of the dorsal part of the rabbits hippocamp was recorded during elaboration of motor conditioned reflex to time. Chronic amphetamine intoxication lowered the ability of hippocampal neurones to form conditioned reactions in response to pairings of sound stimuli with electrocutaneous reinforcement and fully suppressed mechanisms of reproduction by cells of engrams of previous pairings in series of their omissions Single administration of haloperidol to intact animals somewhat increased the number of neurones reacting to the pairing and their omissions in conditioned reflex to time without significantly influencing the intensity and dynamics of reproduction of endogenous cellular reactions in the series of consecutive omissions of pairing. Haloperidol administration during amphetamine intoxication elicited shifts towards normalization of conditioned activity of neurones, eliminating the suppressing action of amphetamine on mechanisms of reproduction of engrams of combined stimuli. Such "therapeutic" effect of haloperidol in many cases did not depend on the character of its psychotropic action. The properties of amphetamine and haloperidol action on the cells of the hippocamp are discussed as compared to their action on the neurones of other brain structures, previously studied in an analogous experimental situation.     

Firing of 5-HT neurones in the dorsal and median raphe nucleus in vitro shows differential alpha1-adrenoceptor and 5-HT1A receptor modulation

The median raphe nucleus and dorsal raphe nucleus together are the major source of ascending 5-HT projections. Here, using in vitro extracellular single unit electrophysiology we examined the responses of individual neurones in the rat median raphe nucleus and dorsal raphe nucleus to alpha(1)-adrenoceptor and 5-HT(1A) receptor activation and made comparisons between the two nuclei. In the presence of the alpha(1)-adrenoceptor agonist phenylephrine (1microM) all spontaneously active neurones recorded in the median and dorsal raphe nuclei fired slowly (<5Hz) and regularly. Most were inhibited by 5-HT (10-50microM), although a few were excited by 5-HT. 5-HT-induced inhibition was attenuated by the 5-HT(1A) receptor antagonist, WAY100635 (100nM). Compared to those in the dorsal raphe nucleus, the neurones in the median raphe nucleus which were inhibited by 5-HT had: (1) lower basal firing rates in the continuous presence of phenylephrine (1microM), (2) smaller excitatory responses to higher concentrations of phenylephrine (3-10microM), (3) smaller excitatory responses to brief application of norepinephrine (10-100microM) and (4) smaller inhibitory responses to 5-HT (10-50microM). The lower sensitivity of median raphe neurones to alpha(1)-adrenoceptor excitation and 5-HT(1A) receptor inhibition will have consequences for 5-HT neurotransmission in forebrain regions innervated by the two nuclei.     

Neuronal specialization of the motor cortex in normal rabbits and following destruction of the visual cortex

The activity of neurones of the anterolateral part of the motor cortex in food-acquisition behaviour was compared in two control rabbits and in three rabbits after the operation of bilateral ablation of the striatal cortex. In two of three operated rabbits the pattern of behavioural specialization lost considerably the specificity peculiar to the motor cortex (predominance of G-neurones activated in grasping of food), approaching (but not becoming identical) the pattern of specialization of the visual cortex neurones: the number of G-neurones decreased in a half, and the number of L-neurones (activated in connection with the acts of instrumental food-acquisition behaviour which animals were trained to in the experimental cage) was doubled. Changes of the activity were significantly less expressed in the third operated rabbit. The number of the neurones activated in food-acquisition behaviour in operated rabbits in comparison with the control ones was reduced in the upper layers of the cortex and increased in the lower layers. The resemblance is discussed of the basic processes of animals learning and behaviour recovery.     

