Dendritic and somatic spikes in mudpuppy amacrine cells: indentification and TTX sensitivity

Pathways and polarities of synaptic interactions in the inner retina of the mudpuppy: I. Synaptic blocking studies

Intracellular recording techniques were applied to the perfused retina-eyecup of the mudpuppy (Necturus maculosus). The use of input resistance measurements and the application of cobalt as a synaptic blocking agent provided evidence about the mode of synaptic operation for depolarizing and hyperpolarizing bipolar cell input to cells of the inner retina. In addition, cobalt produced a more rapid block of hyperpolarizing bipolars compared to depolarizing bipolars; in some postbipolar neurons, a temporary simplification of neuronal response waveform was observed and such cells resembled the depolarizing bipolar. These experiments suggest that bipolar cell input is excitatory and that response characteristics of third-order neurons is partially dependent on the relative input from the two types of bipolar cells.

An intracellular study of dendrodendritic inhibitory synapses on mitral cells in the rabbit olfactory bulb

1. In the rabbit olfactory bulb, intracellular potentials were recorded from mitral cells and from neurones in the granule cell layer (g.c.l.) following lateral olfactory tract (l.o.t.) stimulation. 2. Most recordings from mitral cells showed large (5-21 mV) and prolonged (60-650 msec) i.p.s.p.s subseuqent to the antidromic spikes. These i.p.s.p.s decreased in amplitude and then reversed in polarity by progressive increase in hyperpolarizing current applied intracellularly. They were accompanied by a prominent and long lasting (up to 100 msec) conductance increase of the mitral cell membrane. 3. Reversed i.p.s.p.s of mitral cells having quite different time courses from the original hyperpolarizing i.p.s.p.s suggest that the inhibitory synapses are widely distributed on the soma and dendrites. 4. E.p.s.p.s could be recorded from g.c.l. cells whose onset latency was approximately 0.6 msec shorter than that of mitral cell i.p.s.p.s. Comparison of the behaviour of e.p.s.p.s in g.c.l. cells and that of mitral cell i.p.s.p. under various conditions of l.o.t. stimulation suggests that these g.c.l. cells are the inhibitory interneurones mediating mitral cell inhibition. 5. The results support the hypothesis of dendrodentritic pathways for activation of granule cells and subsequent inhibition of mitral cells.

A comparison of the proximal negative response and ganglion cell responses to sinusoidal flicker

In the mudpuppy retina, sinusoidal light stimulation of the proximal negative response (PNR) demonstrates two main components whose phases are essentially the same as those of the spike discharges of ON/OFF ganglion cells. Oscillations superimposed upon these components are synchronized with the spike discharges of ON/OFF cells, but not of ON or OFF cells. Intracellular recordings from ON/OFF ganglion cells reveal slow potentials with nearly identical waveforms and phases to those of the PNR. These results, together with previously published comparisons between the flesh-evoked PNR and amacrine cell responses, support the suggestion that the PNR arises from activity in the on/off system (amacrine and/or ganglion cells).

Amacrine cells in Necturus retina: evidence for independent gamma-aminobutyric acid- and glycine-releasing neurons

About one-half of on-off ganglion cells have inhibitory postsynaptic potentials (IPSP's) which are blocked by strychnine, while the remainder have IPSP's which are blocked by picrotoxin or bicuculline. These antagonists do not abolish light activity of the presynaptic inhibitory neuron, the amacrine cell. The existence of separate gamma-aminobutyric acid- and glycine-releasing amacrine cells is implied by these results.

The proximal negative response and visual adaptation in the skate retina

The proximal negative response (PNR), a complex extracellular potential derived mainly from amacrine cell activity, was studied in the all-rod retina of the skate. Tetrodotoxin (10(-6) mg/ml) did not affect either the waveform or the latency of the response, indicating that the PNR reflects the graded, nonregenerative components of the amacrine cell potential. As regards its adaptive properties, the PNR exhibited both the extreme sensitivity to weak background light and the slow time course of light and dark adaptation that are characteristic of other responses from the proximal retina. Thus, the PNR, like the b-wave and ganglion cell discharge, appears to reflect adaptive processes located within the neural network of the inner retina.

