Nictitating Membranes Research Articles

Rabbit models of dry eye disease: comparative analysis.

To report ocular changes in rabbits after the implementation of three different induction methods to create dry eye (DE) conditions and provides evidence of DE-related disease evolution. Experimental methods were divided into 3 models. The first model used involved triple injection of complete Freund's adjuvant, 50 µL each, also called the meibomian gland dysfunction (MGD) model. In the second model, DE conditions were created by the resection of nictitating membranes (NM), Harderian glands (HG), and main lacrimal glands (LG), also called the LGR model. The third model involved the topical administration of benzalkonium chloride (BAK) 0.1% solution. The Schirmer test, ocular surface staining with fluorescein, and tear break-up time tests were implemented before and after excision. After euthanasia, the ocular tissues were dissected. Cornea, conjunctiva, and meibomian glands were treated with periodic acid-Schiff (PAS) staining and haematoxylin-eosin staining. The MGD model triggered inflammation of meibomian glands. It detected changes in the lipid layer of the tear film. The bilateral resection of NM, HG, and LG reduced the watering layer of the tear film. The topical administration of BAK of 0.1% solution impacted the mucosal layer of the tear film. Different changes are observed with different DE syndrome models. The composition of the tear film differ depending on which part of the eye is targeted. More studies need to be done to confirm whether an increased thickness of the cornea has any impact on the DE disease.

Morphometric Study of the Eyeball of the Loggerhead Turtle (Caretta caretta) Using Computed Tomography (CT).

The short bibliography referring to the anatomy and pathology of the eyeball of turtles poses a challenge for veterinarians and conservationists given the increasing presence of this type of turtle in veterinary and wildlife centres. Although they nest on land, these animals spend a large part of their lives in the ocean, which entails a series of eye adaptations such as well-developed nictitating membranes, palpebral scales, highly sensitive corneas, or sclerotic rings to protect the eye. In our study, we performed a morphometric analysis of the loggerhead turtle (Caretta caretta) eyeball and its internal structures using advanced imaging techniques such as computed tomography (CT). To the best of the authors' knowledge, there have been no studies published that describe the CT intraocular measurements of presumed normal loggerhead turtle eyes.

Histomorphometric Comparison of Canine and Feline Nictitating Membranes

Histomorphometric Comparison of Canine and Feline Nictitating Membranes

Accessory nictitating membrane in a Lipizzaner colt

SummaryA 2‐year‐old Lipizzaner colt presented for removal of a mass over the left eye. The colt had no blepharospasm or significant ocular discharge, but the cornea underlying the mass was mildly oedematous. The mass protruded from the conjunctiva at the dorsotemporal aspect of the globe and was covered in normal conjunctiva. It had a gross appearance similar to the cartilaginous flap of a nictitating membrane, but in an aberrant location. It was moveable to cover the dorsal aspect of the cornea when the globe was retropulsed. Excision of the mass under general anaesthesia was elected. Histopathology supported a diagnosis of an accessory nictitating membrane, consisting of a cartilaginous band surrounded by glandular epithelium. The colt recovered from surgery without complication and no problems were reported by the owner at 8.5 months post‐operatively. To the author's knowledge, there have not been previous reports of accessory or ectopic nictitating membranes in equine or other species.

Behavioral modification of visually deprived lemon sharks (Negaprion brevirostris) towards magnetic fields

The ability of elasmobranchs to orient to weak electromagnetic fields is well documented. Recently, scientists have employed the use of strong electrosensory stimuli, such as permanent magnets, as a means to evaluate the repellent responses of elasmobranchs and assess the utility of these materials for bycatch repellent technologies. However, several studies have produced contrasting results both between and within species. To explain these results, we hypothesized that conditions leading to vision loss (i.e. turbid water) may be a factor affecting electrosensory repellent success. To simulate a visually deprived environment, the nictitating membranes of juvenile lemon sharks (Negaprion brevirostris) were temporarily sutured closed and the behavioral responses of sharks towards a magnetic apparatus were observed in a pen within the shallows of Bimini, Bahamas. Results demonstrate that the magnet-associated behavior of visually deprived sharks significantly differed from control sharks in regard to: (1) avoidance distance, (2) visit quantity prior to first entrance through the magnet zone, and (3) total entrances/total visits. These findings suggest context-dependent switching, where elasmobranchs may exhibit a heightened reliance on their electrosensory system when the extent of their visual range is reduced. These findings also provide insight into favorable environments (e.g. estuary or other coastal ecosystems) and applications (e.g. inshore fisheries and beach nets) that may yield more consistent and successful future implementations of electrosensory repellents for sharks.