Comparative characteristics of septal "burst" neurons after elimination of afferent effects of the reticular formation in the rabbit

Comparative analysis of characteristics of rhythmic theta-activity in the neurones of the medial septal nucleus and nucleus of diagonal band was performed in intact rabbits after. i. v. injection of pentobarbital, and in rabbits with chronic lesion of the ascending brain-stem afferent fibers. In both conditions theta-bursts disappeared in some cells with unstable periodic rhythmic modulation; substantial population of the septal units preserved regular burst activity. Main characteristics of theta-bursts were almost identical in both states, their mean frequency decreased to 3.5 Hz. The theta-rhythm in hippocampal EEG was usually absent; but low-frequency rhythmic activity could be evoked by electrical or sensory stimulation as well as by injection of bemegrid or physostigmine. The data show that the ascending brain-stem afferents control: the frequency of the bursts in a population of septal units regarded as bursting pace-maker cells; the total number of the septal cells secondarily (synaptically) involved into rhythmic activity. The effect of pentobarbital upon theta-rhythm results from elimination of these influences upon the septal cells.     

Effects of transections and electrical coagulations in the medulla oblongata upon the activities in the respiratory muscles of the crucian carp (author's transl)]

The following conclusions may be drawn from the results in this work. The respiratory cycles are formed by the neuronal machinery in the reticular formation under the posterior part of the vagal motor nucleus. The motor neurones or the neuronal networks composing the motor nucleus of the respiratory muscles tonically discharge the action potentials, when the neurones or the networks are released from the inhibitory influences of the interneurones connecting the neuronal machinery to the motor neurones. Furthermore, the interneurones probably generate the tonic discharges after removing the inhibitory influences of the other interneurones or the neuronal machinery on them. A reflex mouth closing is elicited by a mechanical stimulus applying on the upper lip. The motor neurones of the m. adductor mandibulae are activated via only one synapse in the reflex. The reflex action potentials recorded from the motor nerve reduce in amplitude at the resting phase of the nerve in the respiratory cycles. These results suggest that the respiratory motor neurones are by nature spontaneous generators of the tonic action potentials and, in the time of the normal breathing, the tonic activity is interrupted by an inhibitory influence of the neuronal machinery generating the respiratory cycles.     

Initiation of facial motoneurone migration is dependent on rhombomeres 5 and 6

In mammals, facial branchiomotor (FBM) neurones are born in ventral rhombomere (r) 4 and migrate through r5 to dorsal r6 where they form the facial motor nucleus. This pattern of migration gives rise to the distinctive appearance of the internal genu of the facial nerve, which is lacking in birds. To distinguish between extrinsic cues and intrinsic factors in the caudal migration of FBM neurones, this study takes advantage of the evolutionary migratory difference between mouse and chick in generating mouse-chick chimaeras in ovo. After the homotopic transplantation of mouse r5 and/or r6 into a chick embryo, chick ventral r4 neurones redirected their cell bodies towards the ectopic mouse source and followed a caudal migratory path, reminiscent of mouse FBM neurones. In a second series of grafting experiments, when mouse r4 was transplanted in place of chick r4, mouse r4 neurones were unable to migrate into chick r5, although mouse and chick cells were able to mix freely within r4. Thus, these data suggest that local environmental cues embedded in mouse r5 and r6 are directly involved in initiating caudal migration of FBM neurones. In addition, they demonstrate that chick FBM neurones are competent to recapitulate a migratory behaviour that has been lost during avian phylogeny.     

The modulation of sensory transmission through the medullary dorsal horn during cortically driven mastication

During mastication, reflexes are modulated and sensory transmission is altered in interneurons and ascending pathways of the rostral trigeminal sensory complex. The current experiment examines the modulation of sensory transmission through the most caudal part of the trigeminal sensory system, the medullary dorsal horn, during fictive mastication produced by cortical stimulation. Extracellular single unit activity was recorded from the medullary dorsal horn, and multiple unit activity was recorded from the trigeminal motor nucleus in anesthetized, paralyzed rabbits. The masticatory area of sensorimotor cortex was stimulated to produce rhythmic activity in the trigeminal motor nucleus (fictive mastication). Activity in the dorsal horn was compared in the presence and absence of cortical stimulation. Fifty-two percent of neurons classified as low threshold and 83% of neurons receiving noxious inputs were influenced by cortical stimulation. The cortical effects were mainly inhibitory, but 21% of wide dynamic range and 6% of low threshold cells were excited by cortical stimulation. The modulation produced by cortical stimulation, whether inhibitory or excitatory, was not phasically related to the masticatory cycle. It is likely that, when masticatory movements are commanded by the sensorimotor cortex, the program includes tonic changes in sensory transmission through the medullary dorsal horn.     

