Application Of Horseradish Peroxidase Research Articles

NK1 receptor activation by geniohyoid primary afferents modulates parasympathetic postganglionic neuronal excitability in the rat

Previous studies have indicated that the geniohyoid (GH) muscle receives innervation via both the hypoglossal nerve (CNXII) and the ansa cervicalis. Our recent studies revealed that the efferent root that contributes to the ansa cervicalis is a parasympathetic pathway and contains postganglionic cell bodies. Afferent axons from the GH muscle also travel via the ansa cervicalis, and afferent cell bodies are located in spinal ganglia. The present study attempts to locate the central terminations of these afferents. From the peripheral cut end of the ansa cervicalis, we recorded afferent discharges that coincided with inspiration and these were elicited by stretch of the GH muscle. After cutting CNXII proximal to its union with the ansa cervicalis, we applied horseradish peroxidase to the branch of CNXII that innervates the GH muscle. This procedure labeled cells ipsilaterally in the C2 spinal ganglia but not in the brainstem or upper spinal cord. Substance P-reactive terminals in the peripheral CNXII trunk were in apparent contact with vasoactive intestinal peptide-reactive cell bodies. Addition of the NK1 receptor agonist SP NK1 excited parasympathetic postganglionic neurons and the specific NK1 receptor antagonist GR82334 blocked these effects in vitro. These results suggest that GH primary afferents synapse on parasympathetic postganglionic neurons in the CNXII trunk and that activation of SP NK1 receptors modulates activity in these neurons.

AN HRP STUDY OF LOCALIZATION AND TOPOGRAPHICAL MAPPING OF THE MOTONEURONS SUPPLYING THE RAT SERRATUS ANTERIOR MUSCLE

Shoulder movements are a complex motor act, controlled by many muscles attached to thescapula and the vertebral column. These muscles are innervating by motoneurons (Mns) located in theventral horn of the spinal cord. Motoneurons of the ventral horn are arranged such that several groups ofMns can be distinguished in a transverse section through the spinal cord. The anatomical or functionalimplication of these groups is still unknown. The present research was designed to determine thelocation and topographical mapping of Mns to the rat serratus anterior (SA) muscle.Thirty young adult male rats weighing 180-250g were used in this study. The location anddistribution of the Mns in the rat cervical spinal cord to the serratus anterior (SA) muscle of the rat havebeen studied using horseradish peroxidase (HRP) intramuscular injection and the application of a HRPnerve dipping method to the long thoracic nerve. Following the intramuscular injection of HRP and alsoa nerve dipping for the long thoracic nerve, labeled motoneurons were identified ipsilaterally to the sideof HRP application forming two main cell columns extended rostrocaudally in the ventral horn of bothsides. The column G5 extended longitudinally from the caudal half of the fifth (C5) to the rostral half ofthe seventh (C7) cervical segments in group five. The column G7, located mainly in the rostral half ofthe C7 in group seven. The serratus anterior labeled motoneurons showed a rostrocaudal somatotopicdistribution in each of the columns G5 and G7.These results suggest that there is a specific functional role for motoneurons, and also thatmotoneurons are arranged in the form of a motor pool with a musculotopic pattern of distributioncorresponding to the embryonic origin and anatomical position of the muscles they innervate to.

Structure of internal interneuronal connections in field 17 of the cat cerebral cortex.

The spatial distribution of horizontal internal connections in field 17 of the cat cortex was studied after microiontophoretic application of horseradish peroxidase to individual cortical columns. Cluster analysis of the distribution of labeled cells in the superficial layers in the tangential plane of the cortex was performed. Field 17 included 7 +/- 1 clusters of up to five cells. Clusters were distributed into two layers, separated by 1.2 +/- 0.3 mm. The distance between the centers of the clusters forming rows was 0.8 +/- 0.3 mm. The spatial characteristics of the grouping of cells sending axons into the cortical column were compared with published data based on optical visualization of the activity of neurons in orientational and eye-dominant columns of the visual cortex. It is suggested that columns in field 17 are associated with 6-8 hypercolumns, though only with a single type of neuron within these hypercolumns, in terms of eye dominance and orientational preference.

