Trigeminal inputs to eyeblink motoneurons in the rabbit

The rabbit nictitating membrane and eyeblink response is widely used in studies of classical conditioning. Eyeblinks involve coordinated activation of the orbicularis oculi motoneurons (OOcVII) and accessory abducens motoneurons (AccVI) which close the external eyelids and nictitating membrane, respectively, and inhibition of levator palpebrae motoneurons (LPIII) whose activity raises the upper eyelid. The identification of blink interneurons that may coordinate these responses is an important step in the analysis of mechanisms supporting eyeblink conditioning as they are likely to receive convergent inputs from circuitry associated with learned as well as unlearned responses. We first investigated the distribution of OOcVII motoneurons in the facial nucleus and LPIII motoneurons in the oculomotor nucleus by retrograde tracing of wheat germ-agglutinated horseradish peroxidase (WGA-HRP) injected into the appropriate muscles. We then used an anterograde tracing method to locate trigeminal and paratrigeminal inputs to OOcVII, to AccVI nucleus, and to LPIII. Injections of WGA-HRP were placed into the principal trigeminal nucleus (Vp) and into all divisions of the spinal trigeminal nucleus. We found an area in Vp and the adjacent rostral parts of pars oralis of the spinal trigeminal nucleus that gave clear projections to OOcVII and AccVI motoneurons and adjacent to LPIII motoneurons in the contralateral oculomotor nucleus. We suggest that neurons in this premotor blink area in rabbits can coordinate learned and reflex blink responses involving the external eyelids and the nictitating membrane. In addition, there are direct projections from the pars interpolaris and pars caudalis of the spinal trigeminal nucleus to the facial nucleus that may mediate short latency responses of the external eyelid orbicularis oculi muscle alone.     

Response diversity of pontine and deep cerebellar nuclear neurons to air puff stimulation of the eye in the alert cat

The discharge of antidromically identified brainstem and cerebellar nuclear neurons involved in the corneal reflex was recorded in the alert cat during corneal air puffs. Eye movements were measured with the search coil technique. Recorded sensory, motor, reticular formation and cerebellar nuclear neurons showed a wide diversity in latencies and patterns of response to air puff stimulation. This diversity suggests that each part of the circuit may contribute different properties to information processing for the corneal reflex, for sustained eyelid closure and, possibly, for the classical conditioning of the nictitating membrane response.     

Neurons located in the trigeminal sensory complex and the lateral pontine tegmentum project to the oculomotor nucleus in the rabbit

Neurons located in the trigeminal sensory complex (TSC) and the lateral pontine tegmentum (LPT) have been reported to project to both the accessory abducens and the facial nuclei, which innervate the retractor bulbi and orbicularis oculi muscles respectively, in order to control the nictitating membrane (NM) and eyelid defensive reflex. Since muscles innervated by the oculomotor nucleus (OCM) also appear to be involved in this reflex, retrograde and anterograde tracers were used in this study to determine whether there are projections from the TSC and LPT to the OCM in the rabbit. Injections of horseradish peroxidase (HRP) in the OCM nucleus labeled neurons in the LPT surrounding the trigeminal motor nucleus dorsally, laterally and ventrally. Only a few scattered neurons were found in the principal and spinal trigeminal nuclei. Injection of biocytin in the LPT area containing most of the HRP-labeled neurons caused anterograde labeling of fibers that crossed the midline and ascended just dorsal to the contralateral medial lemniscus. A proportion of these fibers coursed in a dorsal direction to enter and terminate within the OCM contralateral to the injection site. The location of the motoneuronal groups innervating the different extraocular muscles was studied by retrograde transport of HRP, and compared with the distribution of biocytin-labeled terminals. It was found that the terminals were located in the superior rectus and the levator palpebrae zone of the nucleus. We discuss the functional significance of this projection for the eyelid and NM response.     

Tumors of the eye and ocular adnexal tissues

This article reviews options in dealing with tumors of the cornea and conjunctiva, nictitating membrane neoplasms, and eyelid neoplasms. Orbital tumors, optic nerve and other intraocular tumors are also discussed.     

Effects of attenuating cutaneous afferent activity on a preestablished nictitating membrane response in rabbits.

