Descending course of primary afferent collaterals in the cat's spinal cord.

After injecting horseradish-peroxidase into the lower thoracic, lumbar and sacral spinal cord segments of cats, labelled perikarya were found in several spinal ganglia localized cranially to the site of injection. The segmental distance between the injection site and the rostralmost localized ganglion with labelled cells varied depending on the medio-lateral localization of the injection. The longest distance (10 segments) was achieved by medial injections. Primary sensory neurones with long descending collaterals belong to large ganglion cells.     

c-Fos expression in rat brain stem and spinal cord in response to activation of cardiac ischemia-sensitive afferent neurons and electrostimulatory modulation

The purpose of this study was to identify central neuronal sites activated by stimulation of cardiac ischemia-sensitive afferent neurons and determine whether electrical stimulation of left vagal afferent fibers modified the pattern of neuronal activation. Fos-like immunoreactivity (Fos-LI) was used as an index of neuronal activation in selected levels of cervical and thoracic spinal cord and brain stem. Adult Sprague-Dawley rats were anesthetized with urethane and underwent intrapericardial infusion of an "inflammatory exudate solution" (IES) containing algogenic substances that are released during ischemia (10 mM adenosine, bradykinin, prostaglandin E2, and 5-hydroxytryptamine) or occlusion of the left anterior descending coronary artery (CoAO) to activate cardiac ischemia-sensitive (nociceptive) afferent fibers. IES and CoAO increased Fos-LI above resting levels in dorsal horns in laminae I-V at C2 and T4 and in the caudal nucleus tractus solitarius. Dorsal rhizotomy virtually eliminated Fos-LI in the spinal cord as well as the brain stem. Neuromodulation of the ischemic signal by electrical stimulation of the central end of the left thoracic vagus excited neurons at the cervical and brain stem level but inhibited neurons at the thoracic spinal cord during IES or CoAO. These results suggest that stimulation of the left thoracic vagus excites descending inhibitory pathways. Inhibition at the thoracic spinal level that suppresses the ischemic (nociceptive) input signal may occur by a short-loop descending pathway via signals from cervical propriospinal circuits and/or a longer-loop descending pathway via signals from the nucleus tractus solitarius.     

Origins of nerve fibers containing nitric oxide synthase in the rat celiac-superior mesenteric ganglion

The origin of nitric oxide synthase-containing nerve fibers in rat celiac-superior mesenteric ganglion was examined using retrograde tracing techniques combined with the immunofluorescence method. Fluoro-Gold was injected into the celiac-superior mesenteric ganglion. Neuronal cell bodies retrogradely labeled with Fluoro-Gold in the thoracic spinal cord, the dorsal root ganglia at the thoracic level, the nodose ganglion, and the intestine from the duodenum to the proximal colon were examined for nitric oxide synthase immunoreactivity. About 60% of sympathetic preganglionic neurons in the intermediolateral nucleus projecting to the celiac-superior mesenteric ganglion were immunoreactive for nitric oxide synthase, as were approximately 27% of nodose ganglion neurons and about 65% of dorsal root ganglion neurons projecting to the cceliac-superior mesenteric ganglion. Neurons projecting to the celiac-superior mesenteric ganglion were found in the myenteric plexus of the small and large intestine. In the proximal colon, about 23% of such neurons were immunoreactive for nitric oxide synthase. However, in the small intestine, no immunoreactivity was found in these neurons.     

Synaptic transmission in thoracic autonomic ganglia of the dog

Afferent stimulation of one canine thoracic cardiopulmonary nerve can generate compound action potentials in another ipsilateral cardiopulmonary nerve. These compound action potentials persist after acute decentralization of the middle cervical ganglion, indicating that they result from neural activity in the middle cervical ganglion and thoracic nerves. Changing the frequency of stimulation can alter the compound action potentials, suggesting that temporal facilitation or inhibition occurs in this middle cervical ganglion preparation. The compound action potentials can be modified by stimulation of sympathetic preganglionic fibers and by hexamethonium, atropine, phentolamine, propranolol, and (or) manganese. It thus appears that afferent cardiopulmonary nerves can activate efferent cardiopulmonary nerves via synaptic mechanisms in the stellate and middle cervical ganglia. It also appears that these mechanisms involve adrenergic and cholinergic receptors and are influenced by preganglionic sympathetic fibers arising from the cord.     

