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PubMed2003

Sorting and convergence of primary olfactory axons are independent of the olfactory bulb.

Primary olfactory axons expressing the same odorant receptor gene sort out and converge to fixed sites in the olfactory bulb. We examined the guidance of axons expressing the P2 odorant receptor when they were challenged with different cellular environments in vivo. In the mutant extratoes mouse, the olfactory bulb is lacking and is replaced by a fibrocellular mass. In these animals, primary olfactory axons form glomerular-like loci despite the absence of normal postsynaptic targets. P2 axons are able to sort out from other axons in this fibrocellular mass and converge to form loci of like axons. The sites of these loci along mediolateral and ventrodorsal axes were highly variable. Similar convergence was observed for larger subpopulations of axons expressing the same cell surface carbohydrates. The sorting out and convergence of like axons also occurred during regeneration following bulbectomy. Olfactory axon behaviour in these models demonstrates that sorting and convergence of axons are independent of the target, which instead provides distinct topographic cues for guidance.

Animals↗

PubMed1991

Human olfactory epithelium in normal aging, Alzheimer's disease, and other neurodegenerative disorders.

By use of immunohistochemistry, we characterized the molecular phenotype of human olfactory epithelial (OE) cells and assessed the nature of the dystrophic olfactory neurites described initially in Alzheimer's disease (AD). Keratin 8 was present in all classes of OE cells. Sustentacular cells lacked other cell type specific polypeptides and were distinguished from neurons and basal cells because the latter two classes of OE cells expressed neural cell adhesion molecules (N-CAMs) and microtubule associated proteins (MAPs), i.e., MAP5. Basal cells expressed nerve growth factor receptors (NGFRs), which distinguished them from olfactory neurons. Unlike their perikarya, olfactory axons expressed vimentin and GAP-43, but not peripherin or neurofilament (NF) proteins. Olfactory nerves were distinguished from other axons because the latter were positive for all three NF subunits and peripherin, in addition to vimentin and GAP-43. Dystrophic neurites in the OE were GAP-43 positive, but they also expressed proteins that were not detected in normal olfactory nerves (i.e., synaptophysin, MAP2, tau, peripherin, NF proteins). Further, rare NF positive olfactory neurons gave rise to NF positive dystrophic neurites. These neurites were present in all 11 AD cases, 11 of 14 subjects with other neurodegenerative diseases, and 6 of 8 neurologically normal adult controls, but no dystrophic neurites were seen in 9 fetal and neonatal cases. We conclude that the molecular phenotype of different human OE cells is distinct and that dystrophic olfactory neurites occur very frequently in neurologically normal adults. The relevance of these neurites to aging or specific disease processes remains speculative.

Adult↗

PubMed1989

[Pharyngeal pain during lateral suboccipital puncture].

Oropharyngeal pain was referred by five fully conscious and collaborative patients during lateral suboccipital puncture (LSP) of the cisterna magna, performed for myelography and/or cerebrospinal fluid collection. The anastomotic connections between the lower cranial nerves, the sympathetic nerves and the upper cervical spinal nerves are reviewed, with emphasis on the relationship between the first cervical nerve (C1), the superior cervical ganglion of the sympathetic trunk, and the spinal accessory nerve (nerve XI), and their central connections. The authors conclude that pharyngeal pain during LSP is provoked by the stimulation of afferent visceral fibers of C1, or of the gray communicating branches of the superior cervical ganglion to C1.

Adult↗

PubMed1987

Survival and subsequent regeneration of olfactory neurons after a distal axonal lesion.

