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E A Kravitz

Publications and source records attributed to E A Kravitz.

At least 55 records · Page 3Linked to original sources
PubMed1979

Neurotransmitter synthesis in Limulus ventral nerve photoreceptors.

Radiochemical precursor compounds for neurotransmitters were incubated with Limulus ventral nerve photoreceptor preparations. Octopamine was preferentially synthesized by a photoreceptor rich fraction of the nerve, acetylcholine was made by a photoreceptor poor fraction, and gamma-aminobutyric acid was made about equally well in both fractions. The possibility that the ventral nerve photoreceptor cells serve a neurosecretory function in the adult Limulus is discussed.

Acetylcholine↗
PubMed1978

The physiological properties of amine-containing neurones in the lobster nervous system.

1. Our previous studies have shown that octopamine and serotonin are found associated with a system of neurones in the connective tissue sheath of the second roots of lobster thoracic ganglia. To try to understand the mechanism of activation of these neurones, we undertook an examination of their general physiological properties. 2. All of the neurones receive excitatory synaptic input that has a cholinergic pharmacology, which suggests that it may be from sensory neurones. A very limited number of cells, possibly one, provdes the total synaptic input to all the cells in the roots of the second and third thoracic segments. 3. The cells within one root are electronically coupled to each other. The extent of coupling varies widely between cells; on occasion the coupling is sufficiently tight for action potentials originating in one cell to trigger action potentials in the neighbouring cell. 4. The majority of the cells show no spontaneous activity at temperatures below 14 degrees C, but become spontaneously active above that temperature. Cells cycle reversibly from silent to continuously active to bursting and back as the temperature is increased and decreased. 5. Octopamine and serotonin both inhibit the bursting activity. The octopamine response is blocked by phentolamine but not by propranolol, while the inhibitory action of serotonin is unaffected by either of these drugs. The amine-inhibition of the firing could be an autoregulatory mechanism for cell activity. 6. The physiological properties described in this paper suggest that the widely dispersed amine-containing neurones in lobsters behave like a neurosecretory organ in terms of their mechanism of activation.

Action Potentials↗
PubMed1978

Targets of octopamine action in the lobster: cyclic nucleotide changes and physiological effects in hemolymph, heart and exoskeletal muscle.

We have examined three potential targets of octopamine action of the lobster--hemolymph, heart and exoskeletal muscle--and found that each tissue responds to the amine with increases in cyclic adenosine 3': 5'-monophosphate (cAMP) and changes in measurable physiological phenomena. A highly specific octopamine-stimulated increase in cAMP is observed in hemolymph, and this effect is probably due to the presence of a unique octopamine receptor on hematocytes. Pharmacological studies show that synephrine is a potent agonist of the hemolymph receptor for octopamine and that the alpha adrenergic receptor blockers phentolamine and dibenamine and the dopamine receptor blocker, chlorpromazine, are antagonists. Addition of octopamine to lobster hemolymph increases the rate of changes the nature of the clotting reaction. AMP levels in lobster heart are elevated by both octopamine and serotonin. Both amines also increase the rate and the amplitude of the heart beat. Octopamine, serotonin and dopamine all increase cAMP levels in lobster exoskeletal muscle preparations, and each amine causes changes in muscle tension and the strength of nerve evoked contractions. In none of the tissues studied have we been able to establish a direct relationship between amine-stimulated increases in cAMP levels and the physiological responses.

Animals↗
PubMed1976

Octopamine neurons in lobsters: location, morphology, release of octopamine and possible physiological role.

Octopamine cells are found along second thoracic roots, where they serve as neurosecretory neurons capable of releasing octopamine at two distinct points: one into the hemolymph immediately before it enters the gills; one into the hemolymph immediately after it leaves the gills. The octopamine cells receive a cholinergic synaptic input. We presume that this input is from processes of peripheral sensory cells bringing information to the CNS. Octopamine can increase the strength of contraction of exoskeletal muscles and, at higher concentrations, can induce contractures in these muscles. These effects can be interpreted as a resetting of the level of ionized calcium within muscle fibers (the contracture) to a higher value or a possible enhanced entry of calcium ions during nerve stimulation (increased strength of contraction). The observed effects are of a prolonged duration, outlasting the time of application of octopamine by some 20-40 minutes. We do not know if this effect on muscle tension production is the normal physiological role of octopamine. Other possible roles will be explored in the future. The pathway involving the octopamine neurons in lobsters may provide a model neurohumoral system that can be studied and understood in detail from the level of sensory input to the level of behavioral output.

