Cephalic Nerves Research Articles

Infraorbital nerve injury triggers sex-specific neuroimmune responses in the peripheral trigeminal pathway and common pain behaviours

Trigeminal neuropathic pain is emotionally distressing and disabling. It presents with allodynia, hyperalgesia and dysaesthesia. In preclinical models it has been assumed that cephalic nerve constriction injury shows identical molecular, cellular, and sex dependent neuroimmune changes as observed in extra-cephalic injury models. This study sought empirical evidence for such assumptions using the infraorbital nerve chronic constriction model (ION-CCI). We compared the behavioural consequences of nerve constriction with: (i) the temporal patterns of recruitment of macrophages and T-lymphocytes at the site of nerve injury and in the trigeminal ganglion; and (ii) the degree of demyelination and axonal reorganisation in the injured nerve. Our data demonstrated that simply testing for allodynia and hyperalgesia as is done in extra-cephalic neuropathic pain models does not provide access to the range of injury-specific nociceptive responses and behaviours reflective of the experience of trigeminal neuropathic pain. Similarly, trigeminal neuroimmune changes evoked by nerve injury are not the same as those identified in models of extra-cephalic neuropathy. Specifically, the timing, magnitude, and pattern of ION-CCI evoked macrophage and T-lymphocyte activity differs between the sexes.

Morphological and genetic variation of Wuchereria bancrofti microfilariae in carriers in Thailand, Lao PDR and Myanmar: evaluation using Giemsa-stained thick blood films.

There is geographical variation in the morphology and genetics of Wuchereria bancrofti, the major cause of human lymphatic filariasis. This study aims to compare morphological and genetic variation of W. bancrofti microfilariae recovered from carriers in Lao PDR, Myanmar and Thailand. Six morphological parameters (body length, cephalic space length and width, length of head to nerve ring, body width at nerve ring, Innenkȍrper length and number of column nuclei between the cephalic space and nerve ring) were evaluated from microfilariae in Giemsa-stained thick blood films. A portion of the cytochrome c oxidase subunit 1 gene of mitochondrial DNA was sequenced and analysed. Wuchereria bancrofti microfilariae showed a wide variation in their morphology and morphometry among three countries. Phylogenetic analysis confirmed that all microfilariae belonged to W. bancrofti. Higher mutation frequencies were observed in samples from Myanmar, relative to Thailand and Lao PDR. This study highlights the morphological disparities of microfilariae and genetic variability within W. bancrofti among three geographical locations. We found that reported morphometric differences between localities were less clear-cut than previously thought. Further studies are needed to determine the microfilarial periodicity in Lao PDR.

NO‐ting a putative mechanism by which anti‐migraine drugs mitigate trigeminal neuropathic pain

<scp>NO</scp>‐ting a putative mechanism by which anti‐migraine drugs mitigate trigeminal neuropathic pain

Low Voltage Vagal Nerve Stimulation Reduces Bronchoconstriction in Guinea Pigs Through Catecholamine Release

Electrical stimulation of the vagus nerve at relatively high voltages (e.g., >10 V) can induce bronchoconstriction. However, low voltage (≤2 V) vagus nerve stimulation (VNS) can attenuate histamine-invoked bronchoconstriction. Here, we identify the mechanism for this inhibition. In urethanea-nesthetized guinea pigs, bipolar electrodes were attached to both vagus nerves and changes in pulmonary inflation pressure were recorded in response to i.v. histamine and during VNS. The attenuation of the histamine response by low-voltage VNS was then examined in the presence of pharmacologic inhibitors or nerve ligation. Low-voltage VNS attenuated histamine-induced bronchoconstriction (4.4 ± 0.3 vs. 3.2 ± 0.2 cm H(2) O, p < 0.01) and remained effective following administration of a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, and after sympathetic nerve depletion with guanethidine, but not after the β-adrenoceptor antagonist propranolol. Nerve ligation caudal to the electrodes did not block the inhibition but cephalic nerve ligation did. Low-voltage VNS increased circulating epinephrine and norepinephrine without but not with cephalic nerve ligation. These results indicate that low-voltage VNS attenuates histamine-induced bronchoconstriction via activation of afferent nerves, resulting in a systemic increase in catecholamines likely arising from the adrenal medulla.