If an axonal lesion is made close enough to the cell body, injured olfactory neurons degenerate and are replaced by new nerve cells arising from undifferentiated mucosal basal cells. Therefore, under these conditions neural regeneration occurs through a process similar to neuronal development. The use of the long garfish olfactory nerve has revealed that neuronal death is not an inevitable consequence of an axonal injury and that the extent of cell death depends on the distance between the site of injury and the perikaryon. A lesion located up to 40 mm from the cell body induces the death of all mature neurons. Between 60 and 100 mm an increasing proportion of neurons survive the injury (from 60 to more than 90%) and are able to regenerate their distal segment. During regeneration, two populations of growing axons have been characterized. The fastest growing fibres (5.8 mm per day) correspond to the small population of neurons which were already growing at the time of the lesion and are able to survive an injury at any distance along the nerve. The majority of the regenerating fibres grow at 0.8 mm per day and corresponds to the damaged mature neurons. Elongation velocities were not affected by the distance from injury to cell body or by the mode of neural repair (development or regeneration). The initial delay between the injury and the beginning of elongation increases linearly with distance at a rate of 1 day cm-1 and is independent of the elongation velocity of the growing neurons. This indicates that the mechanism responsible for the beginning of axonal growth is initiated at or near the cell body and involves the entire axonal stump and not only the area surrounding the crush site. The ability of nerve cells to survive an injury may depend on the length of the axonal stump remaining attached to the cell body and on the level of protein synthesis at the time of the crush. From preliminary results it can be hypothesized that the length of the initial delay is determined by a reorganization of the cytoskeletal elements in the proximal axonal stump.

Animals↗

PubMed1974

Evidence that tetrodotoxin and saxitoxin act at a metal cation binding site in the sodium channels of nerve membrane.

The effects of monovalent, divalent, and trivalent cations on the binding of tetrodotoxin and saxitoxin to intact nerves and to a preparation of solubilized nerve membranes have been examined. All eight divalent and trivalent cations tested, and the monovalent ions Li(+), Tl(+), and H(+) appear to compete reversibly with the toxins for their binding site. The ability of lithium to reduce toxin binding is paralleled by its ability to reduce tetrodotoxin-sensitive ion fluxes through the nerve membrane. We conclude that the toxins act at a metal cation binding site in the sodium channel and suggest that this site is the principal coordination site for cations (normally Na(+) ions) as they pass through the membrane during an action potential. The dissociation constant for Li(+) is 0.1-0.2 M and for Na(+) > 0.6 M, reflecting the weak binding necessary for rapid passage of sodium ions through the channel.

Animals↗

PubMed2004

Antifeedant compounds from three species of Apiaceae active against the field slug, Deroceras reticulatum (Muller).

Extracts of volatiles from foliage of three plants in the Apiaceae, Conium maculatum L. (hemlock), Coriandrum sativum L. (coriander), and Petroselinum crispum Mill. (Nym.) (parsley), previously shown to exhibit antifeedant activity in assays with the field slug, Deroceras reticulatum (Muller) (Limacidae: Pulmonata), were studied further to identify the active components. Coupled gas chromatography-mass spectrometry (GC-MS) and neurophysiological assays using tentacle nerve preparations resulted in the identification of 11 active compounds from the three extracts. Wheat flour feeding bioassays were used to determine which of these compounds had the highest antifeedant activity. One of the most active compounds was the alkaloid gamma-coniceine, from C. maculatum. The role of potentially toxic alkaloids as semiochemicals and the potential for using such compounds as crop protection agents to prevent slug feeding damage is discussed.

Alkaloids↗

PubMed2006

Temporal dynamics and latency patterns of receptor neuron input to the olfactory bulb.

Odorants are first represented in the brain by distributed patterns of activity in the olfactory bulb (OB). Although neurons downstream of sensory inputs respond to odorants with temporally structured activity, sensory inputs to glomeruli are typically described as static maps. Here, we imaged the temporal dynamics of receptor neuron input to the OB with a calcium-sensitive dye in the olfactory receptor nerve terminals in anesthetized mice. We found that diverse, glomerulus- and odorant-dependent temporal dynamics are present even at this initial input stage. Instantaneous spatial patterns of receptor input to glomeruli changed both within and between respiration cycles. Glomerular odorant responses differed in amplitude, latency, rise time, and degree of modulation by sniffing in an odorant-specific manner. Pattern dynamics within the first respiration cycle recurred in a similar manner during consecutive cycles. When sniff rate was increased artificially, pattern dynamics were preserved in the first sniff but were attenuated during subsequent sniffs. Temporal response properties were consistent across individuals on a coarse regional scale and on a fine scale of individual glomeruli. Latency and magnitude of glomerular inputs were only weakly correlated and might therefore convey independent odorant information. These data demonstrate that glomerular maps of primary sensory input to the OB are temporally dynamic. These dynamics may contribute to the representation of odorant information and affect information processing in the central olfactory system of rodents.

