Electrophysiological properties and synaptic responses of cells in the trigeminal principal sensory nucleus of postnatal rats.
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In the rodent brain stem trigeminal complex, select sets of neurons form modular arrays or "barrelettes," that replicate the patterned distribution of whiskers and sinus hairs on the ipsilateral snout. These cells detect the patterned input from the trigeminal axons that innervate the whiskers and sinus hairs. Other brain stem trigeminal cells, interbarrelette neurons, do not form patterns and respond to multiple whiskers. We examined the membrane properties and synaptic responses of morphologically identified barrelette and interbarrelette neurons in the principal sensory nucleus (PrV) of the trigeminal nerve in early postnatal rats shortly after whisker-related patterns are established. Barrelette cell dendritic trees are confined to a single barrelette, whereas the dendrites of interbarrelette cells span wider territories. These two cell types are distinct from smaller GABAergic interneurons. Barrelette cells can be distinguished by a prominent transient A-type K(+) current (I(A)) and higher input resistance. On the other hand, interbarrelette cells display a prominent low-threshold T-type Ca(2+) current (I(T)) and lower input resistance. Both classes of neurons respond differently to electrical stimulation of the trigeminal tract. Barrelette cells show either a monosynaptic excitatory postsynaptic potential (EPSP) followed by a large disynaptic inhibitory postsynaptic potential (IPSP) or just simply a disynaptic IPSP. Increasing stimulus intensity produces little change in EPSP amplitude but leads to a stepwise increase in IPSP amplitude, suggesting that barrelette cells receive more inhibitory input than excitatory input. This pattern of excitation and inhibition indicates that barrelette cells receive both feed-forward and lateral inhibition. Interbarrelette cells show a large monosynaptic EPSP followed by a small disynaptic IPSP. Increasing stimulus intensity leads to a stepwise increase in EPSP amplitude and the appearance of polysynaptic EPSPs, suggesting that interbarrelette cells receive excitatory inputs from multiple sources. Taken together, these results indicate that barrelette and interbarrelette neurons can be identified by their morphological and functional attributes soon after whisker-related pattern formation in the PrV. (+info)
Hemispheric lateralization in the processing of odor pleasantness versus odor names.
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It is well established that for most people linguistic processing is primarily a left hemisphere activity, whereas recent evidence has shown that basic odor perception is more lateralized to the right hemisphere. Importantly, under certain conditions, emotional responding also shows right hemisphere laterality. Hedonic (pleasantness) assessments constitute basic level emotional responses. Given that olfaction is predominantly ipsilateral in function, it was hypothesized that odor pleasantness evaluations may be accentuated by right nostril perception and that odor naming would be superior with left nostril perception. To test this prediction we presented eight familiar neutral-mildly pleasant odors for subjects to sniff through the left and right nostrils. Subjects smelled each odor twice (once through each nostril) at two different sessions, separated by 1 week. At each session subjects provided pleasantness, arousal and naming responses to each odorant. Results revealed that odors were rated as more pleasant when sniffed through the right nostril and named more correctly when sniffed through the left. No effects for arousal were obtained. These findings are consistent with previously demonstrated neural laterality in the processing of olfaction, emotion and language, and suggest that a local and functional convergence may exist between olfaction and emotional processing. (+info)
Assessing the impact of anosmia: review of a questionnaire's findings.
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The inability to detect odours, anosmia, can cause profound psychological effects resulting in feelings of physical and social vulnerability and victimization. In addition, there may be unhappiness related to the loss of the ability to detect pleasurable food smells and, as a consequence, anosmics may develop problems relating to eating. These profound effects arise from a condition which can have a rapid onset and a very poor prognosis for recovery, and are largely treated with a lack of sympathy and indifference by people with normal olfactory ability. In an attempt to educate, inform and help sufferers, a questionnaire was developed in the early 1980s and sent to those who contacted the Warwick Olfaction Research Group. The responses from this questionnaire form the basis of this review. Feelings of personal isolation, lack of interest in eating and emotional blunting were common responses from these sufferers and it seems that we still have some way to go before an adequate recognition of problems associated with anosmia is gained by the general population and, more importantly, within the medical profession. (+info)
Microvascular decompression for trigeminal neuralgia: comments on a series of 250 cases, including 10 patients with multiple sclerosis.
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OBJECTIVE: To examine surgical findings and results of microvascular decompression (MVD) for trigeminal neuralgia (TN), including patients with multiple sclerosis, to bring new insight about the role of microvascular compression in the pathogenesis of the disorder and the role of MVD in its treatment. METHODS: Between 1990 and 1998, 250 patients affected by trigeminal neuralgia underwent MVD in the Department of Neurosurgery of the "Istituto Nazionale Neurologico C Besta" in Milan. Limiting the review to the period 1991-6, to exclude the "learning period" (the first 50 cases) and patients with less than 1 year follow up, surgical findings and results were critically analysed in 148 consecutive cases, including 10 patients with multiple sclerosis. RESULTS: Vascular compression of the trigeminal nerve was found in all cases. The recurrence rate was 15.3% (follow up 1-7 years, mean 38 months). In five of 10 patients with multiple sclerosis an excellent result was achieved (follow up 12-39 months, mean 24 months). Patients with TN for more than 84 months did significantly worse than those with a shorter history (p<0.05). There was no mortality and most complications occurred in the learning period. Surgical complications were not related to age of the patients. CONCLUSIONS: Aetiopathogenesis of trigeminal neuralgia remains a mystery. These findings suggest a common neuromodulatory role of microvascular compression in both patients with or without multiple sclerosis rather than a direct causal role. MVD was found to be a safe and effective procedure to relieve typical TN in patients of all ages. It should be proposed as first choice surgery to all patients affected by TN, even in selected cases with multiple sclerosis, to give them the opportunity of pain relief without sensory deficits. (+info)
Visualization of cranial motor neurons in live transgenic zebrafish expressing green fluorescent protein under the control of the islet-1 promoter/enhancer.