Conducted 3 experiments with a total of 27 New Zealand albino rabbits. Ss' nictitating membrane response conditioned during high levels of cutaneous afferent activity from the cornea and paraorbital region. Afferent activity levels were controlled by varying UCS locus, corneal applications of a local anesthetic (.5% tetracaine hydrochloride), and exerting mechanical tension on the eyelids. After attainment of criterion levels of responding, levels of afferent activity were varied. Results indicate that subsequent response levels were a direct function of cutaneous afferent activity. Latency and amplitude measurements of the UCR under procedures used to manipulate cutaneous afferent activity did not support the possibility of a mechanical impedence of the response. Stimulus change did not appear to be critically important. (24 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The distribution of afferent neurons in the trigeminal mesencephalic nucleus and the central projection of afferent fibers of the mylohyoid nerve in the rat

Horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) was injected into the proximal cut ends of three branches of the mylohyoid nerve in rats: the branch to the mylohyoid muscle (BrMh), the branch to the anterior belly of the digastricus muscle (BrDg), and the cutaneous branch (BrCu). HRP-labeled cells were detected in the ipsilateral caudal portion of the trigeminal mesencephalic nucleus (Vmes) and the ipsilateral ventromedial division of the trigeminal motor nucleus, except when HRP:WGA was applied to the BrCu. Morphologically, all labeled Vmes cells were of the pseudounipolar type. Projections of the primary afferents of the BrMh were observed in the ipsilateral trigeminal nucleus caudalis, the upper cervical dorsal horns of laminae I-III, and the dorsolateral recticular formation (Rf), whereas the primary afferents of the BrDg terminated in the ipsilateral trigeminal nucleus principalis and Rf. These observations suggest that the role of the afferent inputs of the mylohyoid muscle differs from that of those of the anterior belly of the digastricus muscle in terms of several functions associated with jaw-closing and infrahyoid muscles.     

Comparison of corneal versus through-the-lid A-scan ultrasound biometry

BACKGROUND: Accurate ultrasonography data on axial ocular dimensions in infants and toddlers are essential for understanding ocular development. Conventional methods using corneal contact with topical anesthesia but without sedation are not feasible for most of these patients. We evaluate an alternative method which places the probe on the closed eyelid. METHODS: We compared A-scan ultrasound biometry measurements taken with the probe directly on the cornea with those with the probe on the closed eyelid on the right eye of 35 young adult subjects. RESULTS: There was no significant difference between methods for mean anterior chamber depth (corneal = 3.83 mm, lid = 3.87 mm, p = 0.13, paired t-test). The mean lens thickness (corneal = 3.63 mm, lid = 3.75 mm, p = 0.0001, paired t-test) and mean vitreous chamber depth (corneal = 17.50 mm, lid = 17.68 mm, p = 0.0440, paired t-test) were significantly different. CONCLUSION: Ultrasonography through the closed eyelid appears to be a viable method with acceptable validity compared with corneal ultrasound. Poorer agreement for lens thickness and vitreous chamber depth may be undesirable, but these data should be useful for planning future studies of infants and toddlers.     

Distribution and connections of inspiratory premotor neurons in the brainstem of the pigeon (Columba livia)

We have recorded extracellular, inspiratory-related (IR) unit activity in the medulla at locations corresponding to those of neurons retrogradely labeled by injections of retrograde tracers in the lower brachial and upper thoracic spinal cord, injections that covered cell bodies and dendrites of motoneurons innervating inspiratory muscles. Bulbospinal neurons were distributed throughout the dorsomedial and ventrolateral medulla, from the spinomedullary junction through about 0.8 mm rostral to the obex. Almost all of the 104 IR units recorded were located in corresponding parts of the ventrolateral medulla, rostral to nucleus retroambigualis, where expiratory related units are found. Injections of biotinylated dextran amine at the recording sites labeled projections both to the spinal cord and to the brainstem. In the lower brachial and upper thoracic spinal cord, bulbospinal axons traveled predominantly in the contralateral dorsolateral funiculus and terminated in close relation to the dendrites of inspiratory motoneurons retrogradely labeled with cholera toxin B-chain. In the brainstem, there were predominantly ipsilateral projections to the nucleus retroambigualis, tracheosyringeal motor nucleus (XIIts), ventrolateral nucleus of the rostral medulla, infraolivary superior nucleus, ventrolateral parabrachial nucleus, and dorsomedial nucleus of the intercollicular complex. In all these nuclei, except XIIts, retrogradely labeled neurons were also found, indicating reciprocity of the connections. These results suggest the possibility of monosynaptic connections between inspiratory premotor neurons and inspiratory motoneurons, which, together with connections of IR neurons with other brainstem respiratory-vocal nuclei, seem likely to mediate the close coordination that exists in birds between the vocal and respiratory systems. The distribution of IR neurons in birds is similar to that of the rostral ventral respiratory group (rVRG) in mammals.     