Presence and distribution of serotonin immunoreactivity in the cyprids of the barnacle Balanus amphitrite

In this work, the presence and distribution of serotonin in the cyprid of the barnacle Balanus amphitrite were investigated by immunohistochemical methods. Serotonin-like immuno-reactive neuronal cell bodies were detected in the central nervous system only. Various clusters of immunoreactive neuronal cell bodies are distributed in the brain (protocerebrum, deutocerebrum, optical lobes), and at least, four pairs of neuronal cell bodies were detected in the centrally positioned neuropil of the posterior ganglion. Rich plexuses of immunoreactive nerve fibers in the neuropil area were also observed. Furthermore, bundles of strongly immunoreactive nerve fibers surrounding the gut wall were localized, and immunoreactive nerve terminals in the antennules and compound eyes were observed. These data demonstrate the presence of a serotonin-like immunoreactive substance in the barnacle cyprids; furthermore, its immunolocalization in the cephalic nerve terminals allows us to postulate the involvement of this bioactive molecule in substrate recognition during the settlement process.

Bitter substances suppress afferent responses to an appetitive mixture: evidence for peripheral integration of chemosensory stimuli.

The processes that lead from detection of chemicals, transduction, and coding with the appropriate message to initiate ingestion of a palatable meal or to reject a potentially noxious substance are poorly understood in vertebrates owing to the complex organization of the taste system. As a first step in elucidating the cellular basis of the behavioral differences elicited by appetitive stimuli and bitter compounds, we recorded from the afferent nerves conveying peripheral chemosensory information to the CNS in the head of the leech, Hirudo medicinalis. Superfusion of the chemosensory region of the lip of Hirudo with a mixture of NaCl (150 mM) and arginine (1 mM), an appetitive solution that elicits ingestion, increased the neuronal activity in the afferent cephalic nerves, for example (Zhang X, Wilson RJ, Li Y, Kleinhaus AL. 2000. Chemical and thermal stimuli have short-lived effects on the Retzius cell in the medicinal leech. J Neurobiol 43:304-311.). In the present paper we show that superfusing the lip with quinine or denatonium reduced the basal neural activity in the afferents. Furthermore, these bitter substances in the appetitive solution counteracted the increased activity the appetitive solution evoked in the cephalic nerves. Thus, the neural activity evoked by the application of appetitive and aversive stimuli to the chemosensory area of the lip paralleled the opposite behavioral responses to the same chemicals. The results suggest that individual leech taste cells possess receptors for both types of stimuli. Therefore, the leech may be a good model system in which to study peripheral taste events in cells that may possess multiple receptors and transduction mechanisms that interact to integrate information.

Onychophoran cephalic nerves and their bearing on our understanding of head segmentation and stem-group evolution of Arthropoda

The extant Onychophora are basal representatives of the Arthropoda, resembling Cambrian arthropod stem-group fossils such as Aysheaia and other so-called lobopodians. They thus provide an important model system for early stages in arthropod evolution, especially those of the head. However, homologies between onychophoran and euarthropod head structures have remained uncertain, and previous descriptions of the onychophoran head are contradictory. Our investigation examines the cephalic nerves of two species of onychophoran using immunohistochemical and confocal laser scanning microscopical techniques. Our new reconstruction for the distribution of onychophoran cephalic nerves differs significantly from previous accounts. The so-called “labrum” of the Onychophora appears to be part of the pharynx, and any affinities to the various pre-oral outgrowths of crown-group arthropods referred to as hypostomata and/or labra can be ruled out. The innervation of the mouth is particularly noteworthy, as its nerves originate from three different regions of the brain, including the dorsum. This suggests that the mouth was primitively terminal/frontal, although subsequent ventral rotation of the mouth may have been parallelly achieved in Onychophora and in Euarthropoda. Our model allows the onychophoran cephalic nervous system to be interpreted as a modified circumoral nerve ring, similar to that seen in the nematodes and other cycloneuralians. We regard this as supporting the Ecdysozoa model of arthropod relationships.

