Motor dysfunction in type 5 adenylyl cyclase-null mice

Various neurotransmitters, such as dopamine, stimulate adenylyl cyclase to produce cAMP, which regulates neuronal functions. Genetic disruption of the type 5 adenylyl cyclase isoform led to a major loss of adenylyl cyclase activity in a striatum-specific manner with a small increase in the expression of a few other adenylyl cyclase isoforms. D1 dopaminergic agonist-stimulated adenylyl cyclase activity was attenuated, and this was accompanied by a decrease in the expression of the D1 dopaminergic receptor and G(s)alpha. D2 dopaminergic agonist-mediated inhibition of adenylyl cyclase activity was also blunted. Type 5 adenylyl cyclase-null mice exhibited Parkinsonian-like motor dysfunction, i.e. abnormal coordination and bradykinesia detected by Rotarod and pole test, respectively, and to a lesser extent locomotor impairment was detected by open field tests. Selective D1 or D2 dopaminergic stimulation improved some of these disorders in this mouse model, suggesting the partial compensation of each dopaminergic receptor signal through the stimulation of remnant adenylyl cyclase isoforms. These findings extend our knowledge of the role of an effector enzyme isoform in regulating receptor signaling and neuronal functions and imply that this isoform provides a site of convergence of both D1 and D2 dopaminergic signals and balances various motor functions.

Characterization and expression of the genes for cytochrome c oxidase subunit VIb (COX6b) from rice and Arabidopsis thaliana

Many of the subunits of cytochrome c oxidase (COX) in the mitochondria of higher plants are encoded by nuclear genes. These genes are less characterized compared to mitochondrial-encoded genes. We previously isolated a cDNA encoding COX6b (designated OsCOX6b1 in this study) from the rice nuclear genome and analyzed its expression. The deduced protein had an extended N-terminus compared with human and yeast COX6b proteins. In this study, we identified another COX6b gene (OsCOX6b2) in rice and revealed that it was actually expressed. The deduced protein of this gene did not have an extended N-terminus and had about the same size as the human and yeast proteins. Genomic Southern hybridization analysis revealed that there was at least one OsCOX6b-homologus sequences in the rice genome other than OsCOX6b1 and OsCOX6b2. Furthermore, we identified three COX6b genes in a dicotyledonous plant, Arabidopsis thaliana. One of these genes (AtCOX6b1) was relatively long, with a length similar to that of OsCOX6b1, and the other two (AtCOX6b2 and AtCOX6b3) were shorter, with lengths similar to the length of OsCOX6b2. Genomic Southern hybridization analysis indicated there were no additional COX6b genes in the Arabidopsis genome. The coding regions of OsCOX6b1 and AtCOX6b1 were separated by four introns and those of OsCOX6b2, AtCOX6b2 and AtCOX6b3 were separated by three introns. A Northern hybridization analysis showed that OsCOX6b1, AtCOX6b1 and AtCOX6b3 were expressed in all organs examined, although with some differences in the amount of expression among the organs. OsCOX6b2 and AtCOX6b2 were strongly expressed in roots but most of the transcripts of AtCOX6b2 were degraded. The evolution of COX6b genes from rice and Arabidopsis is discussed.

Biological characteristics of neuroblastoma with partial deletion in the short arm of chromosome 1

BACKGROUND

Neuroblastoma shows remarkable heterogeneity, resulting in favorable and unfavorable outcomes. It is well known that almost all cases with MYCN amplification have a poor prognosis. We have previously reported that unfavorable tumors show high telomerase activity, whereas favorable tumors show low or nil activity. We also found that the unfavorable neuroblastoma often have a loss of heterozygosity (LOH) at the MYCL locus.

PROCEDURE

To clarify the biological and clinical profiles of tumors with genetic abnormalities of the short arm of chromosome 1, we performed deletion mapping on 1p on 92 neuroblastoma tissues and corresponding noncancerous samples obtained from 92 cases for 24 micro- or minisatellite loci.

RESULTS

LOH was detected in at least one locus of 1p in 43 (47%) cases. All samples were classified into four groups according to the deleted pattern: interstitial deletion (group I, n = 20), short terminal deletion (group ST, n = 6), large terminal deletion (group LT, n = 17), and without detectable deletion (group N, n = 49). All group I cases, whose SRO (shortest region of overlap) was at 1p36.1-2, survived disease free, and none of them showed MYCN amplification or high telomerase activity except for one case. On the other hand, in group LT cases, who showed a large terminal deletion from D1S162 (1p32-pter), including the SRO of group 1, only 5 out of 17 have survived disease free, and 13 showed MYCN amplification or high telomerase activity. The six group ST cases showed small terminal deletion from 1p36.3 with modest prognosis, similar to the group N.

