Aplysia giant cell: soma-axon voltage clamp current differences.

Under voltage clamp, local membrane currents have been measured in several regions of the soma. The early inward current appears to pass largely through the membrane of the axon and of the soma near the axon in normal media. After 10(-5) molar tetrodotoxin (TTX) is added to the bathing medium the larger inward current is found in the somatic membrane away from the axon. The late currents are larger at the soma in both normal and TTX media.

Periventricular cerebral impedance after intraventricular injection of calcium.

Injection of small volumes of calcium solution into the lateral ventricle of the cat wa followed by large electrical-impedance changes in gray matter bounding the ventricle, including the caudate nucleus and hippocampus. These changes lasted more than 24 hours and were accompanied by epileptiform electroencephalographic activity. Biweekly injections led to status epilepticus. Injections of similar amounts of magnesium ions were without comparable effects. Possible interactions between calcium ions and intercellular macromolecular material are discussed as a basis for certain impedance shifts in cerebral tissue.

Fertilization events induced by neurotransmitters after injection of mRNA in Xenopus eggs.

Fertilization initiates in the egg a dramatic increase in intracellular calcium that opens ion channels and causes exocytosis. To explore the possibility that these events might involve a receptor-mediated pathway, receptors for serotonin or acetylcholine (M1 muscarinic) were expressed in the Xenopus egg; serotonin or acetylcholine then could initiate a series of responses similar to those normally initiated by sperm. Thus, there may be an endogenous receptor in the egg membrane that is activated by sperm, and the serotonin or M1 muscarinic receptor may replace the sperm receptor in this pathway.

Application of antimony microelectrodes to intracellular pH monitoring.

Some novel studies of the properties of the antimony microelectrode used for intracellular pH measurements are described. First, it is shown that currents in the picoampere range, such as those encountered as leakage in some electrometers, induce important changes in pH sensitivity. The response time of the electrode has also been measured and indicates that the electrode exhibits a rapid time course which would be very useful for dynamic cytoplasmic pH investigations. An example of internal pH recording during cellular acidification in Xenopus laevis oocyte is also presented.

Stimulus parameters for induction of long-term depression in in vitro rat Purkinje cells.

Long-term depression (LTD) was induced in rat cerebellar slices by conjunctive stimulation of parallel fibers (PFs) and climbing fibers (CFs) under perfusion of 20 microM picrotoxin. LTD was estimated by the reduction in the initial rising slope of EPSPs PF-induced in Purkinje cell dendrites. LTD-inducing efficacy was represented by both the average amount of depression and the probability of inducing depression greater than 25%, both measured at 40 min after the onset of conjunctive stimulation. Using 300 regularly recurring pulses given to both CFs and PFs with 0 ms interval, LTD was optimally induced at 1 Hz, and to lesser degrees at other frequencies. When the number of conjunctive stimuli at 1 Hz with zero CF-PF interval was varied from 50 to 500, 300 stimuli induced LTD most robustly. When CF-PF interval was varied while 300 pulses were given at 0.25-4 Hz, LTD was induced even when PF stimuli were delayed after CF stimuli by as much as 2 s, but it was inhibited when PF stimuli preceded CF stimuli by 10-100 ms. LTD was also induced by applying repeated short pulse trains to both CFs and PFs, but repeated application of a PF stimulus train immediately followed by a CF stimulus train as in classical conditioning was effectless. The present results suggest complex processes leading to LTD as a result of conjunctive CF and PF stimulation.

Differential blocking action of Joro spider toxin analog on parallel fiber and climbing fiber synapses in cerebellar Purkinje cells.

Synaptic potentials were recorded intracellularly from Purkinje cells in guinea pig cerebellar slices. EPSPs evoked by stimulation of parallel fibers were effectively blocked by perfusion of a slice with the synthetic analog of Joro spider toxin, 1-naphthylacetyl-spermine (NAS) at 250 microM. However, it did not influence those responses evoked by stimulation of climbing fibers. This action of NAS is in contrast to other commonly used glutamate antagonists, CNQX or APV: CNQX (5 microM) blocked both parallel fiber- and climbing fiber-induced responses, while APV (up to 1 mM) did not influence either except for a weak reduction observed in climbing fiber responses. NAS thus provides a useful tool for pharmacologically distinguishing parallel fiber and climbing fiber synapses.

