Intersensory interactions in the CNS of Helix lucorum

Hair cell responses to adequate stimulation of statocyst, eye and chemoreceptors of the optic tentacle bulb were studied by means of intracellular and extracellular recordings. Hair cells increased firing frequency to titling of the statocyst. Displacement of the statocyst caused a depolarizing wave with superimposed spikes in the hair cell. This depolarizing wave or generator potential increased in proportion to magnitude of displacement. The onset of a light flash and the illumination of eye photoreceptors caused a short-latency (0.3-2 s) increase in the firing frequency of hair cells. The latency of the response was in reversed proportion to the light intensity. Adequate stimulation of chemoreceptors of optic tentacle bulb caused a long-latency (20-40 s) discharge response in the hair cell. In some cases adequate stimulation of photoreceptors and chemoreceptor pathway caused inhibitory responses in 2 of above 50 hair cells.     

Structure-activity relationships of the Helix neuropeptide, SEPYLRFamide, and its N-terminally modified analogues on identified Helix lucorum neurones

Metabotropic and ionotropic effects evoked by the endogenous Helix heptapeptide, SEPYLRFamide, and four analogues, i.e., where the amino acid sequences at the N-terminal (EPYLRFamide, SEGYLRFamide, SRPYLRFamide and SKPYLRFamide) were modified, were compared on identified Helix lucorum LPa2, LPa3, RPa3, RPa2 neurones using two electrode voltage clamp and current clamp techniques. All peptides (bath application) reduce reversibly the inward current to local ionophoretic application of acetylcholine onto the neurone soma with an order of potency: EPYLRFamide=SEGYLRFamide=SRPYLRFamide>SEPYLRFamide+ ++>SKPYLRFamide. The reductions of the acetylcholine-induced inward current evoked by SEPYLRFamide and its analogues at concentrations of 0.01-10 microM are not accompanied by a change of amplitude of the leak inward current caused by constant negative shift of a holding potential. At concentration of 50 microM all peptides increase reversibly the resting membrane conductance to an equal degree. Local application under pressure of SEPYLRFamide and its analogues onto the soma of neurones evoke hyperpolarizations with similar values. These results indicate that the N-terminal three amino acids of the peptide molecule are not responsible for the degree of ionotropic effect on the neurones studied. In contrast the amino acid sequence at the N-terminal modifies the degree of the modulatory effects of the YLRFamide-related analogues. Changes at the SEPYLRFamide N-terminal (Ser1-Glu2-Pro3) intensify the inhibitory action of the analogues as compared with effect evoked by the endogenous peptide, that is, removal of Ser1 (Glu1-Pro2), replacement of Pro3 with Gly3 (Ser1-Glu2-Gly3), replacement of Glu2 with Arg2 (Ser1-Arg2-Pro3). Replacement of Glu2 with Lys2 (Ser1-Lys2-Pro3) reduces the modulatory potency. It is concluded that ionotropic and metabotropic effects of these YLRFamide-related peptides may occur at different membrane binding sites.     

Ionic mechanisms evoked by acetylcholine-, nicotine-, and muscarine-induced depolarization of Helix lucorum RPa4 neurons

Three cholinomimetics: acetylcholine, nicotine and muscarine were applied locally on soma of Helix lucorum RPa4 neuron to study ionic nature of its depolarization. Substances that inhibit Na-, K-, Ca- and Cl-conductances were used. Acetylcholine increased Na-, Ca- and Cl-conductances. As the chlorine response part was small due to the proximity of the resting membrane potential and chlorine equilibrium potential, it may be concluded that the dominating response to acetylcholine is connected with the chemocontrolled input of Na+ and Ca2+ ions into a cell. Nicotine induced mainly Na-conductance and muscarine induced Ca-conductance.     

Neuroradiology of vestibular pathways

Comprehensive efficacious neuroimaging of the vestibular pathways requires cooperation and coordinated efforts between the otologist and the neuroradiologist to avoid duplication of expensive and sometimes invasive study. For peripheral lesions, for example, those of the labyrinthine organ, thin-section CT is optimum as a first examination. For retrolabyrinthine lesions along nerve tracts or in the central pathway, MRI is preferred. When bone erosion occurs, CT can also be helpful in evaluation of the base of the skull to detect and define the extent of these lesions, for example, cholesterol granuloma and glomus tumor.     