The distribution of aminergic neurones and their projections in the brain of the teleost,Myoxocephalus scorpius

Summary Fluorescent histochemistry was carried out on the brain of the teleost Myoxocephalus scorpius to show the distribution of monoaminergic neurones and their projections.Posterior to the obex of the fourth ventricle, at the junction of the spinal chord and medulla, there is an unpaired dorsal nucleus of catecholaminergic cells. A second group of catecholaminergic perikarya are scattered lateral to the vagal and glossopharyngeal motor nuclei. Both groups of aminergic cells contribute to a tract which crosses the fourth ventricle at the obex and runs along the lateral wall of the medulla towards the diencephalon.At the level of the isthmus there is a lateral nucleus composed of large catecholaminergic cells with prominent fluorescent axons and its possible homology with the locus coeruleus is considered. Medially, in the same region a nucleus of serotonergic neurones lies between the paired tracts of the fasciculus longitudinalis medialis.In the diencephalon there are three paraventricular nuclei, the nuclei recessus posterioris and lateralis and the paraventricular organ pars anterior. Ventral to the lateral recess there is a further nucleus less closely associated with the ependyma.The distribution of fluorescent fibres is described and the dispositions of the aminergic nuclei compared to those of other teleosts.     

Changes in NADPH-diaphorase activity in the rat dorsal horn following an acute experimental myositis

Previous neurophysiological experiments have shown that in rats with an acute myositis of the gastrocnemius-soleus muscle, dorsal horn neurones exhibit an increase in responsiveness to peripheral stimulation and in background activity. The present study investigated the possible correlation between changes in NADPH-diaphorase activity and neurophysiological alterations. In the animals used for the electrophysiological experiments the diaphorase activity in sections of the lumbar spinal cord was determined with the NADPH-nitroblue tetrazolium reaction. The main finding was a massive reduction in the number of diaphorase-positive cells in the superficial dorsal horn in animals with a myositis. The staining intensity in the remaining neurones was unchanged. The results are interpreted as indicating that the myositis in addition to the surgical operations represents a supramaximal input to the dorsal horn causing neurotoxic effects in diaphorase- positive neurones.     

The effect of lesions of the dorsal acoustic stria on the levels of glutamic acid decarboxylase and GABA transaminase in the inferior colliculus and cochlear nucleus of the guinea-pig

The levels of glutamic acid decarboxylase (GAD) and γ-amino butyric acid-α-oxoglutarate transaminase (GABA-T) have been investigated in the cochlear nucleus and inferior colliculus of the guinea-pig after hemilateral section of the dorsal acoustic stria. Animals were cerebellectomised and the stria on one side cut. Eleven days later the animals were killed and GAD and GABA-T assayed in the respective nuclei. There was no change in the enzyme levels of the inferior colliculi showing no direct GABA-ergic fibres ascending through the stria and terminating in the inferior colliculi. The levels of both GAD and GABA-T in the cochlear nucleus on the operated side decreased significantly. It is concluded that about 30% of the GAD containing terminals in the cochlear nucleus arise from fibres descending through the dorsal acoustic stria. The bulk of the GABA-ergic transmission in the cochlear nucleus is assumed to involve an intrinsic system of short axoned neurones, the majority of which have their nerve endings in the dorsal part of the nucleus.     

