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At least 19 recordsLinked to original sources

PubMed1978

Oxygenation and EPR spectral properties of Aplysia myoglobins containing cobaltous porphyrins.

Cobalt myoglobins (Aplysia) have been reconstituted from apo-myoglobin (Aplysia) and proto-, meso-, and deutero-cobalt porphyrins. Each of them showed the 30--60 times lower oxygen affinity than those of the corresponding cobalt myoglobins (Sperm whale). Kinetic investigation of their oxygenation by the temperature-junp relaxation technique showed that the low oxygen affinity of cobalt myoglobin (Aplysia) is due to a large dissociation rate constant. the electron paramagnetic resonance (EPR) spectrum of oxy cobalt myoglobin (Aplysia) is affected by the replacement of H2O with D2O, suggesting a possible interaction between the bound oxygen and the neighboring hydrogen atom. A low temperature photodissociation study showed that the product of photolysis of oxy cobalt myoglobin (Aplysia) gives an EPR spectrum different from that of the deoxy-cobalt myoglobin (Aplysia) and from that of the photolysed form of oxy-cobalt myogloin (Sperm whale). These observations suggest that in oxy-cobalt myoglobin (Aplysia) the bound oxygen might interact with amino acid adjacent to it, but the interaction is weaker than that in oxy cobalt myoglobin (Sperm whale).

Animals↗

PubMed1978

Specific glycine uptake by identified neurons of Aplysia californica. II. Biochemistry.

Glycine is taken up twice as rapidly by neurons R3-R14 as by other identified neurons in the Aplysia parietovisceral ganglion. Earlier studies had shown that R3-R14 have much higher glycine concentrations than other Aplysia neurons. Most of the glycine taken up by R3-R14 was biochemically untransformed for at least 1 h following its uptake. Glycine is actively transported into into R3-R14 and other Aplysia neurons by carrier-mediated processes. Glycine uptake by R3-R14 was markedly reduced in the absence of Na+ and in the presence of Hg2+, while these treatments had little effect on glycine uptake by other Aplysia neurons. There appears to be a special glycine uptake system present in R3-R14 and a general glycine uptake system common to all Aplysia neurons. The elevated glycine concentrations and special glycine uptake associated with R3-R14 may indicate that glycine is utilized as a neurotransmitter by those neurons.

Alanine↗

PubMed1977

Intracellular calcium and extra-retinal photoreception of Aplysia Giant neurons.

The early or "instantaneous" current-voltage relationship for the light-activated potassium current in Aplysia giant neurons was linear during the first second of illumination. However, the light current was greatly reduced or abolished by prolonged hyperpolarization. It was also greatly reduced by the injection of calcium EGTA buffers having calcium activities of 5.6 X 10(-8) M and simulated by injecting buffers with calcium activities of 2.8-5.6 X 10(-7) M. Removal of calcium from the extracellular fluid had no effect. Both the light- and calcium-activated outward potassium currents were reduced by tetraethylammonium (TEA) ions. The light current was not affected by substituting rubidium for potassium nor by substituting either lithium or Tris for sodium. The calcium-activated potassium current persisted when the neuron was cooled to 5 degrees C. However, the light response could no longer be elicited. Light hyperpolarizes Aplysia neurons probably by increasing intracellular calcium activity two-to six-fold which activates a membrane potassium conductance. Calcium levels appear to be restored within the cell and are energy dependent. The light-activated release of calcium is inhibited by cooling. The body wall of Aplysia transmits enough visible or 500 nm light to hyperpolarize some Aplysia giant neurons under ambient conditons. These neurons may be involved in the extraretinal light entrainment that occurs in Aplysia.

Animals↗

PubMed1975

Isolation and characterization of acetylcholinesterase and other particulate proteins in the hemolymph of Aplysia californica.

