Table tennis players use superior saccadic eye movements to track moving visual targets

Introduction

Table tennis players perform visually guided visuomotor responses countlessly. The exposure of the visual system to frequent and long-term motion stimulation has been known to improve perceptual motion detection and discrimination abilities as a learning effect specific to that stimulus, so may also improve visuo-oculomotor performance. We hypothesized and verified that table tennis players have good spatial accuracy of saccades to moving targets.

Methods

University table tennis players (TT group) and control participants with no striking-sports experience (Control group) wore a virtual reality headset and performed two ball-tracking tasks to track moving and stationary targets in virtual reality. The ball moved from a predetermined position on the opponent's court toward the participant's court. A total of 54 conditions were examined for the moving targets in combinations of three ball trajectories (familiar parabolic, unfamiliar descent, and unfamiliar horizontal), three courses (left, right, and center), and six speeds.

Results and discussion

All participants primarily used catch-up saccades to track the moving ball. The TT group had lower mean and inter-trial variability in saccade endpoint error compared to the Control group, showing higher spatial accuracy and precision, respectively. It suggests their improvement of the ability to analyze the direction and speed of the ball's movement and predict its trajectory and future destination. The superiority of the spatial accuracy in the TT group was seen in both the right and the left courses for all trajectories but that of precision was for familiar parabolic only. The trajectory dependence of improved saccade precision in the TT group implies the possibility that the motion vision system is trained by the visual stimuli frequently encountered in table tennis. There was no difference between the two groups in the onset time or spatial accuracy of saccades for stationary targets appearing at various positions on the ping-pong table.

Conclusion

Table tennis players can obtain high performance (spatial accuracy and precision) of saccades to track moving targets as a result of motion vision ability improved through a vast amount of visual and visuo-ocular experience in their play.

Transcranial static magnetic field stimulation over hMT+ inhibits visual motion discriminability

Visuomotor performance acting on a moving target is fundamentally based on visual motion discriminability, and its neural basis is presumed to be human MT (hMT+), a motion vision center of the dorsal visual pathway. In this study, we investigated whether and how the accuracy and speed of motion discrimination are affected by applying transcranial static magnetic field stimulation (tSMS) to hMT+, which reduces cortical excitability. Sixteen participants performed a motion direction discrimination (MDD) task using a random dot kinematogram before (Pre-test) and during (During-test) application of the tSMS over left hMT+. The correct rate of the MDD task was significantly lower in the During-test compared to the Pre-test, an effect not seen with the sham condition. The inhibition effects were observed only for the right visual field corresponding to hMT+ in the stimulated hemisphere. On the other hand, no modulatory effect of tSMS was observed in the reaction time. We, therefore, demonstrated the inhibitory effect of tSMS on the left hMT+ impairs the accuracy but not the speed of motion information processing in the contralateral visual field.

Acute exercise has specific effects on the formation process and pathway of visual perception in healthy young men

Visual perception is formed over time through the formation process and visual pathway. Exercise improves visual perception, but it is unclear whether exercise modulates nonspecifically or specifically the formation process and pathway of visual perception. Healthy young men performed the visual detection task in a backward masking paradigm before and during cycling exercise at a mild intensity or rest (control). The task presented gratings of a circular patch (target) and annulus (mask) arranged concentrically as a visual stimulus and asked if the presence and striped pattern (feature) of the target were detected. The relationship between the orientations of the gratings of the target and the mask included iso-orientation and orthogonal orientation to investigate the orientation selectivity of the masking effect. The masking effect was evaluated by perceptual suppressive index (PSI). Exercise improved feature detection (∆PSI; Exercise: -20.6%, Control: 1.7%) but not presence detection (∆PSI; Exercise: 8.9%, Control: 29.6%) compared to the control condition, and the improving effect resulted from the attenuation of the non-orientation-selective (∆PSI; Exercise: -29.0%, Control: 16.8%) but not orientation-selective masking effect (∆PSI; Exercise: -3.1%, Control: 11.7%). These results suggest that exercise affects the formation process of the perceptual feature of the target stimulus by suppressively modulating the neural networks responsible for the non-orientation-selective surround interaction in the subcortical visual pathways, whose effects are inherited by the cortical visual pathways necessary for perceptual image formation. In conclusion, our findings suggest that acute exercise improves visual perception transiently through the modulation of a specific formation process of visual processing.