Chemical and thermal stimuli have short-lived effects on the Retzius cell in the medicinal leech

During the appetitive phase of feeding, hungry leeches detect a prey by the integration of signals perceived by different sensory systems. Earlier reports suggested that chemical or thermal sensory stimulation of the lip was associated with increased afferent activity in cephalic nerves connecting the lip to the central nervous system. These authors further suggested that this activity was relayed to Retzius cells in segmental ganglia, which then released serotonin to initiate and control all aspects of feeding behavior. In this study, we show that chemosensory or thermal activation of the lip lasting for at least 5 min produces a distinct signal in the cephalic nerves consisting of action potentials of low amplitude. These small amplitude signals are clearly distinguishable from the large action potentials evoked by mechanosensory stimuli applied to the same area of the lip. Both types of sensory stimuli also evoke an increase in the firing frequency of the Retzius cells in segmental ganglia. However, the response recorded in the nerves and the Retzius cells during a maintained stimulus is not constant but decreases with an exponential time course. These results agree with our earlier observations on a semi-intact feeding preparation in which we showed that the firing frequency of the Retzius cell decreased as soon as the leech began to ingest its meal. Therefore, our data provide further evidence suggesting that it is unlikely that heat or chemical cues maintain the Retzius cell in an active state throughout the consummatory phase of feeding. © 2000 John Wiley & Sons, Inc. J Neurobiol 43: 304–311, 2000

Chemical and thermal stimuli have short-lived effects on the Retzius cell in the medicinal leech

During the appetitive phase of feeding, hungry leeches detect a prey by the integration of signals perceived by different sensory systems. Earlier reports suggested that chemical or thermal sensory stimulation of the lip was associated with increased afferent activity in cephalic nerves connecting the lip to the central nervous system. These authors further suggested that this activity was relayed to Retzius cells in segmental ganglia, which then released serotonin to initiate and control all aspects of feeding behavior. In this study, we show that chemosensory or thermal activation of the lip lasting for at least 5 min produces a distinct signal in the cephalic nerves consisting of action potentials of low amplitude. These small amplitude signals are clearly distinguishable from the large action potentials evoked by mechanosensory stimuli applied to the same area of the lip. Both types of sensory stimuli also evoke an increase in the firing frequency of the Retzius cells in segmental ganglia. However, the response recorded in the nerves and the Retzius cells during a maintained stimulus is not constant but decreases with an exponential time course. These results agree with our earlier observations on a semi-intact feeding preparation in which we showed that the firing frequency of the Retzius cell decreased as soon as the leech began to ingest its meal. Therefore, our data provide further evidence suggesting that it is unlikely that heat or chemical cues maintain the Retzius cell in an active state throughout the consummatory phase of feeding.

Variations in microfilariae and infective stages of two types of Wuchereria bancrofti from the Thai-Myanmar border

Comparative morphometric and morphological studies of microfilariae and infective stages were undertaken in nocturnally periodic and subperiodic Wuchereria bancrofti. For microfilariae, the body dimensions of nocturnally periodic (NP) were significantly smaller than nocturnally subperiodic (NSP), i.e., body length 268.03+/-14.75 microm (NP), 307.61+/-11.52 microm (NSP); cephalic space length 4.21+/-0.62 microm (NP), 5.32+/-0.79 microm (NSP); head to nerve ring 49.39+/-5.43 microm (NP), 57.40+/-4.46 microm (NSP); innenkörper length 33.05+/-5.89 microm (NP), 44.02+/-8.71 microm (NSP); cephalic space width 4.28+/-0.59 microm (NP), 6.04+/-0.68 microm (NSP); body width at nerve ring 5.01+/-0.57 microm (NP), 7.45+/-0.75 microm (NSP). The number of nuclei between the cephalic space and nerve ring of NP (66.67+/-5.19) was also significantly less than in NSP (94.74+/-6.95). For infective stages, the body dimensions of NP were significantly smaller than NSP, i.e., body length 1632.50+/-131.48 microm (NP), 2002.63+/-222.60 microm (NSP); head to nerve ring 103.09+/-7.47 microm (NP), 122.44+/-9.62 microm (NSP); head to oesophago-intestinal junction 567.69+/-94.84 microm (NP), 666.75+/-110.08 microm (NSP); body width at oesophago-intestinal junction 23.15+/-1.55 microm (NP), 26.78+/-1.62 microm (NSP). It is too early to infer the NP type as an additional sibling species of W. bancrofti but it is reasonable to treat it as a new variety and additional work is needed to clarify its status.