Effect of 5,7-dihydroxytryptamine on the food-aversive conditioning in the snail Helix lucorum L

The effects of 5,7-dihydroxytryptamine (5,7-DHT), a drug which selectively ablates serotonergic terminals, were examined on acquisition of food-aversive conditioned reflex in the snail Helix lucorum. The percent of feeding reactions decreased from 80 to 15% in the conditioned group of animals after 5-8 pairings of food and electric shock. The behavioral performance of 5,7-DHT-injected animals after the same training session coincided with the data received from the unpaired control group: the percent of feeding reactions remained the same as before the training. Conditioning was carried out on the semi-intact 'lip-CNS' preparations as well. Intracellular recordings from the neurons responding to the withdrawal reaction confirmed the results of the behavioral experiments. Elaboration of associative changes was effective on preparations made from normal snails, whereas no changes were noted in 5,7-DHT-treated and pseudoconditioned animals. In 5,7-DHT-treated animals some components of the feeding behavior and withdrawal reaction changed as well. The appetitive phase duration of feeding lengthened significantly, moreover the sensitization of the withdrawal reaction evoked by rhythmic tactile stimulation disappeared in preparations made from drug-treated snails.     

Dolichoectatic arterial compression of the anterior visual pathways: neuro-ophthalmic features and clinical course

AIM: To characterise the clinical findings and natural history of anterior visual pathway compression by dolichoectatic intracranial vessels. METHODS: A retrospective case review of patients evaluated in an outpatient neuro-ophthalmology clinic. RESULTS: 10 patients with this condition were identified. Dolichoectatic compression was confirmed by magnetic resonance scanning in all patients. The average age at presentation was 70.6 years and eight of the 10 were female. The carotid artery was involved in seven patients and the basilar in three. Patterns of visual loss varied depending on the site of compression. The most common pattern in patients with optic neuropathy was nasal field loss. In most patients visual loss showed little progression over time. Over an average follow up interval of 2.8 years, progressive visual loss was documented in only three cases. In one of these, neurosurgical intervention was undertaken with subsequent improvement of vision. CONCLUSIONS: Visual loss resulting from compression of the visual pathways by dolichoectatic arteries is usually mild and only slowly progressive. Most patients are elderly, with other forms of vascular disease. Conservative management is thus usually appropriate in this disorder. In occasional cases with more rapid progression, surgical intervention may be beneficial.     

Desensitization of cholinoreceptors of the somatic membrane of command neurons of Helix lucorum taurica L

Desensitization of receptors by the rhythmic application of acetylcholine (AC) was studied in Helix lucorum command neurons PPa2, PPa3, LPa2, LPa3. Application of AC induced in them monophasic depolarization wave. Repetitive AC stimulation with intervals less than 1-2 min induced a decrement of the response which gradually reached plato. Rate and degree of desensitization were constant in every following series and did not depend on preceding periods of depression. Response restoration was unchanged if intervals between series were equal. Stimulation with higher frequencies induced more considerable desensitization. Desensitization was specific to the locus of the membrane, on which AC was applied. Extrastimulation (intracellular stimulation and application of AC) did not lead to restoration of the response. It is supposed that desensitization is a short-term process and results from changes in receptors. The obtained data are explained by means of the Katz-Thesleff model of desensitization. As certain characteristics of synaptic depression and desensitization are similar, a suggestion is put forward that postsynaptic receptors can participate in the processes of synaptic effectiveness decrement during habituation.     

Neurophysiologic changes and bound calcium dynamics during the elaboration of associative learning in Helix lucorum]

Neurophysiological effects and dynamics of bound calcium (Ca-b) in command neurons of defense behavior (LP11 and RP11) during food aversion conditioning were studied in snail Helix lucorum. It was found that during associative learning both conditioned reaction and nonspecific facilitation of sensory responses were determined in neurons. The nonspecific facilitation of sensory responses was similar to that found during sensitization development in neurons. However, conditioned response appeared 30 min later than long-term sensitization development. Specific dynamics of the Ca-b level in neurons was obtained after three and more conditioning. The dynamics of the Ca-b level correlated with neurophysiological effects and differed from those measured during sensitization development. It is suggested that molecular mechanisms underlying associative learning and sensitization are different in a command neuron of defense behavior in the snail.     

