Biomedical subjects

J P Kessler

Publications and source records attributed to J P Kessler.

18 recordsLinked to original sources

PubMed2000

Cellular and subcellular distribution of the amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunit GluR2 in the rat dorsal vagal complex.

Amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) type glutamate receptors are ligand gated ion channels made up of various combinations of four subunits termed GluR1-4. The GluR2 subunit controls several key features of the receptor including calcium permeability and inward rectification. In the present study, we analysed by immunocytochemistry the cellular and subcellular distribution of the GluR2 subunit in neurons of the dorsal vagal complex of the rat. GluR2 immunoreactivity was found both in the neuropile and in neuronal cell bodies. Perikaryal staining was strong in the dorsal motor nucleus of the vagus nerve and moderate in the medial part of the nucleus tractus solitarii as well as in the area postrema. The lateral part of the nucleus tractus solitarii was almost devoid of immunoreactivity except for the interstitial subnucleus which was filled with numerous strongly immunoreactive perikarya and large cell processes. Ultrastructural examination was carried out in the interstitial subnucleus. Peroxidase staining indicative of GluR2 immunoreactivity was observed in neuronal cell bodies and dendrites. No labeled axon terminal or glial cell body was found. Additional experiments performed using pre-embedding immunogold showed that most of the labeling in immunoreactive dendrites was intracytoplasmic. These results indicate that GluR2 immunoreactivity is differentially distributed among neurons in the dorsal vagal complex, thereby suggesting differences in the functional properties of AMPA receptors between neuronal populations. These results also suggest that AMPA receptors, at least those containing the GluR2 subunit, have no major role as presynaptic receptors within this region. Finally, they indicate the existence of large intracellular pools of GluR2 subunits within dendrites of immunoreactive neurons.

Animals↗

PubMed1999

Postnatal development of synaptophysin immunoreactivity in the rat nucleus tractus solitarii and caudal ventrolateral medulla.

Synaptophysin (SY) is a major integral membrane protein of small synaptic vesicles. In the present study, SY immunohistochemistry was used to investigate the postnatal development of the rat nucleus tractus solitarii (NTS) and nucleus ambiguus/ventrolateral medulla (NA/VLM). Whatever the age of the animal, SY immunoreactivity showed a typical pattern of punctate staining reminiscent of presynaptic terminal labeling. In the NTS and the NA/VLM, SY immunoreactive puncta were few at birth and increased in number during the first postnatal days. These changes were quantified by measuring the volumetric fraction occupied by SY immunoreactive puncta at various postnatal ages. Using volumetric fraction data, an index of the total volume occupied SY immunoreactivity in each region was then calculated. Between birth and adulthood, this index increased by 6-fold in the NTS and by 7-fold in the NA/VLM, suggesting that most of the synaptic development of these regions occurs postnatally.

Aging↗

PubMed1999

Distribution of AMPA receptor subunits GluR1-4 in the dorsal vagal complex of the rat: a light and electron microscope immunocytochemical study.

The dorsal vagal complex, localized in the dorsomedial medulla, includes the nucleus tractus solitarii (NTS), the dorsal motor nucleus of the vagus nerve (DMN) and the area postrema (AP). The distribution of AMPA-preferring glutamate receptors (AMPA receptors) within this region was investigated using immunohistochemistry and antibodies recognizing either one (GluR1 or GluR4) or two (GluR2 and GluR3) AMPA receptors subunits. The distribution of GluR1 immunoreactivity showed high contrast of staining between strongly and lightly labeled areas. Labeling was intense in the AP and weak in the NTS, except for its medial and dorsalmost parts which exhibited moderate staining. Almost no GluR1 immunoreactivity was found in the DMN. GluR2/3 immunolabeling was present in the entire dorsal vagal complex. This labeling was strong in the AP, the DMN and the medial half of the NTS and moderate in the lateral half of the NTS, except for the interstitial subdivision which exhibited intense staining. Labeling induced by the GluR4 antibody was very weak throughout the dorsal vagal complex. Ultrastructural examination showed that GluR1 and GluR2/3 immunoreactivity was localized in neuronal cell bodies and dendrites. No labeled axon terminal or glial cell body was found. Immunoperoxidase staining in labeled cell bodies and dendrites was associated with intracellular organelles (microtubules, mitochondria, cisternae of the endoplasmic reticulum,.) and/or parts of the plasma membrane. Plasma membrane labeling was often associated with asymmetrical synaptic differentiations. No labeled symmetrical synapse was found using either GluR1 or GluR2/3 antibody. The present results show that AMPA receptors have a widespread distribution in neuronal perikarya and dendrites of the rat dorsal vagal complex. They suggest differences in subunit composition between AMPA receptors localized in the NTS, the DMN and the AP. Ultrastructural data are consistent with the fact that AMPA receptors associated with the plasma membrane are mostly synaptic receptors. However, they also suggest the existence of a large intracellular pool of receptor subunits in neuronal soma and dendrites.

