VGluT1- and GAD-immunoreactive terminals in synaptic contact with PAG-immunopositive neurons in principal sensory trigeminal nucleus of rat

AIM

To trace the origin of abundant vesicular glutamate transporter 1-like immunoreactive (VGluT1-LI) axon terminals in the dorsal division of the principal sensory trigeminal nucleus (Vpd) and the relationships between VGluT1-LI, as well as the glutamic acid decarboxylase (GAD)-LI axon terminals, and phosphate- activated glutaminase (PAG)-LI thalamic projecting neurons in the Vpd.

METHODS

Following unilateral trigeminal rhizotomy, triple-immunofluorescence histochemistry for VGluT1, GAD and PAG and the immunogold-silver method for VGluT1 or GAD, combined with the immunoperoxidase method for PAG were performed, respectively.

RESULTS

After unilateral trigeminal rhizotomy, the density of VGluT1-like immunoreactivity (IR) in the Vpd on the lesion side was reduced compared to its contralateral counterpart. Under the confocal laser-scanning microscope, the VGluT1-LI or GAD-LI axon terminals were observed to be in close apposition to the PAG-LI thalamic projecting neuronal profiles, and further electron microscope immunocytochemistry confirmed that VGluT1- and GAD-LI axon terminals made asymmetrical and symmetrical synapses upon the PAG-LI neuronal structures.

CONCLUSION

The present results suggest that the VGluT1-LI axon terminals, which mainly arise from the primary afferents of the trigeminal ganglion, along with the PAG-LI neuronal profiles, form the key synaptic connection involved in sensory signaling.

Demonstration of a trigeminothalamic pathway to the oval paracentral intralaminar thalamic nucleus and its involvement in the processing of noxious orofacial deep inputs

Using combined retrograde labeling and Fos protein immunohistochemistry, we show that after masseter inflammation, a population of neurons in the dorsal portion of the subnuclei interpolaris/caudalis transition zone at the level of the obex was activated and projected to the oval paracentral nucleus (OPC) of the intralaminar thalamic nuclei. The present findings indicate a trigeminothalamic pathway to the OPC intralaminar nucleus involved in central processing of orofacial deep noxious input.

Trigeminal uptake and clearance of inhaled manganese chloride in rats and mice

Inhaled manganese (Mn) can enter the olfactory bulbs via the olfactory epithelium, and can then be further transported trans-synaptically to deeper brain structures. In addition to olfactory neurons, the nasal cavity is innervated by the maxillary division of the trigeminal nerve that projects to the spinal trigeminal nucleus. Direct uptake and transport of inhaled metal particles in the trigeminal system has not been investigated previously. We studied the uptake, deposition, and clearance of soluble Mn in the trigeminal system following nose-only inhalation of environmentally relevant concentrations. Rats and mice were exposed for 10-days (6 h/day, 5 days/week) to air or MnCl2 aerosols containing 2.3 +/- 1.3 mg/m3 Mn with mass median aerodynamic diameter (MMAD) of 3.1 +/- 1.4 microm for rats and 2.0 +/- 0.09 mg/m3 Mn MnCl2 with MMAD of 1.98 +/- 0.12 microm for mice. Mn concentrations in the trigeminal ganglia and spinal trigeminal nucleus were measured 2 h (0-day), 7-, 14-, or 30-days post-exposure using proton induced X-ray emission (PIXE). Manganese-exposed rats and mice showed statistically elevated levels of Mn in trigeminal ganglia 0-, 7- and 14-days after the 10-days exposure period when compared to control animals. The Mn concentration gradually decreased over time with a clearance rate (t1/2) of 7-8-days. Rats and mice were similar in both average accumulated Mn levels in trigeminal ganglia and in rates of clearance. We also found a small but significant elevation of Mn in the spinal trigeminal nucleus of mice 7-days post-exposure and in rats 0- and 7-days post-exposure. Our data demonstrate that the trigeminal nerve can serve as a pathway for entry of inhaled Mn to the brain in rodents following nose-only exposure and raise the question of whether entry of toxicants via this pathway may contribute to development of neurodegenerative diseases.

Glutamate, but not aspartate, is enriched in trigeminothalamic tract terminals and associated with their synaptic vesicles in the rat nucleus submedius

To examine the possible roles of glutamate and aspartate as neurotransmitters in the nucleus submedius (Sm) of rats, the distributions of these amino acids were examined by electron microscopic immunogold labeling. High levels of glutamate were detected in trigeminothalamic tract terminals anterogradely labeled with horseradish peroxidase conjugates. These terminals also displayed a positive correlation between the densities of synaptic vesicles and gold particles signaling glutamate. In contrast, aspartate levels in such terminals were low and displayed no correlation with the density of synaptic vesicles. Terminals of presumed cortical origin contained the highest estimated levels of glutamate, but the positive correlation between glutamate signal and synaptic vesicle density did not reach statistical significance, presumably due to technical factors. The latter terminals also contained relatively high levels of aspartate, though without any correlation to synaptic vesicle density. The present findings provide strong support for glutamate, but not aspartate, as a trigeminothalamic tract neurotransmitter responsible for the fast synaptic transmission of nociceptive signals to neurons in the rat nucleus submedius. Aspartate presumably serves metabolic roles in these terminals. With respect to terminals of presumed cortical origin, our data are not at odds with the notion that also these terminals use glutamate as their neurotransmitter. Our findings do not support a neurotransmitter role for aspartate in the latter terminals, although such a role cannot be entirely refuted.

Synaptic organization of tooth pulp afferent terminals in the rat trigeminal sensory nuclei

Previous studies provide evidence that a structure/function correlation exists in the distinct zones of the trigeminal sensory nuclei. To evaluate this relationship, we examined the ultrastructure of afferent terminals from the tooth pulp in the rat trigeminal sensory nuclei: the principalis (Vp), the dorsomedial part of oral nucleus (Vdm), and the superficial layers of caudalis (Vc), by using transganglionic transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). A total of 93 labeled boutons were serially sectioned, in which some sections were incubated with gamma-aminobutyric acid (GABA) antiserum. Almost all labeled boutons formed asymmetric contact with nonprimary dendrites, in which more than half of labeled boutons in the Vc made synapses with their spines. The labeled boutons could be divided into two types on the basis of numbers of dense-cored vesicles (DCVs) in a boutons: S-type and DCV-type. Almost all labeled boutons in the Vp and Vdm were S-type, whereas two types were distributed evenly in the Vc. In contrast to DCV-type boutons, the S-type was frequently postsynaptic to unlabeled axon terminals containing a mixture of round, oval, and flattened vesicles (p-endings) and forming symmetrical synapses. Most p-endings examined were immunoreactive to GABA. The frequency of axoaxonic contacts was higher for labeled boutons in the Vp than in the Vdm and Vc. These results suggest that the three structures of trigeminal sensory nuclei serve distinct functions in nociceptive processing.

The supratrigeminal region of the rat sends GABA/glycine-cocontaining axon terminals to the motor trigeminal nucleus on the contralateral side

The supratrigeminal region (STR), a reticular zone capping the motor trigeminal nucleus (Tm), contains gamma-aminobutyric acid (GABA)ergic and glycinergic neurons which send axons to the contralateral Tm (J. Comp. Neurol. 373 (1996) 498). In the present study we observed that some single synaptic terminals upon Tm motoneurons showed immunoreactivities (IRs) for both glutamic acid decarboxylase (GAD) and glycine transporter 2 (GlyT2). After injecting biotinylated dextran amine (BDA) into the STR, we further observed in the Tm contralateral to the BDA injection that some BDA-labeled axon terminals in close contact with Tm motoneurons showed both GAD- and GlyT2-IRs. Thus, the STR was indicated to send GABAergic/glycinergic axon terminals contralaterally to Tm motoneurons.