Motor nucleus of the V-th nerve and the control of breathing. Breuer-Hering reflexes and apneustic breathing

Earlier studies from this department have demonstrated that neurones of the V-th nerve motor nucleus (NVmt) have oligosynaptic, inhibitory output to the inspiratory motoneurone themselves under the influence of a polysynaptic input from vagal afferents. To check the hypothesis that NVmt is a part of the pneumotaxic mechanism, we studied the effects of pharmacological microblockade of the NVmt on Breuer-Hering reflexes in halothane-anesthetized, paralyzed and artificially ventilated rabbits. Activities of NVmt neurones and phrenic nerve firing were recorded. Acid-base balance was controlled and histologic examinations were routinely performed. Expiratory activities were regulatory found in NVmt. Its blockade elicited a typical apneustic breathing. During the blockade the Breuer-Hering reflexes gave "paradoxical" effects: an increase in central respiratory frequency following inflation, inspiratory apneusis in response to deflation. We conclude that the NVmt is an important component of the pneumotaxic mechanism or even the anatomical substrate of the pneumotaxic "centre".     

Breuer-Hering reflexes in ketamine-induced apneustic breathing in the rabbit

The effects of ketamine on the activities of the mylohyoid nerve (a branch of the Vth nerve) and of both phrenic nerves were investigated in rabbits anaesthetized with halothane, paralyzed and artificially ventilated. Intravenous administration of ketamine elicited a marked prolongation of the phrenic inspiratory discharge (without significantly affecting its amplitude) and a depression of the mylohyoid expiratory activity. An elimination of the volume-related input from the lungs ("no-inflation manoeuvre") or deflation elicited under these conditions typical apneustic pattern of breathing. The response to tracheal occlusion at peak-inspiration was "classical". We conclude that ketamine inhibits the Vth nerve motor nucleus which is not only an important component of the central inspiratory-inhibitory neurones but also a "relay station" between the vagal and the central inspiratory "off-switch" mechanisms.     

Distribution of binding sites for the plant lectin Ulex europaeus agglutinin I on primary sensory neurones in seven different mammalian species

There is an increasing body of evidence to suggest that different functional classes of neurones express characteristic cell-surface carbohydrates. Previous studies have shown that the plant lectin Ulex europaeus agglutinin-I (UEA) binds to a population of small to medium diameter primary sensory neurones in rabbits and humans. This suggests that a fucose-containing glycoconjugate may be expressed by nociceptive primary sensory neurones. In order to determine the extent to which this glycoconjugate is expressed by other species, in the current study, we have examined the distribution of UEA-binding sites on primary sensory neurones in seven different mammals. Binding sites for UEA were associated with the plasma membrane and cytoplasmic granules of small to medium dorsal root ganglion cells and their axon terminals in laminae I–III of the grey matter of the spinal cord, in the rabbit, cat and marmoset monkey. However, no binding was observed in either the dorsal root ganglia or spinal cord in the mouse, rat, guinea pig or flying fox. These results indicate an inter-species variation in the expression of cell-surface glycoconjugates on mammalian primary sensory neurones.     

The oculomotor nucleus, not the abducent, innervates the muscles which advance the nictitating membrane in birds

The topographic distribution of the neurones that innervate the muscles that advance the nictitating membrane in birds was studied using intra-axonal retrograde transport of horseradish peroxidase. The motor neurones are distributed in the oculomotor complex of the ipsilateral and contralateral sides. In the ipsilateral side, the neurones innervating the pyramidalis muscles were located in the dorsolateral, dorsomedial and ventromedial subnuclei, while those neurones innervating the quadratus muscle were found in the dorsomedial and dorsolateral subnuclei. In the contralateral side the neurones innervating both the pyramidalis and quadratus were distributed in the ventromedial and ventrolateral subnuclei. The sensory neurones were found in the trigeminal ganglion and trigeminal mesencephalic nucleus.