Daily fluctuations in visual motion discriminability contribute to daily fluctuations in continuous visuomotor performance

In ball sports such as table tennis, in which a ball moving at high speed is hit, an athlete's brain needs to process the motion information of the ball, predict the arrival point, and form a motor command to direct the racket there. Therefore, day-to-day fluctuations in visuomotor performance may be ascribed to fluctuations in visual motion discriminability, but it is not clear how the two are related. To examine this point, university table tennis players performed a motion direction discrimination (MDD) task and continuous visuomotor (CVM) task over 10 days as an estimation of visual motion discriminability and visuomotor performance, respectively. In the MDD task, using a joystick, participants distinguished the direction of a global coherent motion of target dots moving in the same direction on a PC monitor from innumerable dots moving in random directions. In the CVM task, participants hit sequential targets moving fast from right to left on the PC monitor by operating the cursor on the left side of the monitor up and down using the prehensile force of their thumb and index finger. The scores in the MDD and CVM tasks fluctuated day by day and showed a significant and moderate correlation between the MDD task score for the visual field in which the participants captured the target in the CVM task and the CVM task score. This correlation was confirmed even with the target moving from left to right. The fluctuations in the onset latency and the endpoint position of the cursor movement approaching the target were correlated with those of the visual motion discriminability, suggesting the contribution of motion vision to the speed and accuracy of the visuomotor performance. Moreover, these relationships were prominent in veteran players. For table tennis athletes, especially experienced players, fluctuations in the visual motion discrimination performance in a visual field specific for capturing a ball may be responsible for the fluctuations in continuous visuomotor (striking) performance.

Spatial Accuracy of Predictive Saccades Determines the Performance of Continuous Visuomotor Action

In a table tennis rally, players perform interceptive actions on a moving ball continuously in a short time, such that the acquisition process of visual information is an important determinant of the performance of the action. However, because it is technically hard to measure gaze movement in a real game, little is known about how gaze behavior is conducted during the continuous visuomotor actions and contributes to the performance. To examine these points, we constructed a novel psychophysical experiment model enabling a continuous visuomotor task without spatial movement of any body parts, including the arm and head, and recorded the movement of the gaze and effector simultaneously at high spatiotemporal resolution. In the task, Gabor patches (target) moved one after another at a constant speed from right to left at random vertical positions on an LC display. Participants hit the target with a cursor moving vertically on the left side of the display by controlling their prehensile force on a force sensor. Participants hit the target with the cursor using a rapid-approaching movement (rapid cursor approach, RCA). Their gaze also showed rapid saccadic approaching movement (saccadic eye approach, SEA), reaching the predicted arrival point of the target earlier than the cursor. The RCA reached in or near the Hit zone in the successful (Hit) trial, but ended up away from it in the unsuccessful (Miss) trial, suggesting the spatial accuracy of the RCA determines the task's success. The SEA in the Hit trial ended nearer the target than the Miss trial. The spatial accuracy of the RCA diminished when the target disappeared 100 ms just after the end of the SEA, suggesting that visual information acquired after the saccade acted as feedback information to correct the cursor movement online for the cursor to reach the target. There was a target speed condition that the target disappearance did not compromise RCA's spatial accuracy, implying the possible RCA correction based on the post-saccadic gaze location information. These experiments clarified that gaze behavior conducted during fast continuous visuomotor actions enables online correction of the ongoing interceptive movement of an effector, improving visuomotor performance.

The combination of acute exercise and eye closure has a synergistic effect on alpha activity

Acute aerobic exercise increases the brain cortical activity in alpha frequency. Eye closure also increases alpha activity. However, whether the two have an additive or a synergistic effect on alpha activity has never been explored. This study observed electroencephalography (EEG) from fifteen participants seated on the cycle ergometer before, during, and after a cycling exercise with the eyes open and with them closed. Exercise intensity was set to a target heart rate (120-130 bpm), corresponding to light-to-moderate intensity exercise. Each epoch was 6 min and the last 4 min (eyes closed in the first 2 min and eyes open in the second 2 min) were analyzed. The EEG power spectrum densities were calculated for alpha frequency band activity (8-13 Hz). At rest, alpha activity was significantly greater with the eyes closed than open. Exercise significantly increased alpha activity in both eye conditions. More importantly, in the occipital site, the alpha-increasing effect of their combination was significantly greater than the sum of the effect of each, showing a synergistic effect. We concluded that acute light-to-moderate intensity exercise with the eyes closed has a synergistic effect on alpha activity.