CONCLUSIONS

Thus, we propose three loci, 1p36.1-2, 1p32-34, and 1p36.3, as the candidate loci of neuroblastoma suppressor genes on chromosome 1p responsible for groups I, LT, and ST, respectively. Among them, the 1p32-34 locus may be associated with aggressiveness of tumor progression, possibly due to MYCN amplification and/or telomerase reactivation, while the remaining two loci may not.

Caloric eye-tracking pattern test: visual suppression and the possibility of simplified differential diagnosis between peripheral and central vertigo

During the examination of patients who complain of vertigo or who have equilibrium disorders, often identifying the etiology of the disorders is difficult (i.e., determining whether it is dependent on a peripheral or a central vestibular disorder). To attempt to determine the etiology in these cases, we devised a new method: the caloric eye-tracking pattern test. In normal subjects and in patients with peripheral disorders, as is well-known, caloric nystagmus has little influence on the eye-tracking pattern. In contrast, in patients with central vestibular disorders, caloric nystagmus evoked abnormalities in the eye-tracking pattern, either superimposed or as saccades, despite the fact that the eye-tracking pattern before caloric stimulation was normal. These findings result from the visual suppression mechanism to vestibular nystagmus. We can conclude that the visual suppression to vestibular nystagmus is evoked more strongly by pursuing a moving visual stimulus than by gazing at a stationary target. These results are interesting, not only from the physiological viewpoint but from the clinical viewpoint. The differential diagnosis should include both peripheral and central vertigo.

Structural and functional differences of two forms of GTP-binding protein, Gq, in the cephalopod retina

The major GTP-binding protein (G-protein) in the rhabdomeric photoreceptor membranes of the squid (Watasenia scintillans) has been identified as a Gq-class G-protein. Anti-Gq alpha antibodies recognized a protein not only in the photoreceptor membranes but also in soluble fractions of the retina. The 42 kD protein in the soluble fractions (soluble Gq alpha) had the same molecular mass and the same reactivities to anti-Gq antibodies as those of membrane-bound Gq alpha. The G beta subunit was scarcely detected in the soluble fractions, being found mostly in the membrane fraction, indicating soluble Gq alpha exists in monomeric form. Soluble Gq alpha had no effect on the GTPase activity of the photoreceptor membranes, suggesting that it does not interact with photoactivated rhodopsin or G beta gamma. Soluble Gq alpha would be an inactive form of Gq alpha. In the retina of Octopus fangsiao, soluble Gq alpha was scarcely detected after dark adaptation, but increased during subsequent light exposure and decreased on returning to dark adaptation. These results with Octopus suggest that functional membrane-bound Gq alpha is converted to soluble Gq alpha on exposure to light. Transformation of membrane-bound Gq alpha into the soluble form by hydroxylamine suggests that the difference between membrane-bound and soluble Gq alpha is associated with the attachment of fatty acid(s).

Identification of cDNA encoding cytochrome c oxidase subunit 5c (COX5c) from rice: comparison of its expression with nuclear-encoded and mitochondrial-encoded COX genes

Little is presently known about the nuclear-encoded genes for cytochrome c oxidase (COX) in higher plants. In rice, only the nuclear-encoded COX5b gene has been reported. To understand the relationship between the expression of nuclear-encoded and mitochondrial-encoded COX genes in rice, we first characterized a cDNA encoding one of the other nuclear COX genes, COX5c, which encodes 63 amino acids. The deduced amino acid sequence of COX5c from rice was highly homologous to that from sweet potato. Genomic Southern hybridization indicated that the rice COX5c subunit is encoded by a single copy of the COX5c gene. Furthermore, we compared the expression patterns of the nuclear-encoded COX5c and COX5b genes with the expression pattern of the mitochondrial-encoded COX1 gene among several organs by Northern blot analysis. The results suggested that regulatory systems of expression between the nuclear-encoded and the mitochondrial-encoded COX genes are different among different organs in rice.