Application of immobilized horseradish peroxidase for the removal of p-chlorophenol from aqueous solution

The development and application of an immobilized horseradish peroxidase (HRP) system with porous aminopropyl glass (APG) beads are reported. The optimal condition for the immobilization of HRP on APG with glutaraladhyde, which leads to a specific activity of 50.7 U/g APG, was identified. Upon immobilization, the operation pH range was broadened downward by one pH unit from 7.5–9.5 to 6.5–9.5 and optimal operation temperature was increased by at least 10 °C. Thermostability of HRP was also improved by approximately 20% upon immobilization. The application of such HRP immobilized APG for the removal of p-chlorophenol from water was investigated. An HPLC method for the quantification of p-chlorophenol was developed to substitute for spectrophotometric methods that are subject to interferences from proteins and other UV-absrobing compounds in the reaction mixtures. The polymerization of p-chlorophenol into insoluble precipitate was completed within 3 h after the initiation of reaction with the addition of hydrogen peroxide with a maximal removal efficiency of 25%, observed at pH 7.5. The addition of poly(ethylene glycol) significantly enhanced the removal efficiency presumably via the formation of a protective shield in the vicinity of the active site of HRP from the free radicals formed during polymerization and can thus reduce the amount of enzymes needed to achieve the desired removal efficiency. The reusability of the HRP immobilized APG was also demonstrated.

Afferent connections of fields 17 and 18 of the cat cerebral cortex formed by neurons of the dorsal lateral geniculate body.

Horseradish peroxidase (HRP) was applied microiontophoretically to nine individual columns in fields 17 and six columns in field 18 of the cat cerebral cortex. Most labeled cells in the dorsal lateral geniculate body were identified in layer A. The ratio of number of labeled cells in layer A to the number of labeled cells in layer A1 was assessed (the A/A1 ratio). Application of HRP to columns in field 17 yielded A/A1 ratios of 0.5 to 2.5; application to field 18 gave ratios ranging from 0.2 to 0.9. This suggests that the fields studied here contained columns which were afferent in relation to the ipsilateral eye and the contralateral eye.

Trigeminal primary afferent projections to the peribrachial area in the guinea pig

Transganglionic transport of horseradish peroxidase (HRP) was used to investigate trigeminal primary afferent endings in the peribrachial area of the guinea pig. After HRP application to several nerve branches of the three divisions of the trigeminal nerve, a projection to the caudal region of the ipsilateral peribrachial region was found for the infratrochlear, ethmoidal, supraorbital, zygomatic, zygomaticofacial, zygomaticotemporal and infraorbital-superior alveolar nerves. Random and scarce endings were also observed for the mental, inferior alveolar, buccal and mylohyoid nerves. No trigeminal primary projection to the peribrachial area was detected when HRP was applied to the sphenopalatine, lingual and auriculotemporal nerves. With the exception of the ethmoidal endings described in the muskrat, a primary afferent projection to the peribrachial region from the other trigeminal nerves has not hitherto been reported in mammals.

A review of contralateral responses to a unilateral inflammatory lesion.

