Search

We have characterized in crustacean neurones in culture a receptor for gamma-aminobutyric acid (GABA) which conforms to the pharmacological profile of the proposed type-C GABA receptor (GABAC) found in the vertebrate retina. It is associated with a chloride-selective ion channel and is blocked by picrotoxin. It is neither inhibited by bicuculline nor activated by baclofen, while diazepam and phenobarbital are without modulatory effect. Like the GABAC-like receptor of the vertebrate retina it is activated by the folded GABA analogue cis-4-aminocrotonic acid (CACA). Desensitization is moderate allowing for a more sustained action of GABA. Single channel recordings revealed a bicuculline-resistant GABA- and CACA-activated chloride channel with a conductance about eight times higher than that described for the bicuculline-resistant GABA receptor channel from the rat retina.

We describe a primary culture system for neurones from the central nervous system of adult crayfish. After enzymatic treatment individual neurones were isolated by suction from abdominal ganglia and the stomatogastric ganglion. On poly-L-lysine as substrate they survived for up to 24 days and grew neuritic processes. Results from current and voltage clamp experiments show that functionally important electrophysiological properties are at least partly maintained or regenerated by cultured neurones.

A simple method for the in vivo visualization of dye filled cells by laser illumination is used to characterize neurons in situ in the segmentai ganglia of the locust and the crayfish (Fig. 1). Neuron visualization provides the structural information necessary for identification of cells during an ongoing physiological experiment (Figs. 2, 3). Sequential penetrations of soma and neuropil as well as simultaneous double neuropil penetrations of spiking and nonspiking cells are facilitated by the visual control afforded by neuron visualization (Figs. 4, 5, 6). Furthermore, neuron visualization allows the sampling of cellular properties at multiple, predetermined sites in the dendritic and axonal arbors of identified neurons (Fig. 7) and aids in establishing synaptic connectivity through double neuropil recordings (Fig. 8).

The morphology of the adult electromotoneurones of the electric ray Torpedo marmorata has been investigated by intracellular injection of horseradish peroxidase. The results show particularly small dendritic fields, poor dendritic branching, and the existence of two distinct types of dendrites. The electrophysiological data demonstrate that the electromotoneurones behave similarly in vivo and in in vitro brain slices. Observations on spontaneous and stimulus-evoked postsynaptic potentials suggest quantal release of transmitter in the Torpedo central nervous system.

1. The LDS interneuron is an identified, nonspiking, local interneuron which mediates across-the-midline lateral inhibition of anteriorally projecting mechanosensory interneurons in the crayfish terminal ganglion (Fig. 1). We used single electrode current clamp techniques to investigate the nature of the synaptic input to the LDS inter-neuron. 2. Afferent derived sensory input to an LDS interneuron consists of EPSPs and IPSPs both of which are depolarizing at the resting potential of the cell (Fig. 3). Stimulation of peripheral nerve roots ipsilateral to the soma of an LDS interneuron evokes EPSPs which have a reversal potential near −20 mV. Stimulation of contralateral nerve roots evokes IPSPs with a reversal potential near −50 mV. Thus an LDS interneuron receives sensory input of opposite sign from the two different sides of the tailfan (Fig. 4). 3. Simultaneous double penetrations in the neuropil ipsilateral and contralateral to the cell's soma (Fig. 5) demonstrate that the EPSPs originate in the ipsilateral neuropil whereas the depolarizing IPSPs are generated in the contralateral neuropilar arborization. 4. The inhibitory effect of IPSPs on concomitantly evoked EPSPs is dependent both on the membrane potential of the LDS cell and on the relative timing of the two PSP types. Inhibition is greatest if the cell is somewhat depolarized and if the IPSPs are timed so as to precede the EPSPs by several milliseconds (Figs. 5 and 6). 5. The lateralization of excitatory and inhibitory input and the specific mode of interaction of the depolarizing IPSPs and EPSPs make the LDS interneuron sensitive to the side of origin of water-borne stimulation. Water movements originating on the side of the tailfan ipsilateral to the inter-neuron's soma result in optimal excitation, water movements originating on the contralateral side of the tailfan result in optimal inhibition of the LDS interneuron (Fig. 7). 6. We postulate that the lateralized inhibition of the LDS interneuron documented here serves to improve the overall contrast enhancement of the directionally sensitive mechanosensory system of the crayfish (Fig. 8).

A beam dump experiment was performed in the CERN Gargamelle neutrino facility in order to look for new heavy penetrating neutral particles. Limits are determined for the mass and lifetimes of such particles, and also the cross section for their production.