New vistas on the initiation and maintenance of insect motor behaviors revealed by specific lesions of the head ganglia

In insects, thoracic pattern generators are modulated by the two head ganglia, the supraesophageal ganglion (brain) and the subesophageal ganglion, which act as higher-order neuronal centers. To explore the contribution of each head ganglion to the initiation and maintenance of specific motor behaviors in cockroaches (Periplaneta americana), we performed specific lesions to remove descending inputs from either the brain or the subesophageal ganglion or both, and quantified the behavioral outcome with a battery of motor tasks. We show that ‘emergency’ behaviors, such as escape, flight, swimming or righting, are initiated at the thoracic level independently of descending inputs from the head ganglia. Yet, the head ganglia play a major role in maintaining these reflexively initiated behaviors. By separately removing each of the two head ganglia, we show that the brain excites flight behavior and inhibits walking-related behaviors, whereas the subesophageal ganglion exerts the opposite effects. Thus, control over specific motor behaviors in cockroaches is anatomically and functionally compartmentalized. We propose a comprehensive model in which the relative permissive versus inhibitory inputs descending from the two head ganglia, combined with thoracic afferent sensory inputs, select a specific thoracic motor pattern while preventing the others.     

Descending influences on escape behavior and motor pattern in the cockroach

The escape behavior of the cockroach is a ballistic behavior with well characterized kinematics. The circuitry known to control the behavior lies in the thoracic ganglia, abdominal ganglia, and abdominal nerve cord. Some evidence suggests inputs may occur from the brain or suboesophageal ganglion. We tested this notion by decapitating cockroaches, removing all descending inputs, and evoking escape responses. The decapitated cockroaches exhibited directionally appropriate escape turns. However, there was a front-to-back gradient of change: the front legs moved little if at all, the middle legs moved in the proper direction but with reduced excursion, and the rear legs moved normally. The same pattern was seen when only inputs from the brain were removed, the suboesophageal ganglion remaining intact and connected to the thoracic ganglia. Electromyogram (EMG) analysis showed that the loss of or reduction in excursion was accompanied by a loss of or reduction in fast motor neuron activity. The loss of fast motor neuron activity was also observed in a reduced preparation in which descending neural signals were reversibly blocked via an isotonic sucrose solution superfusing the neck connectives, indicating that the changes seen were not due to trauma. Our data demonstrate that while the thoracic circuitry is sufficient to produce directional escape, lesion or blockage of the connective affects the excitability of components of the escape circuitry. Because of the rapidity of the escape response, such effects are likely due to the elimination of tonic descending inputs.     

Anatomy of neurons crossing the tritocerebral commissures of the cockroach Periplaneta americana (Blattaria)

The neuronal connections of the tritocerebral commissures of Periplaneta americana were studied in the brain-suboesophageal ganglion complex and the stomatogastric nervous system by means of heavy metal iontophoresis through cut nerve ends followed by silver intensification. The tritocerebral commissure 1 (Tc1) contains mainly the processes of the subpharyngeal nerve (Spn) whose neurons are located in both tritocerebral lobes and in the frontal ganglion. Some neurons of the frontal ganglion project through the Tc1 to the contralateral tritocerebrum. A few fibers in this commissure were observed projecting to the protocerebrum and the suboesophageal ganglion. There are tritocerebral neurons which pass through the Tc1 or the tritocerebral commissure 2 (Tc2) and extend on into the stomatogastric nervous system. One axon of a descending gaint neuron appears in the Tc2. This neuron lies in the tritocerebrum and connects the brain to the contralateral side of the ventral nerve cord. In addition, sensory fibers of the labral nerve (Ln) traverse both commissures to the opposite tritocerebrum. The anatomical and physiological relevance of the identified neuronal pathways is discussed. © 1995 Wiley-Liss, Inc.     