Differential NR2A and NR2B expression between trigeminal neurons during early postnatal development

N-methyl-D-aspartate (NMDA) receptors play an important role in the production of rhythmical trigeminal motor activity resembling suckling and chewing. The developmental relationship between the expression of NMDA receptor subunits and the function of neurons comprising brainstem oral-motor circuitry is not clear. We conducted receptor immunohistochemistry studies to demonstrate the expression of NR2A and NR2B subunits in trigeminal motoneurons (Mo5) and mesencephalic trigeminal neurons (Me5) during the first 2 weeks of development. During this time period, rats begin the transition from suckling to chewing, two distinct motor behaviors. In Mo5, NR2A and NR2B immunoreactivity was observed throughout the time frame sampled. A significant increase in the NR2A:NR2B ratio occurred between P3-4 and P11 due to a reduction in the number of NR2B immunoreactive neurons. The temporal and spatial expression of NR2A and NR2B was differentially regulated between caudal and rostral regions of Me5. In contrast to Mo5, the NR2A:NR2B ratio decreased between P0-1 and P11 in caudal Me5 due to a concurrent increase in the number of NR2A and NR2B immunoreactive neurons. In rostral Me5, NR2A and NR2B immunoreactivity emerged at P3 and P11, respectively. Our data provides further insight into the molecular changes of trigeminal neurons during the transition from suckling to chewing behaviors. The differences in the NR2A:NR2B ratio between Mo5 and Me5 suggest functional differences in these neurons during NMDA-mediated neurotransmission.

Osteopontin-immunoreactivity in the rat trigeminal ganglion and trigeminal sensory nuclei

Osteopontin-immunoreactivity (OPN-ir) was examined in the oro-facial tissues and trigeminal sensory nuclei (principal sensory nucleus and spinal trigeminal nucleus) to ascertain the peripheral ending and central projection of OPN-containing primary sensory neurons in the trigeminal ganglion (TG). No staining was observed using mouse monoclonal anti-OPN antibody preabsorbed with recombinant mature OPN. OPN-immunoreactive (ir) peripheral endings were classified into two types: encapsulated and unencapsulated types. Unencapsulated endings were subdivided into two types: simple and complex types. Simple endings were characterized by the thin neurite that was usually devoid of ramification. These endings were seen in the hard plate and gingiva. The complex type was characterized by the thick ramified neurite, and observed in the vibrissa, hard palate, and molar periodontal ligament. Encapsulated endings were found only in the hard palate. The trigeminal sensory nuclei contained OPN-ir cell bodies and neuropil. The neuropil was devoid of ir in laminae I and II of the medullary dorsal horn (MDH), and had various staining intensities in other regions of the trigeminal sensory nuclei. Transection of the infraorbital and inferior alveolar nerves caused an increase of OPN-ir intensity in ipsilateral TG neurons. The staining intensity of the neuropil also increased in the trigeminal sensory nuclei ipsilateral to the neurotomy excepting laminae I and II of the MDH. The present study indicates that OPN-ir primary sensory neurons in the TG innervate encapsulated and unencapsulated corpuscular endings. Such neurons probably project their central terminals to the trigeminal sensory nuclei except for the superficial laminae of the MDH.

Hypocretin (orexin) input to trigeminal and hypoglossal motoneurons in the cat: a double-labeling immunohistochemical study

In trigeminal and hypoglossal motor nuclei of adult cats, hypocretin immunoreactive fiber varicosities were observed in apposition to retrogradely labeled motoneuron somata and dendrites. Among those lateral hypothalamus neurons that project to the hypoglossal nucleus some were determined to be hypocretin immunoreactive and were located amongst the single-labeled hypocretinergic neurons. These data suggest that hypocretin may play a role in the synaptic control of these motoneurons.

Hypocretin receptor protein and mRNA expression in the dorsolateral pons of rats

The hypocretins (also known as orexins) are hypothalamic peptides that have been implicated in feeding and sleep regulation. Previous reports have described the distribution of the mRNAs encoding two hypocretin receptors (HCRT-R), but the pattern of protein expression has not been investigated. Here we examine the distribution of the mRNA and protein for the HCRT receptor 1 (HCRT-R1) and HCRT receptor 2 (HCRT-R2) in the pontine brainstem and demonstrate that they are present in many pontine nuclei including those associated with REM sleep. Immunohistochemistry indicates that one or both of the receptor subtypes are expressed in the dorsal raphe, the lateral dorsal tegmental (LDT), the pedunculo pontine (PPT), the locus coeruleus (LC), the locus subcoeruleus, pontis oralis, Barrington's, the trigeminal complex (mesencephalic trigeminal and motor nucleus of the trigeminal nerve), the dorsal tegmental nucleus of Gudden (DTG), the ventral cochlear nucleus (VCA), trapezoid nucleus (TZ), pontine raphe nucleus and the pontine reticular formation. These regions have been shown to be involved in mastication, bladder control, gastrointestinal function and in arousal. Given these projection sites and the functions associated with these sites, we suggest that HCRT may play a role in maintaining alertness and vigilance while the animal is engaged in consummatory behavior.

Distribution of pituitary adenylate cyclase activating polypeptide (PACAP) immunoreactive elements in the brain stem of rats studied by immunohistochemistry

In the present work the distribution of pituitary adenylate cyclase activating polypeptide (PACAP) immunoreactive elements in rat brain stem were described using immunohistochemistry. The following structures were PACAP immunoreactive: 1. The dorsomedial and ventrolateral cell columns of the motor nuclei of cranial nerves. 2. Primary somatosensory cells in the mesencephalic nucleus of the trigeminal nerve and central axons of the branchial cranial nerves in the spinal trigeminal tract. 3. Visceral afferent fibers in the solitary tract and cell bodies in the dorsal motor nucleus of the vagus. 4. Second and third order sensory neurons of the cochlear and vestibular systems. 5. Scattered fibers in various regions of the brain stem and well-defined fiber bundles in the interpeduncular area. 6. Cell bodies in the red nucleus, substantia niga, in some cell groups of the reticular formation and in the raphe nuclei, as well as in the pontine dorsolateral tegmentum.