Hemolymph of the marine mollusc, Aplysia californica, contains four large particles: acetylcholinesterase, hemocyanin, a hemagglutinin, and a structure tentatively identified as erythrocurorin. We purified the acetylcholinesterase 20-fold by differential centrifugation and filtration through a column of 4% agarose. The freshly isolated esterase complex was found to have a sedimentation coefficient of 69, but the negatively stained enzyme lacked a definite structure in the electron microscope, and appeared as irregular aggregates of a 60 A subunit. The complex was unstable below pH 5 or during storage at 7 degrees. Under these conditions, enzymatic activity remained essentially unchanged. Treatment of the purified enzyme with trichloroacetic acid, organic solvents, and sodium dodecyl sulfate broke the complex down into two major subunits with molecular weights of about 70,000. Exposure of the enzyme to [3H]diisopropylfluorophosphate resulted in the labeling of one of these subunits. Although similar in specificity, the cholinesterase of the blood differed from the enzyme in Aplysia nervous tissue, which is associated with membrane. Treatment with sodium deoxycholate activated the membrane-associated enzyme but inhibited slightly that of the hemolymph; tyrocidine inhibited the hemolymph enzyme but not the enzyme of nervous tissue; and mild digestion with trypsin released the membrane-bound enzyme in an active, soluble form, but inactivated the enzyme of hemolymph. The other particulates of Aplysia hemolymph were partially characterized. Aplysia hemocyanin was similar in structure to other molluscan hemocyanins. When negatively stained, the unit particle appeared to be a disc with a diameter of 280 A and a width of 45 A. These discs were stacked to form long cylindrical arrays. The purified hemocyanin was found to contain 0.26% copper (dry weight). Using differential centrifugation and gel filtration we also obtained a 9-fold purification of Aplysia hemagglutinin. This particle was 120 A in diameter with a dark staining central core of 40 A consisting of 6 subunits. The particle tentatively identified as erythrocurorin appeared as a structure 200 A in diameter consisting of 5 V-shaped subunits.

Acetylcholinesterase↗

PubMed1979

Two pharmacologically distinct histamine receptors mediating membrane hyperpolarization on identified neurons of Aplysia californica.

Two distinct hyperpolarizing responses are produced when histamine is iontophoretically applied onto the somal membranes of identified neurons within the cerebral ganglion of Aplysia: a biphasic response consisting of a rapid component (less than 5 sec) usually superimposed upon a slowly developing component; or a monophasic slowly developing response 5-20 sec in duration. The reversal potential values for the fast (typically -65 mV) and the slow (typically -89 mV) responses, and their shift to new values when the external potassium or chloride concentrations were altered, revealed that the fast and slow potentials are produced predominantly by conductance increases to chloride and potassium ions, respectively. The effects of histamine H1- and H2-receptor agonists and antagonists were studied to characterize the pharmacological properties of histamine receptors mediating these two ionically dissimilar hyperpolarizing responses. The slow potassium-dependent hyperpolarization could be mimicked by several histamine analogues; the most potent tested were the H1-receptor agonist, 2-methylhistamine, and the H2-receptor agonist, 4-methylhistamine. Neither of these agents mimicked the fast chloride-dependent histamine response. The slow potassium-dependent responses induced by histamine or histamine agonists were completely and reversibly blocked by the H2-receptor antagonist, cimetidine. By contrast, the slow potassium-dependent hyperpolarizations produced by iontophoretically applied acetylcholine or by dopamine to the same neurons were unaffected by cimetidine. Other H1 and H2 antagonists tested were either ineffective, or only partially blocked the slow hyperpolarizations in a non-selective manner. The fast chloride-dependent hyperpolarizations were not selectively antagonized by any of the H1 or H2 reagents tested, although they were effectively suppressed by tubocurarine and strychnine. These data indicate that two pharmacologically distinct histamine receptors mediate potassium- and chloride-dependent hyperpolarizations in Aplysia neurons. Neither of these receptors, however, could be classified as strictly H1 or H2 according to criteria presently used in non-neuronal tissues. The selectivity and reversibility of cimetidine indicate that this particular antihistaminic could be a valuable pharmacological tool for defining putative histaminergic synapses in Aplysia and perhaps other nervous systems.

