Left frontal eye field remembers “where” but not “what”

Short-term memory of basic stimulus features seems to rely upon low-level functional components of the visual pathways. By using a repetition priming paradigm, we previously showed that visual area V5/MT is important for holding motion direction information, but not spatial position information. Here we extend our previous findings and investigate the possible locus of spatial position priming. We compare the effect of repetitive transcranial magnetic stimulation (rTMS) over right angular gyrus and left and right frontal eye fields on priming for spatial position and motion direction. TMS over left frontal eye field selectively and significantly reduced priming for spatial position but there was no significant effect of TMS over right parietal or right frontal eye field. These results suggest that FEF neurons are implicated in short-term memory storage of spatial position, and extend and support the idea that memory for basic stimulus features is retained within the sensory areas that respond to primary stimulus attributes. They add to a growing body of evidence that the frontal eye fields are involved in many visual functions independent of eye movements.

The time course of binocular rivalry reveals a fundamental role of noise

When our two eyes view incongruent images, we experience binocular rivalry: An ongoing cycle of dominance periods of either image and transition periods when both are visible. Two key forces underlying this process are adaptation of and inhibition between the images' neural representations. Models based on these factors meet the constraints posed by data on dominance periods, but these are not very stringent. We extensively studied contrast dependence of dominance and transition durations and that of the occurrence of return transitions: Occasions when an eye loses and regains dominance without intervening dominance of the other eye. We found that dominance durations and the incidence of return transitions depend similarly on contrast; transition durations show a different dependence. Regarding dominance durations, we show that the widely accepted rule known as Levelt's second proposition is only valid in a limited contrast range; outside this range, the opposite of the proposition is true. Our data refute current models, based solely on adaptation and inhibition, as these cannot explain the long and reversible transitions that we find. These features indicate that noise is a crucial force in rivalry, frequently dominating the deterministic forces.

Sleep does not enhance the recovery of deprived eye responses in developing visual cortex

Monocular deprivation (MD) during a critical period of visual development triggers a rapid remodeling of cortical responses in favor of the open eye. We have previously shown that this process is enhanced by sleep and is inhibited when the sleeping cortex is reversibly inactivated. A related but distinct form of cortical plasticity is evoked when the originally deprived eye (ODE) is reopened, and the non-deprived eye is closed during the critical period (reverse monocular deprivation (RMD)). Recent studies suggest that different mechanisms regulate the initial loss of deprived eye responses following MD and the recovery of deprived eye responses following RMD. In this study we investigated whether sleep also enhances RMD plasticity in critical period cats. Using polysomnography combined with microelectrode recordings and intrinsic signal optical imaging in visual cortex we show that sleep does not enhance the recovery of ODE responses following RMD. These findings add to the growing evidence that different forms of plasticity in vivo are regulated by distinct mechanisms and that sleep has divergent roles upon different types of experience-dependent cortical plasticity.

Systemic hypertension, headache, and ocular hemodynamics: a new hypothesis

The association between systemic hypertension and headache remains controversial and its pathophysiologic basis is uncertain. A rather characteristic early-morning pulsating headache is commonly seen in hypertensive patients, and a recent meta-analysis supports the link between these 2 entities. Epidemiologic evidence has paradoxically suggested a negative association between hypertension and headache. Unpredictable clinical association between severe hypertension and headache indicates that another cranial perfusion-related variable exerts a critical role. Neuroanatomically, head and neck pain primarily involves the ophthalmic division of the trigeminal nerve (V1). A link between systemic hypertension, pulsatile choroidal blood flow (CBF), and intraocular pressure (IOP) has been established. I propose that a trait ocular sympathetic hypofunction permits rapid episodic ocular choroidal overperfusion that stretches the ocular globe in the cohort of hypertensive patients with headache. Rapid distension of the pain-sensitive corneoscleral envelope can stimulate corneoscleral and iridial pain-sensitive V1 nerve endings and generate headache. Ocular tamponade function physiologically limits choroidal overperfusion. A higher basal IOP in some patients with moderate-to-severe hypertension may dampen pulsatile CBF and account for the negative epidemiologic link between sustained systemic hypertension and headache. Besides activation of the baroreceptor reflex, the association of hypalgesia with hypertension probably involves activation of the vasopressin-endorphin adaptive system consequent to mechanical stimulation of V1. The analogy between hypertensive headache and angle-closure glaucoma is rather limited because typical ocular and visual signs and symptoms of angle-closure glaucoma are not seen in hypertension-related headache. Hypertensive crises, including those associated with pheochromocytoma, are not accompanied by attacks of angle-closure glaucoma. Glaucoma is not associated with ocular choroidal congestion, but with reduced pulsatile CBF. The predisposition to develop angle-closure glaucoma is theoretically not associated with ocular autonomic hypofunction and should be conceptually dissociated from this hypothesis. The hypothesis can be evaluated by establishing significant circadian elevations of blood pressure, including nondipping nighttime pattern as well as circadian and periheadache measurements of IOP in patients with attacks of hypertension-related headache.