The mesencephalic trigeminal nucleus in the cat

This review is a concise summary of our current knowledge about the MTN neuroanatomy which in turn is necessary to understand the neurochemistry of this nucleus in the cat. In order to solve the puzzle of neurotransmitter related changes in the synaptic and functional organization of the MTN, we provide a comprehensive description of the neurotransmitter content of MTN neurons. Particular emphasis is given to identifying the possible physiological involvement of MTN inputs in the transmission of proprioceptive information at the first synaptic relay. It is shown that under normal circumstances the large MTN neuron subpopulation contains only Glu that is a strong candidate for a major neurotransmitter in this brain region. However, certain small MTN neurons, most likely interneurons, are found to be GABAergic. Furthermore, NOS immunoreactivity can be detected in the caudal as well as the mesencephalic-pontine junction parts of the MTN and this suggests a mediatory role for NO in some aspects of synaptic transmission in the MTN. The divergent neurochemical content of the cells in the nucleus, should it exist, is likely to be linked with different neuronal functions. Remarkably, no immunoreactivity to any of the neuropeptides examined is observed in the cell bodies of MTN neurons and only fibers and their terminals show peptide-immunolabeling. Most of the labeled peptidergic fibers have immunopositive varicosities that form pericellular basket-like arborizations around unlabeled MTN perikarya. It is predicted that under normal conditions the pericellular arborizations can function as an intranuclear key communication medium between immunopositive projections and immunonegative MTN neurons in the proprioceptive information processing. The levels of transmitter substances in MTN neurons may vary in case of marked changes in the environmental conditions. Axotomy-induced alterations include a long-lasting decrease in the content of CaBPs produced in MTN neurons and/or de novo synthesis of GAL, NPY and CGRP, thus implying the interactive nature and a previously unsuspected neurochemical plasticity of MTN neurons. The newly synthesized neuropeptides can enhance neuronal survival and neurite regeneration. Our results support the assumption that a peptide involvement in the proprioceptive function develops mainly in abnormal conditions. Taken together with the existing neuroanatomical and electrophysiological data, the present results give strong evidence for the occurrence of both excitatory (Gluergic) and inhibitory (GABAergic) transmission in the cat MTN. In addition, evidence is also provided that the MTN receives synaptic inputs from peptidergic and catecholaminergic fibers and these possibly play a significant role in the integration and transmission of trigeminal proprioceptive information. These findings have confirmed the existence of a large number of synaptic contacts in the cat MTN with specific morphological features of their boutons and with presumably different neurotransmitter release from the synaptic vesicles. In this way, knowledge of the origin and neurotransmitter nature of the fibers providing the synapses would facilitate the understanding of the important role of MTN neurons responsible for proprioception in this region.

Origin, distribution, and morphology of galaninergic fibers in the rodent trigeminal system

The neuropeptide galanin (Gal) is found throughout the central nervous system. Of particular interest is the fact that Gal is present within the majority of noradrenergic locus coeruleus (LC) neurons. However, very few, if any, Gal-immunoreactive fibers have been identified in many of the major efferent targets of LC, including sensory neocortex and dorsal thalamus. The goal of the present study was to examine the Gal fiber innervation of the rodent trigeminal somatosensory system and its connection to the LC. Our results show that at least two different morphological profiles of Gal-immunoreactive fibers are present within relay nuclei along the ascending trigeminal pathway. Numerous small caliber Gal-immunoreactive fibers with bouton-like swellings were noted within the barrel cortex, the ventroposterior medial (VPM) nucleus, the posterior medial (POm) nucleus, the zona incerta (ZI), the reticular nucleus (nRT) of the thalamus, and the principal (PrV) and spinal (SpV) nuclei of the trigeminal complex. Immunoreactive fibers were prevalent in, but not restricted to, layer I of the barrel cortex. Within the somatosensory thalamus, the density of Gal-immunoreactive fibers was higher in POm than in VPM. Laminae I and II of SpV and the nRT and ZI also contained dense, large-diameter Gal-immunoreactive fibers. These large-diameter Gal-immunoreactive fibers did not co-contain dopamine beta-hydroxylase (DBH). In contrast, virtually every small-caliber Gal-immunoreactive fiber colocalized with DBH. To determine whether Gal-immunoreactive fibers originated from LC, we combined immunohistochemical procedures with fluorescent tracing techniques. After retrograde tracer injections into several trigeminal relay nuclei, we observed that approximately 50% of the labeled LC neuronal population was immunoreactive for Gal. Our results suggest an extensive Gal-immunoreactive fiber innervation of the rodent trigeminal system, much of which may originate from LC neurons in the brainstem.

Osteocalcin-immunoreactive primary sensory neurons in the rat spinal and trigeminal nervous systems

Osteocalcin-immunoreactivity (OC-ir) was examined in spinal and trigeminal primary sensory neurons of the adult rat. Sixteen percent of dorsal root ganglion (DRG) neurons were immunoreactive (ir) for this protein. These neurons were mostly large and measured 594-4583 microm(2) (mean+/-S.D.=2243+/-748 microm(2)). Thirty-four percent of DRG neurons >1200 microm(2) and 4% of those in the range 600-1200 microm(2) showed the ir. Virtually all DRG neurons <600 microm(2) were devoid of OC-ir. In the trigeminal ganglion (TG), 25% of neurons exhibited the ir. Such neurons were of various sizes (range=156-2825 microm(2), mean+/-S.D.=1234+/-543 microm(2)). Forty-five percent of TG neurons >800 microm(2) and 6% of those <400 microm(2) were immunoreactive for this protein. Twelve percent of TG neurons in the range 400-800 microm(2) showed the ir. In the mesencephalic trigeminal tract nucleus (Mes5), 63% of primary sensory neurons contained OC-ir. Virtually all OC-ir DRG and Mes5 neurons co-expressed parvalbumin-ir but not CGRP-ir. On the other hand, only 31% of OC-ir neurons co-expressed parvalbumin-ir and 10% co-expressed CGRP-ir in the TG. The present study indicates that DRG and Mes5 primary sensory neurons co-expressing OC- and parvalbumin-irs are spinal and trigeminal proprioceptors. OC-ir TG neurons which co-express parvalbumin- and CGRP-irs appear to include low-threshold mechanoreceptors and nociceptors, respectively.

NMDA receptor NR1 and NR2A/B subunit expression in trigeminal neurons during early postnatal development

Trigeminal motoneurons (Mo5), mesencephalic trigeminal neurons (Me5), and supratrigeminal (Su5) and intertrigeminal (15) neurons are important constituents of the neural circuitry responsible for jaw movements observed during ingestive behaviors. In addition, in adult animals, N-methyl-D-aspartate (NMDA) receptors are a critical component of the brainstem circuitry responsible for reflex- and centrally activated jaw movements. However, little is known about the expression of this receptor in circuitry used to produce neonatal jaw movements. Receptor immunohistochemistry was used to describe changes in the expression of NMDA NR1 and NR2A/B receptor subunits in Mo5, Me5, Su5, and I5 neurons during postnatal development. Rats at postnatal days (P) 1, 3, 8, 15-16, 21-24, and 28-35 were used. An affinity-purified polyclonal antibody against the NR1 subunit and an affinity-purified polyclonal antibody that recognizes both NR2A and 2B subunits were used to depict the expression of these subunits. In Mo5, immunoreactivity was noted for both antibodies throughout the time frame sampled. NR1 expression in Me5 neurons emerged at P1. NR2A/B expression emerged at P3 in caudal and middle regions of Me5 and at P8 for rostral regions of the nucleus. NR1 immunoreactivity was present at P1 for neurons in I5 and at P3 for neurons in the Su5 region. NR2A/B subunit expression in Su5 and 15 neurons emerged at P8. These results provide evidence for NMDA receptor subunits in neonatal trigeminal neurons used in oral-motor circuitry and suggest a role for the NMDA receptor in synaptogenesis associated with these neurons during postnatal development.