Symmetry is a remarkably constant clinical feature of chronic inflammatory disease. Rheumatoid arthritis is almost by definition symmetrical [1]. Osteoarthritis, psoriasis and some of its associated arthritides are also symmetrical [2–4]. Pulmonary fibrosis, glomerulonephritis and sympathetic ophthalmia are also symmetrical inflammatory conditions. Whilst the pathophysiology behind this symmetry is unexplained, we and others have speculated that it is likely to be mediated via neurological mechanisms crossing through the spinal cord [5, 6]. The two sides of the spinal column have largely been thought to function independently of each other. There are three lines of evidence to suggest that this is not true. Careful anatomical studies of the spinal cord show transmedian fibres decussating posteriorly at all levels of the spinal cord to synapse in the laminae on the contralateral dorsal horn. These neuronal connections have been seen in many different species, including several primates (Fig. 1). Szentagothai [7], using Golgi analysis on young cats and dogs, showed that neurons with their cell bodies in the substantia gelatinosa send contralateral axons that appear to synapse in the contralateral substantia gelatinosa. Perl and Light [8] corroborated these findings after they had applied horseradish peroxidase to rat, cat and monkey dorsal rootlets. They found projections into the contralateral substantia gelatinosa as well as the ventral portion of the nucleus propius. Culberson et al. [9], using cresyl violet acetate (Fink-Heimer method), identified crossed afferent projections throughout the spinal cord, originating and terminating in laminae III–IV, in four mammalian species. These anatomical studies provide evidence that the opportunity exists for crosstalk between the left and the right sides of the spinal column. Functional studies of decerebrate rats demonstrate that such cross-communication can produce contralateral responses. Electrical stimulation of contralateral peripheral nerves is known to inhibit flexor reflex pathways in the spinal cord [10] as well as the long latency of C-fibre-evoked activity in dorsal horn cells [11, 12]. Contralateral dorsal horn cells are inhibited in response to noxious stimuli applied to the limb or tails of rats [13, 14]. Further electrophysiological studies confirm the presence of neurons in the dorsal horn that have bilateral receptive fields. Of relevance to this article is that the number of these neurons with bilateral receptive fields increases in the presence of unilateral inflammation [15, 16]. Grubb et al. [17] also showed that some of the fields on the contralateral side can become excitatory rather than inhibitory. At what level are these contralateral responses mediated? Woolf [16] documented the persistent reduction in flexor reflex thresholds contralaterally after noxious thermal stimuli had been applied to decerebrate rats with an intact brainstem. Fitzgerald [18], using a decerebrate, spinalized rat model, showed that a contralateral effect on dorsal horn fibres need not involve such higher pathways. Although direct contralateral spinal pathways exist in experimental conditions, there are likely to be significant supraspinal influences in vivo. This is suggested by several studies detailing an attenuation of central sensitization and secondary hyperalgesia following spinalization or inactivation of the rostral ventral medulla in a review of rat models of acute pain [19].

Extracellularly applied horseradish peroxidase increases the number of dense core vesicles in leech sensory neurons

The uptake of horseradish peroxidase (HRP), applied as an extracellular tracer, is a classical method for studying endo/exocytosis of synaptic vesicles at the ultrastructural level. It is generally not considered that HRP may affect neuronal function. Reported here is the finding that extracellularly applied HRP (0.1%) perturbs dense core vesicles in the synaptic processes of leech neurons. The strength of the effect varies with neuronal class. In sensory afferents, the number of dense core vesicles increases 5-fold, while there is only a 2-fold increase in central neurons.

Structure of reciprocal connections of visual cortical fields 17 and 18 in the cat.

Microiontophoretic application of horseradish peroxidase to individual columns in fields 17 and 18 of the cat cortex was used to identify the distribution by area and layer of retrograde labeled cells in both fields. After application of marker to fields 17 or 18, the area of labeled cells in field 17 (in the tangential plane) was extended and orientated along the projection of the horizontal meridian of the field of vision. The area of labeled cells in field 18 in these cases was orientated along the projections of the vertical meridian. Similar differences in the organization of the connections of fields 17 and 18 were seen in the projection zone of the central 10 degrees of the field of vision at different elevations. Thus, the spatial distributions of internal and external connections in each field coincide and their orientations in fields 17 and 18 are mutually perpendicular. It is suggested that field 17 performs the more detailed analysis of information on the horizontal components of an image and communicates this to field 18, while field 18 is responsible for the more detailed analysis of information about the vertical components of the same image, communicating this to field 17.