Role of pseudorabies virus Us3 protein kinase during neuronal infection

The pseudorabies virus (PRV) Us3 gene is conserved among the alphaherpesviruses and encodes a serine/threonine protein kinase that is not required for growth in standard cell lines. In this report, we used a compartmented culture system to investigate the role of PRV Us3 in viral replication in neurons, in spread from neurons to PK15 cells, and in axon-mediated spread of infection. We also examined the role of Us3 in neuroinvasion and virulence in rodents. Us3 null mutants produce about 10-fold less infectious virus from neurons than wild-type virus and have no discernible phenotypes for axonal targeting of viral components in cultured peripheral nervous system neurons. After eye infection in rodents, Us3 null mutants were slightly attenuated for virulence, with a delayed onset of symptoms compared to the wild type or a Us3 null revertant. While initially delayed, the symptoms increased in severity until they approximated those of the wild-type virus. Us3 null mutants were neuroinvasive, spreading in both efferent and afferent circuits innervating eye tissues.

Heparan sulphation patterns generated by specific heparan sulfotransferase enzymes direct distinct aspects of retinal axon guidance at the optic chiasm

Retinal ganglion cell (RGC) axons from each eye execute a series of maneuvers as they converge on the ventral surface of the brain at the optic chiasm for sorting into the optic tracts. Heparan sulfate proteoglycans (HSPGs) are extracellular glycoproteins involved in cell-surface interactions. HSPGs exhibit massive structural diversity, conferred partly by extensive post-translational modification including differential sulfation. Here we examine the roles of HSPG sulfation in RGC axon guidance at the chiasm. We identified different axon navigation phenotypes in two heparan sulfate sulfotransferase (Hst) mutant embryos, Hs2st-/- and Hs6st1-/-, each lacking an enzyme that catalyzes a particular HSPG modification. Hs2st-/- embryos display axon disorganization at the chiasm. Hs6st1-/- embryos exhibit prolific inter-retinal innervation. We show that RGCs express Hs2st and Hs6st1 and that navigation errors made by their axons coincide with regions of high Hs2st and/or Hs6st1 expression at the chiasm. Slit proteins are expressed at particular locations in the retina and around the chiasm and are normally deployed to prevent axons entering inappropriate territories. We show that Hs2st and/or Hs6st1 expression coincides with Slit expression domains at locations where RGC axons make navigation errors in Hs2st-/- and Hs6st1-/- mutants and that Hs6st1-/- RGC axons are less sensitive to Slit2 repulsion than their wild-type counterparts in vitro. We suggest that (1) Hs2st and Hs6st1 are each deployed to generate distinct patterns of heparan sulfation on RGCs and at the optic chiasm and (2) this differential sulfation directs retinal axons through the chiasm, at least in part by modulating the response of the navigating growth cone to Slit proteins.

Artificial neural network properties associated with wiring patterns in the visual projections of vertebrates and arthropods

We model the functioning of different wiring schemes in visual projections using artificial neural networks and so speculate on selective factors underlying taxonomic variation in neural architecture. We model the high connective overlap of vertebrates (where networks have a dense mesh of connections) and the less overlapping, more modular architecture of arthropods. We also consider natural variation in these basic wiring schemes. Generally, arthropod networks are as efficient or more efficient in functioning compared to vertebrate networks. They do not show the confusion effect (decreasing targeting accuracy with increasing input group size), and they train as well or better. Arthropod networks are, however, generally poorer at reconstructing novel inputs. The ability of vertebrate networks to effectively process novel stimuli could promote behavioral sophistication and drive the evolution of vertebrate wiring schemes. Vertebrate networks with less connective overlap have, surprisingly, similar or superior properties compared to those with high connective overlap. Thus, the partial connective overlap seen in real vertebrate visual projections may be an optimal, evolved solution. Arthropod networks with and without whole-cell neural connections within neural layers have similar properties. This indicates that neural connections mediated by offshoots of single cells (dendrites) may be fundamental to generating the confusion effect.