Acetylcholine↗

PubMed1977

Stages in the post-hatching development of Aplysia californica.

In order to study the development of the nervous system of the marine mollusc, Aplysia californica, it is necessary objectively to assess the maturity of individual specimens. This can be done by defining stages in the life cycle. The post-hatching development can be divided into four phases: planktonic, metamorphic, juvenile, and adult. These phases can be further subdivided into 13 stages on the basis of behavioral and morphological characteristics visible in living specimens: Stage 1, newly hatched; Stage 2, eyes develop; Stage 3, the larval heart beats; Stage 4, maximum shell size is reached; Stage 5, the propodium develops; Stage 6, red spots appear; Stage 7, the velum is shed; Stage 8, eyebrows appear; Stage 9, pink color develops; Stage 10, white spots appear; Stage 11, rhinophores grow; Stage 12, the genital groove forms; Stage 13, egg laying begins. Reconstructions from serial sections taken from specimens fixed at each of these stages reveal the sequence of formation of the major organ systems. The nervous system develops gradually. The cerebral and pedal ganglia are present at Stage 1, the optic ganglia develop at Stage 2, the abdominal, pleural, and osphradial ganglia at Stage 3, the buccal ganglia at Stage 5, and the genital ganglion at Stage 13. Because Aplysia develops gradually, it is possible to analyze the contribution which gastropod torsion makes to the different phases of the life cycle. The Aplysia embryo undergoes 120 degrees torsion prior to Stage 1. The major visceral organs, the digestive system, heart, gill, and visceral nervous system, develop sybsequently in their post-torsional positions. After metamorphosis, there is a partial de-torsion which involves only the digestive system. Torsion of the digestive system may therefore be beneficial only to the pre-metamorphic larva, and not to the postmetamorphic juvenile.

Animals↗

PubMed1976

Homology of the giant serotonergic neurons (metacerebral cells) in Aplysia and pulmonate molluscs.

The properties of the giant cerebral serotonin-containing neurons of the opisthobranch mollusc Aplysia californica were studied and were compared to the existing data on the giant serotonin-containing neurons (metacerebral cells) of pulmonate mulluscs. Among the properties examined were: axonal distribution, synaptic input and output, pharmacological responses, biophysical characteristics, and plasticity. With only minor exceptions, the properties of the serotonin-containing neurons of Aplysia and of pulmonate molluscs were remarkably similar, and it was concluded that these identified neurons are true homologues. The establishment of the homology of the metacerebral cells of Aplysia to the metacerebral cells of pulmonate molluscs extends the known distribution of these neurons to a second major subclass (Opisthobranchiata) of molluscs. Since pulmonate and opisthobranch molluscs differ substantially in behavioral and anatomical features, the study of the metacerebral cells of these two groups may promote the understanding of the evolutionary adaptation of the nervous system to different environmental pressures.

Acetylcholine↗

PubMed1975

DNA sequence organization in the mollusc Aplysia californica.

