Enhanced responses to NMDA receptor activation in the developing cat caudate nucleus.

An in vitro slice preparation was used to assess the effects of N-methyl-D-aspartate (NMDA) receptor activation in the developing cat caudate nucleus. Removal of Mg2+ from the bathing medium, in the presence of 10 microM bicuculline, increased the amplitude and duration of the excitatory postsynaptic potential induced by local extracellular stimulation at all ages tested. In neurons younger than 35 days of age, removal of Mg2+ in the presence of bicuculline produced an increase in excitatory postsynaptic potential amplitude and duration as well as bursts of action potentials when local extracellular stimulation was applied. The effects of Mg2+ removal were reversibly attenuated by the specific NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid. These findings are important because they demonstrate that NMDA receptor-mediated responses can be induced in developing caudate neurons by local extracellular stimulation and these responses are enhanced in early postnatal periods at ages when motor control is being established.     

A possible visual pathway to the cat caudate nucleus involving the pulvinar

Electrical stimulation of the thalamic nucleus pulvinar was found to influence unit activity in the feline caudate nucleus. Twenty-six (18.3%) units were encountered, in this subcortical region of the brain, that responded to activation of the pulvinar input in anesthetized cats and 41 (54%) in awake animals. In the two types of experiments, stimulation of the pulvinar induced mainly an initial excitatory reaction (81% and 78% of responsive cells, respectively). A latency analysis indicated that the majority of responses occurred at a long latency, while 9 (34.6%) cells in anesthetized cats and 5 (12%) in awake animals were excited at a short latency. The short latency is compatible with the involvement of a monosynaptic pathway between the pulvinar and the caudate nucleus. Units that responded to thalamic stimulation were found predominantly in the posterior regions of the caudate nucleus. These results confirm previous neuroanatomical findings of a direct projection from the pulvinar to the feline caudate nucleus. In awake animals, neurons activated by pulvinar stimulation were also tested, using visual stimuli of various orientations. Out of 41 units, 63% were classified as having visual responses. Of these, 5 cells were found to respond selectively to a particular orientation of the visual stimulus. Three of these were excited at a short latency by pulvinar stimulation. The possible involvement of a direct pathway from the pulvinar to the caudate nucleus in the processing of visual information is discussed.     

Responses of fastigial nucleus neurones to stimulation of the caudate nucleus in the cat.

1. Extracellular records were made of single unit activity evoked in the fastigial nucleus (FN) by electrical stimulation of the caudate nucleus (CN) in cats anaesthetized with sodium thiopentone. 2. Single shock stimulation evoked bilaterally complex responses having up to three components. These were, in temporal order, with percent of units exhibiting them, (a) a short burst of evoked spikes with either a latency of smaller than 5-5 msec and no associated field potential (6 percent) or a latency of 7-5-20 msec and associated with a prominent negative-going field potential (36 percent); (b) suppression of spontaneous discharges for a period of 20-150 msec (90 percent); (c) a resumption of spike discharges with a transient increase in frequency lasting for 25-500 msec (66 percent). 3. Changes in component (c) of the response patterns of some units were noted during repetitive stimulation The nature of the change depended on the laterality of the FN with respect to the stimulated CN. 4. Mechanisms which might account for the responses are discussed, but it is emphasized that some of the results cannot yet be satisfactorily explained.     

Latency variability of responses to visual stimuli in cells of the cat's lateral geniculate nucleus