Animal model explains the origins of the cranial dystonia benign essential blepharospasm

The current study demonstrates that combining two mild alterations to the rat trigeminal reflex blink system reproduces the symptoms of benign essential blepharospasm, a cranial dystonia characterized by uncontrollable spasms of blinking. The first modification, a small striatal dopamine depletion, reduces the tonic inhibition of trigeminal reflex blink circuits. The second alteration, a slight weakening of the lid-closing orbicularis oculi muscle, begins an adaptive increase in the drive on trigeminal sensory-motor blink circuits that initiates blepharospasm. By themselves, neither of these modifications causes spasms of lid closure, but combined, they induce bilateral forceful blinking and spasms of lid closure. A two-factor model based on these rodent experiments may explain the development of benign essential blepharospasm in humans. The first factor, a subclinical loss of striatal dopamine, creates a permissive environment within the trigeminal blink circuits. The second factor, an external ophthalmic insult, precipitates benign essential blepharospasm. This two-factor model may also be applicable to the genesis of other cranial dystonias.     

Fornix reconstruction in ocular pemphigoid with Goretex surgical membrane

After separation of symblepharons in ocular pemphigoid, transplantation of nasal or bucal mucosa is recommended to prevent recurrent lid fusion; however, it is not always successful. BACKGROUND: An 86-year-old patient was referred to our eye clinic because of trichiasis in ocular pemphigoid. In the right eye, the only functional eye, fusion of the lower lid and the globe was present. There was severe trichiasis with multiple lesions of the cornea and beginning neovascularization. The left eye showed complete fusion of the lid fissure and neovascularization of the cornea. To prevent the right eye from suffering the fate of the left, we tried to find a simple surgical method that could easily be performed on the multimorbid patient. METHOD: Under parabulbar anesthesia we separated the lower lid from the globe until free passive motility of the lower lid was achieved. A cut-to-size piece of Gore-Tex surgical membrane was prepared and fixated with resorbable u-sutures on the inner lid. The membrane was left in place for 4 weeks until suture lysis. A silicone tube, which was transitorily fixed to the outer lower lid, had an additional ectropionizing effect. Three months later, lower-lid ectropion surgery was performed, combined with tarsectomy to obtain a long-term effect. RESULT: Six months later the lower-lid fornix had stabilized, and the lid and globe had good motility. The corneal lesions had healed. CONCLUSION: The use of 0.1 mm membrane prevents penetration of cell because of the microstructure. Similar to the "bare sclera" technique, which is used in selected cases in strabismus or pterygium surgery, the inner lid and sclera were epithelialized separately from the remaining conjunctiva. The surgical membrane prevented recurrence of the symblepharon. We think the presented technique is an easy, quick method of preventing recurrence of lid fusion after separation of symblepharons.     

Role of oxidative stress in health and disease

BACKGROUND: Radiation therapy can cause corneal and conjunctival abnormalities that sometimes require surgical treatment. Corneal stem cell dysfunction is described, which recovered after the cessation of radiation. METHODS: A 44-year-old man developed a corneal epithelial abnormality associated with conjunctival and corneal inflammation following radiation therapy for maxillary cancer. He experienced ocular pain and loss of vision followed by conjunctival epithelialisation of the upper and lower parts of the cornea. RESULTS: Examination of brush cytology samples showed goblet cells in the upper and lower parts of the cornea, which showed increased fluorescein permeability, and intraepithelial lymphocytes. Impression cytology showed goblet cells in the same part of the cornea. Specular microscopy revealed spindle type epithelial cells. Patient follow up included artificial tears and an antibiotic ophthalmic ointment. The corneal abnormalities resolved after 4 months with improved visual acuity without any surgical intervention, but the disappearance of the palisades of Vogt did not recover at 1 year after radiation. CONCLUSION: Radiation therapy in this patient caused temporary stem cell dysfunction which resulted in conjunctivalisation in a part of the cornea. Although limbal stem cell function did not fully recover, this rare case suggested that medical options should be considered before surgery.     

Salvage surgery after unsuccessful radiotherapy of laryngeal cancer]

The methods usually employed for reconstruction of total lower eyelid loss include (1) tarsoconjunctival flaps from the upper eyelid and skin-graft cover and (2) chondromucosal grafts and local skin-flap cover. We report a technique for coverage of these defects with an island flap involving the full thickness of the ipsilateral nasal wall based on the dorsal (external) nasal vessels, terminal branches of the ophthalmic vessels. The advantages of this method are (1) the main components of the eyelid (skin, tarsus, conjunctiva) are reconstructed in a single short operation, even under local anesthesia, (2) there is one donor area that can be closed primarily without significant deformity, (3) the upper lid remains intact, and ectropion is improbable, and (4) the procedure involves a short hospitalization. As disadvantages we might mention bulkiness of the new eyelid and difficult dissection of the (subcutaneous) pedicle.     