Orofacial deep and cutaneous tissue inflammation differentially upregulates preprodynorphin mRNA in the trigeminal and paratrigeminal nuclei of the rat

Preprodynorphin (PPD) and preproenkephalin (PPE) gene expression in a rat model of orofacial inflammation were examined in order to further characterize the neurochemical mechanisms underlying orofacial inflammation and hyperalgesia. Deep and cutaneous orofacial inflammation was produced by a unilateral injection of complete Freund's adjuvant (CFA) into the rat temporomandibular joint (TMJ) or perioral skin (PO), respectively. RNA blot analysis of the tissues including the spinal trigeminal complex revealed that the PPD mRNA level ipsilateral to TMJ inflammation was increased by 56.5+/-14.7% (n=4) when compared to the Naive group, and was significantly greater than the contralateral PPD mRNA level (p<0.05). The distribution of neurons that exhibited PPD mRNA after inflammation was localized by in situ hybridization (naive approximately 0). In TMJ-inflamed rats (n=6) PPD mRNA-positive neurons were found ipsilaterally in the medial portion of laminae I-II of the upper cervical dorsal horn (4.5+/-0.3), the dorsal portion of the subnucleus caudalis and caudal subnucleus interpolaris (5.2+/-0.3), and the paratrigeminal nucleus (6.4+/-1.2). A very localized induction of PPD mRNA was also identified in a group of neurons in the intermediate portion of the subnucleus caudalis (2.4+/-0.4) in PO-inflamed rats (n=6). The distribution of these PPD mRNA-positive neurons was somatotopically relevant to the site of injury. There were no significant changes in PPE mRNA expression in both TMJ- and PO-inflamed rats. These results indicate that TMJ inflammation resulted in a more intense and widespread increase in PPD mRNA expression when compared to PO inflammation. These changes may contribute to persistent central hyperexcitability and pain associated with temporomandibular disorders.

Distribution of the low-affinity neurotrophin receptor (p75) in the developing trigeminal brainstem complex in the rat

The low-affinity neurotrophin receptor (p75) binds all members of the neurotrophin family. In the rat, during the first week postpartum, dense p75-immunoreactivity (IR) is present throughout all components of the trigeminal brainstem complex (TBC), largely associated with primary sensory afferents. Within subnucleus caudalis (SpC) of the TBC, intense p75-IR is present in all laminae at birth. During the second and third postnatal weeks, p75-IR in SpC gradually fades within the deeper laminae, becoming generally restricted in the adult to laminae I and II. Similar declines in p75-IR intensity occur in the subnucleus oralis (SpO); in the SpO in the adult, p75-IR is confined to the dorsalmost portion of SpO. In subnucleus interpolaris, an emerging, vibrissa-related pattern of p75-IR is detectable on PD0 (first 24 hr postpartum), which becomes fully differentiated during PD4-PD7. However, this pattern gradually disappears during the third postnatal week. Ventrally in the nucleus principalis (PrV), a pattern of p75-IR that mirrors the topographical arrangement of the vibrissae is detectable by PD0-PD1, is fully differentiated by the end of the first postnatal week, and persists into adulthood. Perinatal unilateral sectioning of the infraorbital nerve on PD0-PD1, but not as late as PD4, disrupts p75-IR patterning in the adult PrV. Although p75 appears to be associated with primary afferent pattern formation, to determine whether it is essential, we examined mutant mice unable to form functional p75. In the TBC of these knockout mice, examined as adults, patterns of cytochrome oxidase staining (which parallel those of p75-IR) appeared to be normal. In summary, during early development, p75 is widely expressed in the TBC during periods of active synaptogenesis and pattern formation, whereas in the adult, its expression is restricted to association with populations of primary sensory afferents. However, the absence of functional p75 in genetically altered mice does not appear to prevent primary afferent pattern formation.

Outward currents influencing bursting dynamics in guinea pig trigeminal motoneurons

To initiate and maintain bursts (and plateau potentials) in the presence of serotonin, guinea pig trigeminal motoneurons utilize L-type Ca2+ and persistent Na+ inward currents. However, the intrinsic currents that contribute to burst termination and determine the duration of the interburst interval are unknown. Therefore we investigated the roles of outward currents, whose slow activation is coupled to cytosolic cation (Ca2+ and Na+) accumulation. First we examined a Ca2+-dependent K+ current (IK-Ca) with apamin and Ba2+-substituted, low-Ca2+ solution. Blockade of IK-Ca lengthened burst duration and cycle time but did not abolish bursting. Next we studied the Na+/K+-ATPase pump current (Ip) with cardiac glycosides. In the presence of apamin or low-Ca2+/Ba2+ solution, blocking Ip (with ouabain or strophanthidin) decreased both burst duration and cycle time and ultimately transformed bursting into tonic spiking. We conclude that IK-Ca and Ip contribute to burst termination in trigeminal motoneurons. These currents influence temporal bursting properties such as burst duration and cycle time and may help determine the phasic activity of motoneurons during rhythmic oral-motor behaviors.

Peptide 19 in the dorsal root ganglion and the mesencephalic trigeminal tract nucleus of the adult rat

Peptide 19-immunoreactivity (PEP 19-ir) was examined in the dorsal root ganglion (DRG) and the mesencephalic trigeminal tract nucleus (Mes5) of the adult rat. Thirty-eight percent of DRG cells were immunoreactive (ir) for PEP 19. These neurons were small to large and measured 167-4583 micron2 (mean+/-S.D.=2048+/-913 micron2). Seventy-five percent of DRG cells >2000 micron2 and 15% of those <1000 micron2 exhibited PEP 19-ir. Thirty-six percent of DRG neurons in the range 1000-2000 micron2 showed the ir. In the Mes5, 87% of primary neurons were ir for this peptide. Muscle spindles in the soleus and masseter muscles contained PEP 19-ir spiral axon terminals. Double immunofluorescence methods revealed the co-expression of PEP 19 and calcium binding proteins. Eighty-six percent of parvalbumin-ir neurons exhibited PEP 19-ir. Conversely, 60% of PEP 19-ir neurons showed parvalbumin-ir. The cell size analysis revealed that 55% of PEP 19-ir neurons >600 micron2 showed parvalbumin-ir and that all PEP 19-ir neurons <600 micron2 were devoid of it. Ninety percent of PEP 19-ir DRG neurons showed S100-ir, whereas 60% of S100-ir ones co-expressed PEP 19-ir. In the Mes5, virtually all PEP 19-ir primary neurons exhibited parvalbumin-ir. The co-expression of PEP 19 and S100 could not be observed in the nucleus. The present study indicates that PEP 19-ir neurons which co-express parvalbumin-ir are proprioceptors in the spinal and the trigeminal systems. PEP 19-ir small DRG neurons without S100-ir are probably exteroceptors and may include unmyelinated nociceptors.