Animals↗

PubMed1997

Immunohistochemical detection of glutamate in rat vagal sensory neurons.

Vagal primary afferent neurons have their cell bodies located in the nodose (inferior) and jugular (superior) vagal ganglia and send terminals into the nucleus tractus solitarii (NTS) which lies in the dorsomedial medulla. The presence of glutamate (Glu)-containing neurons in the rat nodose ganglion was investigated using immunohistochemistry. Glu-immunoreactivity on nodose sections was found in neuronal perikarya and nerve fibers, but not in non-neuronal elements such as Schwann cells and satellite cells. Both immunoreactive and non-immunoreactive ganglion cells were observed. The immunoreactive ganglion cells amounted to about 60% of the nodose population. No specific intraganglionic localization was observed for the non-immunoreactive cells. Immunoreactive perikarya were slightly smaller than the non-immunoreactive ones, but no relationship was found between size and staining intensities of immunoreactive neurons. The present data indicate that immunodetectable Glu is present in a large population of vagal afferent neurons. They therefore add to a growing body of evidence suggesting that Glu may be the main neurotransmitter released by vagal afferent terminals within the nucleus tractus solitarii.

Animals↗

PubMed1997

Postnatal ontogeny of glutamate receptors in the rat nucleus tractus solitarii and ventrolateral medulla.

The nucleus tractus solitarii and the ventrolateral medulla are two brainstem regions involved in regulation of autonomic functions. Glutamate (Glu) receptors localized within these two regions play a key role in neural control of swallowing and breathing and in blood pressure regulation. In the present study, postnatal changes in global [3H]Glu binding and in [3H]Glu binding to N-methyl-D-aspartate (NMDA) receptors were analyzed in the nucleus tractus solitarii and the ventrolateral medulla using in vitro receptor autoradiography. Similar results were obtained in both regions. When expressed as density values (fmol/mg tissue), both global and NMDA-sensitive Glu binding increased by approximately 50-70% between birth and postnatal day 9 (P9) and then decreased until P30. When expressed as binding per nucleus (i.e., after correction for tissue growth), global Glu binding still increased between birth and P9 and decreased between P9 and P30 whereas NMDA-sensitive binding increased until P9 and remained stable thereafter. Saturation studies showed a postnatal increase in Glu receptor number per nucleus, which occurred mainly between birth and P9, and a decrease in Glu receptor affinity between P9 and adulthood. These results indicate that dramatic changes in glutamatergic neurotransmission occur in the nucleus tractus solitarii and the ventrolateral medulla during the first month of postnatal life. They suggest that both neonates and young animals may not be fully mature as regard to central regulation of autonomic functions.

Animals↗

PubMed1995

Postnatal changes in glutamate binding in the lower medulla of the rat.

Changes in [3H]glutamate (Glu) binding occurring in the lower medulla of the rat between birth (P0) and adulthood (P72) were investigated on cryostat sections using in vitro receptor autoradiography. Densitometric measurements were performed in both autonomic (nucleus tractus solitarii, dorsal motor nucleus of the vagus nerve, ventrolateral medulla) and non-autonomic (inferior olive, spinal trigeminal nucleus) medullary regions. In all these areas, binding densities peaked at P9 and then gradually declined. Values close to those measured in adult animals were reached by P23-P30. These data indicate that glutamatergic neurotransmission within the lower medulla undergoes developmental changes during the early postnatal period. They thereby suggest that the neural circuits essential in organizing autonomic functions are still immature at birth.