Cervical sympathectomy regulates expression of key angiogenic factors in the rat choroid

Age-related macular degeneration is the leading cause of blindness in people over the age of 55. In addition to an increased risk of vision loss due to macular degeneration, aging results in a substantial loss of sympathetic nerve activity. We have previously shown that loss of sympathetic nerve activity to the eye causes significant remodeling of the choroidal vasculature. The hypothesis of the present study was that the choroidal remodeling noted after sympathectomy was due to alterations in key angiogenic growth factors. To test this hypothesis, female Sprague-Dawley rats underwent superior cervical ganglionectomy, which eliminates all sympathetic innervation to the eye. Six weeks after surgery, eyes were removed, and the choroidal tissue was processed for real-time PCR to measure gene expression and western blot analysis to assess protein expression. Gene and protein expression were significantly increased for vascular endothelial growth factor (VEGF) and pigment epithelial-derived growth factor (PEDF) in the sympathectomized eye, as compared to the contralateral eye (P < 0.05). Protein expression was increased 4-fold for angiopoietin1, with no change in steady-state gene expression. For both p53 and placental growth factor, steady-state mRNA levels were significantly decreased, while protein expression was significantly increased. Protein expression for Flt-1 was decreased significantly, with reduced gene expression. These results suggest that the vascular remodeling noted in the choroidal blood vessels after sympathectomy is a complex process involving numerous growth factor families. Therefore, modulation of sympathetic nerve activity may be a suitable mechanism to prevent the vascular growth associated with macular degeneration.

Bunazosin, a Selective α1 -Adrenoceptor Antagonist, as an Anti-glaucoma Drug: Effects on Ocular Circulation and Retinal Neuronal Damage

Bunazosin hydrochloride is a potent and selective alpha1-adrenoceptor antagonist that has been clinically used both as a systemic antihypertensive as well as an ocular hypotensive drug. In a number of studies, we have examined some effects of bunazosin hydrochloride that might indicate its potential as an anti-glaucoma drug. In normal rabbit eyes, topically instilled bunazosin hydrochloride reached the posterior retina by local penetration at concentrations sufficient to attenuate the phenylephrine- or endothelin-1 (ET-1)-induced constriction of retinal arteries. Furthermore, bunazosin hydrochloride improved the impairment of optic nerve head (ONH) blood flow, the prolongation of visual-evoked potentials (VEP) implicit time, the enlargement of the optic disk cup, and the decrease in the number of retinal ganglion cell layer cells induced by repeated injections of ET-1 in rabbits. Topically instilled bunazosin hydrochloride improved the reductions in ONH capillary blood flow and VEP amplitude induced in rabbit eyes by nitric oxide synthase inhibition. In rat primary retinal cultures, bunazosin hydrochloride reduced glutamate-induced neuronal cell death, presumably through a Na+ channel blocking effect. In healthy humans, topically instilled bunazosin hydrochloride reportedly increases blood velocity in the ONH, retina and choroid, without significantly altering either blood pressure or heart rate. These results indicate that bunazosin hydrochloride exerts both an improvement effect within the ocular circulation and a direct neuroprotective effect. Hence, bunazosin hydrochloride may be useful as a therapeutic drug against ischemic retinal diseases (such as glaucoma and retinal vascular occlusive diseases) that are associated with disturbances of the ocular circulation.