Endocytosis by absorptive cells in the middle segment of the suckling rat small intestine.

In neonatal suckling rats, the absorptive cells of the duodenum, jejunum and ileum endocytose maternal milk macromolecules, including antibodies from the lumen. To determine whether the absorptive cells from the middle segment of small intestine have an apical endocytic membrane system that is the same as that of the duodenum, jejunum or ileum, we applied horseradish peroxidase by intraluminal injection, and examined the absorptive cells using light and transmission electron microscopy. In the middle segment of the small intestine, the absorptive cells had an apical endocytic membrane system including apical coated pits, apical invaginations, coated vesicles, vesicles, tubules, early endosomes, late endosomes and a large homogeneous electron-dense lysosome at the supranuclear region. This would suggest that the endocytic membrane system in the absorptive cells from the middle segment of the small intestine is specialized for quick and active intracellular digestion. The apical endocytic membrane system of the absorptive cells varied according to the segment of the small intestine, and the absorptive cells made their transition gradually from jejunal type to middle type, and then from middle type to ileal type at the suckling stage. The jejunal and ileal type of absorptive cells increased with growth, in contrast to the middle type.

Kinetic studies on veratryl alcohol transformation by horseradish peroxidase.

A number of peroxidases, such as lignin peroxidase and manganese peroxidase have proved to be useful for industrial applications. Some studies on the effects of temperature and pH stability have been carried out. It is known that veratryl alcohol increases their stability in the range 28-50 degrees C and is oxidized, leading to veratryl aldehyde formation. Similar results with horseradish peroxidase (HRP) in the presence of cofactors were found, but the oxidation of veratryl alcohol in the absence of cofactors was extremely labile at acid pH and inactivated in a few minutes. Considering the growing industrial application of HRP, knowledge of its stability and denaturation kinetics is required. In this study, horseradish peroxidase pool (HRP-VI) and its isoenzymes HRP-VIII (acid) and HRP-IX (basic) have been shown to catalyze the oxidation of veratryl alcohol to veratryl aldehyde in the presence of hydrogen peroxide at pH 5.8 in the 35-45 degrees C range and in the absence of any cofactors. Heat and pH denaturation experiments in the presence and absence of veratryl alcohol incubation were conducted with HRP-VI and HRP-IX isoenzymes. HRP-IX was the most active isoenzyme acting on veratryl alcohol but HRP-VI was the most stable for the temperature range tested. At 35 degrees C the HRP pool presented decay constant (Kd) values of 5.5 x 10(-2) h(-1) and 1.4 10(-2) h(-1) in the absence and presence of veratryl alcohol, respectively, with an effective ratio of 3.9. These results present a new feature of peroxidases that opens one more interesting application of HRP to industrial processes.

Transport of epidurally applied horseradish peroxidase to the endoneurial space of dorsal root ganglia: A light and electron microscopic study

Abstract The route by which an epidurally applied macromolecule might reach the endoneurial space of spinal nerve roots was assessed with light and electron microscopy in a pig model established to explore the pathophysiology of disk herniation. Horseradish peroxidase (HRP) dissolved in saline was infused epidurally. Animals were sacrificed after 5 minutes (n = 5) or 30 minutes (n = 5). Two control animals received only a saline infusion and were sacrificed after 30 minutes. Nerve root specimens were collected, fixed, and exposed to the HRP substrate, 3.3′‐di‐amino‐benzidine (DAB). The distribution of HRP reaction product in the nerve tissue was studied with light and electron microscopy. In 5‐minute specimens, HRP was found in epidural and intradural vessel walls. At the nerve root level, HRP was detected in meningeal membranes but was not seen in periaxonal space. In addition to engaging the outer cell layers of the dorsal root ganglion (DRG) capsule, HRP was detected as a gradient among the peripherally located nerve cell bodies and sometimes among the emerging afferent axons. The 30‐minute group demonstrated similar findings. The results confirm that HRP can reach the periaxonal spaces of lumbar DRG within 5 minutes after epidural application. Although the transport mechanism is not fully understood, the DRG may constitute an anatomical location allowing epidurally applied macromolecules entrance to the endoneurial space, either by direct diffusion or via vascular transport. The demonstrated transport route may have implications in the pathophysiology of sciatica in conjunction with lumbar disc herniation.