Animals↗
PubMed1976

The association of octopamine with specific neurones along lobster nerve trunks.

Octapamine and its synthetic enzyme, tyramine beta-hydroxylase (TBH), are found in high concentrations at two points along second thoracic nerve roots in lobsters. The first is in the proximal section of the second root between the ventral nerve cord and the bifurcation of the root into medial (to flexor muscles) and lateral (to extensors) branches. The second region of high concentration is within a well known crustacean neurosecretory system, the pericardial organ, located close to the ends of the lateral branches of the roots. 2. With several different staining procedures, small clusters of nerve cell bodies are found within the connective tissue sheath in the proximal regions of the second roots. No cell bodies are seen in the pericardial organ regions. Cell bodies are variable in number and position between corresponding roots in the same animal and homologous roots among different animals. The average numbers of cell bodies, however, correlate well with TBH and octopamine content, and with the synthesis of octopamine in these same regions of roots. 3. Small clusters of root cell bodies dissected from preparations have greater than 500-fold higher activities of TBH than isolated efferent excitatory and inhibitory or afferent sensory axons. 4. Along with octopamine, the preferential synthesis of acetylcholine and serotonin is also seen in proximal segments of roots. Acetylcholine synthesis in these regions may represent transmitter synthesized in the nerve terminals innervating the root cells. The role of serotonin in these regions is not understood at this time but the amounts of endogenous serotonin found are only a tenth of the amounts of octopamine present. 5. Dopamine is not synthesized from tyrosine in second thoracic roots. However, if DOPA or dopamine are used as precursor compounds, then noradrenaline, which is usually not found in lobsters, can be accumulated in proximal segments of roots. 6. Phenolamines are converted to two further metabolites by lobster tissues. The compounds are unidentified and are named fast and slow product on the basis of their migration on electrophoresis at acid pH. Some partial characterization of slow product reveals that it is a mixture of compounds that can be converted on mild acid hydrolysis to fast product and the parent phenolamine. 7. The several lines of evidence presented suggest that nerve cells found in the proximal segments of the second thoracic roots contain and can synthesize octopamine. Since not all the cells in any single root have been analysed for octopamine or TBH, however, the possibility that one or more of the cells contain physiologically interesting substances other than octopamine is not eliminated.

Animals↗
PubMed1976

Octopamine release at two points along lobster nerve trunks.

Nerve cells in the proximal regions of second thoracic roots in lobsters have been injected with the fluorescent dye Procion Yellow. Examination of the roots reveals an elaborate array of cell branches in a superficial layer of the root in the vicinity of the cell bodies. Large varicosities, up to 10 mum in diameter, are seen lined up along fine nerve branches. 2. In these same regions, electron microscopic examination shows the presence of large profiles filled with 0-1-0-2 mum dense cored granules, and having the appearance of nerve endings. These profiles probably correspond to the varicosities seen in the Procion Yellow injections. The dense cored granules within the endings have a crystalline substructure. All the endings are found within 7 mum of the surface of the root and no obvious physiological target tissue exists in their surroundings. Endings have not been traced directly to root cell bodies.However, granules of similar dimensions to those seen in endings are found in cell bodies, axon-hillock regions and numerous axonal profiles in the superficial root regions near cell bodies. The morphological studies suggest that the root neurones have the typical appearance of neurosecretory cells. 3. Octopamine pools in cell body regions of second thoracic roots can be isotopically labelled by incubation with either [3H]tyramine or [3H]-tyrosine. After labelling, pulsing with 100 mM potassium causes an increase in the rate of release of radioactive material. Upon return to normal media background rates of release are re-established. The enhanced efflux has the following properties: (a) repeated pulses of potassium release less radio-active material each time; (b) a prolonged potassium pulse produces first a peak of release, then a decline to a plateau, and the plateau level of release is maintained for the duration of the potassium pulse; (c) release is dependent on the presence of calcium ions in the bathing fluid and 40 mM cobalt prevents release; (d) release is selective for octopamine. With tyrosine as a precursor compound, as much radioactive tyrosine as octopamine is found in tissues after incubation, yet pulsing with potassium causes an enhanced efflux only of octopamine from preparations. 4. Release of octopamine also can be demonstrated from pericardial organs near the ends of lateral branches of the roots and the properties of the release are identical to those seen with cell body regions. 5. Physiological studies, in which root cells are antidromically activated while recording from cell bodies, suggest that the distal endings of at least some of the root cells are at the pericardial organs. 6. The results suggest that root cell neurones are neurosecretory cells capable of releasing octopamine at two points: one near cell bodies, the other at the pericardial organs near the distal ends of the roots...