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We generated germ line-transmitting transgenic zebrafish that express green fluorescent protein (GFP) in the cranial motor neurons. This was accomplished by fusing GFP sequences to Islet-1 promoter/enhancer sequences that were sufficient for neural-specific expression. The expression of GFP by the motor neurons in the transgenic fish enabled visualization of the cell bodies, main axons, and the peripheral branches within the muscles. GFP-labeled motor neurons could be followed at high resolution for at least up to day four, when most larval neural circuits become functional, and larvae begin to swim and capture prey. Using this line, we analyzed axonal outgrowth by the cranial motor neurons. Furthermore, by selective application of DiI to specific GFP-positive nerve branches, we showed that the two clusters of trigeminal motor neurons in rhombomeres 2 and 3 innervate different peripheral targets. This finding suggests that the trigeminal motor neurons in the two clusters adopt distinct fates. In future experiments, this transgenic line of zebrafish will allow for a genetic analysis of cranial motor neuron development. (+info)
Evidence for nicotinic acetylcholine receptors on nasal trigeminal nerve endings of the rat.
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The peripheral chemoreceptors of the trigeminal system in the nasal cavity are presumed to be free nerve endings arising from Adelta and C fibers. These fibers appear to be scattered throughout the nasal epithelium, and arise from the nasopalatine and ethmoid branches of the trigeminal nerve. In the present study, the effects of nicotinic acetylcholine receptor (nAChR) blockers on ethmoid nerve responses to nicotine and cyclohexanone were examined. Multiunit neural recordings were obtained from the ethmoid nerve of Sprague-Dawley rats. Vapor-phase nicotine (12.5 p.p.m.) and cyclohexanone (450 p.p. m.) were delivered to the rats' nares via an air-dilution olfactometer. The magnitude of the response to nicotine decreased after the administration of the nAChR blockers dihydro-beta-erythroidine hydrobromide (DHBE) and mecamylamine hydrochloride. DHBE is a competitive nicotinic receptor antagonist specific for the alpha4beta2 receptor subtype and mecamylamine is known to bind alpha3beta4 and alpha4beta2 receptors. The nAChR blockers had no effect on ethmoid nerve responses to cyclohexanone. These results suggest that the mechanism by which at least one irritant stimulates nasal trigeminal nerve endings involves the binding of irritant with a specific receptor. (+info)
Identification of maxillary factor, a maxillary process-derived chemoattractant for developing trigeminal sensory axons.
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Trigeminal sensory axons project to several epithelial targets, including those of the maxillary and mandibular processes. Previous studies identified a chemoattractant activity, termed Maxillary Factor, secreted by these processes, which can attract developing trigeminal axons in vitro. We report that Maxillary Factor activity is composed of two neurotrophins, neurotrophin-3 (NT-3) and Brain-Derived Neurotrophic Factor (BDNF), which are produced by both target epithelium and pathway mesenchyme and which are therefore more likely to have a trophic effect on the neurons or their axons than to provide directional information, at least at initial stages of trigeminal axon growth. Consistent with this, the initial trajectories of trigeminal sensory axons are largely or completely normal in mice deficient in both BDNF and NT-3, indicating that other cues must be sufficient for the initial stages of trigeminal axon guidance. (+info)
Acute and chronic craniofacial pain: brainstem mechanisms of nociceptive transmission and neuroplasticity, and their clinical correlates.
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This paper reviews the recent advances in knowledge of brainstem mechanisms related to craniofacial pain. It also draws attention to their clinical implications, and concludes with a brief overview and suggestions for future research directions. It first describes the general organizational features of the trigeminal brainstem sensory nuclear complex (VBSNC), including its input and output properties and intrinsic characteristics that are commensurate with its strategic role as the major brainstem relay of many types of somatosensory information derived from the face and mouth. The VBSNC plays a crucial role in craniofacial nociceptive transmission, as evidenced by clinical, behavioral, morphological, and electrophysiological data that have been especially derived from studies of the relay of cutaneous nociceptive afferent inputs through the subnucleus caudalis of the VBSNC. The recent literature, however, indicates that some fundamental differences exist in the processing of cutaneous vs. other craniofacial nociceptive inputs to the VBSNC, and that rostral components of the VBSNC may also play important roles in some of these processes. Modulatory mechanisms are also highlighted, including the neurochemical substrate by which nociceptive transmission in the VBSNC can be modulated. In addition, the long-term consequences of peripheral injury and inflammation and, in particular, the neuroplastic changes that can be induced in the VBSNC are emphasized in view of the likely role that central sensitization, as well as peripheral sensitization, can play in acute and chronic pain. The recent findings also provide new insights into craniofacial pain behavior and are particularly relevant to many approaches currently in use for the management of pain and to the development of new diagnostic and therapeutic procedures aimed at manipulating peripheral inputs and central processes underlying nociceptive transmission and its control within the VBSNC. (+info)