Structural and Ultrastructural Study of the Intracranial Portion of the Oculomotor, Trochlear and Abducent Nerves in Dog

The right intracranial portion of the oculomotor, trochlear and abducent nerves were removed from six adult German shepherd dogs and analysed by light and electron microscopy. In all cases the nerve sectional area was calculated. Unmyelinated and myelinated fibres were analysed and number, diameter and cross-sectional area were calculated. In myelinated fibres, also calculated were the corresponding axon area and diameter, and myelin sheath thickness. The mean number of myelinated fibres was 8543.50 +/- 1231.85 being the unmyelinated 1402 +/- 241.58 in the oculomotor nerve; 1509 +/- 223.17 and 287.67 +/- 72.28 in the trochlear nerve and 2473.00 +/- 211.41 and 231.25 +/- 92.67 respectively in the abducent. The mean diameter was 10.23 +/- 0.68 microm in myelinated and 0.43 +/- 0.21 for unmyelinated in oculomotor nerve, 10.53 +/- 0.55 microm and 0.33 +/- 0.04 for the trochlear, and 10.45 +/- 1.27 microm and 0.47 +/- 0.09 in the abducent nerve respectively. This study reveals that oculomotor, trochlear and abducent nerves of the dog show structural and ultra-structural features similar to the same nerves in other species.

A comparison of mepivacaine versus lidocaine for episcleral (sub-tenon's) block for cataract surgery in an ambulatory setting

BACKGROUND AND OBJECTIVES

For eye surgery, motor block is still often requested by the surgeon. For cataract surgery, rapid block resolution allows eyelids to move and allows eye-patch removal. Therefore, short-duration block is useful in early rehabilitation for ambulatory surgery. Lidocaine is classically assumed to have shorter duration than mepivacaine. Therefore, lidocaine alone might be considered as an alternative to mepivacaine.

METHODS

In this randomized, double-blind study, we compared mepivacaine 2% (n = 22) and lidocaine 2% (n = 25) in 47 patients who received episcleral (sub-Tenon's) block for cataract surgery. Akinesia score was measured 1, 5, 10, and 15 minutes and 1, 2, 4, and 6 hours after the end of injection. Primary outcome was block duration (time from injection to full recovery). Secondary outcomes were time to block onset and best akinesia score for each patient. Complications were recorded.

RESULTS

The 2 groups were similar for demographic and anesthetic features. We observed no significant difference between mepivacaine and lidocaine in terms of onset, quality of akinesia, and block duration. One case of ocular hypertonia and 1 case of strabismus were observed in the lidocaine group, which could be imputed to hyaluronidase unavailability during the study period or to increased lidocaine myotoxicity.

CONCLUSIONS

We found no argument to favor lidocaine over mepivacaine in episcleral (sub-Tenon's) eye block, especially in terms of motor-block duration.

Delayed Convulsions and Brief Contralateral Hemiparesis After Retrobulbar Block

OBJECTIVE

This case report describes convulsions and hemiparesis after retrobulbar injection with good outcome in a patient undergoing outpatient cryocoagulation of his right eye.

CASE REPORT

We report a young man in which localized convulsions of the ipsilateral face occurred 9 minutes after retrobulbar injection followed shortly by convulsions of the contralateral arm and leg. After the convulsions, the patient experienced left-sided hemiparesis resolving approximately 1 hour after the injection. There was no hemodynamic instability during this period. It was difficult to determine the exact cause of convulsions and hemiparesis.

CONCLUSIONS

We believe these complications occurred because of unintentional injection of local anesthetic agent into the subarachnoid space without affecting the brainstem. Possible mechanisms of spread of local anesthetic agent into the central nervous system after retrobulbar block are discussed.

Changes of parvalbumin immunoreactive neurons and GFAP immunoreactive astrocytes in the rat lateral geniculate nucleus following monocular enucleation

The expression of calcium binding proteins (CaBPs) has been linked to protection of neurons. The present study investigated the effects of monocular enucleation on the distribution of parvalbumin immunoreactive (PV-IR) neurons and glial fibrillary acidic protein immunoreactive (GFAP-IR) astrocytes in both the dorsal (dLGN) and ventral (vLGN) regions of the lateral geniculate nucleus (LGN). Our results demonstrated an increase in PV-IR neuronal density on the contralateral vLGN at 1-week post-enucleation (PE), which was maintained without significant change for 12 weeks. By contrast, PV-IR neurons in dLGN decreased significantly at all time point examined. The number of GFAP-IR astrocytes showed an initial increase from 1 to 4 weeks PE and then gradually decreased until 48 weeks in both regions of the LGN with contralateral side predominance. The present results suggest that monocular enucleation results in variable expression of PV-IR neurons and GFAP-IR astrocytes in the LGN complex, which may play an important role in neuronal degeneration and neuroplasticity of the rat visual system.