Localization of a visual Gq protein in the photoreceptors of a polychaete, Perinereis brevicirris (Annelida)

Heterotrimeric GTP-binding proteins (G proteins) play an important role in phototransduction. The presence of G-protein subclasses has been reported in photoreceptive membranes, e.g., the Gi subgroup (transducin) in vertebrate rods, and the Gq subgroup in the eyes of the Arthropoda and the Mollusca. We examined the immunoreactivity and distribution of a Gq homologue in the cerebral ocelli of Perinereis brevicirris (Polychaeta, Annelida) using an anti-GqC antibody raised against a conserved sequence at the C-terminal of the alpha-subunit of Gq (Gq-alpha). The anti-GqC antibody labeled a 48-kDa band on the Western blot of proteins from the Perinereis ocelli. The anti-GtC antibody, which is raised against the C-terminal sequence of bovine transducin alpha-subunit (Gt-alpha), did not cross-react to the ocellar proteins of Perinereis. The rhabdomeric layers of the anterior and posterior ocelli were strongly labeled by anti-GqC on light-microscopic immunohistology. Immunoelectron microscopy showed that the Gq molecules were specifically localized in the photoreceptive membrane of the rhabdomeric microvilli. These results suggest that the Gq protein plays a role in the phototransduction of the Perinereis ocelli.

Telomerase activity in neuroblastoma: is it a prognostic indicator of clinical behaviour?

Neuroblastomas show remarkable biological heterogeneity, resulting in favourable prognosis or unfavourable prognosis due to aggressive growth despite multimodal therapy. Recently, we proposed that aggressive tumours express telomerase at a high level while the favourable tumours lack or have low telomerase expression. To evaluate the correlation between telomerase activity and other biological characteristics reported as prognostic markers (MYCN gene amplification, loss of heterogeneity (LOH) in the short arm of chromosome 1, trk-A expression, Ha-ras p21 expression, and DNA ploidy), we investigated these biological features in 105 untreated neuroblastomas. In these cases, 23 showed high telomerase activity, 78 showed low activity, and telomerase activity was undetectable in 4 cases. Most tumours with genetic alterations (MYCN amplification or 1p32 LOH) showed high telomerase activity. Most tumours with low or undetectable activity were aneuploid, and showed trk-A and Ha-ras expression. Three of the four tumours with undetectable telomerase activity regressed. In 2 of the tumours with low telomerase activity, the residual tumours maturated and showed repression of telomerase activity. Thus, the level of telomerase activity correlated with other genetic alterations and/or gene expression and may be a useful prognostic indicator in neuroblastoma.

Clinical investigation of neuroblastoma with partial deletion in the short arm of chromosome 1

Several loci on the short arm of chromosome 1 (1p) have been reported as the consensus deleted regions for the putative suppressor genes of neuroblastoma by deletion mapping. The significance of deletion in 1p on the clinical features of neuroblastoma remains controversial. To clarify the relationship between the clinical features of neuroblastoma cases and genetic status of 1p, we performed deletion mapping on 1p on samples obtained from 58 cases with neuroblastoma using 12 highly polymorphic microsatellite or minisatellite loci. Loss of heterozygosity of 1p was detected in 19 cases (33%) of primary tumors and in 21 cases (36%) when metastatic and recurrent sites were included. They were classified into two groups according to the 1p deletion pattern: interstitial deletion (group I, n = 11) and terminal deletion (group T, n = 10). The shortest region of overlap in group I ranged between FGR and D1S170 (1p36.1-2). Clinically, all group I cases survived disease free, and none of these cases showed MYCN amplification. However, in group T, eight (80%) cases showed a large terminal deletion from D1S162 (1p32-pter), including the shortest region of overlap of group I, and two (20%) showed a very terminal deletion from D1S160 (1p 36.3). Of the group T cases, only two survived disease free, and seven (70%) showed MYCN amplification. Thus, the candidates for the locations of neuroblastoma suppressor genes on 1p may involve at least two regions, which demonstrate different clinical features.

Use of the visual suppression test using post-rotatory nystagmus to determine skill in ballet dancers

Twelve ballet dancers with various levels of dancing experience and skill were examined with the visual suppression test using post-rotatory nystagmus (PRVST) and caloric stimulation (CVST). The PRVST results showed a suppression rate that was higher than in untrained subjects. The CVST results showed a suppression rate similar to that in untrained subjects. A correlation between the PRVST and CVST suppression rates and the length of dancing experience showed that the suppression rate increased as the level of experience and skill rose. These results indicate that the PRVST and CVST can aid in the clinical and quantitative assessment of the function of the central nervous system in visual-vestibular interactions in ballet dancers. Additionally, testing may have determined function of vestibulo-cerebellar pathways through habituation of visual-vestibular interactions. Findings indicate that it may be possible to use suppression rates of PRVST and CVST to determine the approximate level of a dancer's experience and skill.