Acetylcholine from the nucleus basalis magnocellularis facilitates the retrieval of well-established memory

Retrieval deficit of long-term memory is a cardinal symptom of dementia and has been proposed to associate with abnormalities in the central cholinergic system. Difficulty in the retrieval of memory is experienced by healthy individuals and not limited to patients with neurological disorders that result in forgetfulness. The difficulty of retrieving memories is associated with various factors, such as how often the event was experienced or remembered, but it is unclear how the cholinergic system plays a role in the retrieval of memory formed by a daily routine (accumulated experience). To investigate this point, we trained rats moderately (for a week) or extensively (for a month) to detect a visual cue in a two-alternative forced-choice task. First, we confirmed the well-established memory in the extensively trained group was more resistant to the retrieval problem than recently acquired memory in the moderately trained group. Next, we tested the effect of a cholinesterase inhibitor, donepezil, on the retrieval of memory after a long no-task period in extensively trained rats. Pre-administration of donepezil improved performance and reduced the latency of task initiation compared to the saline-treated group. Finally, we lesioned cholinergic neurons of the nucleus basalis magnocellularis (NBM), which project to the entire neocortex, by injecting the cholinergic toxin 192 IgG-saporin. NBM-lesioned rats showed severely impaired task initiation and performance. These abilities recovered as the trials progressed, though they never reached the level observed in rats with intact NBM. These results suggest that acetylcholine released from the NBM contributes to the retrieval of well-established memory developed by a daily routine.

Noradrenaline modulates neuronal and perceptual visual detectability via β-adrenergic receptor

RATIONALE

Noradrenaline (NA) is a neuromodulator secreted from noradrenergic neurons in the locus coeruleus to the whole brain depending on the physiological state and behavioral context. It regulates various brain functions including vision via three major adrenergic receptor (AR) subtypes. Previous studies investigating the noradrenergic modulations on vision reported different effects, including improvement and impairment of perceptual visual sensitivity in rodents via β-AR, an AR subtype. Therefore, it remains unknown how NA affects perceptual visual sensitivity via β-AR and what neuronal mechanisms underlie it.

OBJECTIVES

The current study investigated the noradrenergic modulation of perceptual and neuronal visual sensitivity via β-AR in the primary visual cortex (V1).

METHODS

We performed extracellular multi-point recordings from V1 of rats performing a go/no-go visual detection task under the head-fixed condition. A β-AR blocker, propranolol (10 mM), was topically administered onto the V1 surface, and the drug effect on behavioral and neuronal activities was quantified by comparing pre-and post-drug administration.

RESULTS

The topical administration of propranolol onto the V1 surface significantly improved the task performance. An analysis of the multi-unit activity in V1 showed that propranolol significantly suppressed spontaneous activity and facilitated the visual response of the recording sites in V1. We further calculated the signal-to-noise ratio (SNR), finding that the SNR was significantly improved after propranolol administration.

CONCLUSIONS

Pharmacological blockade of β-AR in V1 improves perceptual visual detectability by modifying the SNR of neuronal activity.

Serotonin improves behavioral contrast sensitivity of freely moving rats

Serotonin (5-HT) is a neuromodulator secreted from serotonergic neurons located in the pons and upper brain stem in a behavioral context-dependent manner. The serotonergic axon terminals innervate almost the whole brain, causing modulatory actions on various brain functions including vision. Our previous study demonstrated the visual responses of neurons in the primary visual cortex (V1) of anesthetized monkeys were modulated by the activation of 5-HT receptors depending on the response magnitude, in which 5-HT2A receptor-selective agonists enhanced weak visual responses but not strong responses. This observation suggests that the activation of serotonergic receptors modulates neuronal visual information processing to improve the behavioral detectability of a stimulus. However, it remains unknown if 5-HT improves visual detectability at the behavioral level. To investigate this point, visual detectability was measured as contrast sensitivity (CS) in freely moving rats using a two-alternative forced-choice visual detection task (2AFC-VDT) combined with the staircase method. The grating contrast was decreased or increased step by step after a correct choice (hit) or incorrect choice (miss), respectively. CS was evaluated as an inverse value of the visual contrast threshold. The effect of the intraperitoneal administration of fluoxetine (FLX, 5 mg/kg), a selective serotonin reuptake inhibitor, on CS was tested. The CS of rats was significantly higher in FLX than control conditions, and the drug effect showed specificity for the spatial frequency (SF) of a grating stimulus, in which CS improvement was observed at optimal SF but not non-optimal high SF. Thus, we conclude that endogenously-secreted serotonin in the brain improves visual detectability, which may be mediated by vision-related neurons acquiring SF information of the visual stimulus.