We constructed average histograms from responses evoked by flashing stimuli and noted previously described variations in the shape of the response profile, particularly with respect to sharpness of the peak. To express this variable, we measured the half-rise latency, which is the latency from stimulus onset required to reach half the maximum response. A short half-rise latency, which is characteristic of nonlagged cells, is associated with a brisk response and sharp peak; a long half-rise latency, characteristic of lagged cells, is associated with a sluggish response and broad peak. Nonlagged cells were readily seen; we attempted to identify cells with long latencies as lagged, but we were unable to do so unambiguously due to failure to observe lagged properties other than latency. We thus refer to these latter cells as having lagged-like responses to indicate that we are not certain whether these are indeed lagged cells. In addition to the histograms, we analyzed the individual response trials that were summed to create each histogram, and we used spike density analysis to estimate the initial response latency to the flashing spot for each trial. We found that lagged-like responses were associated with more variability in initial response latency than were nonlagged responses. We then employed an alignment procedure to eliminate latency variation from individual trials; that is, responses during individual trials were shifted in time as needed so that each had a latency equal to the average latency of all trials. We used these aligned trials to create a second, aligned response histogram for each cell. The alignment procedure had little effect on nonlagged responses, because these were already well aligned due to consistent response latencies amongst trials. For lagged-like responses, however, the alignment made a dramatic difference. The aligned histograms looked very much like those for nonlagged responses: the responses appeared brisk, with a sharply rising peak that was fairly high in amplitude. We thus conclude that the slow build up to a relatively low peak of firing of the lagged-like response histogram is not an accurate reflection of responses on single trials. Instead, the sluggishness of lagged-like responses inferred from average response histograms results from temporal smearing due to latency variability amongst trials. We thus conclude that there is relatively little difference in briskness between nonlagged and lagged-like responses to single stimuli.     

Unitary responses of the caudate nucleus to direct stimulation

Unitary responses of the caudate nucleus to stimulation of various parts of it were investigated by extracellular recording. Latent periods of response discharges varied from 3.5 to 40 msec. Most neurons were excited by stimulation of the most rostral part of the head of the caudate nucleus. Irrespective of the site of stimulation, in most cases responses consisted of initial excitation in the form of one or, less frequently, two discharges followed by a period of depression of spontaneous activity. Recovery of activity took place gradually, without postinhibitory facilitation. No afterdischarges or periodic repetitions of spikes were observed after the initial response. Repetitive stimulation of the caudate nucleus showed that the neurons of this nucleus reproduce frequencies of stimulation badly above 30/sec, and under these circumstances in many cases they continued to discharge on average at a frequency of 5–15/sec. The results are examined from the standpoint of participation of the caudate nucleus in the formation of spindle activity.Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 497–506, September–October, 1976.     

Skin conductance responses to visual sexual stimuli.

Previous research showed that the asymmetrical direction of bilateral skin conductance responses (SCRs) remains constant regardless of task (with larger left SCRs in men and larger right SCRs in women). However, SCRs are controlled ipsilaterally by structures also associated with sexual arousal, hence it could be expected that larger right SCRs are specifically elicited by sexual stimuli. In order to test the two competing hypotheses, left and right SCR magnitude to three stimulus categories (sexually explicit, sexually non-explicit and neutral) were compared in 54 subjects (27 females). The direction of the asymmetry remained constant across stimulus types, however, unexpected sex differences occurred, as males had larger right SCRs and there was no lateralization in females. Interestingly, this interaction disappeared after controlling for indicators of subjective sexual arousal, suggesting that a specific (not previously hypothesized) processing of sexual information could take place.     

Release of adenosine in vivo from cat caudate nucleus

A push-pull perfusion technique was used to study the release of endogenously synthesized [3H]-adenosine from caudate nucleus in the anaesthetized cat. The spontaneous release of [3H]adenosine newly synthesized from [3H]adenine reached a steady state level 40 min after the beginning of superfusion and continued for 4 h. Potassium and veratridine increased the release of newly synthetized [3H]-adenosine. The action of veratridine was completely blocked by tetrodotoxin. We conclude that spontaneous and evoked release of adenosine occurs in the cat striatum and might potentially affect central nervous function.     

Competitive dynamics in cortical responses to visual stimuli

Neurons in the visual cortex of the macaque monkey exhibit a variety of competitive behaviors, including normalization and oscillation, when presented with multiple visual stimuli. Here we argue that a biophysically plausible cortical circuit with opponent inhibition, spike-frequency adaptation, and synaptic depression can account for the full range of behaviors. The governing parameter is the strength of inhibition between competing neuronal pools. As the strength of inhibition is increased, the pattern of network behavior shifts from normalization mode to oscillatory mode, with oscillations occurring at progressively lower frequency until, at the extreme, winner-take-all behavior appears.     