Anatomical pathways connecting lip sensory structures and central nervous system in hirudinid leeches visualized by carbocyanine dyes and laser scanning confocal microscopy.

Chemoreception in Hirudo medicinalis is thought to be mediated by ciliated cells grouped in sensory structures, the sensilla, arranged in bands on the animal's dorsal lip (Elliott, 1986; Zipser et al., 1994). Furthermore, chemical and/or thermal stimulation of the dorsal lip in reduced preparations evokes changes in the electrical activity of the cephalic nerves that connect the head with the central nervous system. However, the complete trajectory by which the sensory afferents reach the cerebral ganglia has not been demonstrated anatomically. In this study, we traced these pathways following retrograde and/or anterograde transport of carbocyanine dyes (DiI, DiA and DiD) in the cephalic nerves of Hirudo medicinalis and a closely related species, Macrobdella decora. While information regarding Macrobdella's chemoreception is scarce, the two species show some differences with regard to their chemical preferences. Dyes were applied to the sensillar structures along the dorsal lip, or to the cut ends of individual cephalic nerves in fixed preparations that included the lip and attached nerves with or without the head ganglia. After a two week incubation, specimens were mounted and imaged using a confocal microscope. The results show that the axons of the sensory neurons in the sensilla project through the four pairs of cephalic nerves. The sensillar projections are however more numerous in the dorsal nerves than they are in the ventral ones. In addition, the organization of the sensillar bands, the morphology of the pathways and the sensory structures themselves appear to be identical for Hirudo and Macrobdella and therefore the behavioral differences in response to appetitive stimuli cannot be readily explained by differences in morphology.

Glutamate as a transmitter in the sensory pathway from prostomial lip to serotonergic Retzius neurons in the medicinal leech Hirudo.

The involvement of glutamate in putative ingestive sensory pathways affecting the excitability of serotonergic Retzius neurons (RZ) in the leech CNS was investigated with a pharmacological approach. Exposure of the prostomial lip to 150 mM NaCl and 1 mM arginine produced excitatory as well as inhibitory responses in RZ found in the reproductive segments, while only excitatory responses were elicted in standard midbody RZ. Antagonists of glutamatergic receptors of the kainate/quisqualate type effectively inhibited chemosensory dependent excitation of RZ. Antagonists of glutamatergic receptors of the N-methyl D-aspartate type were ineffective in this regard. Cephalic nerve stimulation, like chemical stimulation of the lip, produced segment-specific responses in midbody RZ. Both the polysynaptic and monosynaptic components of the excitatory response of standard midbody RZ following cephalic nerve stimulation were inhibited in the presence of the kainate/quisqualate antagonist DNQX. These data suggest a role for glutamate as a transmitter in the neural circuitry from receptors of the leech prostomial lip to serotonergic RZ.

Dextran backfill tracers combined with Lucifer Yellow injections for neuroanatomic studies of the leech head ganglion

Several neuronal tracing substances were applied to the cut ends of leech cephalic nerves and the resulting backfills into the subesophageal ganglion (sbEG) were mapped. A 12 h incubation in 3 kDa dextrans conjugated either to a fluorochrome or to biotin (subsequently tagged with peroxidase) was satisfactory. In separate experiments, possible targets of cephalic nerve afferents (R3 Retzius neurons) were injected with Lucifer Yellow (LY) to visualize their projections. Comparison of the LY-R3 Retzius neuron map with that of the dextran-backfilled D 1 nerve revealed extensive overlap in the sbEG. Experiments were performed combining the two protocols, confirming this observation. Moreover, confocal microscopy placed D 1 nerve processes in close proximity to R3 Retzius neuron processes, suggesting that they could make synaptic contact with one another in the sbEG. With modifications, this method could be used to identify such contacts using electron microscopy.