Discretion for behavioral selection affects development of habit formation after extended training in rats

As training progresses, animals show a transition from goal-dependent behavior to goal-independent behavior (habitual responses). Habit formation is influenced by several factors, including the amount of training and action-outcome contingency. However, it remains unknown whether and how discretion for behavioral selection influences habit formation. To this end, we trained male rats in two types of two-alternative forced-choice task: visual association and nonvisual association tasks. In the first type of task, rats learned the association between reward and a visual cue, the position of which was randomly changed per trial so that rats had to make a judgmental decision about which choice delivered the reward in each trial (discreet judgment group); in the second type of task, the rats learned that a reward was delivered after either choice following task initiation (uncontrolled judgment group). To test the sensitivity to contingency manipulation, the extinction tests were conducted in short- and long-term trained groups, with the result that the overtrained rats in the uncontrolled judgment group, but not the other three groups, showed less sensitivity. To further investigate the reward sensitivity in the long-term trained groups from another perspective, we continuously and periodically altered the reward size for each trial. The rats of the discreet judgment group changed intertrial intervals depending on reward size, while this tendency was weaker in the uncontrolled judgment group. These results suggest that discreet judgment maintained goal-directed rat behavior, whereas uncontrolled judgment led to the development of habit-like behavior.

Noradrenaline Improves Behavioral Contrast Sensitivity via the β-Adrenergic Receptor

Noradrenaline (NA) is released from the locus coeruleus in the brainstem to almost the whole brain depending on the physiological state or behavioral context. NA modulates various brain functions including vision, but many questions about the functional role of its effects and mechanisms remain unclear. To explore these matters, we focused on three questions, 1) whether NA improves detectability of a behavior-relevant visual stimulus, 2) which receptor subtypes contribute to the NA effects, and 3) whether the NA effects are specific for visual features such as spatial frequency (SF). We measured contrast sensitivity in rats by a two-alternative forced choice visual detection task and tested the effects of NA receptor blockers in three SF conditions. Propranolol, a β-adrenergic receptor inhibitor, significantly decreased contrast sensitivity, but neither prazosin nor idazoxan, α1- and α2-adrenergic receptor inhibitors, respectively, had an effect. This β blocker effect was observed only at optimal SF. These results indicate that endogenous NA enhances visual detectability depending on stimulus spatial properties via mainly β-adrenergic receptors.

Cholinergic and serotonergic modulation of visual information processing in monkey V1

The brain dynamically changes its input-output relationship depending on the behavioral state and context in order to optimize information processing. At the molecular level, cholinergic/monoaminergic transmitters have been extensively studied as key players for the state/context-dependent modulation of brain function. In this paper, we review how cortical visual information processing in the primary visual cortex (V1) of macaque monkey, which has a highly differentiated laminar structure, is optimized by serotonergic and cholinergic systems by examining anatomical and in vivo electrophysiological aspects to highlight their similarities and distinctions. We show that these two systems have a similar layer bias for axonal fiber innervation and receptor distribution. The common target sites are the geniculorecipient layers and geniculocortical fibers, where the appropriate gain control is established through a geniculocortical signal transformation. Both systems exert activity-dependent response gain control across layers, but in a manner consistent with the receptor subtype. The serotonergic receptors 5-HT1B and 5HT2A modulate the contrast-response curve in a manner consistent with bi-directional response gain control, where the sign (facilitation/suppression) is switched according to the firing rate and is complementary to the other. On the other hand, cholinergic nicotinic/muscarinic receptors exert mono-directional response gain control without a sign reversal. Nicotinic receptors increase the response magnitude in a multiplicative manner, while muscarinic receptors exert both suppressive and facilitative effects. We discuss the implications of the two neuromodulator systems in hierarchical visual signal processing in V1 on the basis of the developed laminar structure.