Onset and duration of mivacurium-induced neuromuscular blockade in children with Charcot-Marie-Tooth disease. A case series with five children

BACKGROUND

The Charcot-Marie-Tooth (CMT) disorders are a group of hereditary motor and sensory neuropathies characterized clinically by peripheral muscle wasting and weakness. We hypothesized that unknown involvement of the muscle used for monitoring neuromuscular block may account for the conflicting reports about the effect of nondepolarizing neuromuscular agents in these patients. The aim of this study was to compare onset and recovery from mivacurium-induced neuromuscular block on the adductor pollicis and orbicularis oculi muscles.

METHODS

We used mivacurium 0.2 mg.kg(-1) in five children (aged 7-12 years) with CMT type I undergoing propofol-fentanyl-oxygen-air anesthesia for orthopedic surgery. Using acceleromyography, neuromuscular transmission was monitored in parallel in the eye and thumb muscles, and onset and duration times were recorded.

RESULTS

Following bolus administration of 0.2 mg.kg(-1) of mivacurium the onset time ranged between 135 and 240 s and 75 and 165 s in the eye and in the thumb, respectively. The recovery time varied between 5.3 and 16 min and 6 and 31.3 min in the eye and in the thumb, respectively.

CONCLUSIONS

In our small series of patients with CMT the clinical duration of mivacurium-induced neuromuscular block was similar to data known from children without neuromuscular disease.

Structure and Function of Myelinated Nerve Fibers in the Rabbit Eye Following Ischemia/Reperfusion Injury

The rabbit eye presents a valuable model to study the effects of vascular occlusion on the function and structure of myelinated nerve fibers. The rabbit eye has a band of myelinated nerve fibers within the intraocular compartment that are supplied by a narrow band of retinal vasculature. These vessels were transiently occluded ( approximately 8 hours) using laser photocoagulation and the transmission of electrical signals along the nerve fibers was assessed by recording the visual evoked response (VER). Morphological damage was assessed by histological techniques. The ischemic insult produced no permanent change in retinal function as assessed by electroretinography, but the VER was suppressed, indicating failure of nerve fiber transmission. Histologically, the visible damage to the region supported by the retinal vasculature worsened following reperfusion, showing evidence of demyelination and necrosis followed by macrophage responses and gliosis. This rabbit model of ischemia/reperfusion of the retinal vasculature offers a rare opportunity to reliably study the response of myelinated nerve fibers to ischemia/reperfusion insults and has demonstrated the susceptibility of myelinated nerve fibers to such insults.

Optic nerve sheath fenestration with endoscopic accessory instruments versus the free electron laser (FEL)

BACKGROUND AND OBJECTIVE

The free electron laser (FEL) can efficiently produce an optic nerve sheath fenestration using an endoscopic approach. To develop a surgical protocol, this study compared effectiveness of available accessory endoscopic instruments to endoscopic FEL delivery effectiveness in producing optic nerve sheath fenestrations.

STUDY DESIGN/MATERIALS AND METHODS

An endoscope was used to perform optic nerve sheath fenestrations on goat optic nerves. Accessory endoscopic instruments and glass-hollow waveguides (250 and 320 microm in diameter) were inserted into the instrument channel for comparison. FEL energy (6.45 microm, 30 Hz) was delivered to the tissue through the waveguides and histological analysis was performed.

RESULTS

The endoscopic instruments alone were unable to incise the optic nerve sheath. The FEL successfully incised the sheath and the biopsy forceps extricated the circular flap.

CONCLUSIONS

Endoscopic optic nerve sheath fenestration using FEL energy followed by biopsy forceps for sheath extrication produced good results, thereby creating a feasible protocol for optic nerve sheath fenestration.