Animals↗

PubMed1997

Combinatorial and chemotopic odorant coding in the zebrafish olfactory bulb visualized by optical imaging.

Odors are thought to be represented by a distributed code across the glomerular modules in the olfactory bulb (OB). Here, we optically imaged presynaptic activity in glomerular modules of the zebrafish OB induced by a class of natural odorants (amino acids [AAs]) after labeling of primary afferents with a calcium-sensitive dye. AAs induce complex combinatorial patterns of active glomerular modules that are unique for different stimuli and concentrations. Quantitative analysis shows that defined molecular features of stimuli are correlated with activity in spatially confined groups of glomerular modules. These results provide direct evidence that identity and concentration of odorants are encoded by glomerular activity patterns and reveal a coarse chemotopic organization of the array of glomerular modules.

Amino Acids↗

PubMed2005

Defining the role of olfactory ensheathing cells in facilitating axon remyelination following damage to the spinal cord.

Olfactory ensheathing cells (OECs) are unique cells that are responsible for the successful regeneration of olfactory axons throughout the life of adult mammals. More than a decade of research has shown that implantation of OECs may be a promising therapy for damage to the nervous system, including spinal cord injury. Based on this research, several clinical trials worldwide have been initiated that use autologous transplantation of olfactory tissue containing OECs into the damaged spinal cord of humans. However, research from several laboratories has challenged the widely held belief that OECs are directly responsible for myelinating axons and promoting axon regeneration. The purpose of this review is to provide a working hypothesis that integrates several current ideas regarding the mechanisms of the beneficial effects of OECs. Specifically, OECs promote axon regeneration and functional recovery indirectly by augmenting the endogenous capacity of host Schwann cells to invade the damaged spinal cord. Together with Schwann cells, OECs create a 3-dimensional matrix that provides a permissive microenvironment for successful axon regeneration in the adult mammalian central nervous system.

Animals↗

PubMed1975

[Development of the telencephalon of Salmo irideus Gib].

A developmental study of the Telencephalon of the trout (Salmo irideus) has been done. The stages of fixation were 18 days after fecondation, hatching; 5 days, 1, 2, and 3 months, and 1 year after hatching. The different cell-masses are summarized in table 1. In the young trout, eversion is not important. Just, 2 olfactory bulbs are evaginated. In front of the commissura anterior, we can see: the Nucleus ventroventralis and the Nucleus ventrodorsalis, on the one hand; a voluminous dorsal area which includes: the Nucleus dorsolateralis, the Nucleus dorsomedialis, the Nucleus dorsocentralis and the dorso and ventro-lateral groups, on the other hand. The different Nuclei of the dorsal area are differentiated from a primordial territory which is the area intermedius at the hatching stage. On the hemispheric wall at the level of the tela, we can see the Nucleus teniae. Behind the plan of the commissura anterior, the Nucleus posterior is already seeing at the end of the first month after the hatching. A Golgi-Cox study showed some aspects of different kinds of neurons, and an important neuropil at the level of the Nucleus dorsocentralis too.

Animals↗

PubMed2001

Dual coupling of opioid receptor-like (ORL1) receptors to adenylyl cyclase in the different layers of the rat main olfactory bulb.