Spatiotemporal characteristics of surround suppression in primary visual cortex and lateral geniculate nucleus of the cat

In the primary visual cortex (V1), a neuronal response to stimulation of the classical receptive field (CRF) is predominantly suppressed by a stimulus presented outside the CRF (extraclassical receptive field, ECRF), a phenomenon referred to as ECRF suppression. To elucidate the neuronal mechanisms and origin of ECRF suppression in V1 of anesthetized cats, we examined the temporal properties of the spatial extent and orientation specificity of ECRF suppression in V1 and the lateral geniculate nucleus (LGN), using stationary-flashed sinusoidal grating. In V1, we found three components of ECRF suppression: 1) local and fast, 2) global and fast, and 3) global and late. The local and fast component, which resulted from within 2° of the boundary of the CRF, started no more than 10 ms after the onset of the CRF response and exhibited low specificity for the orientation of the ECRF stimulus. These spatiotemporal properties corresponded to those of geniculate ECRF suppression, suggesting that the local and fast component of V1 is inherited from the LGN. In contrast, the two global components showed rather large spatial extents ∼5° from the CRF boundary and high specificity for orientation, suggesting that their possible origin is the cortex, not the LGN. Correspondingly, the local component was observed in all neurons of the thalamocortical recipient layer, while the global component was biased toward other layers. Therefore, we conclude that both subcortical and cortical mechanisms with different spatiotemporal properties are involved in ECRF suppression.

Efficient training protocol for rapid learning of the two-alternative forced-choice visual stimulus detection task

The potential of genetically engineered rodent models has accelerated demand for training procedures of behavioral tasks. Such training is generally time consuming and often shows large variability in learning speed between animals. To overcome these problems, we developed an efficient and stable training system for the two-alternative forced-choice (2AFC) visual stimulus detection task for freely behaving rodents. To facilitate the task learning, we introduced a spout-lever as the operandum and a three-step training program with four ingenuities: (1) a salient stimulus to draw passive attention, (2) a reward-guaranteed trial to keep motivation, (3) a behavior-corrective trial, and (4) switching from a reward-guaranteed trial to a nonguaranteed one to correct behavioral patterns. Our new training system realizes 1-week completion of the whole learning process, during which all rats were able to learn effortlessly the association between (1) lever-manipulation and reward and (2) visual stimulus and reward in a step-by-step manner. Thus, our new system provides an effective and stable training method for the 2AFC visual stimulus detection task. This method should help accelerate the move toward research bridging the visual functions measured in behavioral tasks and the contributing specific neurons/networks that are genetically manipulated or optically controlled.

Blockade of muscarinic receptors impairs the retrieval of well-trained memory

Acetylcholine (ACh) is known to play an important role in memory functions, and its deficit has been proposed to cause the cognitive decline associated with advanced age and Alzheimer's disease (the cholinergic hypothesis). Although many studies have tested the cholinergic hypothesis for recently acquired memory, only a few have investigated the role of ACh in the retrieval process of well-trained cognitive memory, which describes the memory established from repetition and daily routine. To examine this point, we trained rats to perform a two-alternative forced-choice visual detection task. Each trial was started by having the rats pull upward a central-lever, which triggered the presentation of a visual stimulus to the right or left side of the display monitor, and then pulling upward a stimulus-relevant choice-lever located on both sides. Rats learned the task within 10 days, and the task training was continued for a month. Task performance was measured with or without systemic administration of a muscarinic ACh receptor (mAChR) antagonist, scopolamine (SCOP), prior to the test. After 30 min of SCOP administration, rats stopped manipulating any lever even though they explored the lever and surrounding environment, suggesting a loss of the task-related associative memory. Three hours later, rats were recovered to complete the trial, but the rats selected the levers irrespective of the visual stimulus, suggesting they remembered a series of lever-manipulations in association with a reward, but not association between the reward and visual stimulation. Furthermore, an m1-AChR, but not nicotinic AChR antagonist caused a similar deficit in the task execution. SCOP neither interfered with locomotor activity nor drinking behavior, while it influenced anxiety. These results suggest that the activation of mAChRs at basal ACh levels is essential for the recall of well-trained cognitive memory.