Spatial organization of vestibulospinal neurons in the guinea pig

Quantitative characteristics of spatial organization of neuron populations of vestibular nuclei, forming projections into the spinal cord, were obtained in experiments on guinea pigs by the retrograde axonal transport of horseradish peroxidase, injected unilaterally into the upper cervical and lower thoracic segments of the spinal cord, method. Neurons accumulating the enzyme were found ipsilaterally in the lateral vestibular nucleus and bilaterally in the descending and medial vestibular nuclei. The distribution of vestibulospinal neurons along the length of the spinal cord was studied. Neuron populations of the medial and descending vestibular nuclei whose projection regions coincide with those of fibers of the corticospinal and rubrospinal systems were discovered. The role of vestibulospinal systems in the structure of supra-segmental control of the neuronal apparatus of the spinal cord is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 353–362, May–June, 1991.     

Descending unpaired median neurons with bilaterally symmetrical axons in the suboesophageal ganglion of Manduca sexta larvae

Three large median cell bodies with a diameter between 40 and 70 μm that exhibit octopamine immunoreactivity were identified in the posterior part of the suboesophageal ganglion of the tobacco hawkmoth larva, Manduca sexta. These neurons possess bilaterally symmetrical axons in the posterior neck connectives, and at least one of them extends through the whole ventral nerve cord to the terminal abdominal ganglion. Therefore, these neurons belong to the class of descending ventral unpaired median neurons. From each cell body, a primary neurite ascends anteriorly, which after bending dorsally turns posteriorly and then bifurcates to give rise to two descending axons. From the primary neurite two main dendritic branches ascend anteriorly, and four characteristic branches can be distinguished originating from them: two descending dendritic branches and two ascending dendritic branches. Dense arborizations from all these branches exist in all neuromeres of the suboesophageal ganglion. Intracellular recordings from these neurons show that in contrast to the ventral unpaired median neurons of thoracic and abdominal ganglia, they do not produce overshooting action potentials but exhibit passive soma spikes only. During pharmacologically evoked fictive motor patterns these neurons show coupling to various motor patterns such as crawling, feeding and molting.     

Descending Neurons of the Epipharyngeal Ganglion in the Dragonfly Aeschna Larva

Using staining with methylene blue, several descending neurons were revealed in the epipharyngeal ganglion of the dragonfly Aeschna larva. Among them there is a neuron that has extensive arborization and unites a significant part of the epipharyngeal ganglion. The contacts of this neuron with the bundle of optic fibers from the lobule are found, which allows suggesting its participation in the descending visual pathway. A neuron of the central complex of the descending tract is revealed.     

Ascending and descending projections of the lateral vestibular nucleus in the rat

The tracer neurobiotin was injected into the lateral vestibular nucleus in rat and the efferent fiber connections of the nucleus were studied. The labeled fibers reached the diencephalon rostrally and the sacral segments of the spinal cord caudally. In the diencephalon, the ventral posteromedial and the gustatory nuclei received the most numerous labeled fibers. In the mesencephalon, the inferior colliculus, the interstitial nucleus of Cajal, the nucleus of Darkschewitch, the periaqueductal gray matter and the red nucleus received large numbers of labeled fibers. In the rhombencephalon, commissural and internuclear connections originated from the lateral vestibular nucleus to all other vestibular nuclei. The medioventral (motor) part of the reticular formation was richly supplied, whereas fewer fibers were seen in the lateral (vegetative) part. In the spinal cord, the descending fibers were densely packed in the anterior funiculus and in the ventral part of the lateral funiculus. Collaterals invaded the entire gray matter from lamina IX up to lamina III; the fibers and terminals were most numerous in laminae VII and VIII. Collateral projections were rich in the cervical and lumbosacral segments, whereas they were relatively poor in the thoracic segments of the spinal cord. It was concluded that the fiber projection in the rostral direction was primarily aimed at sensory-motor centers; in the rhombencephalon and spinal cord, fibers projected onto structures subserving various motor functions.     

Localization of the site of effect of a wasp's venom in the cockroach escape circuitry

The parasitic wasp Ampulex compressa stings a cockroach Periplaneta americana in the neck, toward the head ganglia (the brain and subesophageal ganglion). In the present study, our aim was to identify the head ganglion that is the target of the venom and the mechanisms by which the venom blocks the thoracic portion of the escape neuronal circuitry. Because the escape responses elicited by a wind stimulus in brainless and sham-operated animals were similar, we propose that the venom effect is on the subesophageal ganglion. Apparently, the subesophageal ganglion modulates the thoracic portion of the escape circuit. Recordings of thoracic interneuron responses to the input from the abdominal giant interneurons showed that the thoracic interneurons receive synaptic drive from these interneurons in control and in stung animals. Unlike normal cockroaches, which use both fast and slow motoneurons for producing rapid escape movements, stung animals activate only the slow motoneuron. However, we show that in stung animals, the fast motoneuron still can be recruited with bath application of pilocarpine, a muscarinic agonist. These results indicate that the descending control from the subesophageal ganglion is presumably exerted on the premotor thoracic interneurons to motoneurons connection of the thoracic escape circuitry. Accepted: 19 December 1998     