The sequence organization of the DNA of the mollusc Aplysia californica has been examined by a combination of techniques. Close-spaced interspersion of repetitive and single copy sequences occurs throughout the majority of the genome. Detailed examination of the DNA of this protostome reveals great similarities to the pattern observed in the two deuterostome organisms previously examined in detail in this laboratory, Xenopus laevis and Strongylocentrotus purpuratus. Labeled and unlabeled Aplysia DNA were prepared from developing embryos and sheared to a fragment length of 400 nucleotides. The kinetics of reassociation were studied by means of hydroxyapatite chromatography, single-strand-specific S1 nuclease, and optical methods of assay. Aplysia DNA of this fragment length contains at least five resolvable kinetic fractions. One classification of these fractions, listed with their reassociation rate constants (l M-1 sec-1) is: single copy (0.00057), slow (0.047), fast (2.58), very fast (4000), and foldback (greater than 10(5)). Sequence arrangement was deduced from: the kinetics of reassociation of DNA fragments of length 400 or 2000 nucleotides; the hyperchromicity of reassociated fragments containing duplex regions; the size of duplex regions resistant to S1 nuclease; and the reassociation of labeled fragments of various lengths with short driver fragments. More than 80% of the single copy DNA sequences are interspersed with repetitive sequences. The maximum spacing of the repeats is about 2000 nucleotides, and the average less than 1000. The very fast fraction does not show interspersion with single copy sequences or with other kinetic fractions. The foldback fraction sequences are fairly widely interspersed. The slow fraction sequences are interspersed with the fast fraction, and possibly also with the single copy DNA. The fast fraction is the dominant interspersed repetitive fraction. Its sequences are adjacent to the great majority of the single copy sequences and have an average length of about 300 nucleotides.

Animals↗

PubMed1978

Receptors for gamma-aminobutyric acid (GABA) on Aplysia neurons.

Aplysia neurons show 5 different types of response (three excitatory and two inhibitory) to iontophoretic application of gamma-aminobutyric acid (GABA). Four of these are associated with a membrane conductance increase, but one is associated with a conductance decrease. The most common response is a fast hyperpolarization which reverses at about--58 mV and is sensitive to manipulation of external Cl- concentration, and thus is due to a specific increase in Cl- conductance. There is an infrequent, slower hyperpolarizing response which does not reverse above about--80 mV and is insensitive to external Cl-. This response appears to result from a conductance increase to K+. Two types of depolarizing responses are associated with conductance increases. These responses differ in their latency, duration and sensitivity to curare. The more frequent is relatively rapid (peak at 1-2 sec) and is depressed by curare at high concentrations. In other neurons, GABA causes a slower response, peaking at 6-10 sec, which is not curare-sensitive. Usually for both types of response, the voltage and conductance changes are completely abolished by perfusion with Na+-free seawater, and the responses cannot be reversed with depolarization. In other neurons such as L11, the response can be reversed with depolarization, and appears to result from a conductance increase to both Na+ and Cl-. In neuron R15, GABA causes a slow depolarizing response (peak at about 9 sec) which is associated with a decreased membrane conductance, probably to K+. The classical GABA antagonists, picrotoxin and bicuculline, block Cl- responses but no others, while the fast Na+ and Cl- responses are depressed by curare. Strychnine does not affect any GABA response. The multiplicity of GABA responses, the specificity of their organization and the fact that only some neurons have receptors for GABA, argue that GABA may have a role as a neurotransmitter in Aplysia. Furthermore, the existence of several types of excitatory GABA response suggests that GABA may function both as an inhibitory and excitatory neurotransmitter.

Acetylcholine↗

PubMed1979

Motorneuronal control of locomotion in Aplysia.

We have carried out a combined behavioral and cellular analysis of escape locomotion in Aplysia. Using videotape recording we obtained a detailed description of the coordinated movements of the different regions of the foot and body during locomotion. Alternating waves of extension and longitudinal contraction begin at the head and propagate caudally through each pedal segment at a constant rate. Cobalt backfill of pedal nerves indicated that certain regions of the pedal ganglia were likely to contain motor neurons for the foot and body wall musculature. We examined these areas using intracellular techniques and identified three unique cells and three regional classes of neurons having clear motor effects on the foot and body wall. We also found that locomotion is driven by a central program. The basic locomotor pattern of the identified motor neurons and regional classes of motor neurons persists even after the circumesophageal ganglia have been isolated from the periphery. The motor neurons are not synaptically interconnected; patterned bursting during locomotor activity is produced by cyclic synaptic input. Because the locomotor system has large neurons favorable for cellular analysis and because locomotion is characterized by features of both stereotypy and flexibility, Aplysia promises to be useful for investigating the mechanisms underlying both the generation and modulation of a central program.