Cholinesterase inhibitor, donepezil, improves visual contrast detectability in freely behaving rats

Acetylcholine (ACh) modulates neuronal activities in extensive brain regions to play an essential role in various brain functions including attention, learning and memory, and cognition. Although ACh is known to modulate information processing in the primary visual cortex (V1) in many species including rodent, its functional role in visual ability has remained unknown. We examined whether and how ACh influences behavioral contrast detectability in rat. The detectability was assessed as the contrast sensitivity (CS) to a grating stimulus. Measurements were performed in a two-alternative forced-choice task combined with a staircase method in freely behaving rats. The contrast sensitivity function of rats under the no drug condition showed a low-pass spatial frequency (SF) tuning peaking at 0.1 cycles/degree (cpd) of SF (SF(peak)) that bottomed at 0.5 cpd (SF(bottom)), which was sensitive to the stimulus size, but to neither the temporal frequency nor orientation of the stimulus. The stimulus size was correlated with the CS only at the low SF range. The effect of donepezil on the size- and SF-dependency of the CS was examined using three stimulus conditions: an easy detectability condition with large grating at SF(peak), a difficult detectability condition with small grating at SF(peak), and an upper limit SF condition with large grating at SF(bottom). Donepezil improved the CS at SF(peak), especially in the difficult detectability condition. Therefore, we conclude that ACh plays an important role in enhancing behavioral CS at sensitive SF ranges, but not in improving the upper limit of SF.

Modulation-specific and laminar-dependent effects of acetylcholine on visual responses in the rat primary visual cortex

Acetylcholine (ACh) is secreted from cholinergic neurons in the basal forebrain to regions throughout the cerebral cortex, including the primary visual cortex (V1), and influences neuronal activities across all six layers via a form of diffuse extrasynaptic modulation termed volume transmission. To understand this effect in V1, we performed extracellular multi-point recordings of neuronal responses to drifting sinusoidal grating stimuli from the cortical layers of V1 in anesthetized rats and examined the modulatory effects of topically administered ACh. ACh facilitated or suppressed the visual responses of individual cells with a laminar bias: response suppression prevailed in layers 2/3, whereas response facilitation prevailed in layer 5. ACh effects on the stimulus contrast-response function showed that ACh changes the response gain upward or downward in facilitated or suppressed cells, respectively. Next, ACh effects on the signal-to-noise (S/N) ratio and the grating-phase information were tested. The grating-phase information was calculated as the F1/F0 ratio, which represents the amount of temporal response modulation at the fundamental frequency (F1) of a drifting grating relative to the mean evoked response (F0). In facilitated cells, ACh improved the S/N ratio, while in suppressed cells it enhanced the F1/F0 ratio without any concurrent reduction in the S/N ratio. These effects were predominantly observed in regular-spiking cells, but not in fast-spiking cells. Electrophysiological and histological findings suggest that ACh promotes the signaling of grating-phase information to higher-order areas by a suppressive effect on supragranular layers and enhances feedback signals with a high S/N ratio to subcortical areas by a facilitatory effect on infragranular layers. Thus, ACh distinctly and finely controls visual information processing in a manner that is specific for the modulation and cell type and is also laminar dependent.

Cholinergic modulation of response gain in the primary visual cortex of the macaque

ACh modulates neuronal activity throughout the cerebral cortex, including the primary visual cortex (V1). However, a number of issues regarding this modulation remain unknown, such as the effect and its function and the receptor subtypes involved. To address these issues, we combined extracellular single-unit recordings and microiontophoretic administration of ACh and measured V1 neuronal responses to drifting sinusoidal grating stimuli in anesthetized macaque monkeys. ACh was found to have mostly facilitatory effects on the visual responses, although some cases of suppressive effects were also seen. To assess the functional role of ACh, we further examined how ACh modulates the stimulus contrast-response function, finding that the response gain increased with the facilitatory effect. The response facilitation was completely or strongly blocked by atropine (At), a muscarinic ACh receptor (mAChR) antagonist, in almost all neurons (96% of cells), whereas any residual effect after At administration was fully removed by mecamylamine, a nicotinic AChR (nAChR) antagonist, suggesting a predominant role for mAChRs in this mechanism. Furthermore, we found no laminar distribution bias for the facilitatory modulation, although the relative contribution of mAChRs was smaller in layer 4C than in other layers. The suppressive effect was blocked completely by At. These results demonstrate that ACh plays an important role in visual information processing in V1 by controlling the response gain via mAChRs across all cortical layers and via nAChRs, mainly in layer 4C.