PERIOCULAR ANTERIOR ADNEXAL ANATOMY AND CLINICAL ADNEXAL EXAMINATION OF THE ADULT ASIAN ELEPHANT (ELEPHAS MAXIMUS)

Formalin preserved ocular-associated anterior adnexa tissues from five necropsied Asian elephants (Elephas maximus) were dissected with attention to the palpebrae, conjunctiva, nictitating membranes, nasolacrimal ducts, and periocular glandular tissues. Gross and histologic examination revealed that lacrimal and tarsal glands were not present. Evidence of the lacrimal drainage apparatus, including lacrimal punctae or any remnant of lacrimal sacs, was also absent. In contrast, well-developed sebaceous glands associated with accessory hairs along the palpebrae were exceptionally abundant. Mixed-secreting accessory lacrimal glands were noted in the deep stroma posterior to the tarsus of both palpebrae and the gland of the nictitating membrane. Apparently, the Asian elephant has developed a novel tear system in the absence of lacrimal and tarsal (meibomian) glands. Clinical examinations and bacterial cultures of the visible periocular tissues were performed on eight living adult Asian elephants to confirm the postmortem anatomic findings and provide guidance to the clinician during examination of the elephant conjunctiva.

A preliminary study of changes in tear film proteins in the feline eye following nictitating membrane removal

To investigate the influence of nictitating membrane (third eyelid) removal on selected proteins in feline tears. Domestic short-haired cats (7-17 months; 2.6-5.2 kg) were used. Eye-flush tears were collected periodically for up to 18 weeks from both eyes of animals with nictitating membranes removed, but nictitating gland left intact, (n = 4) or with nictitating membranes intact (n = 4). Tear comparisons were based on total protein content (TPC) using micro bicinchoninic acid assay, immunoglobulin A (IgA), and matrix-metalloproteinase (MMP)-9 measurements using sandwich enzyme-linked immunosorbent assay (ELISA) and tear gelatinase activity using gelatin zymography. Expression of MMP-2 and -9 in nictitating membranes removed at baseline (week 0) and eyes collected at 18 weeks were also investigated in histological sections using immunoperoxidase for visualization. Nictitating membrane removal did not significantly change TPC and MMP-9 in tears within the first 4 weeks. MMP-9 was not detected by ELISA in tears from eyes without nictitating membranes from week 5 onwards. IgA (%IgA of TPC) data varied between animals. Gelatin zymography showed increased MMP-2 and -9 activity in tears from eyes without nictitating membranes at week 1 and a decrease following week 2 post-surgery. MMP-2 and -9 were immunolocalised to conjunctival goblet cells of removed nictitating membranes and to the conjunctival epithelium, respectively. After 18 weeks, the distribution of MMPs in tissue was comparable between eyes with and without nictitating membranes. Based on this preliminary study, nictitating membrane removal appeared to cause long-term changes in expression of tear proteins, including reduced MMP-9 expression.

Dual actions of some N-(1-phenylethyl)guanidines on the nictitating membrane of conscious cats

Abstract After 6 hr, high doses (10 or 20 mg/kg) of some adrenergic neuron blocking drugs derived from N-(1-phenylethyl)guanidine produce relaxation of the nictitating membranes of conscious cats which is less than that produced by small doses (2.5 or 5 mg/kg). After 24 hr, there were marked responses to some drugs that had produced little effect after 6 hr. High doses of the drugs contract the nictitating membranes of cats treated with pempidine or (—)-N-(1-phenylethyl)guanidine; low doses do not. This contraction opposes the relaxation evoked by the adrenergic neuron blockade and could account for the anomalous dose-response relationships. The contraction may result from localized release of noradrenaline from the nictitating membrane.

Symblepharon with aberrant protrusion of the nictitating membrane in the snowy owl (Nyctea scandiaca).

Two young snowy owl chicks were presented with aberrant protrusion of the nictitating membranes. This was caused by conjunctival adhesions causing symblepharon secondary to a previous septicemia episode. While symblepharon has been noted in birds before, this unusual presentation of the nictitating membrane has not been reported. Surgical intervention ameliorated the clinical signs, allowing vision in one bird by removal of the nictitating membranes, a technique which appeared to have no deleterious effects on the ocular surface.