Dextran backfill tracers combined with Lucifer Yellow injections for neuroanatomic studies of the leech head ganglion

Several neuronal tracing substances were applied to the cut ends of leech cephalic nerves and the resulting backfills into the subesophageal ganglion (sbEG) were mapped. A 12 h incubation in 3 kDa dextrans conjugated either to a fluorochrome or to biotin (subsequently tagged with peroxidase) was satisfactory. In separate experiments, possible targets of cephalic nerve afferents (R3 Retzius neurons) were injected with Lucifer Yellow (LY) to visualize their projections. Comparison of the LY-R3 Retzius neuron map with that of the dextran-backfilled D 1 nerve revealed extensive overlap in the sbEG. Experiments were performed combining the two protocols, confirming this observation. Moreover, confocal microscopy placed D 1 nerve processes in close proximity to R3 Retzius neuron processes, suggesting that they could make synaptic contact with one another in the sbEG. With modifications, this method could be used to identify such contacts using electron microscopy.

Ingestive Sensory Inputs Excite Serotonin Effector Neurones and Promote Serotonin Depletion From the Leech Central Nervous System and Periphery

Thermal and chemical stimuli known to promote ingestive behaviours in the medicinal leech Hirudo medicinalis were tested for their physiological effects on Retzius neurones and for their biochemical effects on serotonin levels in the central nervous system, pharynx and body wall. Retzius neurones throughout the leech nerve cord receive excitatory synaptic input during thermal or chemical stimulation of the prostomial lip. These neurones respond to the rate of change of temperature as well as to absolute temperature at the lip. Exposure of the lip to sodium chloride excites Retzius neurones, whereas exposure to arginine has little effect. Thermal stimulation of the lip elicits a more rapid but less prolonged excitation of Retzius neurones than does chemical stimulation. Stimulation of the prostomial lip is associated with afferent activities in the cephalic nerves D1, D2 and V1-2. Thermal stimulation of the prostomial lip results in depletion of serotonin from midbody ganglia, whereas chemical stimulation has no effect. Conversely, chemical stimulation of the lip results in depletion of serotonin from the body wall, whereas thermal stimulation does not. Pharyngeal serotonin content is decreased with either modality. These data distinguish two important feeding-related sensory input pathways to central serotonergic effector neurones in Hirudo medicinalis.

Neuronal pathways of classical crustacean neurohormones in the central nervous system of the woodlouse, Oniscus asellus (L.)

Neuropeptide-immunoreactive neurons have been mapped by immunocytochemistry in whole-mount preparations and sections of the central nervous system of Oniscus asellus . We tested rabbit antisera against decapod crustacean hyperglycemic hormone (CHH), moult inhibiting hormone (MIH ), pigment dispersing hormone (PDH) and red pigment concentrating hormone (RPCH). four CHH- and three PDH-immunoreactive neurons localized in the superior median protocerebrum of the brain constitute neurosecretory pathways to the neurohaemal sinus gland. No immunoreactive structures have been detected with an antiserum against MIH of Carcinus maenus . Another, newly identified neurosecretory pathway is formed by a group of RPCH-immunoreactive neurons in the mandibular ganglion. These neurons project to the neurohaemal lateral cephalic nerve plexus, further PDH- and RPCH-immunoreactive neurons and fibres occur in the brain and the ventral nerve cord (VNC). Two groups of PDH-immunoreactive neurons supply brain and optic lobe neuropils, the bases of the ommatidia, and probably give rise to descending fibres innervating all VNC-neuropils. Two groups and five individuals of RPCH-immunoreactive neurons that innervate several brain neuropils or occur as ascending neurons in the VNC have been reconstructed. The CHH-immunoreactive neurons, and distinct types of PDH- and RPCH-immunoreactive neurons obviously belong to classical hormone-producing neurosecretory pathways. At least the CHH-immunoreactive cells seem to be part of an isopod homologue of the decapod X-organ. The existence of other PDH- and RPCH-immunoreactive interneurons suggests additional functions of these peptides as neurotransmitters or neuromodulators, which is in agreement with similar observations in the decapod central nervous system.