Age Factors↗

PubMed1993

Involvement of excitatory amino acids in the activity of swallowing-related neurons of the ventro-lateral medulla.

Previous studies have shown that swallowing-related (SR) neurons are present in the ventro-lateral medulla (VLM), within and around the nucleus ambiguus. During deglutition, these SR neurons receive an excitatory input from the swallowing network located within the nucleus tractus solitarii and exhibit a swallowing activity, i.e. a burst of spikes occurring in close temporal relationship with the swallowing motor contraction. The present experiments were carried out to evaluate the possible contribution of excitatory amino acids (EAA) receptors to the swallowing activity of VLM neurons. The effects of ionophoretic or pressure applications of EAA agonists and antagonists were investigated on the activity of SR neurons located in the VLM of decerebrate rats. All SR neurons were excited by ionophoretic applications of N-methyl-D-aspartate (NMDA) and kainate, a non-NMDA receptor agonist. Furthermore, the swallowing response of the neurons was depressed by ionophoretic applications of both the broad spectrum EAA antagonist, tau D-glutamyl-glycine, and the selective NMDA antagonist, DL-2-amino-5-phosphonovalerate, and by pressure applications of the preferential non-NMDA receptors blocker, 6-cyano-7-nitroquinoxaline-2,3-dione. These results indicate that the swallowing activity of SR neurons located in the VLM depends on the activation of EAA receptors. They moreover suggest that both NMDA and non-NMDA receptor subtypes are involved.

2-Amino-5-phosphonovalerate↗

PubMed1993

[A simplified technique for decerebrating rats].

A simple and effective technique is described for decerebration of rat. The brain tissue at the precollicular level was gently and slowly aspirated. The two cut surfaces of the brainstem were covered with small pieces of gelfoam sponge or cotton balls soaked in thrombin solution. No ligation or clamp of the common carotid arteries of their branches was performed. After decerebration with this technique, the respiration rate, the heart rate and the mean femoral arterial pressure of the animals were stable for more than 10 hours. Successful intracellular recordings and labelings of medullary respiratory neurons were obtained from this type of preparation of rat. The technique for decerebrating rats described here may be used for acute experiments in which brainstem regulatory functions are investigated.

Animals↗

PubMed1991

Evidence that activation of N-methyl-D-aspartate (NMDA) and non-NMDA receptors within the nucleus tractus solitarii triggers swallowing.

Swallowing is a patterned motor activity generated by neurons located within the nucleus tractus solitarii (NTS). Previous experiments have shown that administration of excitatory amino acids within the NTS induces swallowing. The present study was undertaken to identify the receptor subtypes involved in this effect. Pressure microinjections of L-glutamate (10-100 pmol), quisqualate (0.1-10 pmol) and N-methyl-D-aspartate (NMDA, 0.1-10 pmol) were performed into the NTS of decerebrate rats. Glutamate and quisqualate microinjections elicited short series of swallows while NMDA microinjections induced long-lasting, rhythmic swallowing. Pretreatment with the selective NMDA antagonist, DL-2-amino-5-phosphonovalerate (50 pmol), almost completely suppressed the response elicited by NMDA (10 pmol) but did not induce a significant modification of swallowing triggered by either glutamate (25 pmol) or quisqualate (10 pmol). Pretreatment with 6-cyano-7-nitroquinoxaline-2,3-dione (50 pmol), a selective blocker of non-NMDA receptors, suppressed the swallows elicited by glutamate and strongly inhibited the response elicited by quisqualate microinjections. The same pretreatment induced only a slight modification of the swallowing elicited by NMDA. These data demonstrate that deglutition can be triggered by activating either NMDA or non-NMDA receptors localized within the NTS, and therefore suggest that both receptor subtypes may be involved in swallowing elicited under physiological conditions.

2-Amino-5-phosphonovalerate↗

PubMed1990

Swallowing responses induced by microinjection of glutamate and glutamate agonists into the nucleus tractus solitarius of ketamine-anesthetized rats.