Regenerative amacrine cell depolarization and formation of on-off ganglion cell response

1. Recordings from amacrine and ganglion cells in the mudpuppy retina suggest mechanisms whereby the relatively slow, sustained light responses measured in bipolar cells are converted to rapid, brief, transient activity in the on-off ganglion cells. 2. Double-barrel electrodes were used to control the membrane potential under voltage clamp. The clamp revealed synaptic currents, but eliminated the otherwise obvious spike activity elicited by steps of illumination in both amacrine and ganglion cells, suggesting that the spikes are initiated near the somata. 3. The synaptic current in the on-off ganglion cells was biphasic: a brief inward (depolarizing) membrane current preceded a transient outward (hyperpolarizing) membrane current by about 20 msec. Each component could be isolated by polarizing the membrane to a level near the reversal potential for the other. Each was apparently due to a transient conductance increase of sawtooth shape with a 40 msec time to peak and a decay longer than 400 msec. 4. Synaptic membrane current in amacrine cells was monophasic and inward (depolarizing) of similar sawtooth shape at all potential levels. It was apparently mediated by a conductance increase to ions with a reversal potential more positive than the dark level. 5. When amacrine cells were depolarized in the dark under voltage clamp, a large transient inward membrane current with threshold within 4 mV of the dark level was generated. This regenerative event is capable of boosting a small, 4 mV e.p.s.p. to more than 30 mV in a few milliseconds, thereby generating the leading edge of a rapid sawtooth response. 6. The results suggest that the rapid transient on-off activity in ganglion cells is mediated by opposing sawtooth shaped synaptic currents with different latencies. It is inferred that each of these antagonistic imputs is generated by a regenerative depolarization in amacrine cells which then form synaptic inputs to the ganglion cells.

Identification of amacrine and ganglion cells in the carp retina

1. Amacrine and ganglion cells in the carp retina were identified from such criteria as photoresponses, intracellular dye staining, responses to optic nerve stimulation and behaviour to a synapse blocking agent. 2. Responses of ganglion cells were accompanied by spike discharges., either facilitated or suppressed by photic stimulation. The cells were also invaded by antidromic impulses, which survived after chemical synapses had been blocked by application of atomized CoCl2 solution. In subsequent histology of the Procion-stained neurones, the cell bodies were found in the ganglion cell layer and the axons were often traced. 3. Amacrine cells were subdivided into two types. The first type gave rise to transient depolarizations at both on- and offsets of spot and annulus illuminations, usually being associated with spike discharges of which the amplitudes varied in different cells. In histology, the cell bodies of this type were situated in the inner nuclear layer and dendrites ramified in two or more discrete sublayers of the inner plexiform layer (the stratified amacrine cell of Cajal). 4. The second type of amacrine cells produced sustained responses during illumination, being associated with no spike but with small oscillatory wavelets. The cell bodies were situated in the inner nuclear layer and the dendrites ramified in a single sublayer of the inner plexiform layer (the monolayered amacrine cell). 5. An attempt was made to see the effect of activation of centrifugal fibres on amacrine cells, but almost all of about 200 cells examined did not respond to optic nerve stimulation. Only two cells produced, with long latency, a small post-synaptic depolarization which disappeared after chemical synapses in the retina had been blocked. It is considered that the physiological role of the centrifugal system is insignificant in the carp retina.

Synaptic organization and ionic basis of on and off channels in mudpuppy retina. II. Chloride-dependent ganglion cell mechanisms

Extracellular ganglion cell recordings in the perfused mudpuppy eyecup show that a chloride-free (c-f) perfusate abolishes the center and surround excitation of on-center cells, the surround excitation of off-center cells, and the on discharge of on-off cells. These changes in ganglion cell receptive field organization are anticipated in view of the effects of a c-f environment on the neurons which are presynaptic to the ganglion cells. However, chloride-dependent inhibitory postsynaptic (IPS) responses have been observed in on-off ganglion cells. These inhibitory postsynaptic potentials (IPSP's) are preceeded by (ESPS's) exitatory postsynaptic potentials and are apparently mediated by amacrine cells. The light-activated hyperpolarization of off cells is not the result of a chloride-dependent IPSP and probably results from disfacilitation.