Regulation of intrinsic and synaptic properties of neonatal rat trigeminal motoneurons by metabotropic glutamate receptors

We studied how metabotropic glutamate receptor (mGluR) activation modifies the synaptic and intrinsic membrane properties of neonatal rat trigeminal motoneurons using the broad-spectrum mGluR agonist (1S,3R)-1-amino-1,3-cyclopentane-dicarboxylic acid [(1S,3R)-ACPD], group I/II antagonist (+/-)-alpha-methyl-4-carboxy-phenylglycine (MCPG), and group III agonist L-2-amino-4-phosphonobutanoate (L-AP4). (1S,3R)-ACPD depressed excitatory transmission to trigeminal motoneurons presynaptically and postsynaptically via presynaptic inhibition and by reducing the currents carried by ionotropic glutamate receptors selective for AMPA. (1S,3R)-ACPD also depolarized trigeminal motoneurons and increased input resistance by suppressing a Ba2+-sensitive leakage K+ current. These effects were not mimicked by L-AP4 (100-200 microM). High-threshold Ca2+ currents were also suppressed by (1S,3R)-ACPD. Repetitive stimulation of excitatory premotoneurons mimicked the postsynaptic effects of (1S, 3R)-ACPD. The postsynaptic effects of (1S,3R)-ACPD and repetitive stimulation were both antagonized by MCPG, suggesting that mGluRs were similarly activated in both experiments. We conclude that mGluRs can be recruited endogenously by glutamatergic premotoneurons and that mGluR-mediated depression of excitatory transmission, combined with increased postsynaptic excitability, enhances the signal-to-noise ratio of oral-related synaptic input to trigeminal motoneurons during rhythmical jaw movements.

Neuronal nicotinic acetylcholine receptors in rat trigeminal ganglia

The application of nicotine to the various epithelia served by the trigeminal nerve produces irritation and/or pain by activating neuronal nicotinic acetylcholine receptors (NnAChRS) in sensory neurons. In this study the NnAChRs were identified in rat trigeminal ganglia (TG) using RT-PCR and immunocytochemistry. With RT-PCR the subunits of NnAChRs in rat TG were determined, and with immunocytochemistry the localization of three prominent subunits (alpha 7, alpha 4 and beta 2) were localized in intact TG neurons. The relative abundance of the alpha and beta subunits were: alpha 7 approximately alpha 3 > alpha 6 > alpha 4 approximately alpha 5 > alpha 9 > or = alpha 2, and beta 2 approximately beta 3 > beta 4. This is the first report of the alpha 9 subunit in TG. Immunohistochemical studies revealed that almost all TG neurons contained alpha 7-LI and alpha 4-LI, and that 85% had beta 2-LI. For these three subunits much of the label was internalized. Immunocytochemical studies using antibodies raised against chick alpha 8 subunits did not specifically label rat TG. These data reveal that rat TG neurons contain the entire spectrum of mammalian NnAChR subunits.

Immunocytochemical localization of the AMPA receptor subunits in the mesencephalic trigeminal nucleus of the rat

The mesencephalic trigeminal nucleus is composed of large (35-50 microns) pseudo-unipolar neurons. Closely associated with them are small (< 20 microns) multipolar neurons. An unique peculiarity of the pseudo-unipolar perikarya is that they receive synaptic input from various sources, which sets them apart from the dorsal root and cranial nerves sensory ganglia neurons. Whereas glutamate is the best neurotransmitter candidate in pseudo-unipolar neurons, glutamatergic input into them has not yet been reported. AMPA glutamate receptors are implicated in fast excitatory glutamatergic synaptic transmission. They have been localized ultrastructurally at postsynaptic sites. This study demonstrates that the pseudo-unipolar neurons of the mesencephalic trigeminal nucleus express AMPA glutamate receptor subunits, which indicates that these neurons receive glutamatergic input. Serial sections from the rostral pons and midbrain of Sprague-Dawley rats were immunostained with antibodies against C-terminus of AMPA receptor subunits: GluR1, GluR2/3, and GluR4. The immunoreaction was visualized with avidin-biotin-peroxidase/DAB for light and electron microscopy. With GluR1 antibody only the smallest multipolar neurons were recognized as immunopositive within the mesencephalic trigeminal nucleus. GluR2/3 stained the pseudo-unipolar neurons intensely within the entire rostro-caudal extent of the nucleus. In addition the former antibody stained small multipolar neurons within the mesencephalic trigeminal nucleus, though with somewhat larger dimensions than those immunoreactive for GluR1. Whereas the overall staining with GluR4 antibody was scant, those pseudo-unipolar neurons that were stained, were strongly stained. Furthermore, a considerable number of microglial cells within and surrounding the mesencephalic trigeminal nucleus displayed very intense immunoreactivity for GluR4. These results are discussed in the light of the glutamate receptor subunit composition.

Effect of a serotonin agonist (sumatriptan) on the peptidergic innervation of the rat cerebral dura mater and on the expression of c-fos in the caudal trigeminal nucleus in an experimental migraine model

The supratentorial cerebral dura of the albino rat is equipped with a rich sensory innervation including nociceptive axons and their terminals, which display intense calcitonin gene-related peptide (CGRP) immunoreactivity both in the connective tissue and around blood vessels. Stereotactic electrical stimulation of the trigeminal (Gasserian) ganglion, regarded as an experimental migraine model, induces marked increase and disintegration of club-like perivascular CGRP-immunopositive nerve endings in the dura. Intravenous administration of sumatriptan, prior to electrical stimulation, prevents disintegration of perivascular terminals and induces accumulation of CGRP in terminal and preterminal portions of peripheral sensory axons. Consequently, immunopositive terminals and varicosities increase in size; accumulation of axoplasmic organelles results in a "hollow" appearance of many varicosities. Since sumatriptan exerts its anti-migraine effect by virtue of its agonist action on 5-HT1D receptors, we suggest that sumatriptan prevents the release of CGRP from dural perivascular terminals by an action at 5-HT1D receptors. In the caudal trigeminal nucleus electrical stimulation of the trigeminal ganglion induces, in interneurons, increased expression of the oncoprotein c-fos which is not prevented by intravenous application of sumatriptan. Disparate findings regarding this effect are partly due to the fact that sumatriptan very poorly passes the blood-brain barrier and partly to different experimental paradigms used by different authors.

Dopamine-immunoreactivity in the rat mesencephalic trigeminal nucleus: an ultrastructural analysis

The ultrastructure and distribution of dopaminergic boutons within the rat mesencephalic trigeminal (Me5) nucleus was examined with the use of electronmicroscopic immunocytochemistry. A total of 5102 boutons, comprising axosomatic and axodendritic synaptic terminals as well as non-synaptic boutons (or varicosities), located in the ventrocaudal portion of Me5 was analysed. Approximately 20% of these boutons were dopamine-immunoreactive. Morphological analysis showed that the dopaminergic synaptic terminals, axodendritic as well as axosomatic, were exclusively of the S- and G-bouton type; they contained, respectively, small spherical vesicles or small pleomorphic vesicles in combination with large granular dense-cored vesicles. All dopaminergic varicosities in the Me5 were of the G-bouton type. Quantitative analysis revealed that most of the dopaminergic synaptic terminals in the Me5 nucleus contacted dendrites, while only a minority (12%) contacted Me5 somata. This dopaminergic somatic input comprised about half (52%) of the total axosomatic input on Me5 neurons. The present results and previous findings with respect to the prominent serotonergic component of the axosomatic input to Me5 neurons indicate that dopamine and serotonin account for most of the axosomatic input in the ventrocaudal part of the Me5 nucleus. In fact, the present results seem to support previous observations regarding the existence of a population of afferent neurons in which dopamine and serotonin are colocalized.

CGRP in the trigeminal nucleus, spinal cord and hypothalamus: effect of gonadal steroids

Calcitonin gene-related peptide (CGRP) contents were assayed in cervical spinal cord, trigeminal nucleus and hypothalamus throughout the estrous cycle and in male and ovariectomized rats. In the trigeminal nucleus, neither testosterone nor 17 beta-estradiol seem to affect CGRP accumulation, but progesterone seems to decrease it. In the cervical spinal cord, ovarian steroids seem to decrease CGRP while testosterone does not seem to influence it. In the hypothalamus, CGRP was only detectable in the male rat suggesting a positive effect of testosterone. It had marked circadian rhythm. In conclusion, CGRP content appears to be affected by gonadal steroids in the hypothalamus, the cervical spinal cord and the trigeminal nucleus in the rat.