BOLD fMRI mapping of brain responses to nociceptive stimuli in rats under ketamine anesthesia

Ketamine is one of the most commonly used anesthetics, but its effects on nociceptive responses are not clearly defined. This study used blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to hemodynamically map responses to formalin stimuli under ketamine anesthesia. All imaging was performed on a 4.7-T fMRI system. During dynamic image acquisition, formalin was injected into the rat hindpaw as a painful stimulant. Correlation coefficients were calculated, and each image was registered and fused with the corresponding rat brain atlas so as to avoid inaccuracies arising from manual definition of the brain area and to achieve atlas-based normalization among subjects. Formalin injections were found to increase BOLD signals in the cingulate cortex, sensory-motor cortices, insular cortex, striatum, nucleus accumbens, medial thalamus, ventrolateral thalamic group, and hippocampus. Moreover, in contrast to previous pain investigations, the frontal subcortical regions were strongly activated in ketamine-anesthetized rats.     

Reflection of visceral afferentation in unit activity in the caudate nucleus

Responses of spontaneously active neurons to visceral (splanchnic nerve) stimulation were recorded extracellularly in the head of the caudate nucleus of immobilized cats. The presence of multimodal neurons responding to stimulation of visceral, somatic, and auditory sensory systems in this structure also was established. It is concluded from these facts that neurons of the caudate nucleus may play a role in the mechanisms of interaction of visceral impulses with somatic and auditory impulses.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 62, No. 2, pp. 189–195, February, 1976.     

Unit responses of the turtle forebrain to visual stimuli

Background activity and unit responses to diffuse and local illumination, to flashes, and to formed visual stimuli were studied in various forebrain structures of the turtle (Emys orbicularis). Most neurons responded to a change in the ambient illumination. Receptive fields of the neurons covered all the field of vision, had an on-off response and, in most cases, were binocular. Striatal neurons were characterized by clear relationships between responses and stimulus characteristics; cortical neurons were characterized by rapid and prolonged habituation of responses to repeated stimuli. It is suggested that several polysynaptic pathways transmit visual information to the reptilian forebrain.     

Vertical cell responses to sound in cat dorsal cochlear nucleus.

The dorsal cochlear nucleus receives input from the auditory nerve and relays acoustic information to the inferior colliculus. Its principal cells receive two systems of inputs. One system through the molecular layer carries multimodal information that is processed through a neuronal circuit that resembles the cerebellum. A second system through the deep layer carries primary auditory nerve input, some of which is relayed through interneurons. The present study reveals the morphology of individual interneurons and their local axonal arbors and how these inhibitory interneurons respond to sound. Vertical cells lie beneath the fusiform cell layer. Their dendritic and axonal arbors are limited to an isofrequency lamina. They give rise to pericellular nests around the base of fusiform cells and their proximal basal dendrites. These cells exhibit an onset-graded response to short tones and have response features defined as type II. They have tuning curves that are closed contours (0 shaped), thresholds approximately 27 dB SPL, spontaneous firing rates of approximately 0 spikes/s, and they respond weakly or not at all to broadband noise, as described for type II units. Their responses are nonmonotonic functions of intensity with peak responses between 30 and 60 dB SPL. They also show a preference for the high-to-low direction of a frequency sweep. It has been suggested that these circuits may be involved in the processing of spectral cues for the localization of sound sources.     

Interactions of the evoked responses to visual, somatic, and auditory stimuli in polysensory areas of the cat cortex

Recordings of evoked potentials in the middle suprasylvian gyrus were obtained to pairings tf visual, anditory, and somatic stimuli, and two response measures were compared. Amplitude recovery of the response to the second stimulus was delayed for pairings of like stimuli as compared to unlike pairings, an effect not altered by varying the intensity of the first stimulus.