Transport of epidurally applied horseradish peroxidase to the endoneurial space of dorsal root ganglia: a light and electron microscopic study.

The route by which an epidurally applied macromolecule might reach the endoneurial space of spinal nerve roots was assessed with light and electron microscopy in a pig model established to explore the pathophysiology of disk herniation. Horseradish peroxidase (HRP) dissolved in saline was infused epidurally. Animals were sacrificed after 5 minutes (n = 5) or 30 minutes (n = 5). Two control animals received only a saline infusion and were sacrificed after 30 minutes. Nerve root specimens were collected, fixed, and exposed to the HRP substrate, 3.3'-di-amino-benzidine (DAB). The distribution of HRP reaction product in the nerve tissue was studied with light and electron microscopy. In 5-minute specimens, HRP was found in epidural and intradural vessel walls. At the nerve root level, HRP was detected in meningeal membranes but was not seen in periaxonal space. In addition to engaging the outer cell layers of the dorsal root ganglion (DRG) capsule, HRP was detected as a gradient among the peripherally located nerve cell bodies and sometimes among the emerging afferent axons. The 30-minute group demonstrated similar findings. The results confirm that HRP can reach the periaxonal spaces of lumbar DRG within 5 minutes after epidural application. Although the transport mechanism is not fully understood, the DRG may constitute an anatomical location allowing epidurally applied macromolecules entrance to the endoneurial space, either by direct diffusion or via vascular transport. The demonstrated transport route may have implications in the pathophysiology of sciatica in conjunction with lumbar disc herniation.

Peroxidative degradation of selected PCB: a mechanistic study

The enzyme-induced decomposition and biodegradation of PCB were investigated. 2,5-Dichlorobiphenyl (PCB 9) and 2,2 ′,5,5 ′-tetrachlorobiphenyl (PCB 52) were used as example compounds to study efficiency and mechanism of the degradation processes. It was found that the application of horseradish peroxidase (HRP) together with defined amounts of hydrogen peroxide removed 90% of the initial concentration of PCB 9 and 55% of the initial concentration of PCB 52 from an aqueous solution after a reaction period of 220 min. Dechlorination was observed as the initial step. Although the metabolites identified were mainly chlorinated hydroxybiphenyls, benzoic acids and non-substituted 1,1 ′-biphenyl, some higher chlorinated biphenyl isomers also appeared. The biodegradation of PCB 9 using the white rot fungus Trametes multicolor took about four weeks and reduction was about 80% of the initial concentration. The metabolites produced (dichlorobenzenes, chlorophenols and alkylated benzenes) were not quite the same as those observed upon incubation with HRP.

Chronic dexamethasone treatment potentiates insult to olfactory receptor cells produced by 3-methylindole

The effect of chronic dexamethasone treatment on damage to olfactory receptor cells produced by 3-methylindole (3-MI) was examined. Twelve rats were injected, every other day, with dexamethasone (1.5 mg/kg, i.p.), and 12 rats with saline alone. Injections began 1 week before and continued, in different rats, from 1 to 4 weeks after a single intraperitoneal administration of 150 mg/kg 3-MI. One, two, three, and four weeks after exposure to 3-MI, different groups of rats, three specimens per each treatment condition, received bilateral application of horseradish peroxidase to the olfactory mucosa and were subsequently sacrificed. Anterograde labeling of primary afferents, i.e., an inverse correlate of the degree of cellular damage, was quantitatively determined by measuring the mean optical density (MOD) of staining in sections of the olfactory bulb. In saline-injected rats, the MOD values were 27.0, 46.6, 87.1, and 104.7 for one, two, three, and four post-3-MI weeks, respectively. The corresponding values in the dexamethasone-treated rats were 15.7, 29.7, 87.5, and 110.5. The MOD values of the dexamethasone-injected rats were significantly lower than those of the saline-injected rats for post-3-MI weeks 1 and 2, indicative of stronger damage to olfactory receptor cells in the rats treated with the glucocorticoid. The data suggest that dexamethasone potentiates the 3-MI olfactotoxicity during the first 2 weeks after insult. This effect, at least partly, may be due to the inducing action of dexamethasone on the cytochrome P450 responsible for metabolic bioactivation of 3-MI.