Swallowing is a patterned motor activity generated by neurons located within the nucleus tractus solitarius (NTS). An excitatory amino acid (EAA) neurotransmitter, such as glutamate (GLU), is suspected of being involved in the initiation of swallowing by NTS neuronal components. However, swallowing can still be elicited in animals anesthetized with ketamine, an antagonist of the N-methyl-D-aspartate (NMDA) subclass of EAA receptors. The present experiments were therefore designed to investigate the influence of EAA administration within the NTS on the swallowing motor activity of rats anesthetized with ketamine. Pressure microinjections of GLU in doses ranging from 25 to 500 pmol elicited swallowing. This effect was dose-dependent and was not reproduced when control injections of the vehicle solution were performed. Microinjections of the GLU agonists, quisqualate (QUIS) and NMDA, in doses ranging between 2.5 and 50 pmol, also induced swallowing motor activities. QUIS, like GLU, elicited a short series of swallows at a brief latency while NMDA generated long-lasting rhythmic swallowing with a longer latency. Swallowing induced by GLU microinjections (100 pmol) was suppressed almost completely by local pretreatment with either the broad spectrum EAA receptor antagonist, gamma-D-glutamylglycine (250 pmol), or the more selective non-NMDA antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (50-100 pmol), but not by pretreatment with the selective NMDA antagonist, DL-2-amino-5-phosponovalerate (250 pmol). On the other hand, pretreatment with DL-2-amino-5-phosphonovalerate (50 pmol) suppressed the deglutitions induced by NMDA microinjections (10 pmol) but not those elicited by QUIS microinjections (10 pmol).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Association of neurotensin binding sites with sensory and visceromotor components of the vagus nerve.

Specific neurotensin (NT) binding sites were recently shown to be highly concentrated in the nucleus of the solitary tract (NTS), which receives primary vagal afferents, and in the dorsal motor nucleus of the vagus (DMN), which contains the cell bodies of origin of vagal preganglionic neurons. To investigate the relationship of these binding sites with sensory and visceromotor components of the vagus nerve, they were labeled here in vitro, using monoiodo[Tyr3]neurotensin (125I-NT) and visualized by light microscopic radioautography in the dorsomedial medulla of both intact and unilaterally vagotomized rats, in the nodose ganglia of intact animals, and in ligated vagus nerves. Unilateral vagotomy performed above the nodose ganglion resulted in a significant ipsilateral decrease in 125I-NT binding within both the NTS and the DMN, suggesting that NT binding sites were associated with both primary afferent fibers and preganglionic nerve cell bodies. The selective radioautographic labeling of a subpopulation (approximately 15%) of neuronal perikarya in the nodose ganglion confirmed that a proportion of vagal afferent neurons contained NT binding sites. Following vagus nerve ligation, a pile up of radiolabeled NT binding sites was observed on both sides of the nerve crush, indicating that NT receptor components were transported both anterogradely and retrogradely along fibers of the vagus nerve. We conclude that NT receptors are synthesized and transported within a subpopulation of afferent and efferent components of the vagus nerve and that NT may therefore act presynaptically upon vagal axon terminals in both central and peripheral nervous systems.

Animals↗

PubMed1988

Central serotonergic projections to the nucleus tractus solitarii: evidence from a double labeling study in the rat.

Projections from several brainstem serotonergic nuclei to the nucleus tractus solitarii were investigated in the rat. Experiments were performed using a double labeling method combining retrograde radioautographic tracing and serotonin immunohistochemistry. After injection of the radioactive tracer ([3H] wheat germ agglutinin) into the lateral nucleus tractus solitarii, nerve cell bodies exhibiting both radioautographic labeling and immunostaining were detected in all the serotonergic nuclei investigated, namely the nucleus raphe magnus, the ventromedial paragigantocellular nucleus, the nuclei raphe pontis, medianus and dorsalis, the medial lemniscus and the reticulotegmental nucleus of the pons. Most of the double labeled perikarya observed were in the nucleus raphe magnus, the adjacent part of the paragigantocellular nucleus and the nucleus raphe dorsalis. Nerve cell bodies retrogradely labeled but devoid of immunostaining were also observed, together with the double labeled perikarya, within serotonergic nuclei. These results provide direct evidence that brainstem serotonergic neurons contribute to the innervation of the nucleus tractus solitarii. They indicate that the nucleus raphe magnus and the nucleus raphe dorsalis constitute two major sources of central serotonergic projections to the nucleus tractus solitarii.