The central morphology of the giant interneurons and their spatial relationship with the thoracic motorneurons in the cockroach, Periplaneta americana (Insecta)

Three groups of giant fibers are found in the cockroach ventral nerve cord. A latero-dorsal group (dorsal GIs), a latero-ventral group (ventral GIs) and a medio-ventral group. The morphology of all three groups of fibers within the thoracic ganglia is described. The morphology of the dorsal and ventral GI pathways in the abdominal and suboesophageal ganglia is also described. The projection patterns of the neurons in each ganglion are remarkably similar which suggests a common function. When motorneurons 5rl (depressor) and 6Br4 (levator) are stained simultaneously with the dorsal and ventral GI groups, some branches from both motor and giant neurons converge. The branching of the remaining medio-ventral group of fibers and their proximity to areas receiving motorneuronal input suggests that these are the small diameter axons described by Dagan and Parnas (1970).     

Properties of descending dorsal unpaired median (DUM) neurons of the locust suboesophageal ganglion

A group of six dorsal unpaired median (DUM) neurons of the suboesophageal ganglion (SOG) of locusts was studied with neuroanatomical and electrophysiological techniques. The neurons are located posteriorly in the SOG and have axons that descend into the ganglia of the ventral nerve cord, some as far as the terminal abdominal ganglion. Within thoracic ganglia the neurons have profuse dendritic ramifications in many neuropiles, including ventral sensory neuropiles. Based on their projection patterns three different morphological types of neurons can be distinguished. These neurons receive excitatory inputs through sensory pathways that ascend from the thoracic ganglia and are activated by limb movements. They may be involved in the modulation of synaptic transmission in thoracic ganglia.     

Tyrosine hydroxylase protein expression in ventral nerve cord of Neotropical freshwater crab

Given the importance of catecholamines in coordinating physiological and behavioral responses in brachyurans, the present study was designed to investigate the distribution of tyrosine hydroxylase (TH)-positive cells and fibers in the ventral nerve cord of Dilocarcinus pagei the Neotropical freshwater crab. TH immunoreactivity was visualized in adult crabs of both sexes, during the intermolt period. We found TH-positive cells that have not been previously described in brachyurans. Specifically, we found a pair of TH-positive cells in the ventral region of the thoracic ganglion, and in ventral and dorsal regions of the abdominal (pleonic) ganglion, suggesting catecholaminergic modulation of claws’ function and abdominal structures. In addition, great population of TH-positive cells was observed in the subesophageal ganglion, indicating conservation during evolution of catecholamines in this ganglion of decapods. Dopamine is present in cells and fiber tracts of brachyuran ventral nerve cord, projecting to endocrine, cardiac and digestive structures, suggesting widespread modulation and control of physiological functions and behavior. Dopamine plays a central role in movement and psychiatric disorders in humans. Information on dopaminergic function in the nervous system of invertebrates should improve the understanding of its function in more complex systems, such as human beings.     

Sensomotor Organization of Motor Acts in the Cockroach <Emphasis Type="Italic">Periplaneta americana</Emphasis>

The experimental data are presented which indicate modulating effects of different sensor inputs on impulse activity of identified motoneurons included in the neuronal module regulating walking rhythm in the American cockroach Periplaneta americana. At a light stimulation of complex eyes in the cup and α-lobe of mushroom bodies (MB) and in the adjacent neuropil there are revealed neurons differentiated by their ability to reproduce stimulation rhythm, by the latent period of impulse response, and by intensity of summation effect in the case of bimodal stimulation—light and tactile. Data of extracellular marking of these neurons with cobalt ions are presented, which indicate the existence of direct connections between MB and optic lobes in the American cockroach protocerebrum. There are discussed morphological and electrophysiological characteristics of the system of descending dorsal connective fibers that participate in transmission of descending influences of head ganglia on segmental motor centers as well as functional unity of associative structures of the subesophageal ganglion that integrate interganglionary and neuronal modules if the III thoracic ganglion that form as a whole the hierarchically organized distributed system.__________Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 41, No. 3, 2005, pp. 247–253.Original Russian Text Copyright © 2005 by Lapitskii, Nikitin.To the 100-anniversary of A.K. Voskresenskaya     