GABAergic and glycinergic neurons projecting to the trigeminal motor nucleus: a double labeling study in the rat

The distribution of GABAergic and glycinergic premotor neurons projecting to the trigeminal motor nucleus (Vm) was examined in the lower brainstem of the rat by a double labeling method combining retrograde axonal tracing with immunofluorescence histochemistry. After injection of the fluorescent retrograde tracer, tetramethylrhodamine dextran amine (TRDA), into the Vm unilaterally, neurons labeled with TRDA were seen ipsilaterally in the mesencephalic trigeminal nucleus, and bilaterally in the parabrachial region, the supratrigeminal and intertrigeminal regions, the reticular formation just medial to the Vm, the principal sensory and spinal trigeminal nuclei, the pontine and medullary reticular formation, especially the parvicellular part of the medullary reticular formation, the alpha part of the gigantocellular reticular nucleus, and the medullary raphe nuclei. Some of these neurons labeled with TRDA were found to display glutamic acid decarboxylase (the enzyme involved in GABA synthesis)-like or glycine-like immunoreactivity. Such double-labeled neurons were seen mainly in the supratrigeminal region, the reticular region adjacent to the medial border of the Vm, and the dorsal part of the lateral reticular formation of the medulla oblongata; a number of them were further scattered in the intertrigeminal region, the alpha part of the gigantocellular reticular nucleus, the nucleus raphe magnus, the principal sensory trigeminal nucleus, and the interpolar subnucleus of the spinal trigeminal nucleus. These neurons were considered to be inhibitory (GABAergic or glycinergic) neurons sending their axons to motoneurons in the Vm, or to local interneurons within and around the Vm.

Differential expression of cell adhesion molecules on trigeminal cutaneous and muscle afferents

Previous work from our laboratory (Woodbury and Scott, 1995) suggested that embryonic cutaneous and muscle afferents might express different surface cell adhesion molecules (CAMs) on their growth cones. To examine this possibility directly we measured the relative levels of expression of various adhesion molecules on growth cones of neurons from the dorsomedial portion of the trigeminal ganglion (DM-TG), which are largely cutaneous, and from the trigeminal mesencephalic nucleus (TMN), which are exclusively muscle afferents. Axonin-1,L1, BEN, and N-cadherin were expressed more abundantly on DM-TG growth cones, whereas N-CAM was more abundant on TMN neurons. Expression of polysialated N-CAM was similar on the two populations, addition of NGF and NT-3 appeared to increase expression of polysialated N-CAM on TMN neurons. Although the levels of L1 and axonin-1, both of which bind L1, were markedly different on TMN and DM-TG neurons, these differences were not sufficient to cause dramatic differences in the growth rates of TMN and DM-TG neurons on L1.

Electron microscopy of immunoreactivity patterns for glutamate and gamma-aminobutyric acid in synaptic glomeruli of the feline spinal trigeminal nucleus (Subnucleus Caudalis)

We studied the ultrastructure of the synaptic organization in the feline spinal trigeminal nucleus, emphasizing specific neurotransmitter patterns within lamina II of the pars caudalis/medullary dorsal horn. Normal adults were perfused, and Vibratome sections from pars caudalis were processed for electron microscopy. Ultrathin sections were reacted with antibodies for the excitatory neurotransmitter glutamate (Glu) and for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) by using postembedding immunogold techniques. Both single- and double-labeled preparations were examined. Results with single labeling show that Glu-immunoreactive terminals have round synaptic vesicles and form asymmetric synaptic contacts onto dendrites. GABA-immunoreactive axon terminals and vesicle-containing dendrites have pleomorphic vesicles, and the axon terminals form symmetric contacts onto dendrites and other axons. Double labeling on a single section shows glomeruli with central Glu-immunoreactive terminals that are presynaptic to dendrites, including GABA+ vesicle-containing dendrites. These Glu+ terminals are also postsynaptic to GABA+ axon terminals, and these GABA-immunoreactive terminals may also be presynaptic to the GABA+ vesicle-containing dendrites. Quantitative analyses confirm the specificity of the Glu and GABA immunoreactivities seen in the various glomerular profiles. The results suggest that a subpopulation of Glu-immunoreactive primary afferents (excitatory) may be under the direct synaptic influence of a GABA-immunoreactive intrinsic pathway (inhibitory) by both presynaptic and postsynaptic mechanisms.

Distribution of Fos-like immunoreactivity in the caudal medullary reticular formation following noxious facial stimulation in the rat

To investigate the topographic organization of nociceptive neurons in the caudal medullary reticular formation, the distribution of cells that exhibit c-fos expression was examined following a unilateral noxious facial stimulus: subcutaneous injection of formalin into the vibrissal pad of awake rats. Labelling for Fos-like immunoreactivity was present in a somatotopic distribution in a region of the lateral reticular formation adjacent to trigeminal nucleus caudalis, which corresponds approximately to lamina V of the medullary dorsal horn. Labelling in adjacent regions of the reticular formation showed no somatotopy but was predominantly ipsilateral. Contralateral labelling was concentrated ventrolaterally around the lateral reticular nucleus and dorsally near the nucleus of the solitary tract.

Enkephalin-like immunoreactivity in the chick brainstem: possible relation to the cochlear efferent system

Mammalian lateral olivocochlear (LOC) neurons that are immunoreactive for choline acetyltransferase (ChAT) are also immunoreactive for enkephalin (Enk). To determine whether cochlear efferent neurons in birds might also contain Enk-like immunoreactivity (Enk-LI), we studied the auditory brainstem of the domestic chicken using antisera to ChAT, leucine-enkephalin (L-Enk) and methionine-enkephalin (M-Enk). Enk-LI terminals are found around, but not within, the superior olivary nucleus (SO) and the nucleus of the lateral lemniscus, pars intermedia (LLi). A moderate concentration of Enk-LI terminals is found ventromedial to the ventral facial nucleus (VIIv) where the ventrolateral group of ChAT-I cochlear efferent neurons is located. After colchicine injections into the lateral ventricle, a population of intensely stained Enk-LI perikarya was found in the nucleus of the lateral lemniscus, pars ventralis (LLv) with scattered cells in the LLi and the nucleus subceruleus ventralis (SCv). The distribution of Enk-LI and ChAT-I somata, however, never overlapped, even in adjacent sections. Thus, in the chick, Enk-LI perikarya are not distributed in areas where cochlear efferent neurons are found. Instead, a dense concentration of Enk-I terminals can be found in areas containing ChAT-I cochlear efferent neurons. The source of these enkephalinergic terminals may be a population of Enk-LI cells in the LLv.

Immunocytochemical localization of tyrosine hydroxylase and gamma-aminobutyric acid in the mesencephalic trigeminal nucleus of the cat: a light and electron microscopic study

BACKGROUND

Recent studies conducted on the rat have demonstrated that the mesencephalic trigeminal nucleus (MTN) neurons, involved in the proprioceptive transmission, contain some neuroactive substances, including classical and amino acid neurotransmitters. In addition, there is evidence that serotonin could not act as a neurotransmitter at the first synaptic relay in the cat MTN. In the present study, we aimed to examine two other possible neurotransmitter systems, i.e., catecholamines and gamma-aminobutyric acid (GABA), and the relationships between GABA-immunoreactive (IR) neurons and tyrosine hydroxylase (TH)-IR axonal varicosities in the MTN of the cat.