Enriched expression of serotonin 1B and 2A receptor genes in macaque visual cortex and their bidirectional modulatory effects on neuronal responses

To study the molecular mechanism how cortical areas are specialized in adult primates, we searched for area-specific genes in macaque monkeys and found striking enrichment of serotonin (5-hydroxytryptamine, 5-HT) 1B receptor mRNA, and to a lesser extent, of 5-HT2A receptor mRNA, in the primary visual area (V1). In situ hybridization analyses revealed that both mRNA species were highly concentrated in the geniculorecipient layers IVA and IVC, where they were coexpressed in the same neurons. Monocular inactivation by tetrodotoxin injection resulted in a strong and rapid (<3 h) downregulation of these mRNAs, suggesting the retinal activity dependency of their expression. Consistent with the high expression level in V1, clear modulatory effects of 5-HT1B and 5-HT2A receptor agonists on the responses of V1 neurons were observed in in vivo electrophysiological experiments. The modulatory effect of the 5-HT1B agonist was dependent on the firing rate of the recorded neurons: The effect tended to be facilitative for neurons with a high firing rate, and suppressive for those with a low firing rate. The 5-HT2A agonist showed opposite effects. These results suggest that this serotonergic system controls the visual response in V1 for optimization of information processing toward the incoming visual inputs.

Metacontrast masking suggests interaction between visual pathways with different spatial and temporal properties

We examined the spatiotemporal characteristics of metacontrast using sinusoidal grating stimuli as the target and mask for quantitative comparison with the functional properties of the visual cortex. The magnitude of metacontrast effects depended on the stimulus features such as the orientation and spatial frequency of the target and mask. The characteristics of metacontrast dynamically changed depending on the stimulus onset asynchrony (SOA). At short SOAs (0 to approximately 40 ms), metacontrast exhibited a high stimulus feature specificity and a low contrast sensitivity, whereas at long SOAs ( approximately 40 to 80 ms), metacontrast exhibited a low stimulus feature specificity and a high contrast sensitivity. We suggest that metacontrast is explained by the interaction between two parallel visual pathways: one with a low contrast sensitivity and a high feature specificity, and the other with a high contrast sensitivity and a low feature specificity.

Similarity of direction tuning among responses to stimulation of different whiskers in neurons of rat barrel cortex

Cells in the rat barrel cortex exhibit stimulus-specific response properties. To understand the network mechanism of direction selectivity in response to facial whisker deflection, we examined direction selectivity of neuronal responses to single- and multi-whisker stimulations. In the case of regular-spiking units, i.e., putative excitatory cells, direction preferences were quite similar between responses to single-whisker stimulation of the principal and adjacent whiskers. In multi-whisker stimulation at short (< or = 5 ms) interstimulus intervals (ISIs), response facilitation was evoked only when the whiskers were deflected to the preferred direction of the response to the single whisker stimulation. These results suggest that there are neuronal networks among cells with different whisker preferences but with a common direction preference that could be the neuronal basis of the direction-selective facilitation of the response to multi-whisker stimulation. In contrast, multi-whisker stimulation at long (> or = 6 ms) ISIs caused non-direction-selective suppression of the response to the second stimulus. In the case of fast-spiking units, i.e., putative inhibitory cells, poor direction selectivity was exhibited. Thus stimulus direction is represented as the direction-selective responses to the single- and multi-whisker stimulations of putative excitatory cells rather than those of putative inhibitory cells.

Relationship between excitation and inhibition underlying size tuning and contextual response modulation in the cat primary visual cortex

In the primary visual cortex (V1), the single-neuron response to a grating stimulus placed in the classical receptive field (CRF) is suppressed by a similar stimulus presented in the CRF surround. To assess the input mechanism underlying the surround suppression, we tested the effects of iontophoretically administered GABA(A)-receptor antagonist, bicuculline methiodide (BMI), for the 46 V1 neurons in anesthetized cats. First, the stimulus-size tuning curves were studied, with or without BMI administration, for each neuron by changing the size of the grating patch. During the BMI administration, the shape of the normalized size tuning curve did not change considerably. Second, the dependency of surround suppression on the orientation of the surround grating was examined. In the control, the surround suppression showed the clear orientation tuning that peaked at an orientation the same as the optimal orientation of the CRF response. The BMI administration did not change the orientation dependency of surround suppression. We also estimated the relative contribution of excitation and inhibition to the size and orientation tuning of surround suppression. It was concluded that cortical excitation and inhibition were well balanced, having similar tuning profiles for both stimulus size and orientation of the surround grating. Furthermore, surround stimuli used for V1 neurons suppressed the CRF response of neurons in the lateral geniculate nucleus. These results suggest that surround suppression is not primarily attributable to the intracortical inhibition, but because of a reduction of thalamocortical inputs, which drive the cortical excitation and inhibition, and a subsequent decrease in the cortical excitatory interactions.