Animals↗

PubMed1979

Spectral characterization of the neuronal pigments of Aplysia juliana.

Spectral analysis at liquid N2 temperature of the circumesophageal ganglia of Aplysia juliana showed that carotenoids and a hemoglobin-like pigment are contained in concentrations of approx. 25 and 3 micronM, respectively, in the whole ganglia. Microspectrophotometrical measurements of Aplysia neurons indicated that the carotenoids reside on lipochondria in a concentration of approx. 38 mM. In addition to lipochondria, two types of pigmented particulate having absorption maxima at about 512 and 525 nm, respectively, were found in the neurons. The neuronal carotenoids consist of violaxanthin, beta-carotene and one minor component; among them the first occupies approx. 77% of total carotenoids. Two principal absorption maxima of the carotenoids, when existing in both ganglial homogenates and Triton X-100 extracts, show a red shift of 10 nm compared with those of free pigments in hexan. The red shift may be interpreted as due to the solvation of the carotenoids by surrounding lipids.

Animals↗

PubMed1979

Specific association of neurotransmitter with somatic lysosomes in an identified serotonergic neuron of Aplysia californica.

Injection of [3H]serotonin directly into the cell body of the giant metacerebral neuron (GCN), an identified serotonergic cell in the Aplysia cerebral ganglion, revealed a striking association of the labeled transmitter with large lysosomes. Most of the [3H]serotonin in the neuron is sequestered by lysosomes, which may function as storage depots for the transmitter. This localization is specific: [3H]serotonin was not found in similar lysosomes in the perikaryon of R2, an identified Aplysia cholinergic neuron. [3H]Dopamine, [3H]histamine, and [3H]-N-acetylgalactosamine injected into the serotonergic neuron were not localized in lysosomes. Because of this specificity, it may be possible to use lysosomal binding of labeled transmitter as a radioautographic method for identifying the transmitter type of a nerve cell body. These organelles are lysosomal in origin because they contain acid phosphatase activity. Moreover, examination of isolated GCN cell bodies by fluorescence microscopy revealed the presence of abundant autofluorescent yellow pigment characteristic of lipofuscin. We suggest that [3H]serotonin labels organelles containing membranes that once were integral components of the serotonergic vesicle. Lysosomes might accumulate the transmitter with a high degree of specificity because they contain membranes, perhaps recycled from the neuron's synaptic terminals, that retain their ability to concentrate and bind serotonin.

Acid Phosphatase↗

PubMed1979

Photoresponses of a sensitive extraretinal photoreceptor in Aplysia.

1. The light-evoked membrane current, photo-current, of an extraretinal photo-receptor, the ventral photoresponsive neurone (v.p.n.), in the abdominal ganglion of Aplysia californica, was studied using the voltage clamp method. Flashes and steps of monochromatic light were used as stimuli. 2. Flashes of light 100 msec in duration elicit slowly developing outward currents which peak at 5--10 sec and then return to dark levels within 30--60 sec. 3. The peak of the action spectrum of v.p.n. is at 470 nm and is similar to the peak for R2, another photoresponsive extraretinal Aplysia neurone, and to the peak of absorption spectra of molluscan rhodopsins. V.p.n. also contains membrane-bound cytoplasmic pigmented granules similar to those found in R2, and these are thought to mediate the light response. 4. Photo-current is associated with an increase in membrane conductance. In normal sea water photo-current has a reversal potential at the K equilibrium potential, EK and the reversal potential has a Nernstian relationship with external K concentration. The current--voltage relationships for peak and steady-state photo-current are fitted by the same constant field equation; currents measured when voltage was changed in steps at peak photo-current also have a similar relationship with voltage. The results are similar when saturating or non-saturating light intensities were used. Thus it appears that the light-activated K+ conductance is neither time nor voltage dependent. 5. Minimally detectable responses occurred at flash photon densities of 10(12) photons cm-2 which is 10(-3) that for R2. This value is comparable to those reported for retinal photoreceptors of Pecten irradians, a scallop, and Salpa democratica, a pelagic tunicate, and is lower than values reported for extraretinal photoreceptors such as the pineal photoreceptors of Salmo gairdnerii irideus, the rainbow trout, and the caudal photoreceptor in the sixth abdominal ganglion of Procambarus clarkii, a crayfish. 6. V.p.n. has a linear amplitude response range for low intensities of light and a non-linear range that saturates at high intensities. In the accompanying paper the response wave form and its temperature dependence are interpreted according to a diffusion-based model.