Decreased Uptake and Release of D-Aspartate in the Guinea Pig Spinal Cord After Partial Cordotomy

This study attempts to determine if L-glutamate and/or L-aspartate may be transmitters of neural tracts descending from the brain to the spinal cord. The uptake and electrically evoked release of D-[3H]aspartate, a putative marker for L-glutamate and L-aspartate, were measured in the cervical enlargement of the guinea pig spinal cord. These activities were compared using unlesioned animals and others with a lesion on the right side of the spinal cord. Partial cordotomy (segment C5) produced a heavy loss of descending fibers, a small loss of primary sensory fibers, and a depression of the uptake and the Ca2+ -dependent, electrically evoked release of D-aspartate ipsilateral and caudal to the lesion. Contralaterally, there was a moderate loss of corticospinal fibers, some loss of other descending axons, and a depression of D-aspartate release. Dorsal rhizotomy (segments C4-T1) produced a heavy loss of primary sensory fibers ipsilateral to the lesion. Ipsilaterally, but not contralaterally, the uptake and release of D-aspartate were depressed. Degeneration after partial cordotomy in combination with dorsal rhizotomy was assumed to be the sum of that produced by each lesion separately. This combined lesion depressed D-aspartate uptake ipsilaterally and depressed D-aspartate release on both sides of the cervical enlargement. None of the lesions altered the uptake and the evoked release of [3H]GABA. These findings support the hypothesis that the synaptic endings of one or more neural tracts descending from the brain to the spinal cord mediate the uptake and release of D-aspartate and, therefore, may use L-glutamate or L-aspartate as a transmitter.     

Afferent and efferent components of the facial nerve in a frog,Rana pipiens

Summary The seventh cranial nerve in Rana pipiens is a slender nerve with limited peripheral distribution. We investigated the afferent and efferent components of this nerve by labeling its major branch, the hyomandibular, with horseradish peroxidase. The efferent portion of the seventh nerve originates from a small cell group in the upper medulla which contains two subdivisions. Afferent fibers carried in nerve VII travel in the solitary tract and the dorsolateral funiculus. The solitary component consists of a small number of ascending fibers that reach the level of the trigeminal nucleus and a large descending component that terminates slightly caudal to the obex in the commissural nuclei of the solitary complex. Afferent fibers also descend in the dorsolateral funiculus; many of these fibers cross dorsal to the central canal in the lower medulla. Most of the fibers in the dorsolateral funiculus terminate in the ipsilateral and contralateral dorsal horns and in nuclei of the dorsal column. A few ipsilateral fibers reach lower thoracic levels of the spinal cord.     

Left vagal stimulation induces dynorphin release and suppresses substance P release from the rat thoracic spinal cord during cardiac ischemia

Electrostimulatory forms of therapy can reduce angina that arises from activation of cardiac nociceptive afferent fibers during transient ischemia. This study sought to determine the effects of electrical stimulation of left thoracic vagal afferents (C(8)-T(1) level) on the release of putative nociceptive [substance P (SP)] and analgesic [dynorphin (Dyn)] peptides in the dorsal horn at the T(4) spinal level during coronary artery occlusion in urethane-anesthetized Sprague-Dawley rats. Release of Dyn and SP was measured by using antibody-coated microprobes. While Dyn and SP had a basal release, occlusion of the left anterior descending coronary artery only affected SP release, causing an increase from lamina I-VII. Left vagal stimulation increased Dyn release, inhibited basal SP release, and blunted the coronary artery occlusion-induced release of SP. Dyn release reflected activation of descending pathways in the thoracic spinal cord, because vagal afferent stimulation still increased the release of Dyn after bilateral dorsal rhizotomy of T(2)-T(5). These results indicate that electrostimulatory therapy, using vagal afferent excitation, may induce analgesia, in part, via inhibition of the release of SP in the spinal cord, possibly through a Dyn-mediated neuronal interaction.