Imaging anatomy of the vestibular and visual systems

PURPOSE OF REVIEW: This review will outline the imaging anatomy of the vestibular and visual pathways, using computed tomography and magnetic resonance imaging, with emphasis on the more recent developments in neuroimaging. RECENT FINDINGS: Technical advances in computed tomography and magnetic resonance imaging, such as the advent of multislice computed tomography and newer magnetic resonance imaging techniques such as T2-weighted magnetic resonance cisternography, have improved the imaging of the vestibular and visual pathways, allowing better visualization of the end organs and peripheral nerves. Higher field strength magnetic resonance imaging is a promising tool, which has been used to evaluate and resolve fine anatomic detail in vitro, as in the labyrinth. Advanced magnetic resonance imaging techniques such as functional magnetic resonance imaging and diffusion tractography have been used to identify cortical areas of activation and associated white matter pathways, and show potential for the future identification of complex neuronal relays involved in integrating these pathways. SUMMARY: The assessment of the various components of the vestibular and the visual systems has improved with more detailed research on the imaging anatomy of these systems, the advent of high field magnetic resonance scanners and multislice computerized tomography, and the wider use of specific techniques such as tractography which displays white matter tracts not directly accessible until now.     

Identification of cholinoreceptors on the soma of RPa3 and LPa3 neurons in Helix lucorum]

Selective cholinomimetics and cholinolytics were employed to identify cholinoreceptors on the somatic membrane in Helix lucorum RPa3 and LPa3 neurons using recording of transmembrane ionic currents. Agonists of nicotinic and muscarinic cholinoreceptors evoked reversible activation and following nonreversible inhibition of receptors (except carbamylcholine). Selective cholinomimetics were connected with the same membrane sites that were activated by acetylcholine. Nicotinic and muscarinic cholinolytics decreased the amplitude of inward current induced by acetylcholine (scopolamine and platyphylline had no effect). It is concluded that somatic membrane of RPa3 and LPa3 Helix neurons contains nicotinic and muscarinic cholinoreceptors. These receptors have several pharmacological peculiarities as compared with those of the vertebrates. Muscarinic cholinoreceptors of RPa3 and LPa3 neurons must be included into a special subtype that differs from well-known M1 and M2 subtypes.     

Organization of the ophidian amygdala: chemosensory pathways to the hypothalamus.

Although recent studies in squamate reptiles have importantly clarified how chemical information is processed in the reptilian brain, how the amygdala relays chemosensory inputs to the hypothalamus to influence chemically guided behaviors is still poorly documented. To identify these chemosensory pathways, the amygdalo-hypothalamic projections, intra-amygdaloid circuitry and afferents from the lateral cortex (LC) to the amygdala were investigated by injecting conjugated dextran-amines into the hypothalamus, amygdala, and LC of garter snakes. The amygdala was divided into olfactory recipient (ventral anterior and external amygdalae), vomeronasal recipient (nucleus sphericus, NS, and medial amygdala, MA), and nonchemosensory (e.g., posterior dorsal ventricular ridge, PDVR, and dorsolateral amygdaloid nucleus, DLA) subdivisions. Rostroventral (LCrv) and dorsocaudal subdivisions of the LC were distinguished. In addition to receiving afferents from the main olfactory bulb, the olfactory amygdala receives afferents from NS and projects to the NS, PDVR, and dorsal hypothalamus. The NS has only a minor projection to the lateral hypothalamus, whereas the MA, which receives afferents from the LCrv and NS, has projections to the ventromedial hypothalamic (VMH) and lateral posterior hypothalamic nuclei. Among the nonchemosensory amygdaloid structures, the PDVR receives afferents from the LCrv and the olfactory amygdala and projects to the VMH, whereas DLA receives afferents from the LCrv and NS, and projects to the periventricular hypothalamus. These results substantially clarify the olfactory and vomeronasal tertiary connections and demonstrate that parts of the nonchemosensory amygdala play a major role in relaying chemosensory information to the hypothalamus.     