Morphological evidence of M cells in healthy canine conjunctiva-associated lymphoid tissue.

To characterize the follicle-associated epithelium (FAE) and organized lymphoid nodules from dog nictitating membranes to determine if canine conjunctiva-associated lymphoid tissue (CALT) contains M cells analogous to those described in other regions of mucosa-associated lymphoid tissue (MALT). Nictitan lymphoid follicles from 15 healthy dogs (30 eyes) were harvested immediately post-mortem. Twelve follicles from each nictitating membrane were isolated. Four follicles from each eye of 10 dogs were examined by light microscopy, transmission electron microscopy and scanning electron microscopy. Five of the 10 dogs were treated with a heat-killed staphylococcal topical suspension immediately prior to euthanasia. Nictitan follicles from five other dogs were processed for immunohistochemistry to characterize follicle lymphocyte populations. The FAE overlying CALT demonstrated morphology characteristic of M cells, including attenuated apical cell surface with blunted microvilli and microfolds, invaginated basolateral membrane forming a cytoplasmic pocket containing lymphocytes and macrophages, and diminished distance between the apical and pocket membrane. Heat-killed bacteria were bound to the surface and transcytosed to the cytoplasmic pocket of CALT M cells. Immunohistochemistry of organized lymphoid tissue subtending the FAE demonstrated B-cell germinal centers with T-cell predominant apical caps. In canine CALT, the FAE overlying lymphoid follicles, as well as the distribution of T and B lymphocytes subtending this region, contain morphologic and functional features analogous to MALT described in other regions. Documentation of canine conjunctival M cells is of clinical relevance in the study of primary ocular diseases, as well as a potential means of vaccination or drug delivery.

Immunohistochemical detection of scrapie prion proteins in clinically normal sheep in Pennsylvania.

Following diagnosis of scrapie in a clinically suspect Suffolk sheep, 7 clinically normal flockmates were purchased by the Pennsylvania Department of Agriculture to determine their scrapie status using an immunohistochemical procedure. Two of the 7 euthanized healthy sheep had positive immunohistochemical staining of the prion protein of scrapie (PrP-Sc) in their brains, nictitating membranes, and tonsils. The PrP-Sc was localized in the areas of the brain where, histopathologically, there was neurodegeneration and astrocytosis. The PrP-Sc occurred within germinal centers of the affected nictitating membranes and tonsils and was located in the cytoplasm of the dendrite-like cells, lymphoid cells, and macrophages. These results confirm that immunohistochemical examination of the nictitating membrane can be used as a screen for the presence of scrapie infection in clinically normal sheep at a capable veterinary diagnostic laboratory. In sheep with a PrP-Sc-positive nictitating membrane, the diagnosis of scrapie should be confirmed by histopathology and immunohistochemical examination of the brain following necropsy. Following full validation, immunohistochemistry assays for detection of PrP-Sc in nictitating membrane lymphoid tissues can improve the effectiveness of the scrapie control and eradication program by allowing diagnosis of the disease in sheep before the appearance of clinical signs.

The actions of bretylium: Adrenergic neurone blocking and other effects

The actions of bretylium: Adrenergic neurone blocking and other effects

Comparison of peripheral and central nervous system sympatholytic actions of prazosin using the cat nictitating membrane

Prazosin is a highly selective α 1-adrenoceptor antagonist that decreases blood pressure by actions on both the peripheral and central (CNS) divisions of the nervous system. The present investigation was undertaken in an attempt to characterize the relative contribution of these two sympatholytic sites of action. Submaximal contractions of the nictitating membranes were evoked by electrical stimulation of the preganglionic cervical sympathetic nerve trunk and by stimulation of the posterior hypothalamus in anesthetized cats. In initial control experiments, phenoxybenzamine (0.1–3.0 mg/kg i.v.) produced an equivalent depression of evoked nictitating membrane responses from both peripheral and CNS sites of activation which suggests only a peripheral blocking action as well as functional equivalence of the intensity of CNS and peripheral nerve stimulation. In contrast, prazosin (3–300 μg/kg i.v.) caused a differential dose-related depression of the evoked responses with ED 50s of 81.5 μg/kg (peripheral stimulation) and 12.5 μg/kg (CNS stimulation) respectively; P < 0.05. Pretreatment with rauwolscine (500 μg/kg i.v.) totally prevented the differential CNS sympatho-inhibition produced by prazosin. These results indicate that. although both CNS and peripheral sites of drug action are manifest, the ED 50 for prazosin-induced CNS sympatho-inhibition is approximately 6-fold less than that required for direct α 1-adrenoceptor blockade at the end organ. In additiom, prazosin produces CNS sympatho-inhibition indirectly by means of an α 2-adrenoceptor mechanism.