Animals↗

PubMed1978

Picrotoxin prevents habituation of the gill withdrawal reflex in Aplysia.

The gill withdrawal reflex evoked by tactile stimulation of the siphon in Aplysia habituates with repeated presentation of the stimulus. This adaptive behaviour is mediated by the integrated activity of the central (CNS) and peripheral (PNS) nervous systems. The PNS mediates the basic reflex and its habituation while the CNS exerts both suppressive and facilitatory control over the PNS. This results in greater adaptability of the reflex behaviours. In young Aplysia the CNS control is absent and this is due to the imcomplete development of pathways in the CNS. In an attempt to identify the pathway an attempt was made to manipulate the CNS's suppressive influence by agents which antagonize putative neurotransmitters. The application of picrotoxin-containing seawater over the CNS removed the CNS's suppressive influence but not its facilitatory influence. Thus the reflex amplitude was increased, the reflex latency decreased, and repeated stimulation did not result in habituation. This effect of picrotoxin was completely reversible. It is thus proposed that gamma-aminobutyric acid, a putative neurotransmitter, plays an important role in the mediation of the CNS's suppressive influence.

Animals↗

PubMed1979

The development of central nervous system control of the gill withdrawal reflex evoked by siphon stimulation in Aplysia.

In older Aplysia, the central nervous system (CNS) (abdominal ganglion) exerts suppressive and facilitatory control over the peripheral nervous system (PNS) which initially mediates the gill withdrawal reflex and its subsequent habituation evoked by tactile stimulation of the siphon. In young animals, both the suppressive and facilitatory CNS control were found to be absent. In older animals, removal of branchial nerve (Br) input to the gill resulted in a significantly reduced reflex latency and, with ctenidial (Ct) and siphon (Sn) nerves intact, a significantly increased reflex amplitude and an inability of the reflex to habituate with repeated siphon stimulation. In young animals, removal of Br had no effect on reflex latency and with Ct and Sn intact, the reflex amplitude latency was not increased and the reflex habituated. Older animals can easily discriminate between different intensity stimuli applied to the siphon as evidenced by differences in reflex amplitude, rates of habituation, and evoked neural activity. On the other hand, young animals cannot discriminate well between different stimulus intensities. The lack of CNS control in young animals was found to be due to incompletely developed neural processes within the abdominal ganglion and not the PNS. The lack of CNS control in young Aplysia results in gill reflex behaviours being less adaptive in light of changing stimulus conditions, but may be of positive survival value in that the young will not habituate as easily. The fact that CNS control is present in older animals strengthens the idea that in any analysis of the underlying neural mechanisms of habituation the entire integrated CNS-PNS must be taken into account.

Animals↗

PubMed1979

Interactions between bilateral clusters of neuroendocrine cells in Aplysia.