Ipsilateral cortical connections of motor, premotor, frontal eye, and posterior parietal fields in a prosimian primate, Otolemur garnetti

The ipsilateral connections of motor areas of galagos were determined by injecting tracers into primary motor cortex (M1), dorsal premotor area (PMD), ventral premotor area (PMV), supplementary motor area (SMA), and frontal eye field (FEF). Other injections were placed in frontal cortex and in posterior parietal cortex to define the connections of motor areas further. Intracortical microstimulation was used to identify injection sites and map motor areas in the same cases. The major connections of M1 were with premotor cortex, SMA, cingulate motor cortex, somatosensory areas 3a and 1, and the rostral half of posterior parietal cortex. Less dense connections were with the second (S2) and parietal ventral (PV) somatosensory areas. Injections in PMD labeled neurons across a mediolateral belt of posterior parietal cortex extending from the medial wall to lateral to the intraparietal sulcus. Other inputs came from SMA, M1, PMV, and adjoining frontal cortex. PMV injections labeled neurons across a large zone of posterior parietal cortex, overlapping the region projecting to PMD but centered more laterally. Other connections were with M1, PMD, and frontal cortex and sparsely with somatosensory areas 3a, 1-2, S2, and PV. SMA connections were with medial posterior parietal cortex, cingulate motor cortex, PMD, and PMV. An FEF injection labeled neurons in the intraparietal sulcus. Injections in posterior parietal cortex revealed that the rostral half receives somatosensory inputs, whereas the caudal half receives visual inputs. Thus, posterior parietal cortex links visual and somatosensory areas with motor fields of frontal cortex.

A macroscopic investigation of the nerves to the eye and ocular annexes in the Van cat

The orbital nerves were examined grossly in eight adult Van cats from either sex. The optic nerve, in a sigmoid curl, reached the eyeball after coursing between the retractor bulbi and medial rectus muscles. The oculomotor nerve gave off dorsal and ventral branches between the retractor bulbi and lateral rectus muscles. The ciliary ganglion was located on the lateral subbranch of the ventral branch of this nerve in all materials. There were short ciliary nerves originated from the ciliary ganglion in all the materials observed. The lacrimal nerve was a branch of the maxillary nerve.

Extraocular dorsal signal affects the developmental fate of the optic vesicle and patterns the optic neuroepithelium

Dorsal-ventral (DV) specification in the early optic vesicle plays a crucial role in the proper development of the eye. To address the questions of how DV specification is determined and how it affects fate determination of the optic vesicle, isolated optic vesicles were cultured either in vitro or in ovo. The dorsal and ventral halves of the optic vesicle were fated to develop into retinal pigment epithelium (RPE) and neural retina, respectively, when they were separated from each other and cultured. In optic vesicles treated with collagenase to remove the surrounding tissues, the neuroepithelium gave rise to cRax expression but not Mitf, suggesting that surrounding tissues are necessary for RPE specification. This was also confirmed in in ovo explant cultures. Combination cultures of collagenase-treated optic vesicles with either the dorsal or ventral part of the head indicated that head-derived factors have an important role in the fate determination of the optic vesicle: in the optic vesicles co-cultured with the dorsal part of the head Mitf expression was induced in the neuroepithelium, while the ventral head portion did not have this effect. The dorsal head also suppressed Pax2 expression in the optic vesicle. These observations indicate that factors from the dorsal head portion have important roles in the establishment of DV polarity within the optic vesicle, which in turn induces the patterning and differentiation of the neural retina and pigment epithelium.

Abnormal crossing of the optic fibres shown by evoked magnetic fields in patients with ocular albinism with a novel mutation in the OA1 gene

AIM

To perform genealogical and clinical studies in Finnish families with X linked ocular albinism (OA1), including characterisation of the potential misrouting of optic fibres by evaluating visual evoked magnetic fields (VEFs), and to determine the mutation behind the disease.

METHODS

Three families with OA1 were clinically examined. VEFs were measured in two affected males and in one female carrier to characterise the cortical activation pattern after monocular visual stimulation. The neuronal sources of the VEFs were modelled with equivalent current dipoles (ECDs) in a spherical head model. All coding exons of the OA1 gene were screened for mutations by single strand conformation analysis and direct polymerase chain reaction sequencing.

RESULTS

Genealogical studies revealed that the three families were all related. The affected males had foveal hypoplasia with reduced visual acuity varying from 20/200 to 20/50, variable nystagmus, iris transillumination, and hypopigmentation of the retinal pigment epithelium. The ECD locations corresponding to the VEFs revealed abnormal crossing of the optic fibres in both affected males, but not in the carrier female. A novel point mutation, leading to a STOP codon, was identified in the fifth exon of the OA1 gene.