Evidence from lack of decentralization‐induced supersensitivity that β2‐ adrenoceptors of the cat nictitating membrane are non‐innervated

The right superior of cervical sympathetic trunk of cats was sectioned preganglionically under anaesthesia. Six days later the blood pressure, heart rate and contractions of the left (control) and right (decentralized) nictitating membranes were recorded under chloralose anaesthesia (80 mg kg-1). The alpha-adrenoceptor-mediated contractile responses of the nictitating membrane to intravenous adrenaline were greater on the decentralized side than the control side, with a significant shift of the dose-response curve to the left. After phentolamine (8 mg kg-1 i.v.), adrenaline administered intra-arterially exerted beta-adrenoceptor-mediated relaxation of the nictitating membranes. However, there was no difference in the sensitivity or magnitude of responses between decentralized and control sides. In a separate series of experiments, the alpha-adrenoceptor-mediated contractile responses of the nictitating membrane to intra-arterial noradrenaline displayed supersensitivity on the decentralized side, the dose-response curve being significantly shifted to the left. In the same animals, the beta-adrenoceptor-mediated relaxation responses to intra-arterial isoprenaline were non-significantly greater on the decentralized side, presumably because of raised tone. However, when expressed as a percentage of the maximum relaxation, there was no difference in sensitivity. This study shows that the alpha-adrenoceptor-mediated contractile response of the nictitating membrane displays supersensitivity after preganglionic section of the sympathetic innervation. This is presumably because of an up-regulation arising from loss of sympathetic traffic onto the receptor. The relaxation response is mediated via adrenoceptors of the beta 2-subtype and shows no supersensitivity. This suggests that these receptors are not under the influence of the sympathetic innervation.

Serotonin uptake inhibitors and the prejunctional effects of serotonin on peripheral sympathetic nerves

The experiments were designed to study whether the inhibitors of the uptake of serotonin (5-HT) potentiated the prejunctional effects of 5-HT on peripheral sympathetic nerves. The effect of two selective 5-HT uptake inhibitors, citalopram and fluoxetine, were studied on the presynaptic actions of 5-HT in the cat isolated nictitating membrane and in the guinea-pig isolated atria. Frequency-effect curves to nerve stimulation and concentration-response curves to noradrenaline (NA) were performed in both preparations. The facilitation that 0.1 μM 5-HT causes on the contractile responses to nerve stimulation of the nictitating membrane of the cat was not potentiated but entirely prevented by both 0.01 μM citalopram and 1.0 μM fluoxetine. On the other hand the diminution that 1.0 μM 5-HT evokes on the chronotropic responses to nerve stimulation of guinea-pig isolated atria was not modified at all by 0.1 and 1.0 μM fluoxetine and only partially prevented by 10.0 μM fluoxetine and by 0.001 μM, 0.01 μM and 0.1 μM citalopram. This latter effect of citalopram was unrelated to the concentration employed. The 5-HT uptake inhibitors did not modify per se either the responses to nerve stimulation or the sensitivity to exogenous NA in both tissues studied. In addition, the 5-HT uptake inhibitors did not interfere with the contractile responses caused by 5-HT in the cat isolated nictitating membrane. Taken together, these observations might indicate a pharmacological rather than a physiological role for the effects of 5-HT in guinea-pig isolated atria and cat nictitating membranes. It is concluded that the 5-HT uptake inhibitors do not potentiate but even antagonize the presynaptic effects of 5-HT. Our results also show that 5-HT uptake inhibitors are more effective to interfere with the facilitation rather than with the inhibition that 5-HT causes on sympathetic responses.

Peripheral sympatholytic effects of 1-alpha-acetylmethadol.