Distribution of FMRF-amide-like peptide in the nervous system of a mermithid nematode, Romanomermis culicivorax.

The nervous system of the mermithid nematode Romanomermis culicivorax was investigated at different developmental stages for the distribution of the neuropeptide FMRF-amide. An FMRF-amide-like peptide was detected by an indirect immunofluorescence technique. The peptidergic nervous system increased in complexity during development. In adults, FMRF-amide-like peptide was present in the nerve ring, cephalic papillary ganglia, cephalic nerves, amphids, ganglia posterior to the nerve ring, longitudinal nerve cords and several mid-body region ganglia. The distribution of peptidergic ganglia in the tail region was different for each sex. Four clusters of ganglia were present in the tail of females, whereas such ganglia were absent in the tail of males. The results suggest that FMRF-amide-like peptide is widely distributed within the nervous system of R. culicivorax and might function as a neurohormone or neurotransmitter in controlling physiological and developmental processes.

Distribution of catecholamine(s) in the nervous system of a mermithid nematode, Romanomermis culicivorax.

The nervous system of the mermithid nematode Romanomermis culicivorax was investigated at different developmental stages for the distribution of catecholamine(s). The catecholaminergic nervous system increased in complexity during development. In the adult nematode, catecholamine(s) occurred in the nerve ring and associated ganglia, cephalic nerves, ventral and dorsal nerve cords and mid-body region ganglia. The distribution of catecholaminergic ganglia in the tail region was different for each sex. The tail region of males contained 16-20 catecholaminergic ganglia, whereas the tail of females contained only 2 ganglia. The catecholamine widely distributed throughout the nervous system of R. culicivorax is not dopamine, since immunoreactivity to dopamine was observed only in the amphids. The results suggest that the catecholamine(s) is widely distributed within the nervous system of R. culicivorax and might function as a neurohormone or neurotransmitter in controlling physiological and developmental processes.

Note On Some Anatomical Features (Neurosecretory Organs and Median Ocelli) of Paramphisopus Palustris (Glauert, 1924) (Isopoda, Phreatoicidae)

Previous studies of the endocrine organs and frontomedial ocelli of the Isopoda revealed that structural differences exist in the hitherto observed suborders. The Phreatoicidea, the oldest known suborder, are studied for the first time. A Bellonci organ was not discovered. The sinus gland has a globular form, it seems to be linked with the lateral cephalic nerve plexus. Similar sinus glands are known from the Oniscidea. The median ocelli are reduced to the number of 3, while other Isopoda may have 2 to maximally 5 ocelli.

Immunocytochemical studies of the distribution of acetylcholine in the crayfish brain.

A number of studies indicate that acetylcholine is an important transmitter in most crustacean primary afferents and in at least several central pathways. Little is known, however, regarding the structure or distribution of cholinergic pathways in the central nervous system. The recent introduction of antibodies to choline-protein conjugates provides a potentially powerful means for localizing putative cholinergic neurons and pathways in the nervous system. Acetylcholine was localized with immunocytochemical procedures in the axons and terminals of cephalic primary afferents and in interneurons of the crayfish brain. The most intensely reactive loci were the primary sensory neuropiles, which contain the terminals of the statocyst afferents (parolfactory lobes) and antennal afferents (antennal lobe). These results are generally in accord with previous findings based upon choline uptake and enzyme assay in lobster cephalic nerves. We also found evidence consistent with the presence of acetylcholine in the globular interneurons of the accessory lobe and in descending interneurons which originate in the dorsal medial and anterior clusters of the protocerebrum. The axons of several neurons in the circumesophageal connective (descending interneurons and primary afferents) are also reactive to the choline antibody.