Selective blockade of substance P or neurokinin A receptors reduces the expression of c-fos in trigeminal subnucleus caudalis after corneal stimulation in the rat

Stimulation of the cornea activates neurons in two distinct regions of the spinal trigeminal nucleus: at the transition between trigeminal subnucleus interpolaris and subnucleus caudalis and at the transition between trigeminal subnucleus caudalis and the upper cervical spinal cord as estimated by expression of the immediate early gene, c-fos. To determine if receptors for substance P or neurokinin A, neurokinin 1 and neurokinin 2 receptors, respectively, contribute to the production of Fos-positive neurons in these brainstem regions, receptor-selective antagonists were given intracerebroventricularly 15 min prior to stimulation of the cornea in anesthetized rats. The number of Fos-positive neurons produced in superficial laminae at the trigeminal subnucleus caudalis/cervical cord transition by application of the selective small fiber excitant, mustard oil, to the corneal surface was reduced by the neurokinin 1 receptor antagonist, CP99,994 (5-100 nmol, i.c.v.) and the neurokinin 2 receptor antagonist, MEN10,376 (0.01-1.0 nmol, i.c.v.). Combined pretreatment with CP99,994 and the competitive N-methyl-D-aspartate receptor antagonist, CPP, caused a greater reduction in c-fos expression at the subnucleus caudalis/cervical cord transition than after either drug alone suggesting interaction between receptors for glutamate and substance P. Tachykinin receptor antagonists did not reduce the number of Fos-positive neurons produced at the subnucleus interpolaris/subnucleus caudalis transition. The elevation in plasma concentration of adrenocorticotropin, but not the increases in arterial pressure or heart rate, evoked by corneal stimulation was prevented by pretreatment with CP99,994 or MEN10,376 at doses lower than those needed to reduce c-fos expression. The results indicate that receptors for substance P and neurokinin A contribute to the transmission of sensory input from corneal nociceptors to brainstem neurons in trigeminal subnucleus caudalis and to increased activity of the hypothalamo-pituitary axis that accompanies acute stimulation of the cornea.     

Signals of eye position and velocity in the first-order afferents from pigeon extraocular muscles

Responses of first-order afferents from the extraocular muscles of the pigeon were studied by extracellular recording in the ophthalmic part of the trigeminal ganglion of decerebrate, paralysed pigeons. The afferents responded to both the amplitude and velocity of ramp displacements of the intact eye with amplitude sensitivities ranging from 0.9 to 8 impulses/s/deg of eye displacement beyond the response threshold. Once a new stable position had been reached, the afferent signal depended only upon the absolute position of the eye within the orbit. The responses adapted in seconds rather than minutes so these units would not provide a continuous signal of the position of an immobile eye; they are best described as signalling position and velocity in relation to eye movements.     

Involuntary contractions of the striated anal sphincters as a cause of constipation: report of a case

PURPOSE: To report a case of corneal ulcer associated with deposits of norfloxacin. METHOD: Case report. A 40-year-old man with right trigeminal and facial nerve palsies and decreased tear secretion developed a corneal ulcer with white deposits in the right eye. The deposits were removed and analyzed by high-performance liquid chromatography. RESULTS: High-performance liquid chromatography results disclosed that the deposits on the corneal surface had the same retention time as norfloxacin. The patient discontinued norfloxacin ophthalmic solution and recovered successfully. CONCLUSION: Clinicians should be aware that frequent applications of topical norfloxacin in patients with decreased tear secretion may result in deposition of the drug on the cornea.     

Induced mutagenesis in Ustilago maydis. II. An in vivo biochemical assay

Cholinesterase (ChE) activities of the rat cornea were demonstrated histochemically by using both light and electron microscopes. Acetylcholinesterase (AChE) reaction was localized in the axolemma of the nerves in the corneal stroma. The epithelial cell membranes and the intraepithelial nerve endings also showed AChE reaction. Non-specific cholinesterase (NsChE) activity was observed only in the endothelial cell membranes. Cervical sympathectomy, ciliary ganglionectomy and stereotactic coagulation of the ophthalmic division of the trigeminal nerve were performed in order to study the routes of the AChE-containing nerves to the cornea. The disappearance of AChE-containing nerves was observed only after ophthalmic neurotomy. It is suggested that the AChE-containing nerves are distributed to the rat cornea exclusively via the ophthalamic nerve. They seem to be sensory nerves.     