1-alpha-Acetylmethadol (LAAM), 1.4 mg/kg or greater, decreased the response of the cat nictitating membrane to pre- and postganglionic sympathetic nerve stimulation. LAAM had a greater effect on the low-frequency (0.5 Hz) than on the high-frequency (5-20 Hz) responses. No difference was observed between the effects of LAAM on the pre- as opposed to the postganglionic responses. The responses ot the nictitating membranes to intravenous epinephrine were not affected by LAAM. LAAM appears to act at the nerve terminal. The minimum dose of LAAM (1.4 mg/kg) which decreased the nictitating membrane responses also decreased blood pressure and heart rate. Naltrexone, 300 micrograms/kg, s.c., antagonized the effects of LAAM on the nictitating membrane responses and the cardiovascular actions of the drug. In anesthetized dogs, naltrexone completely blocked the blood pressure response to LAAM and partially blocked the effects of LAAM on heart rate and contractile force. The data suggest that LAAM may produce its cardiovascular effects, in part, by an action on the peripheral sympathetic nervous system which involves opiate binding sites. LAAM also appears to have direct actions on the heart to decrease heart rate and contractile force that do not involve opiate binding sites.

Agonist interaction and decentralization supersensitivity in the nictitating membrane of the cat.

1. The responses to individual drugs and to combinations of two drugs were studied in normal and chronically decentralized nictitating membranes (NM) of cats. Noradrenaline (NA), acetylcholine (ACh), serotonin (5HT) and potassium chloride (KCl) and the combinations NA + ACh, NA + 5HT, NA + KCl and ACh + 5HT were injected intra-arterially towards the smooth muscle. 2. Chronic decentralization resulted in supersensitivity to each of these agonists when injected alone. 3. The contraction of the normal NM caused by each drug combination showed potentiation in comparison to the sum of contractions caused by the same drugs given separately. The same drug combinations showed no potentiation in decentralized muscle. 4. Decentralization supersensitivity and potentiation due to agonist interactions in normal preparations may share a common mechanism. The involvement of calcium in this phenomenon is discussed.

Release of radioactive purines from cat nictitating membrane labeled with 3H-adenine

Cat nictitating membranes were incubated with 1–2 × 10 −7 M 3H-adenosine for 1 h. A tissue-bath ratio of about 15 was found for both compounds in intact and denervated membranes. In intact nictitating membranes sympathetic nerve stimulation (4 Hz, 5 min) caused a net release of purines (0.66 ± 17% of the tissue content), which was reduced by α-blockade. Noradrenaline (1–3 μM) or tyramine (60 μM), which produced the same contractile response as did nerve stimulation, increased purine release to the same extent as did nerve stimulation. The effect of either agent was reduced or abolished by phentolamine. Purine release could also be induced by acetylcholine and ATP. This release was not altered after surgical denervation. There was an excellent correlation between the contractile response and the purine release induced by nerve stimulation, noradrenaline, tyramine and acetylcholine. However, ATP caused a larger release of 3H-purines than expected from the contractile responses, possibly indicating displacement. The results indicate that most if not all of the 3H-purines released by nerve stimulation in the cat nictitating membrane are derived from postjunctional elements.

Regional sympathectomy induced by intra-arterial 6-hydroxy-dopamine

Single intra-carotid injections of 5–15 mg of 6-OH-DA HBr in adult cats reduced or abolished the responses of the ipsilateral nictitating membrane to electrical stimulation of post-ganglionic sympathetic nerves and intra-carotid injections of tyramine; the responses of the contralateral nictitating membrane to the same stimuli remained normal. One to five days after 6-OH-DA, the ipsilateral nictitating membranes, unresponsive to sympathetic stimulation, were hypersensitive to i.v. injections of adrenaline or noradrenaline. The advantages of regional over systemic chemical sympathectomy are discussed.

Conditions for dominance of one eye during competitive development of central connections in visually deprived cats

Three groups of visually deprived cats were studied for evidence that one eye gained a competitive advantage over the other during development of central connections. We attempted to detect such an advantage by measuring lateral geniculate cell sizes, by recording the proportion of lateral geniculate Y-cells and the ocular dominance of cortical neurons, and/or by testing visual orienting behavior. Three cats were raised with one eye covered by the lids, and the other, by the nictitating membrane. Lids reduce illumination by 3--4 log units, nictitating membranes, by about one log unit, and both eliminate spatial patterns. Neither eye in these cats appeared to develop with a competitive advantage over the other. Four cats raised with monocular nictitating membrane closure developed with a clear advantage to the open eye, and in all ways data from these cats were indistinguishable from those previously reported for monocularly lid sutured cats. Finally, 4 cats reared with binocular lid closure, but with additional, temporally modulated stimulation through the right lids, showed no evidence of a competitive advantate to either eye. We conclude that interocular differences in light intensity or temporal patterns do not confer a significant competitive advantage to either eye during development of central connections.