SCREENING-PIGMENT MIGRATION IN THE OCTOPUS RETINA INCLUDES CONTROL BY DOPAMINERGIC EFFERENTS

The extent of screening-pigment (SP) migration in the intact octopus retina and the amplitude of the early receptor potential (ERP) correspond with the degree of adaptation to light or darkness. The light-adapted retina has SP granules concentrated in an apical layer, at the tips of the photoreceptor rhabdoms and supporting cells, and the ERP is barely detectable. In the fully dark-adapted retina, the SP granules are mostly at the base of the rhabdoms, and the ERP is at its maximum. Retinae at intermediate stages, between the fully dark- and light-adapted states, show corresponding intermediate stages of SP migration and ERP amplitude. A series of experiments demonstrates the effects on SP migration of the efferent nerves, which form a subset of fibres in the optic nerves. When the optic nerves to one half of the retina have been severed, there is a dramatic difference in the distribution of SP in areas of the retina (of the dark-adapted eye) connected with severed or intact nerves: apical versus basal, respectively. On incubation of a light- adapted retina with 5 micromolar dopamine, but not with other catecholamines or other putative neurotransmitter substances, SP migrates basally and the ERP is significantly larger than for controls. In octopuses treated with reserpine, SP stays in an apical location and the ERP remains very small, regardless of the state of adaptation and of whether the optic nerves are intact. It is concluded that dopaminergic efferents from the optic lobes effect dark-adaptational SP migration in the cephalopod retina. The arrival in the retina of efferent signals that effect adaptational changes through the mediation of dopamine is a remarkable analogue of the vertebrate system.

Visual suppression test using post-rotatory nystagmus. Clinical course in patients with motion sickness

With the results of VS test (%) we were able to classify patients into three groups as follows: Group I, hyper range of visual suppression, VS (%) = 100-90; Group II, normal range of VS (%) = 89-45; Group III, reduced or abolished range of VS (%) = less than 44. The results with VS test using post-rotatory nystagmus (PRN) were in Group I 58 cases, in Group II 28 cases and in Group III 1 case, and using caloric nystagmus (CN) the results in Group I were 39 cases, Group II 29 cases, and Group III 1 case. With the correlation of VS test between PRN and CN we were able to classify patients into four types as follows: Type I, hyper range of VS in both PRN and CN; Type II, hyper range of VS in PRN; however, normal range of VS in CN; Type III, normal range of VS in both PRN and CN; Type IV reduced or abolished range of VS in both PRN and CN. It was very interesting in the clinical course of motion sickness that patients under 11 years of age (18 cases) of Type I (31 cases) showed marked improvement to Type III (11 cases) at the time of disappearance of symptoms; however, patients over 12 years of age (13 cases) of Type I remained stationary Type I (9 cases) at the time of disappearance of symptoms.

[Cell kinetic study on the healing process of indomethacin-induced gastric mucosal lesion of rats]

In healing process of indomethacin (IND)-induced gastric mucosal lesion of rats, cell kinetics in the cells from margin of mucosal lesion, background mucosa and pyloric gland mucosa were investigated with histochemistry using bromodeoxyuridine. Results obtained were as follows; 1) In marginal cells of mucosal lesion, cell number of s-phase expressing the cell renewal abruptly increased 6 hours after IND injection, showed maximal value at 24 hours and kept higher value even at 72 hours, when the lesions were in scar stage. 2) In background mucosal cells, the cell number of s-phase showed higher value at 12 hours after IND injection, although statistically not significant, and significantly lower value at 24 and 48 hours after IND injection. 3) Some s-phase cells were observed in the surface epithelial cells covering the mucosal defect. 4) In pyloric gland mucosal cells, there was no remarkable change in cell number of s-phase during the experimental period. It was concluded that in healing process of acute gastric mucosal lesion, there was a time lag between the macroscopic observation and cell kinetics in normalization of s-phase cell number.

