Neurotransmitter actions in the thalamus and cerebral cortex and their role in neuromodulation of thalamocortical activity.

Isolated single units in rat dorsal hippocampus and fascia dentata were classified as 'Theta' or 'Complex-Spike' cells, and their firing characteristics were examined with respect to position, direction and velocity of movement during forced choice, food rewarded search behavior on a radial eight arm maze. Most spikes from CS cells occurred when the animal was located within a particular place on the maze and moving in a particular direction. Theta cells had very low spatial selectivity. Both cell categories had discharge probabilities which increased somewhat as a function of running velocity but tended to asymptote well before half-maximal velocity. The place/direction specificity of CS cells was significantly higher in CA1 than in CA3 and CA3 CS cells exhibited a striking preference for the inward radial direction. The pronounced directional selectivity of CS cells, at least in the present environment, suggests that they fire in response to complex, but specific, stimulus features in the extramaze world rather than to absolute place in a non-egocentric space. An alternative possibility is that the geometrical constraints of the maze surface have a profound influence on the shapes of the response fields of CS cells.

/pdf/the-contributions-of-position-direction-and-velocity-to-3mdiwb6joq.pdf

The contributions of position, direction, and velocity to single unit activity in the hippocampus of freely-moving rats.

The stereotrode: A new technique for simultaneous isolation of several single units in the central nervous system from multiple unit records

1. The consequences of repetitive activation of excitatory synaptic inputs to the CA1 pyramidal cells of rat hippocampus have been studied using in vitro techniques. 2. Single stimulation trains of 100 pulses at rates of 5-100/sec resulted in potentiation of population spike amplitudes lasting the duration of a 5 min test period in thirty-four out of thirty-five cases. Trains of 100 pulses delivered at 1/sec resulted in depression of the stimulated pathway in ten out of twelve experiments. 3. Responses to test stimulation of other excitatory inputs to the same cell population were depressed following conditioning trains at frequencies in the range 1-100/sec. Depression was seen both in the population spike amplitude (reflecting synchronous cell discharge) as well as the extracellularly recorded population e.p.s.p., and appeared to be maximal at lower frequencies. 4. Trains of antidromic stimulation of the CA1 cell population produced subsequent decreases in synaptically evoked responses, indicating that repetitive firing of pyramidal neurones or interneurones do not cause potentiation, but may be involved in heterosynaptic depression. 5. The results suggest that potentiation and heterosynaptic depression arise from different mechanisms, and that potentiation is confined to the set of terminals activated by a conditioning train, whereas the depression is generalized to the whole neurone.

Long-term potentiation and depression of synaptic responses in the rat hippocampus: localization and frequency dependency.

1 The effects of adenosine and various derivatives were examined in the in vitro hippocampal slice preparation from rat

2 The amplitudes of extracellularly recorded field potentials from the CA1 region were depressed by adenosine, and this effect could be antagonized by methylxanthines Because presynaptic field potentials were unaffected by adenosine, while the field epsp was depressed, adenosine would appear to act at a synaptic site to depress transmission

3 Adenosine deaminase, which breaks down adenosine to inosine, increased the amplitude of synaptic responses, while hexobendine, which blocks reuptake of adenosine, had a depressant effect This strongly suggests that the endogenous release of adenosine from the hippocampal slice preparation is sufficient to exert a tonic inhibitory influence on the amplitude of synaptic responses

4 Cyclic adenosine 3′,5′-monophosphate (cyclic AMP) and its dibutyryl derivative had depressant effects on the amplitude of field responses which were blocked by theophylline, suggesting that they are able to act at the extracellular adenosine receptor (-)-Isoprenaline (which raises tissue cyclic AMP levels), and the 8-p-chlorophenylthio derivative of cyclic AMP both increased the amplitude of population spike responses, and these effects were not blocked by theophylline, suggesting that the physiological effects of adenosine are not mediated via a cyclic AMP-dependent mechanism

5 Since adenosine is not the transmitter at this CA1 pyramidal cell synapse, but is apparently present in the extracellular compartment in sufficient concentrations to affect the synaptic physiology of this region, this provides strong evidence in favour of the concept of a neuromodulatory role for adenosine in the central nervous system

ADENINE NUCLEOTIDES AND SYNAPTIC TRANSMISSION IN THE in vitro RAT HIPPOCAMPUS

https://escholarship.org/content/qt2b76x53b/qt2b76x53b.pdf?t=niu5q2

A microdrive for use with glass or metal microelectrodes in recording from freely-moving rats ☆

ADENOSINE is postulated to function in the brain as an inter-cellularly active neurohumoral substance. This has been suggested by in vitro studies showing that adenosine can be released from brain tissue by electrical stimulation at quantities which are sufficient to increase the formation of cyclic AMP1. The finding that adenosine derivatives are released from dendrites and particularly axon terminals points to the neurones as a major source for the released nucleotides2. Thus, nucleotides may function as ‘secondary’ or ‘additional’ neuronal transmitters mediating long lasting effects of a neurone on the metabolism and function of its target cells. Further evaluation of these hypotheses will require demonstrations that endogenous adenosine or its derivatives are actually released by synaptic connections in the intact brain and that this process is influenced by activation of these connections. We have carried out experiments in which tritiated adenosine was transported from cell bodies into a population of terminals, and in which the amount of radioactive materials taken up by the target cells of these terminals was measured in the presence and absence of synaptic stimulation. Stimulation was found to increase the release of 3H-adenosine derivatives from central axon terminals to their postsynaptic neurones.

Stimulation-dependent release of 3H-adenosine derivatives from central axon terminals to target neurones.

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A microdrive for use with glass or metal microelectrodes in recording from freely-moving rats ☆

Stimulation-dependent release of 3H-adenosine derivatives from central axon terminals to target neurones.