The coupling of opioid receptor-like (ORL1) receptors to adenylyl cyclase has been investigated in specific layers of the rat main olfactory bulb. Membranes prepared from the olfactory nerve-glomerular layer (ON-G layer), external plexiform layer (EP layer) and granule cell layer (GR layer) displayed specific binding sites for [(3)H]-nociceptin/orphanin FQ ([(3)H]Noc/OFQ). In each layer, the presence of high-and low-affinity binding sites, with K(D) values in the picomolar and nanomolar range, respectively, was detected. The binding of [(3)H]Noc/OFQ was displaced by unlabelled Noc/OFQ, but not by opioid antagonists. In each layer, Noc/OFQ significantly stimulated [(35)S]GTPgammaS binding with nanomolar potencies. In ON-G layer, Noc/OFQ inhibited basal adenylyl cyclase activity and the enzyme stimulations by corticotropin releasing hormone (CRH), Ca(2+)/calmodulin (Ca(2+)/CaM) and forskolin (FSK). In EP layer, Noc/OFQ inhibited Ca(2+)/CaM-and FSK-stimulated enzyme activities. Conversely, in GR layer the peptide stimulated basal cyclase activity and potentiated the enzyme activation by CRH. The Noc/OFQ stimulation was counteracted by the GDP-bound form of the alpha subunit of transducin and was mimicked by transducin betagamma subunits. In the same tissue layer, Ca(2+)/CaM-and FSK-stimulated enzyme activities were inhibited. Naloxone failed to antagonize all the actions of Noc/OFQ. Western blot and RT-PCR analysis revealed the expression of Ca(2+)-insensitive and -sensitive adenylyl cyclases in the three layers. These results demonstrate that in rat main olfactory bulb ORL1 receptors can differentially affect distinct forms of adenylyl cyclase in a layer specific manner.

Adenylyl Cyclases↗

PubMed1997

Postembryonic changes in the structure of the olfactory bulb of the chinook salmon (Oncorhynchus tshawytscha) across its life history.

Juvenile chinook salmon (Oncorhynchus tshawytscha) memorize odors characteristic of their natal stream, then use these imprinted olfactory cues to return to that same stream years later as sexually mature adults. In a preliminary effort to identify neuroanatomical changes in the salmon olfactory system that may underlie these behavioral capabilities, the structure of the olfactory bulb (OB) was studied at three developmental periods across the life history: in early juvenile development (0.1-4 months of age), in late juvenile development (11-16 months), and as spawning adults (48 months). Using antibodies that selectively label primary olfactory afferents (anti-keyhole limpet hemocyanin), combined with a thionin counterstain, the telencephalon (TEL), OB, and two of the bulb's laminar components, the olfactory nerve-glomerular layer (ONL-GL) and inner cell layer (ICL), could be easily identified. Laminar organization and relative volume (i.e. percent of OB comprised by ONL-GL or ICL) were then compared across groups, and absolute volumes of the OB, ONL-GL, and ICL were compared to that of the TEL at each stage. Three age-related processes were observed across the life history. First, a rapid increase in organizational and structural maturity of the OB was found to be confined to early juvenile life. Second, an increase in OB, ONL-GL, and ICL volume, relative to TEL volume, was found to occur across the entire life history. Lastly, the composition of the OB itself changed, in that an increase in the relative volume of the ONL-GL, and a decrease in that of the ICL, were observed across the life history. Taken together, these results indicate that the OB of young salmon matures dramatically while the fish is still in the freshwater phase of its life history. Then, during migration to the ocean and growth to the adult stage, the volume of the OB, relative to that of the telencephalon, and the relative volume of the input layer of the bulb, both undergo a marked, continuous increase. These changes in the structure, and presumably the function, of the olfactory bulb of salmon may be important in the behavioral phenomena of olfactory imprinting as juveniles and homing as adults.

Age Factors↗

PubMed1972

The binding of labelled tetrodotoxin to non-myelinated nerve fibres.