Relative number of cells projecting from contralateral and ipsilateral nucleus isthmi to loci in the optic tectum is dependent on visuotopic location: Horseradish peroxidase study in the leopard frog

The leopard frog optic tectum is the principal target of the contralateral retina. The retinal terminals form a topographic map of the visual field. The tectum also receives bilateral topographic input from a midbrain structure called nucleus isthmi. In this study we determined the relative strength of n. isthmi projections to different loci in the tectum. Horseradish peroxidase (HRP) was applied at single superficial tectal locations in a series of leopard frogs. The application sites were distributed across the tectum. Retrogradely filled cells were counted in ipsilateral and contralateral nucleus isthmi. Although all regions of the tectum receive input from both n. isthmi, the relative number of labeled cells in the two n. isthmi is dependent on visuotopic location. Input to the rostromedial tectum representing the visual field ipsilateral to the labeled tectum comes primarily from the contralateral n. isthmi. Input to the caudolateral tectum representing the visual field contralateral to the labeled tectum originates mostly from the ipsilateral n. isthmi. Tectal application sites representing the visual midline had approximately equal numbers of labeled cells in the two n. isthmi. The results are similar at postapplication survival times ranging from 2 to 14 days. Using application of HRP to rostral tectum and application of nuclear yellow to caudal tectum, we show that the anisotropy in isthmi labeling is not due to take up of these labels by isthmotectal fibers passing through the application sites that terminate elsewhere.

Anatomical and functional connectivity of the transected ulnar nerve after intercostal neurotization in cats.

Acute transfer of three intercostal nerves to the ulnar nerve was performed in cats for histological and clinical evaluation of a distal muscle reinnervation. Infraclavicular intercostal-ulnar communications were created after dividing the motor branches of the upper intercostal nerves in 14 adult cats. Reinnervation of distal forelimb muscles in the ulnar territory was assessed by electromyographic (EMG) studies and motor function rating each month until 18 months postsurgery. In five of these treated animals, and in tour controls, horseradish peroxidase (HRP) was applied to the ulnar or intercostal nerves to study the amount and distribution of retrograde motor neuron labeling in the spinal cord. Also, samples of reinnervated muscles and neurotized ulnar nerves were processed to assess regeneration. Simple ulnar transection without reconstruction led to permanent atrophy of ulnar muscles, lack of recovery according to EMG or clinical studies, and disappearance of the ulnar motor neuron pool. In contrast, ulnar neurotization with the intercostal nerves led to a high rate of functional recovery, which began 5 months postsurgery, and progressed from muscle activity synchronized with ventilatory movements to spontaneous movements that were independent of respiration. This recovery was accompanied by substantial retrograde labeling of intercostal motor neurons after HRP application in the ulnar nerve. Cell counts showed that practically the whole motor neuron pool of the involved intercostal nerves contributed to reinnervation of the transected ulnar nerve. These findings demonstrate that the use of intercostal nerves to neurotize long brachial plexus nerves can achieve long-lasting and successful reinnervation of distal forelimb muscles.

Evaluation of Hand Values of Cotton Weaves Treated by Enzyme Bleaching Agents.