Divalent cation changes in cerebellar Purkinje cells after climbing fiber deafferentation.

A secondary ion mass spectrometry (SIMS) microscope was used to detect intracellular stores of calcium, magnesium, sodium and potassium. Measurements were made in semithin sections of fixed tissues of normal and climbing fiber deafferented cerebellar cortex. Quantitative data were collected from 150 microns diameter image fields in the molecular and granule layers. The results indicate smaller quantities of both calcium and magnesium in the deafferented cerebellar cortex compared to the normals, the molecular as well as the granule layer being affected. The results are discussed in terms of the usefulness and limitations of the SIMS microscope for histological preparations.

Loading and localization of Fluo-3 and Fluo-3/AM calcium indicators in sinapis alba root tissue.

Stimulus-induced changes in free cytosolic Ca2+ in different types of plant cells have been monitored with the aid of fluorescent calcium indicator dyes. However, there is no simple and convenient method for introducing these dyes into the plant cell cytoplasm. This paper reports tests of different procedures for loading either free fluorescent dyes or their acetoxymethyl esters (Fluo-3 and Fluo-3/AM, respectively) into Sinapis alba root tissue. Loading of Fluo-3 was pH and temperature dependent. Moreover, in the presence of beta-escin (saponin) in the loading medium very high fluorescent signals in root tissues were observed. The highest signals were recorded when tissue was loaded in a medium containing 0.1% beta-escin, at pH 5.0 and 30 degrees C. Only very weak fluorescence signals were found in mustard roots loaded with Fluo-3/AM. Acidity and temperature of the medium had no significant effect on the process. However, addition of eserine, a cholinesterase inhibitor led to a dramatic increase in fluorescence in the root cells. On the basis of these observations rapid and efficient methods of loading both Fluo-3 and Fluo-3/AM into mustard root tissues are proposed.

On the fibers of the III, IV and VI cranial nerves of the cat.

The fiber content and diameter spectra of the cranial nerves III, IV and VI were analysed in cat. A semi-automatic technique of measuring fiber diameters is presented and compared to the manual method. The number of fibres was counted in the proximal part of the three main nerves and in each of their distal branches before they enter the EOM. Compared to the muscle weight, the branch to the RB had fewer fibers than all the other muscle branches. The diameter spectra of the proximal part of the three main nerves were compared with the diameter spectra of each of their distal branches. Minor differences were found among them. Only the RB had a striking difference in the spectrum which was skewed toward the large diameters.

Increased calbindin-D28K immunoreactivity in rat cerebellar Purkinje cell with excitatory amino acids agonists is not dependent on protein synthesis.

The calcium binding protein Calbindin-D28K (CaBP) is abundantly expressed in cerebellar Purkinje cells and show increased immunoreactivity (CaBP-IR) when challenged with glutamate or an analog agonist for the ionotropic glutamate receptor (iGluR). Here we report that t-ACPD, a metabotropic glutamate receptor (mGluR) agonist, produced small increases in CaBP-IR which was potentiated by a mGluR antagonist The increase in CaBPIR was not due to de novo protein synthesis because the translational inhibitors (cycloheximide and emetine) or transciptional inhibitors (actinomycine-D and a-amanitine), did not prevent the EAA enhanced CaBP-IR. The CaBP-IR in the PC appears to be coupled to the ionotropic rather than the metabotropic glutamate receptors, but the latter become effective in the presence of their blocker, L-AP3. The results suggest that CaBP may increase its IR through a conformational change of the protein itself.

Synaptic long-term depression (LTD) in vivo recorded on the rat cerebellar cortex.

Long-Term Depression (LTD) of the parallel fiber synapses of the cerebellar cortex has been intensively studied over the last 20 years and is now considered to be a physiological mechanism underlying learning and memory of the cerebellar cortex. With microelectrode recording in vivo, the induced LTD is recorded reliably up to 2 hours. Using surface electrodes we have recorded parallel fiber responses due to the currents generated by the AMPA type receptors of the dendritic spines in the intact vermal cortex of decerebrated rats. We have found that by conjunctively stimulating the climbing and parallel fiber pathways, an LTD was induced which persisted for as long as the recording conditions permitted. The longest lasting LTD of our present results was for 5 hours.