1. Tritiated tetrodotoxin has been prepared and purified, and its binding to rabbit, lobster, and garfish non-myelinated nerve fibres examined.2. In each case a component of the binding curve was found that saturated at concentrations of a few nanomolar.3. In addition, non-specific binding, indicated by a linear dependence of the amount bound on concentration, occurred.4. The kinetics of wash-in and wash-out of the radioactive toxin were consistent with a model in which all binding was rapid and reversible and in which diffusion into and out of the nerve bundle was rate-limiting. This was shown by numerical solution of the appropriate non-linear diffusion equation. An extension of the limited biophase model that allows for non-specific binding was shown to give good semiquantitative approximations to the proper diffusion equation; and (unlike the latter) the extension was shown to have a relatively simple solution.5. A number of pharmacological agents were tested for competition with, or perturbation of, tetrodotoxin binding: sodium, calcium and hydrogen ions, lidocaine, batrachotoxin and saxitoxin. Apart from a small calcium effect, only saxitoxin, whose effect on sodium current is similar to that of tetrodotoxin, was found to interfere with binding. Increasing saxitoxin concentrations resulted in reduced amounts of tetrodotoxin binding in a manner consistent with a competition between the two toxins for the same site.

Animals↗

PubMed1988

Serotonergic projections to the spinal cord but not those to the olfactory bulb also contain substance P. A combined immunocytochemical and autoradiographic study following retrograde axonal transport of [3H]serotonin labeled products.

Co-localization of substance P with serotonin in raphe projection neurons was studied by combining substance P immunocytochemistry and autoradiography following uptake and retrograde axonal transport of [3H]serotonin and/or its products from target areas. In this study, two central pathways in the rat were investigated: the serotonergic projections of the midbrain raphe to the olfactory bulb and those of the medullary raphe that innervate the thoracic spinal cord. Two hours after pargyline pretreatment, injections of 10(-4) M [3H]serotonin were made either into the olfactory bulb or into the spinal cord and respectively 24 or 60 h thereafter, rats were administered with colchicine. After a 24 h survival time, the paraformaldehyde fixed brains were investigated for substance P immunocytochemistry and then treated for light and electron microscopy autoradiography. Combining both methods, we can define on the same tissue sections at least three labeled neuronal populations: substance P immunolabeled neurons, radiolabeled neurons and doubly immuno-radiolabeled neurons. In the midbrain raphe cells as well as in the olfactory bulb nerve terminals, two kinds of labeled profiles were detected: substance P immunoreactive profiles and radiolabeled ones. The radiolabeled cell bodies of the midbrain raphe (403 counted cells) were never reactive to substance P antibodies. Moreover, they were distributed caudally to substance P stained perikarya. In contrast, in the medullary raphe, of the 336 radiolabeled cell bodies 162 were stained after substance P antibody treatment. They represent about 48% of the serotonin radiolabeled neurons projecting to the thoracic spinal cord, where a great number of varicosities were observed immunolabeled, radiolabeled and doubly immuno-radiolabeled in the dorsal horn. At the ultrastructural level, cell bodies and dendritic processes were also doubly labeled. Both labelings were observed over the cytoplasm and some organelles or perikarya. These observations provide a morphological basis to support the hypothesis that substance P can occur within some but not all serotonergic neurons and raise questions about the expression of this peptide in these systems as well as the modes of interaction of these transmitter molecules.

Animals↗

PubMed2004

G protein activation and cyclic AMP modulation by naloxone benzoylhydrazone in distinct layers of rat olfactory bulb.