1. Activity of bilateral clusters of electrotonically coupled neuroendocrine cells (the bag cells) was studied using multiple-site intracellular and extracellular recording techniques in isolated parietovisceral ganglia of three species of Aplysia. Bilateral afterdischarges typically began with spike initiation on one side near the neurite terminals along the pleurovisceral connective; propagation of action potentials then proceeded toward the somata with potentiation to full somatic invasion in the ipsilateral bag cell cluster. This activity potentiated across the parietovisceral ganglion until contralateral spikes were initiated at a point near the bag cell somata (designated site A) and compound bag cell activity was then propagated both inward toward the somata and outward toward the circumesophageal ring of head ganglia. This sequence of events, i.e., "in one side, out the other," could occur several times during an afterdischarge, although outward propagation of activity was rarely maintained for more than 20 spikes. Synchrony between clusters was best during these periods of activity. Usually after a few episodes of this sequence, the sites of spike initiation spontaneously shifted to near the neurite terminals of each side and activity was initiated distally and propagated inward. Asychrony between clusters commonly developed when the sites for spike initiation were near the neurite terminals of each side. 2. Waveforms and temporal sequence of recorded events indicate that at least two sites for spike initiation exist within the neuritic tree of each bag cell cluster. These are the distal terminations of the neurites and a proximal site near the somata. Action potentials could be generated at this proximal site spontaneously or when electrotonically driven by contralateral activity. Removal of the bag cell somata did not interfere with bilateral behavior of the bag cell system. The proximal site is, therefore, not somatic. Activity initiated there was always more synchronous and propagated with a higher conduction velocity than activity initiated at the distal ends of the neurites. 3. Experiments were performed with and without the circumesophageal ring of head ganglia intact. Removal of the head ganglia had no effect on bilaterality of or synchrony within the bag cell system. Systematic stimulations and cuts of head ring connectives suggested that the cerebral ganglion may participate in orthodromic activation of the bag cells. 4. Our findings indicate the bag cells of Aplysia are a homogeneous population of neuroendocrine cells with multiple sites for spike initiation. Either cluster can serve as a pacemaker for the other through potentiation and electrotonic activation of the contralateral cluster at proximal sites on the neurites.

Action Potentials↗

PubMed1979

Circadian organization in Aplysia californica.

Substantial progress has been made in unraveling the organization of the circadian system of Aplysia californica. There are at least three circadian pacemakers in Aplysia. One has been localized in each eye and a third lies outside the eyes. Removal of the eyes disrupts the free-running locomotor activity rhythm; however, an extraocular oscillator can mediate a free-running rhythm in some eyeless animals. Although photoreceptors sufficient for entrainment of the ocular oscillator have been localized in the retina, photoreceptors outside the eyes are capable of "driving" a diurnal rhythm of locomotor activity and may also influence entrainment of ocular pacemakers. Finally, attention has been focused on the optic nerve as a coupling pathway between various parts of the system. The evidence suggests that information transmitted in the optic nerves is involved in entrainment of the ocular pacemaker by light, and in ocular control of the locomotor activity rhythm.

Action Potentials↗

PubMed1976

The abdominal ganglion of Aplysia brasiliana: a comparative morphological and electrophysiological study, with notes on A. dactylomela.

The ultrastructure and electrophysiological properties of neurons in the abdominal (visceral) ganglion of the marine opisthobranch gastropod Aplysia brasiliana have been investigated to determine whether this preparation compares favorably with the well studied A. californica for neurobiological research. In general, the topography, morphology and physiological characteristics, including synaptic connections, of neurons in this ganglion are quite similar to those of A. californica. There is close correspondence between the two animals in terms of each of the identified cells or neuronal clusters in the ganglion, including the presence of the cell L10 (interneuron I) in A. brasiliana which makes synaptic connections comparable with those in A. californica. New follower cells of this interneuron have been found in A. brasiliana. This species offers some advantages in that the connective tissue surrounding the ganglion is thinner and more transparent, making cell identification and penetration easier. A. brasiliana appears to exhibit the behaviors of A. californica that have been used in previous functional analyses of neural circuits. In addition, this species swims and exhibits a "burrowing" activity less commonly seen in A. californica. The rich repertoire of behaviors and accessibility of large identifiable and functionally interconnected neurons makes this species of Aplysia an excellent model preparation for future neurobiological studies. Similar, less thorough, investigations of the abdominal ganglion of A. dactylomela indicate that this species is also very similar to A. californica in terms of the identified cells in the abdominal ganglion.

Animals↗