Animals↗
PubMed1972

Acetylcholine and lobster sensory neurones.

Experiments are presented in support of the hypothesis that acetylcholine functions as a sensory transmitter in the lobster nervous system.1. Several different peripheral sensory structures incorporate radioactive choline into acetylcholine. The preparation most enriched in sensory as opposed to other nervous elements (the antennular sense organs of the distal outer flagellum) does not incorporate significant amounts of glutamate, tyrosine or tryptophan into any of the other major transmitter candidates.2. There is a parallel between the distribution of the enzyme choline acetyltransferase and the proportion of sensory fibres in nervous tissue from many parts of the lobster nervous system.3. Isolated sensory axons contain at least 500 times as much choline acetyltransferase per cm of axon as do efferent excitatory and inhibitory fibres.4. Abdominal ganglia and root stumps show a decline in the rate of incorporation of choline into acetylcholine 2 to 8 weeks after severing the first and second roots bilaterally (leaving the connectives and third roots intact). Extracts of the root stumps exhibit a significantly lower level of choline acetyltransferase 2 weeks after this operation.5. Curare and atropine partially block an identified sensory synapse in the lobster abdominal ganglion.

Acetylcholine↗
PubMed1971

Localization of the sites of gamma-aminobutyric acid (GABA) uptake in lobster nerve-muscle preparations.

The principal sites of gamma-aminobutyric acid (GABA) uptake in lobster nerve-muscle preparations have been determined with radioautographic techniques after binding of the amino acid to proteins by aldehyde fixation. Semiquantitative studies showed that about 30% of the radioactive GABA taken into the tissue was bound to protein by fixation. Both light and electron micrographs showed dense accumulations of label over Schwann and connective tissue cell cytoplasm; muscle was lightly labeled, but axons and terminals were almost devoid of label. The possible role of Schwann and connective tissue cells in the inactivation of GABA released from inhibitory axons is discussed.

Aldehydes↗
PubMed1970

The metabolism of gamma aminobutyric acid in the lobster nervous system. Enzymes in single excitatory and inhibitory axons.

gamma-aminobutyric acid (GABA) is the inhibitory transmitter compound at the lobster neuromuscular junction. This paper presents a comparison of the enzymes of GABA metabolism in single identified inhibitory and excitatory axons from lobster walking legs. Inhibitory axons contain more than 100 times as much glutamic decarboxylase activity as do excitatory axons. GABA-glutamic transaminase is found in both excitatory and inhibitory axons, but about 50% more enzyme is present in inhibitory axons. The kinetic and electrophoretic behavior of the transaminase activity in excitatory and inhibitory axons is similar. Succinic semialdehyde dehydrogenase is found in both axon types, as is an unknown enzyme which converts a contaminant in radioactive glutamic acid to GABA. In lobster inhibitory neurons, therefore, the ability to accumulate GABA ultimately rests on the ability of the neuron to accumulate the enzyme glutamic decarboxylase.

Aminobutyrates↗
PubMed1968

Neuronal geometry: determination with a technique of intracellular dye injection.

In a study of the specificity of neuronal connections in lobster abdominal ganglia, the dye Procion Yellow M4RS was electrophoretically injected into identified cell bodies. This dye spreads into fine branches of cells, survives fixation and routine histological procedures, and permits the reconstruction of cell shapes through examination of serial sections of ganglia. Certain cells were found to have an internal bilateral symmetry. Repeated injection of the same cells in ganglia from different animals showed that cells have characteristic shapes and that the neuropil is highly structured. This method of dye injection should have general applicability in studies where a knowledge of the geometry of specific cells is important.

Animals↗