1 Naloxone benzoylhydrazone (NalBzoH) has initially been developed as an agonist of the pharmacologically defined kappa3-opioid receptor and has recently been employed as an antagonist at the opioid receptor-like (ORL1) receptor. In the present study, we investigated the ability of NalBzoH to elicit agonist-like effects on receptor signalling in distinct layers of rat olfactory bulb, a brain region where we have demonstrated the presence of opioid and ORL1 receptors coupled to both stimulation and inhibition of cyclic AMP formation. 2 In membranes of the olfactory nerve-glomerular layer (ON-GL), external plexiform layer (EPL) and granule cell layer (GRL), NalBzoH elicited a concentration-dependent stimulation of guanosine-5'-O-(3-[35S]-thio)triphosphate ([35S]GTPgammaS) binding with pEC50 values ranging from 7.36 to 7.86, whereas the kappa1-opioid receptor agonists (-)-U-50,488 and U-69,593 were inactive. 3 In membranes of GRL, but not ON-GL and EPL, NalBzoH stimulated basal adenylyl cyclase activity by 40% with a pEC50 of 8.14, and significantly potentiated the net enzyme stimulation elicited by corticotropin-releasing hormone and pituitary adenylate cyclase-activating peptide 38. Pertussis toxin prevented the NalBzoH stimulations of [35S]GTPgammaS binding and adenylyl cyclase activity. 4 In membranes of EPL and GRL, but not ON-GL, NalBzoH elicited a concentration-dependent inhibition of forskolin-stimulated adenylyl cyclase activity with pEC50 values of 8.07 and 8.08, respectively. 5 At concentrations that completely blocked the actions of nociceptin/orphanin FQ (N/OFQ), the ORL1 receptor antagonists CompB and [Nphe1]N/OFQ(1-13)NH2 failed to antagonize either the stimulatory or the inhibitory effect of NalBzoH on cyclic AMP formation. Similarly, the kappa1-opioid receptor antagonist nor-binaltorphimine counteracted the NalBzoH effects with relatively low potencies (pKi values=7.67-8.09). 6 Conversely, the selective delta-opioid receptor antagonist TIPP (pKi=9.10) and the selective mu-opioid receptor antagonist CTAP (pKi=8.27) reduced the inhibitory effect of NalBzoH by 70 and 30%, respectively. Moreover, TIPP and CTAP potently inhibited the NalBzoH stimulation of cyclic AMP, each antagonist maximally causing 50% blockade of the agonist response. 7These data demonstrate that in the olfactory bulb NalBzoH activates receptor signalling by acting through delta- and mu-opioid receptors and independently of ORL1 and kappa1-opioid receptors.

Adenylyl Cyclases↗

PubMed2004

Cellular transplantation strategies for spinal cord injury and translational neurobiology.

Basic science advances in spinal cord injury and regeneration research have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Among these interventions are cell-based approaches involving transplantation of neural and non-neural tissue elements that have potential for restoring damaged neural pathways or reconstructing intraspinal synaptic circuitries by either regeneration or neuronal/glial replacement. Notably, some of these strategies (e.g., grafts of peripheral nerve tissue, olfactory ensheathing glia, activated macrophages, marrow stromal cells, myelin-forming oligodendrocyte precursors or stem cells, and fetal spinal cord tissue) have already been translated to the clinical arena, whereas others have imminent likelihood of bench-to-bedside application. Although this progress has generated considerable enthusiasm about treating what once was thought to be a totally incurable condition, there are many issues to be considered relative to treatment safety and efficacy. The following review reflects on different experimental applications of intraspinal transplantation with consideration of the underlying pathological, pathophysiological, functional, and neuroplastic responses to spinal trauma that such treatments may target along with related issues of procedural and biological safety. The discussion then moves to an overview of ongoing and completed clinical trials to date. The pros and cons of these endeavors are considered, as well as what has been learned from them. Attention is primarily directed at preclinical animal modeling and the importance of patterning clinical trials, as much as possible, according to laboratory experiences.

Animals↗

PubMed1994

[A 65-year-old woman with headache, facial pain, and progressive multiple cranial neuropathy].