Wire-core tree technique for accurate three-dimensional modelling of arterial trees

Reflex lid closure often protects the eyes during facial burns. Although corneal burns are uncommon, other ophthalmic injuries occur more frequently. Ophthalmic burns are usually associated with marked facial damage and possible inhalation injury. Failure to recognize and appropriately treat ophthalmic burns can lead to catastrophic sequelae. We performed a 2-year survey of all facial burns in our burn unit. Forty-four patients with thermal facial burns were identified. Sixteen patients had ophthalmic injuries. Corneal injury was detected in 13 per cent (2/16). Intubation was required in 43.75 per cent (7/16) of patients with ophthalmic injuries. Mortality was 25 per cent (4/16). We conclude that patients with facial burns severe enough to cause ophthalmic injuries may be associated with other lethal injuries, and a high index of suspicion should be maintained until all lethal injuries are ruled out. All ophthalmic injuries should be evaluated by an ophthalmologist.     

Mechanism of mitochondrial dysfunction and cytotoxicity induced by tropolones in isolated rat hepatocytes

The hair cell orientation patterns present on the saccules of fishes may be important for encoding the direction of a sound source. This study was conducted to determine whether primary afferent projections to the medulla are organized by the best directions for the hair cells they innervate. The toadfish saccule has hair cells oriented primarily in the vertical plane: both the rostral and the caudal saccule have hair cell orientations sweeping from 0 degrees to 45 degrees, and the middle saccule has hair cells oriented at 90 degrees. Fluorescent dextran amines were used singly and in combination to label regions of the saccular nerve innervating rostral, middle, and caudal saccule. The projections of those afferents were examined in detail in the anterior and descending octaval nuclei, which are auditory nuclei in this species. There was no evidence of topographic projections based on location along the length of the saccule or based on hair cell orientation. There was some evidence that parallel inputs are present from each region of the saccule examined, which may be based on the 180 degrees opposition of hair cells found throughout the saccule; however, afferents from the rostral, middle, and caudal saccule appear to have overlapping projections to the anterior and descending octaval nuclei. These data suggest that in toadfish, calculations of the direction of the sound source may begin in either of these primary auditory nuclei by comparing afferent input from along the saccule.     

Covariation of alternative measures of responding in rabbit (Oryctolagus cuniculus) eyeblink conditioning during acquisition training and tone generalization.

The likelihood, size, and speed of eyelid movements are thought to covary during the acquisition and expression of conditioning in rabbits (Oryctolagus cuniculus) and are generally accepted as interchangeable measures of the associative strength activated by the conditioned stimulus (CS). To test this assumption, the authors examined the patterns of covariation in these eyelid movement measures in acquisition and stimulus generalization in the upper eyelid and nictitating membrane. Rather than the expected covariation among these measures, eyelid movement magnitudes during the CS were distributed in approximately a bimodal manner. That is, eyelid activity consisted largely of a mixture of very small ( 1 mm) movements. The results are discussed with respect to their implications for real-time models of eyelid conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Afferent connections of the medial frontal cortex of the rat. II. Cortical and subcortical afferents

In order to compare the frontal cortex of rat and macaque monkey, cortical and subcortical afferents to subdivisions of the medial frontal cortex (MFC) in the rat were analyzed with fluorescent retrograde tracers. In addition to afferent inputs common to the whole MFC, each subdivision of the MFC has a specific pattern of afferent connections. The dorsally situated precentral medial area (PrCm) was the only area to receive inputs from the somatosensory cortex. The specific pattern of afferents common to the ventrally situated prelimbic (PL) and infralimbic (IL) areas included projections from the agranular insular cortex, the entorhinal and piriform cortices, the CA1-CA2 fields of the hippocampus, the subiculum, the endopiriform nucleus, the amygdalopiriform transition, the amygdalohippocampal area, the lateral tegmentum, and the parabrachial nucleus. In all these structures, the number of retrogradely labeled cells was larger when the injection site was located in area IL. The dorsal part of the anterior cingulate area (ACd) seemed to be connectionally intermediate between the adjacent areas PrCm and PL; it receives neither the somatosensory inputs characteristic of area PrCm nor the afferents characteristic of areas PL and IL, with the exception of the afferents from the caudal part of the retrosplenial cortex. A comparison of the pattern of afferent and efferent connections of the rat MFC with the pattern of macaque prefrontal cortex suggests that PrCm and ACd areas share some properties with the macaque premotor cortex, whereas PL and IL areas may have characteristics in common with the cingulate or with medial areas 24, 25, and 32 and with orbital areas 12, 13, and 14 of macaques.