Metabolic changes in vestibular and visual cortices in acute vestibular neuritis

Five right-handed patients with a right-sided vestibular neuritis were examined twice with fluorodeoxyglucose positron emission tomography while lying supine with eyes closed: once during the acute stage (mean, 6.6 days) and then 3 months later when central vestibular compensation had occurred. Regional cerebral glucose metabolism (rCGM) was significantly increased (p <0.001 uncorrected) during the acute stage in multisensory vestibular cortical and subcortical areas (parietoinsular vestibular cortex in the posterior insula, posterolateral thalamus, anterior cingulate gyrus [Brodmann area 32/24], pontomesencephalic brainstem, hippocampus). Simultaneously, there was a significant rCGM decrease in the visual (Brodmann area 17 to 19) and somatosensory cortex areas in the postcentral gyrus as well as in parts of the auditory cortex (transverse temporal gyrus). Fluorodeoxyglucose positron emission tomography thus allows imaging of the cortical activation pattern that is induced by unilateral peripheral vestibular loss. It was possible to demonstrate that the central vestibular system including the vestibular cortex exhibits a visual-vestibular activation-deactivation pattern during the acute stage of vestibular neuritis similar to that in healthy volunteers during unilateral labyrinthine stimulation. Contrary to experimental vestibular stimulation, the activation of the vestibular cortex was not bilateral but was unilateral and contralateral to the right-sided labyrinthine failure.     

Protein kinase C in central vestibular,cerebellar, and precerebellar pathways of the rat

The protein kinase C family of enzymes is composed of at least ten different isoforms that display a variety of distinct biochemical specificities. Many of these isoforms are highly expressed in brain, and some show regional specificity in their distribution, suggesting that they may serve specific functions. By using immunocytochemistry to localize the βI, βII, γ, or δ isoforms of protein kinase C in the central vestibular system of the adult rat, we found the vestibular ganglion and its peripheral and central processes of the eighth nerve to be heavily labeled with protein kinase C βI immunoreactivity. Labeled axons and terminals were also found in all four vestibular nuclei. Some neurons of the vestibular ganglion were weakly stained with the antibody to protein kinase C βII, as were scattered axons in the eighth nerve, and scattered axons and terminals were found in all four vestibular nuclei among weakly labeled neurons. A few axons in the vestibular portion of the eighth nerve were labeled with protein kinase C γ immunoreactivity, and neurons of the spinal, lateral, and superior vestibular nuclei were heavily decorated with synapses, presumably derived from Purkinje neurons, which were also strongly immunoreactive. Neurons of the medial vestibular nucleus were not as heavily innervated. With the antibody to protein kinase C δ, we found scattered, weakly immunoreactive neurons in the vestibular portion of the eighth nerve. Myelinated fiber bundles of the spinal vestibular nucleus contained moderate numbers of labeled axons, and the other vestibular nuclei were well innervated by protein kinase C δ axons and terminals. Most of these probably derive from Purkinje cells, which were labeled in longitudinal bands interspersed with bands of labeled basket cells. These data suggest that particular protein kinase C isoforms play specific roles in vestibular and cerebellar function. J. Comp. Neurol. 385:26–42, 1997. © 1997 Wiley-Liss, Inc.     

Functional imaging of the visual pathways

Functional neuroimaging has provided a new view of activity in human visual cortex. There have been a series of interesting developments in understanding the relationship between the functional signals, particularly functional MRI, and basic measurements of action potentials and local field potentials. The new human neuro-imaging measurements have clarified some of the similarities and differences between the general organization of visual areas in human and macaque visual cortex, and there have been some interesting new results concerning cortical visual plasticity and dysfunction. The new fMRI focus on measurements of the human brain will drive new relationships between neurology and visual neuroscience that should help us learn much more about the neural basis of perception.     

Androgen and estrogen concentrating neurons in chemosensory pathways of the male Syrian hamster brain.

The medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), and medial amygdaloid nucleus (Me) are essential for male sexual behavior in the Syrian hamster. These nuclei received chemosensory stimuli and gonadal steroid signals, both of which are required for mating behavior. The objective of this study was to compare the distribution of androgen- and estrogen-concentrating neurons in MPOA, BNST, and Me in the adult male hamster using steroid autoradiography for estradiol (E2), testosterone (T) and dihydrotestosterone (DHT). Adult males (n = 4 per group) received two i.p. injections of tritiated steroid 4-7 days after castration. Six-microns frozen sections through the brain were mounted onto emulsion-coated slides, and exposed for 11-16 months. In MPOA, BNST, and Me, neurons were more abundant and heavily labelled after [3H]E2 treatment than after either [3H]T or [3H]DHT. Tritiated estradiol- and DHT-labeled cells were found throughout the rostrocaudal extent of Me, with a high concentration in posterodorsal Me. Tritiated testosterone treatment labelled cells largely within posterodorsal Me. In MPOA, the majority of E2-, T-, and DHT-labelled neurons were in the medial preoptic nucleus (MPN) and the preoptic continuation of the posteromedial bed nucleus of the stria terminalis (BNSTpm). Few T-labelled cells were present outside these subdivisions. In the BNST, E2- and DHT-labelled neurons were present in all subdivisions, whereas T labelling was confined to the antero- and posteromedial subdivisions of BNST. These results suggest that the distribution of androgen- and estrogen receptor-containing neurons overlap considerably in nuclei which transmit chemosensory signals in the control of mating behavior.     

Morphologic representation of visual and antennal information in the ant brain.

Ants in general are primarily olfactory animals, but many species also express visual behaviors. We analyze in 14 species, which range from purely olfactory to predominantly visually behaving ants, how the brains are equipped to control such behavior. We take the size and manifestation of the eyes as an indicator for the prevalence of vision in a given species, and we correlate it with the size of particular brain regions. Our morphometric data show that the size of the eyes generally correlates well with that of the optic lobes. The antennal lobes and the mushroom bodies have a surprisingly constant relative volume whereas, as expected, the relative size of the optic lobes varies strongly across species. Males of different species are more similar. Compared with workers, they all have large eyes, relatively larger optic lobes, smaller mushroom bodies, and similarly sized antennal lobes. The input regions of the mushroom bodies, the lip and the collar, generally correlate with the size of the optic and antennal lobe, respectively. Accordingly, the composition of the calyx reflects the importance of vision for the animal. We present data supporting the view that the mushroom bodies may participate in spatial orientation, landmark recognition, and visual information storage.     

Posttetanic potentiation at an identified synapse of the central nervous system of Helix lucorum during different types of tetanization

Posttetanic potentiation (PTP) of the identified synapse (LPa9-LPa3) in the central nervous system of snail (Helix lucorum L.) was investigated. PTP was observed both after tetanization of presynaptic neuron LPa9 by intracellular current pulses and after tetanization of the same presynaptic neuron by extracellular stimulation of its axonal branch.     

Rhombomeric organization of vestibular pathways in larval frogs

Rhombencephalic subnuclei and projection pathways related to vestibular function were mapped in larval ranid frogs. The retention of overt postembryonic rhombomeres (r) allowed direct visualization of the locations of neurons retrogradely labeled with fluorescent dextran amines from the midbrain oculomotor complex, cerebellum, vestibular nuclei, and spinal cord. Oculomotor projecting vestibular neurons were mainly located in bilateral r1/2, ipsilateral r3, and contralateral r5-8, and spinal projecting vestibular neurons mainly in ipsilateral r4 and contralateral r5. Vestibular commissural neurons were located in r1-3 and r5-7 and were largely excluded from r4. Cerebellar projecting neurons included contralateral inferior olivary neurons in r8 and vestibular neurons in bilateral r6/7 and contralateral r1/2. Mapping these results onto adult anuran vestibular organization indicates that the superior vestibular nucleus derives from larval r1/2, the lateral vestibular nucleus from r3/4, and the major portions of the medial and descending vestibular nuclei from r5-8. The lateral vestibulospinal tract projects from an origin in r4, whereas a possible ascending tract of Deiters arises in r3. Rhombomere 5 contains a nuclear group that appears homologous to the tangential nucleus of fish, reptiles, and birds and thus likely serves gravistatic and linear vestibulomotor reflexes. Comparisons between frogs and other vertebrates suggest that vestibular neurons performing similar computational roles during head movements originate from the same segmental locations in different species.