Animals↗

PubMed1987

Distribution of neurotensin binding sites in the caudal brainstem of the rat: a light microscopic radioautographic study.

Specific high-affinity neurotensin binding sites were labeled in sections of the rat caudal brainstem using a monoiodinated ligand, and their distribution was examined by light microscopic radioautography after fixation with glutaraldehyde. In the medulla, labeled binding sites were mainly concentrated within the dorsal motor nucleus of the vagus, the nucleus of the solitary tract, the external cuneate nucleus, the lateral reticular nucleus, the medial vestibular nucleus, the retrofacial nucleus, the linearis nucleus, the paragigantocellular nucleus and the nucleus raphe pallidus. Within the pons, neurotensin binding sites were detected in the reticulotegmental nucleus, the pontine nuclei, the dorsal tegmental nucleus, the laterodorsal and pedunculopontine tegmental nuclei and the nuclei raphe dorsalis and medianus. Most nuclei found here to contain high densities of neurotensin binding sites have been shown to stain intensely for acetylcholinesterase, suggesting a possible association between this enzyme and neurotensin receptors.

Animals↗

PubMed1986

Effect of catecholamines on the swallowing reflex after pressure microinjections into the lateral solitary complex of the medulla oblongata.

The present study was carried out to elucidate the influence of catecholamines on swallowing, a polysynaptic reflex organized by an interneuronal network localized mainly within the lateral solitary complex (LSC) of the medulla oblongata. The effects of catecholaminergic agents were investigated in the rat, on rhythmic swallowing elicited by repetitive stimulation of the superior laryngeal nerve (SLN). Catecholaminergic agents were microinjected by pressure application, through multibarrelled glass micropipettes, into the LSC including the tractus solitarius, the swallowing region of the nucleus of the solitary tract and the adjacent reticular formation. Microinjections of noradrenaline (NA, 0.1-5 nmol, 50 nl) induced a significant decrease of the number and the amplitude of the rhythmic swallows elicited by stimulation of the ipsilateral SLN. This inhibitory effect was dose-related. Microinjections of clonidine (2.5 nmol, 50 nl), dopamine (0.25-2.5 nmol, 50 nl) and apomorphine (0.5 nmol, 50 nl), also inhibited swallowing. No significant modification of swallowing was induced by control injections of the vehicle (50 nl) within the active sites. Moreover the NA-induced inhibition of swallowing, was significantly antagonized by pretreatment with the alpha-adrenergic blocker phentolamine applied locally in the LSC. Furthermore neither blood pressure, nor respiratory rhythm were consistently modified by the catecholaminergic microinjections, indicating that the catecholamine-induced inhibition of swallowing was not a secondary side effect originating from alteration of these functions. It can therefore be concluded that the present results demonstrate the existence within the LSC of a catecholaminergic inhibition of the swallowing reflex. This inhibitory effect likely arises from activation of specific catecholaminergic receptors and affects the swallowing structures localized within the LSC, i.e., the laryngeal swallowing afferents running in the solitary tract and/or the swallowing interneurons within the nucleus of the solitary tract.

Animals↗

PubMed1986

The excitation by neurotensin of nucleus tractus solitarius neurons induces apneustic breathing.

The possible involvement of neurotensin in the regulation of respiratory drive has been tested on single brainstem respiratory related neurons and on the global respiratory output. The neuropeptide was locally applied either by microiontophoresis or by pressure injection in the dorsal and ventral respiratory areas of the anesthetized bivagotomized cat. Effects of neurotensin applications were studied, on the one hand on the firing discharge of respiratory related neurons and on the other hand on the phrenic nerve activity and on arterial blood pressure. An increase of the firing frequency of respiratory related neurons was induced by neurotensin applied by iontophoresis or by pressure injection (0.005-33.5 fmol/s) on single neurons. In the latter case, neurotensin was active at concentration 10(3) times lower than glutamate. A bilateral apneustic pattern was induced on the phrenic nerve activities by microinjection of neurotensin (0.23-0.54 pmol/s) in one ventrolateral nucleus tractus solitarius without alteration of arterial blood pressure. These results suggest that the release of neurotensin in the nucleus tractus solitarius regulates respiratory rhythmogenesis by increasing the inspiratory duration.