METHODS

To ensure the localization of immunoreactive structures, the experiments were carried out at the light and electron microscopic level using single immunostaining for TH and GABA alone. The correlation between GABA-IR cell bodies and TH-IR fibers was investigated by means of double-labeling immunogold and peroxidase technique for GABA and TH.

RESULTS

Light microscopically, a few GABA-IR neurons were observed in the cat MTN. These small-size, labeled cells, most likely interneurons, were apposed to unstained large mesencephalic trigeminal cells. Most of the large nonreactive MTN neurons were closely surrounded by fine TH-IR varicose or nonvaricose fibers and dot-like structures, presumably nerve terminals. Under the electron microscope, TH-IR fibers were not seen in synaptic contact and only rarely appeared to be in close proximity to neuronal profiles of small GABAergic cells, which contained gold particles.

CONCLUSIONS

Taken together with earlier studies from other laboratories, the present findings suggest that GABAergic system might play an indirect role in the proprioceptive information processing in the cat MTN by interactions of GABA-immunoreactive neurons with the systems that control the transmission of selected sensory information. In contrast, the presence of TH-IR fibers in direct apposition to the majority of MTN neurons provide further evidence that presumed GABAergic interneurons have extensive interactions with catecholamine varicosities and raise the possibility that catecholamines could modify the transmission on these neurons.

Serotonin-containing projections to the mesencephalic trigeminal nucleus of the cat

BACKGROUND

It is well known that the mesencephalic trigeminal nucleus (MTN) neurons transmit somatosensory information from proprioceptors in the oral-facial region. Several mechanisms of sensory transduction in these specialized receptors have been proposed, but the neurotransmitters which are responsible for mediating proprioceptive information are still unknown. The current study concentrates on the distribution of one putative neurotransmitter system, serotonin (SER), in the cat MTN. A second objective was to clarify the location and sources of serotoninergic projections on the MTN neurons.

METHODS

To determine whether SER was localized in the MTN, the peroxidase-antiperoxidase (PAP) immunocytochemical technique was applied at light and electron microscopic levels in colchicine-treated animals. The origin of SER-containing fibers in the MTN was studied using a double-labeling method combining retrograde transport with wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and SER immunocytochemistry.

RESULTS

There were no SER-containing neurons in the MTN. The cell bodies of immunonegative MTN neurons were closely surrounded by fine SER-positive fibers and terminals. The labeled fibers were in most cases very thin and sometimes varicose. Ultrastructurally, direct synaptic contacts between SER-containing terminals and perikarya of MTN neurons of all sizes could be seen. The majority of SER-labeled structures were synaptic terminals in which the immunoreactive material was located within the small round clear as well as the small granular vesicles (diameter 50-80 nm) and a few large dense-cored vesicles (up to 150 nm). Retrograde tracing demonstrated that most of cells in the nuclei raphe dorsalis, pontis and magnus were WGA-HRP-labeled.

CONCLUSIONS

These results indicated that MTN neurons received serotoninergic projections from the raphe nuclei of the brainstem. In light of these morphological data, it is concluded that the MTN of the cat is under the influence of SER-containing axons and this serotoninergic input may modulate MTN neuronal activity at the first synaptic relay.

Cytochemical characteristics of neurons in the trigeminal mesencephalic nucleus of hatchling chicks

The goal of the present study was to identify cytochemical markers characteristic of muscle afferents in hatchling chicks. To this end, we stained neurons in the trigeminal mesencephalic nucleus with a variety of markers that label subsets of neurons in avian dorsal root ganglia. We found that trigeminal mesencephalic neurons are surprisingly heterogeneous in their cytochemical make-up, expressing, to varying degrees, substance P, cholecystokinin, carbonic anhydrase, calbindin D-28k, parvalbumin, and S-100 beta. Calbindin D28k and S-100 beta appeared to be expressed equally in medial and lateral divisions of the trigeminal mesencephalic nucleus. In contrast, substance P- and cholecystokinin-immunoreactive neurons were more abundant in the medial division, whereas carbonic anhydrase activity and parvalbumin immunoreactivity were stronger in the lateral division. We were unable to detect met-enkephalin, neuropeptide Y, calcitonin gene-related peptide, vasoactive intestinal peptide, somatostatin, gamma-aminobutyric acid, or tyrosine hydroxylase in the trigeminal mesencephalic nucleus. Moreover, these neurons did not appear to bind the lectin Dolichos biflorus agglutinin. The heterogeneity of expression of markers among trigeminal mesencephalic nucleus neurons, especially between neurons in the medial and lateral divisions, suggests that these neurons are functionally diverse.

Paired helical filament-like inclusions and Hirano bodies in the mesencephalic nucleus of the trigeminal nerve in the aged rat

The alterations appearing in trigeminal mesencephalic primary sensory neurons during ageing have been analyzed by electron microscopy in the Wistar-Louvain rat. Two phases have been distinguished, similar to those observed in dorsal root ganglion neurons. Up to 24 months, the mesencephalic trigeminal neurons progressively accumulate lipofuscins, while filamentous inclusions start to appear around 24 months of age. Hirano bodies and paired helical filament-like structures have been identified in animals aged 24 months or more. This time-course parallels the one observed previously in dorsal root ganglion neurons, indicating that the blood-brain barrier does not seem to influence the ageing of mesencephalic trigeminal neurons. The relationship between the paired helical filament-like inclusions and Hirano bodies, as well as similar structures already described by other authors, is discussed.

Immunoelectron microscopic localization of basic FGF in neuroglias and neurons of the trigeminal mesencephalic and motor nuclei

Discrepancies between previous light microscopic studies on the localization of basic fibroblast growth factor (bFGF) in neuroglias and neurons of the normal rat brain prompted us to investigate, by electron microscopy, the subcellular localization of bFGF-like immunoreactivity in neuroglias and neurons of the trigeminal motor and mesencephalic nuclei. Immunostaining intensity differed from astrocyte to astrocyte; in astrocytes labeled heavily with bFGF antiserum, the precise subcellular location of immunoreaction deposits was difficult to determine, whereas mildly labeled astrocytes contained reaction products in subcellular regions apart from gliofilaments, mitochondria and Golgi apparatus. A comparison of immunostained sections with negative control ones at the light and electron microscopic levels revealed that astrocyte nuclei occasionally showed bFGF immunoreactivity. Immunoreactive astrocyte processes were also found in close apposition to blood vessels. bFGF was detected mainly in intracellular structures close to free ribosomes and the endoplasmic reticulum of immunoreactive oligodendrocytes and neurons; microglias rarely showed immunostaining. The nuclei of the cells with bFGF contained immunoreaction deposits of varying intensity, mainly in the euchromatin and rarely in the heterochromatin. Occasionally, bFGF of neuroglial origin accumulated in the vicinity of the interface between neurons and neuroglias. The extracellular matrix was not immunoreactive in any of the areas examined. These findings suggest that certain populations of astrocytes and oligodendrocytes as well as neurons in the normal brain contain bFGF-like substances.