Early diagnosis of acoustic neuroma (1989) after experience of 37 cases

Although the diagnosis of acoustic neuroma as classically described is generally thought to be easy, this is not always true for this so-called "ear tumor" which is localized within the internal auditory meatus. Recently, remarkable progress has been made in the diagnostic instrumentation and operative techniques used to treat acoustic neuroma, emphasizing the need for early diagnosis so that treatment can take place earlier than before. Through early diagnosis, some cases of total resection of acoustic neuroma have recently become possible, with preservation of not only facial nerve function, but preservation of auditory function as well. In the present report, we outline the early diagnosis of acoustic neuroma by summarizing 37 cases of acoustic neuroma experienced at our institution. We discuss historical presentations, and laboratory tests used in diagnosis including pure tone audiometry, speech audiometry, auditory brainstem evoked response (ABR), vestibular caloric stimulation, and computed tomography (CT) enhanced by introduction of air into the posterior fossa. Two representative cases are also presented. It should be emphasized that no clinical test is 100% sensitive or specific, and attention must be paid to chronological discrepancies in the patient's presentation and "cookbook"-type approaches to evaluation should be avoided.

Positional nystagmus of benign paroxysmal type (BPPN) due to cerebellar vermis lesions. Pseudo-BPPN

Positioning nystagmus accompanied by severe vertigo has been reported in patients with partial lesions of the inner ear, especially otolith lesions. Typically, this type of nystagmus shows a latent period and subsequent fatiguability. We concur with this finding and have constantly emphasized the significance of this phenomenon in clinical diagnosis. Since we started using CT-scanning, this type of nystagmus has been noted in 47 patients, all of whom had cerebellar vermis lesions. Attention should be focused on this association; if such a combination were seen in only 1 or 2 patients, it could simply be attributed to coincidence. But its occurrence in as many as 47 patients indicates a causal role of cerebellar vermis lesions. Its mechanism may be explained by incomplete inhibition of the vestibulo-oculomotor system including the cerebellar flocculonodular lobe or vestibulo-cerebellum.

Positional nystagmus of benign paroxysmal type (BPPN) due to cerebellar vermis lesions. Pseudo-BPPN

Positioning nystagmus accompanied by severe vertigo had been reported in patients with partial lesions of the inner ear, especially otolith lesions. Typically this type of nystagmus represents a latent period and subsequent fatiguability. We concur with this finding and have constantly emphasized the significance of this phenomenon in clinical diagnosis. Since we started to use CT-scanning, this type of nystagmus has been noted in 20 patients, all of whom had cerebellar vermis lesions. Attention should be focused on this association. A simple coincidence could not be excluded if such a combination were seen in only 1 or 2 patients, it could be attributed to simple coincidence. But its occurrence in as many as 20 patients a causal role of cerebellar vermis lesions. Its mechanism may be explained by incomplete inhibition of the vestibulo-oculomotor system including the cerebellar flocculonodular lobe or vestiburo-cerebellum.

Classification of non-nystagmic spontaneous pathological eye movements

We attempted to classify the well-known spontaneous pathological eye movement (SPEM), to provide a unified nomenclature, to describe its pathophysiology, and to determine its significance in determining a differential diagnosis. Nomenclature was according to the first reporter. These phenomena are easy to confuse with artifact when recording ENGs. A careful analysis which considers history and general neurological findings can identify many of these as true clinical findings which may be as important as nystagmus in the establishing of a clinical diagnosis. Each SPEM, once confirmed, plays a decisive role in the localization of lesions within the central nervous system.

[Classification of optokinetic after-nystagmus and its topographical-diagnostic significance in man]

The existence of optokinetic after-nystagmus (OKAN) has long been known, as far back as the age of Bárány. The term OKAN means nystagmus appearing after first inducing optokinetic nystagmus, and then the optokinetic stimulation is removed. It appears easily with the eyes open in a dark place. There have been various theories about the mechanism of the onset of OKAN. Sakata et al. previously classified the types of OKAN into the following 7 types: 1) The normal type, (2) the directional preponderance type, (3) the disinhibitory type, (4) the inversive type, (5) the inhibitory type, (6) the dysmetric type, (7) the clonic type. In the present study, the authors performed a vestibular equilibrium function inspection, including an OKAN inspection, on about 10,000 patients who visited the Department of Neuro-Otology with complaints of vertigo and equilibrium disturbance. The results of the inspection were classified in accordance with Sakata's method, and the diagnostic contribution of the OKAN inspection was examined. The diagnostic significance of the OKAN inspection is considered as follows: (1) This inspection can detect a very small difference between the left and right of nystagmus in the vestibular-optokinetic system, which difference cannot be detected with OKP inspection giving a rather strong stimulation or with the caloric test giving a non-physiological strong stimulation. (2) This can be a focal localization diagnostic method by the classification by type.