Action Potentials↗

PubMed1986

Inhibitory influence of monoamines and brainstem monoaminergic regions on the medullary swallowing reflex.

Swallowing is a polysynaptic reflex organized by a neuronal network localized mainly within the lateral region of the nucleus tractus solitarius (NTS). Monoamine microinjections (serotonin, noradrenaline; 1 nmol, 50 nl) within the swallowing region of the NTS produced a significant decrease in the number of swallows elicited by repetitive stimulation of the superior laryngeal nerve. Stimulation, with concentric bipolar electrodes, of several brainstem structures overlapping monoaminergic regions such as the nucleus raphe magnus, the nucleus raphe pallidus, the lemniscus medialis, the ventrolateral reticular formation, the locus coeruleus and the nucleus commissuralis, induced an inhibition of the laryngeal-initiated swallowing. These results indicate the existence, within the NTS, of a monoaminergic inhibition of the swallowing reflex which might originate from monoaminergic brainstem regions.

Animals↗

PubMed1985

Inhibition of the swallowing reflex by local application of serotonergic agents into the nucleus of the solitary tract.

Swallowing is a medullary polysynaptic reflex organized by an interneuronal network localized mainly within the nucleus of the solitary tract (NST). The existence of several putative neurotransmitters within the NST has been well demonstrated. The presence of serotonin (5-HT) in nerve terminals and fibers has been particularly well-documented. This study was therefore designed to determine the role of 5-HT in the swallowing reflex. The effects of serotonergic agents were investigated in the rat, on rhythmic swallowing elicited by long repetitive stimulation of the superior laryngeal nerve (SLN). The agents were microinjected by pressure application, within the swallowing region of the NST. Microinjections of 5-HT (0.3-5 nmol, 30-50 nl) significantly decreased the number and the amplitude of swallows elicited by stimulation of the ipsilateral SLN without changing the swallowing reflex induced by contralateral SLN stimulation. The decrease induced by 5-HT microinjections was dose-related. No significant modification of swallowing was induced by control injections of the vehicle within the active sites. Moreover, the effect of 5-HT microinjections was significantly antagonized by pretreatment with metitepine (0.4 nmol) applied locally in the NST and microinjections of quipazine (2.5 nmol) also decreased the number of swallows. It can therefore be concluded that the present findings suggest the existence within the NST of a serotonergic inhibition of the swallowing reflex elicited by laryngeal afferents.

Animals↗

PubMed1985

Identification of the medullary swallowing regions in the rat.

The aim of the present study was to identify the central structures involved in the organization of the swallowing reflex in the rat. Using concentric bipolar electrodes, the medulla and pons were systematically explored in order to determine which central areas responded to stimulation by inducing swallowing. These areas, which were located in the dorsal medulla oblongata, were the solitary tract, the nucleus of the solitary tract (NST) and the adjacent reticular formation. Stimulation of the ventral ponto-medullary regions was ineffective with regard to the initiation of the swallowing reflex. The activity of medullary swallowing neurons was recorded using extracellular microelectrodes. These swallowing neurons responded with a burst of spikes (swallowing activity) which was closely linked to the swallowing reflex elicited by stimulation of the superior laryngeal nerve (SLN). Under SLN stimulation, the activity of some of the swallowing neurons furthermore showed an initial response consisting of 1 or 2 spikes after a brief latency. According to their location and the latency of their initial response, swallowing neurons were divided into two groups. Group I neurons were located in a dorsal area of the medulla oblongata corresponding to the NST and the adjacent reticular formation. All these neurons exhibited an initial response with a very short latency (1 to 4 ms), the swallowing activity of most of these neurons started before the onset of the swallowing motor sequence. Group II neurons were located either in a ventral area corresponding to the nucleus ambiguus and the surrounding reticular formation or in a dorsal and medial area corresponding to the hypoglossal nucleus and its vicinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