CONCLUSIONS

The data indicate that the novel mutation 640C>T in the OA1 gene is the primary cause of the eye disease in the family studied. VEFs with ECD analysis was successfully used to demonstrate abnormal crossing of the optic fibres.

Ultrastructural Study of Normal and Degenerating Nerve Fibers in the Protocerebral Tract of the Crab Ucides cordatus

Wallerian degeneration is a very well described phenomenon in the vertebrate nervous system. In arthropods, and especially in crustaceans, nerve fiber degeneration has not been described extensively. In addition, literature shows that the events do not follow the same patterns as in vertebrates. In this study we report, by qualitative and quantitative ultrastructural analyses, the features and time course of the protocerebral tract degeneration following extirpation of the optic stalk. No remarkable changes were observed seven days after lesion. After 28 days the protocerebral tracts presented apparently preserved small and large diameter axons and some degenerating medium axons, with irregular contours and empty-looking aspect of the axoplasm. Forty days after the ablation of the optic stalks, both small (type I) and medium (type II and III) axons revealed signs of partial or total degeneration, but large nerve fibers (type IV) were still intact. After 45 days, the tract showed signs of advanced stage of degeneration and, apart from large axons, normal-looking fibers were almost absent. At these 3 last time points, degenerating axons displayed different electron densities and aspects, probably correlating to different onset times of the process. In addition, cells with granules in their cytoplasm, possibly hemocytes, were quite distinct, especially at 40 and 45 days after axotomy. These cells might share with glial cells the function of phagocytosis of cellular debris during the protocerebral tract degeneration. Quantitative analysis showed that the number of degenerating fibers increased significantly from 28 to 40 days after lesion, whereas the number of normal fibers decreased accordingly. Measurements of cross-sectional areas of normal and degenerating axons showed that types II and III (medium) start to degenerate before type I (small). Type IV (large) axons do not degenerate, even after 40 days. Therefore, we can conclude that degeneration in these afferent fibers starts late after axotomy, but proceeds at a faster rate afterwards until the complete degeneration of small and medium axons.

Lateralized predatory responses in the ornate dragon lizard (Ctenophorus ornatus)

Lateralized responses for visually elicited feeding behaviour have been reported in toads and birds but not in the phylogenetically intermediate class of vertebrates, the reptiles. Here we examined small social groups of ornate dragon lizards Ctenophorus ornatus (family Agamidae) and provide the first report in reptiles of right eye lateralization (left brain hemisphere) for predatory responses to prey. However, right eye lateralization was not evident initially but became stronger with time supporting a shift to right eye lateralization as the prey became increasingly familiar. The study is in agreement with recent findings in toads, adding credence to the hypothesis that lateralization originated in an early ancestor and highlighting the supposition that the strength and direction of lateralization is dependent on experience.

Somatostatin immunoreactivity in quail pterygopalatine ganglion

In the ciliary ganglion of the chicken and quail, somatostatin (SOM) is an exclusive marker for parasympathetic postganglionic neurons innervating the choroid. A second parasympathetic pathway projecting to the choroid originates from the pterygopalatine ganglion. The aim of this study was to investigate SOM immunoreactivity in the pterygopalatine ganglion of the Japanese quail (Coturnix coturnix japonica) and on neurons within the choroid, the intrinsic choroidal neurons (ICN). We did so using immunohistochemistry and subsequent light, electron and confocal laser scanning microscopy. Pterygopalatine neurons were characterized by nNOS-immunohistochemistry or NADPH-diaphorase cytochemistry. SOM immunoreactivity was absent in the perikarya, but neurons were densely surrounded by SOM-positive nerve fibres. Electron microscopy revealed that these fibres formed contacts with and without membrane specializations on pterygopalatine neurons. In the choroid, neuronal nitric-oxide synthase (nNOS)-immunoreactive ICN were likewise closely apposed by SOM-immunoreactive nerve fibres, as revealed by confocal microscopy. There was no detectable co-localization of the markers. In the absence of tracing studies, it is open to speculation whether SOM immunoreactivity originates from preganglionic fibres of the superior salivatory nucleus, postganglionic fibres of the ciliary ganglion or fibres of the brainstem via as yet unknown pathways. SOM may regulate the production of NO in pterygopalatine neurons and ICN, respectively, and is therefore involved in neuronal circuits regulating ocular homeostasis.