Basic fibroblast growth factor-like immunoreactivity in the trigeminal proprioceptive and motor systems

Basic fibroblast growth factor (bFGF) isolated from the brain and pituitary, has been shown to induce cell divisions in a variety of cell types. It also acts as a potent stimulator of angiogenesis, and it is important in the survival of several types of cultured neurons. Despite considerable information on the functions of bFGF, there is incomplete knowledge about the ways in which it reaches remote tissues and its subcellular localization in the adult brain. Here we report our findings that a certain population of neurons with free ribosomes and rough endoplasmic reticulum immunoreactive for bFGF in the mesencephalic nucleus of the trigeminal nerve sends proprioceptive fibers to muscle spindles in the masseter muscle, and immunoreactive axons to the trigeminal motor nucleus to form synapses with the bFGF-containing motoneurons whose axons further constitute myoneural junctions in the periphery. Moreover, some bFGF neurons contain electron dense immunoreaction deposits in the euchromatin but not in the heterochromatin of the nucleus. These findings suggest that endogenous bFGF is transported within nerve processes and functions in mature neuronal circuits subserving the masseteric reflex arcs, and that bFGF is produced in free ribosomes and/or rough endoplasmic reticulum and is transported into the genetically active euchromatin as well.

Noradrenergic facilitation of motor neurons: localization of adrenergic receptors in neurons and nonneuronal cells in the trigeminal motor nucleus

Both alpha- and beta-adrenergic receptors (ARs) are involved in the facilitation of the monosynaptic jaw-closing reflex in the trigeminal motor nucleus (MoV) caused by norepinephrine (NE). The amplitude of muscle spindle afferent-evoked EPSPs in masseter motor neurons is 65% greater when noradrenergic axons to the motor nucleus are concomitantly activated and seems to be due to a presynaptic mechanism (Vornov, J. J., and J. Sutin. 1986. J. Neurosci. 6: 30-37). To determine the subtypes of ARs located on motor neurons and other cells, the cytotoxic lectin Ricin communis was injected into the masseter nerve of the trigeminal motor root to eliminate motor neurons in the masseter subnucleus of MoV. Autoradiography following incubation of tissue sections in the alpha 1 ligand 125IBE 2254 (125I-HEAT) or the nonselective beta ligand [125I]iodocyanopindolol (125ICYP) showed a decrease in alpha 1-AR binding related to the motor neuron degeneration and an increase in beta-AR binding associated with the glial reaction. To determine the extent to which glial proliferation was responsible for the increase in beta-ARs, cytosine arabinofuranoside (AraC) was administered to inhibit mitosis. Following AraC treatment, the total number of glial cells in the ricin-treated MoV was similar to that in normal MoV. Both beta-AR density and GFAP immunoreactivity remain increased, but to a lesser degree than following the ricin treatment alone. AraC also partially prevented the increase of immunolabeled or histochemically visualized microglia and capillary endothelial cells. The coincidence of the increases in beta-AR binding and GFAP in a region devoid of neurons argues that reactive astrocytes and other nonneuronal cells express beta-ARs in vivo. To determine whether the increase in astroglial beta-ARs was due to an up-regulation resulting from transynaptic degeneration of NE terminals, NE content was measured in MoV tissue punches, and NE terminals were visualized by immunocytochemical labeling of dopamine-beta-hydroxylase. NE content and NE terminal density remained unchanged following ricin-induced motor neuron degeneration.

Quantitative analysis and postsynaptic targets of GABA-immunoreactive boutons within the rat trigeminal motor nucleus

We have used the post-embedding immunogold labelling method using antibodies to gamma-aminobutyric acid (GABA) to obtain quantitative data on the distribution, frequency, postsynaptic targets and ultrastructural characteristics of GABA-immunoreactive (GABA-IR) boutons in the trigeminal motor nucleus of rats. We have also combined this method with horseradish peroxidase tracing to obtain specific evidence for termination of some GABA-IR boutons onto identified jaw-elevator motoneurones. Twenty-eight percent of all synapses in the motor nucleus involved GABA-IR boutons. Seventy-three percent of the GABA-IR boutons formed axo-dendritic synapses, 13% axo-somatic synapses and 14% axo-axonic synapses. Ninety-three percent of GABA-IR boutons formed symmetrical synapses. Overall, 58% of all boutons contained only flattened vesicles, while 26% contained round vesicles and 16% a mixture of vesicle types. Measurements of bouton cross sectional area, apposition length, and active zone length were obtained from serial reconstructions of 15 GABA-IR boutons and 30 unlabelled boutons. In each case mean values for GABA-IR boutons were significantly smaller than those for nonlabelled boutons.

Immunohistochemical mapping of neurophysins and calcitonin gene-related peptide in the human brainstem and cervical spinal cord

Our study investigates the distribution of neurophysins (Nph), proteins that are part of the precursors for vasopressin and oxytocin, and calcitonin gene-related peptide (CGRP) in the human brainstem by immunohistochemistry. Both peptides were found in discrete regions of the human hindbrain. Nph could be demonstrated exclusively in fibers and punctate perineural varicosities that were travelling within the mesencephalic central gray, substantia nigra, as well as locus coeruleus, medial longitudinal fascicle, raphe, nucleus of the solitary tract, lateral reticular nucleus and area postrema. A few varicosities were seen in the substantia gelatinosa of the spinal trigeminal tract and its continuation into the dorsal horn of the cervical spinal cord. In contrast to these observations. CGRP-immunoreactive fibers were found to be densest in the spinal tract of the trigeminal nerve and the dorsal horn of the spinal cord. In addition, fibers and varicosities could be demonstrated in numerous distinct brain regions, such as locus coeruleus and subcoeruleus, solitary tract, cuneate nucleus, raphe and periaqueductal gray. CGRP-immunoreactivity was also present in perikarya in the ventral horn of the spinal cord, as well as motor nuclei of cranial nerves, i.e., hypoglossal nucleus, ambiguous nucleus. Our results suggest that Nph-immunoreactivity in the human brainstem may be present predominantly within long fiber projections from hypothalamic neurosecretory nuclei, in analogy to data obtained from rodents, whereas CGRP may play a role in the branchiomotor system as well as in intrinsic or extrinsic projections involved in autonomic regulation and integration of sensory information.

Immunohistochemical and ultrastructural studies of the various nuclei of the trigeminal complex in the human newborn

The various nuclei of the trigeminal complex were studied by immunohistochemical (enkephalin localization) and ultrastructural means in the brainstems of eight newborn human babies that died within 24 h after birth. Positive enkephalin neurons were detected in the chief sensory and spinal trigeminal nuclei as well as in some fibers of the trigeminal nerve. Ultrastructurally, two morphologically distinct types of neuron were observed, respectively, in the motor nucleus, the spinal nucleus and the mesencephalic nucleus of the trigeminal complex, whereas three morphologically distinct types of neuron were observed in the chief sensory nucleus. "Glomerulus" formation was a frequently observed feature in the chief sensory nucleus. In the spinal nucleus, rolls of synaptic terminals stacking up one on top of another and synapsing onto the final synaptic element were very much in evidence. Axosomatic, axodendritic, dendrodendritic and dendroaxonic synapses were demonstrated in all the different nuclear areas of the trigeminal complex but axoaxonic synapses were absent in the mesencephalic nucleus. Some of the findings in the present human study were similar to those reported in the rats and cats.