We report a 65-year-old woman with progressive multiple cranial neuropathy. She had been suffered from bronchial asthma since 1979 for which prednisolone had been prescribed. She noted an onset of pain around her nose in October, 1989, which extended into the periorbital regions bilaterally. In February, 1990, she was treated with stellate ganglion block and trigeminal nerve block; these treatments partially alleviated her pain. In May of 1991, she noted a difficulty in swallowing solid foods. In November of the same year, she developed right facial paresis; two weeks later, she noted numbness in her left face, and was hospitalized to our service on December 16, 1991. On admission, she was afebrile and general physical examination was unremarkable except for piping rales in her both lung fields. On neurologic examination, she was alert and oriented to all spheres; higher cerebral functions were intact. In the cranial nerves, her olfactory sense was lost bilaterally; her vision was markedly diminished bilaterally only to recognize hand movements; the optic fundi appeared normal; the pupils were isocoric and reacted to light promptly. The extraocular muscles were moderately weak to most of the directions more on the left; no nystagmus was present. Facial sensation was diminished bilaterally; the jaw deviated to right; right facial paresis of peripheral type was present; her hearing was diminished bilaterally more on the right. The movement of the soft palate was diminished on the right side; dysphagia was present; her voice was horse; the gag reflex was diminished. The sternocleidomastoid muscle was weak bilaterally; the tongue appeared normal. Examination of gait was differed because of headache, however, no apparent motor weakness was present. No ataxia or involuntary movement was noted. Deep reflexes were normally elicited and symmetric. Plantar response was flexor. Sensation in the extremities was intact. Kernig's sign was positive at 70 degree leg extension; eyeball tenderness was also present bilaterally, however, no nuchal stiffness was noted. Following abnormalities were present in the laboratory examination: WBC 11,400/microliters, ESR 50 mm/hr, CRP 6.1 mg/dl. The lumbar CSF was under a normal pressure containing 29 WBC/microliters (neutrophils 7, lymphocytes 20, others 2), 67 mg/dl of protein, and 53 mg/dl of sugar; cultures for acid-fast bacilli as well as for other bacteria were negative; no malignant cells were found. A cranial CT scan revealed an isodensity mass in the orbit and ill-defined low density areas in the white matters of the frontal lobes.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗

PubMed1994

Dynamics of propagating waves in the olfactory network of a terrestrial mollusk: an electrical and optical study.

1. The procerebral (PC) lobe of the terrestrial mollusk Limax maximus contains a highly interconnected network of local olfactory interneurons that receives ipsilateral axonal projections from superior and inferior noses. This network exhibits an approximately 0.7-Hz intrinsic oscillation in its local field potential (LFP). 2. Intracellular recordings show that the lobe contains at least two classes of neurons with activity phase locked to the oscillation. Neurons in one class produce periodic bursts of spikes, followed by a period of hyperpolarization and subsequently a depolarizing afterpotential. There is a small but significant chance for a second burst to occur during the depolarizing afterpotential; this leads to a double event in the LFP. Bursting neurons constitute approximately 10% of the neurons in the lobe. 3. Neurons in the other class fire infrequently and do not produce periodic bursts of action potentials. However, they receive strong, periodic inhibitory input during every event in the LFP. These nonbursting cells constitute the major fraction of neurons in the lobe. There is a clear correlation between the periodic burst of action potentials in the bursting neurons and the hyperpolarization seen in nonbursting neurons. 4. Optical techniques are used to image the spatially averaged transmembrane potentials in preparations stained with voltage-sensitive dyes. The results of simultaneous optical and electrical measurements show that the major part of the optical signal can be interpreted as a superposition of the intracellular signals arising from the bursting and nonbursting neurons. 5. Successive images of the entire PC lobe show waves of electrical activity that span the width of the lobe and travel its full length along a longitudinal axis. The direction of propagation in the unperturbed lobe is always from the distal to the proximal end. The wavelength varies between preparations but is on the order of the length of the preparation. 6. One-dimensional images along the longitudinal axis of the lobe are used to construct a space-time map of the optical activity, from which we calculate the absolute contribution of bursting and nonbursting neurons to the optical signal. The contribution of the intracellular signals from the two cell types appears to vary systematically across the lobe; bursting cells dominate at middle and proximal locations, and nonbursting cells dominate at distal locations. 7. The direction and form of the waves can be perturbed either by microsurgical manipulation of the preparation or by chemical modulation of its synaptic and neuronal properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