A photoproduct with 13-cis retinal generated by irradiation with violet light in the octopus retina

The photoconversion between rhodopsin (R) and metarhodopsin (MR) was investigated in the retina of Octopus ocellatus by measurements of the fast photovoltage (FPV) in conjunction with high pressure liquid chromatography (HPLC). Following conversion of most of R to MR by short-term exposure to an intense violet light, a large vitreous negative FPV due to photon absorption by MR was observed with an orange test flash. By continuing the exposure to the same violet light, however, the negative FPV became very small, though long-term irradiation with blue-green light produced a recovery. With the violet light exposure a substance other than R and MR is produced, which hardly contributes to FPV generation. Analysis of retinal isomers with HPLC show that such an exposure produces a substance with 13-cis retinal as its chromophore and that it was significantly reduced after exposure to blue-green light.

Recent development of the study on clinical significance of abnormal eye movement

As a general trend, the diagnosis in medical clinics often depends on laboratory test results. Neurotological diagnosis, however, requires detailed neurological examinations on a patient by a neurotologist. Therefore, there are differing diagnostic skills among physicians, and there is a kind of "man-made flavor" in neurotological diagnostic procedure. In the present study, current development in the knowledge on the clinical diagnostic significance of pathological eye movement during the last 2-3 years is summarized. Acquired pendular wondering eye-movement. Fixation jerks. Spontaneous and transitory eyeball burst or seizure. Vertical rebound nystagmus. Optokinetic vertical ocular dysmetria. Divergence nystagmus. Counterolling, pure rotatory positioning nystagmus. Inversion of optokinetic after-nystagmus (OKAN). Vertical congenital nystagmus and inversion of optokinetic nystagmus (OKN). Treatment of congenital nystagmus. Vertical spontaneous nystagmus to lower eyelid or so-called "downbeat nystagmus." Downbeat nystagmus seen in bilateral labyrinthine dysfunction. The significance of bilateral vestibular lesion, or symmetric lesion in other is emphasized in the present report for reader's reference and criticism. Our experience on the clinical significance of the abnormal eye movement was reported. It is our wish that accumulation of data on important cases along with the results of experimental studies directly connected with clinical medicine may contribute to the progress of our neurotology in the right direction as "neurology of the posterior fossa."

Vertical ocular dysmetria--vertical rebound nystagmus and optokinetic vertical ocular dysmetria

Ocular dysmetria in vertical eye movement was confirmed by electronystagmographic recording in 100 cases. Ocular dysmetria in spontaneous vertical ocular movement was reported in seven cases. It can be called vertical rebound nystagmus. This phenomenon was more prominent in vertical movement of the eyes returning from upward gazing to mid-position than in the movements of downward gazing. Optokinetic vertical ocular dysmetria induced by vertical optokinetic stimulation was observed in 93 cases. This phenomenon was far more prominent in upward optokinetic nystagmus than in downward optokinetic nystagmus. The pattern of optokinetic vertical ocular dysmetria was classified into the following four types: the dysrhythmic type, the overshoot type, the ataxic type and the saccadic (semi-inversive) type. The pathophysiological mechanism of horizontal ocular dysmetria should be different from the mechanism of vertical ocular dysmetria.

UV-visible antagonism in extraocular photosensitive neurons of the anthomedusa, Spirocodon saltatrix (Tilesius)

Attempts were made to identify extraocular photosensitive cells in the subtentacular region (the area between the ocelli and the nerve ring) and around the inner-nerve ring of the anthomedusan Spirocodon saltatrix. Irradiation with ultraviolet light (UV) led to inhibition of spontaneous impulses and after UV-off, an afterinhibition which lasted for a few minutes. This afterinhibition was rapidly overcome by exposure to visible light (VIS). UV-VIS antagonism of this type was identified in six different impulse systems monitored in extracellular recordings. Intracellular recordings from two of the six cell types showed that UV irradiation causes hyperpolarization which inhibits spontaneous activity. The other cell types showed no membrane potential changes during UV irradiation even though the cells' spontaneous outputs were inhibited. It was concluded that the photosensitivity lies in three kinds of nerves which are distributed widely through the subtentacular region and the nerve ring.