Bleaching system applying horseradish peroxidase (HRP) was lately attracted industrial attention for its economizing energy and its significancy to protect the dye transfer. Since fabric mechanical properties should change during processing chemical treatment, it is worth to examine how the physical property changed. And this topic might be most important from the view point of fabric end-use. The fabric physical quality was evaluated objectively on the unfinished/finished cotton fabrics by using mechanical properties such as tensile, bending, shear, compressional and surface properties from the measurement. Unfinished sample and samples finished with two kinds of bleached system were prepared: one with a mixture of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) and the other with percarbonate. Fabric mechanical properties and hand values derived from physical values were compared among samples and discussed the effect of each systems on the fabric quality. A mixture of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) system reduced the fabrics hairiness and protected the disordering of intra -yarn. These structural change would reflect the high performance of handle values, which was higher than that of the other samples.

Anatomical regeneration and behavioral recovery following crush injury of the trigeminal root in lamprey

In normal larval lamprey, bilateral application of horseradish peroxidase (HRP) to the dorsal part of the anterior oral hood labeled subpopulations of trigeminal components on both sides of the brain; peripherally projecting motoneurons, medullary dorsal cells (sensory), and spinal dorsal cells (sensory), as well as centrally projecting afferents in the trigeminal descending tracts. Following unilateral crush injury of the right trigeminal root, HRP labeling of sensory and motor trigeminal components on the right side gradually increased with increasing recovery time, between 2 weeks and 12 weeks postcrush (PC). Axons of trigeminal motoneurons appeared to exhibit robust regeneration, whereas restoration of projections in the descending trigeminal tract ipsilateral to the injury was incomplete. Control experiments indicated that motor and sensory axons from the intact side of the oral hood did not sprout across the midline to the denervated side. Several results suggested that regenerated trigeminal sensory fibers made synapses with brain neurons that have direct or indirect inputs to reticulospinal (RS) neurons. Following a unilateral crush injury of the right trigeminal root, escape behavior in response to stimulation of the right side of the oral hood gradually returned to normal. Muscle recordings at various recovery times confirmed that anatomical regeneration of trigeminal sensory axons was functional. In addition, at 8 or 12 weeks PC, brief stimulation of the oral hood ipsilateral or contralateral to the crush injury elicited synaptic responses in RS neurons on either side of the brain, similar to that in normal animals. In the lamprey, compensatory mechanisms probably allow recovery of behavioral function despite incomplete regeneration of trigeminal sensory axons within the central nervous system.

Endolymphatic Hydrops Reduces Retrograde Labeling of Trigeminal Innervation to the Cochlea

This paper reports that endolymphatic hydrops causes a significant reduction of retrogradely labeled cell bodies of the ipsilateral trigeminal ganglion following application of horseradish peroxidase in the cochlea. We previously showed that the trigeminal ganglion is a source of primary sensory innervation to the cochlear blood vessels. The innervation of the cochlea from the trigeminal ganglion may provide the basis of an alternative mechanism for Ménière's syndrome (imbalance, hearing loss, tinnitus, and a sensation of fullness in the ear) for which a central neural basis has been speculated. Innervation patterns of sensory nerves from the trigeminal ganglion to the cochlear blood vessels were studied using retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Healthy and hydropic guinea pigs were unilaterally implanted with an osmotic pump and a cannula for cochlear delivery of 2% WGA-HRP or vehicle alone. In other guinea pigs the cochlea was pretreated with 100 μmol capsaicin before administering 2% WGA-HRP. Histological sections of the ipsi- and contralateral trigeminal ganglia were obtained 48 h after WGA-HRP infusion. In the hydropic guinea pig, the number of labeled nerve cell bodies observed in the anteriomedial portion of the trigeminal ganglion at the origin of the ophthalmic nerve was reduced by 70% relative to normal animals. Capsaicin pretreatment nearly eliminated the labeled sensory fibers as expected. These data indicate that the trigeminal innervation to the cochlea could be involved in inner ear homeostatic disturbances, including the hydrops that is symptomatic of Ménière's disease.