Blockade of cyclic AMP-dependent protein kinase does not prevent the reverse ocular dominance shift in kitten visual cortex

Monocular deprivation (MD) during the critical period for the development of visual cortex causes a loss of binocular response of neurons and a shift to the open eye, a normal ocular dominance (OD) shift. However, when MD is combined with chronic inactivation of the visual cortex by muscimol, the OD distribution of the neurons shifts to the deprived eye (reverse OD shift). We have previously shown that the normal OD shift is abolished by chronic infusion of the protein kinase A (PKA) inhibitor, 8-chloroadenosine-3', 5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-Cl-cAMPS), into kitten visual cortex. In this study, we investigated the effect of this inhibitor on the reverse OD shift. Combination of MD and muscimol infusion into the visual cortex of 6-wk-old kittens caused a reverse OD shift that was comparable to that seen in previous studies. However, a reverse OD shift was also seen with concurrent infusion of the PKA inhibitor with muscimol. The strongest OD shift was observed in layer IV regardless of the presence or absence of the PKA inhibitor. This suggests that the dissociation of pre- and postsynaptic activities, which occurs mainly at thalamocortical synapses, induces the reverse OD shift and that inhibition of PKA does not prevent it. Presumably, an inhibition of PKA has no effect in silent cortex. We conclude that 1) an activation of PKA is not required for the induction of the reverse OD shift, and 2) the intracellular signaling mechanism underlying MD-induced OD plasticity differs between normal and reverse OD shifts.

Effects of aging on capillary number and luminal size in rat soleus and plantaris muscles

To clarify aging-related changes in the capillary network in skeletal muscle, we morphometrically examined the capillary supply to individual muscle fibers and capillary luminal size in young (3-month-old) and old (19-month-old) male Wistar rats. All morphometric parameters for capillary and muscle fiber were determined in the cross sections of the perfusion-fixed soleus (SOL) and plantaris (PL) muscles. The range of fiber size was larger in the old muscles because of hypertrophy and atrophy of fibers. However, the capillary supply to individual muscle fibers, assessed as the mean of capillary contacts around a muscle fiber, did not change with aging in SOL muscle (young rats = 7.8 +/- 0.4 vs old rats = 8.1 +/- 0.8) or PL muscle (young rats = 6.4 +/- 0.3 vs old rats = 7.0 +/- 0.9). The ratio of individual muscle fiber area to the number of capillary contacts around a muscle fiber did not differ between young rats (SOL = 361.7 +/- 76.0; PL = 264.7 +/- 20.9) and old rats (SOL = 350.2 +/- 61.3; PL = 296.8 +/- 44.9). The mean capillary luminal diameter did not differ statistically in young and old rats (SOL, young rats = 5.3 +/- 0.5 vs old rats = 5.1 +/- 0.1; PL, young rats = 5.0 +/- 0.3 vs old rats = 5.4 +/- 0.2). In conclusion, the relationship between capillary supply and muscle fiber size is similar for both young and old rats, and the luminal size of each capillary was maintained with advancing age.

Suppressive effects of receptive field surround on neuronal activity in the cat primary visual cortex

Effects of sinusoidal grating stimulus presented outside the classical receptive field (CRF) on neuronal responses were studied in the primary visual cortex of anaesthetized cats. Among 101 cells electrophysiologically recorded, the predominant effect of the stimulus in the receptive field surround (SRF) was the suppression of responses to the CRF stimulation, and the SRF grating suppressed them up to 56% of the responses (44% suppression) to the CRF stimulus alone. The strong suppression was observed more often in layer II/III cells than in other layers and in complex cells more often than in simple cells. The modulatory effects by SRF stimulus might be enhanced by the cortical recurrent excitation particularly in the superficial layers. We also examined whether the modulation by the surround grating exhibits a differential effect according to the presence or absence of figure-ground segregation in the stimulus configuration. For this purpose, effects of stimulus configuration with orientation-, direction-contrast or relative spatial phase difference between CRF and SRF stimuli (figure-ground segregated configuration) were compared with those of uniform configuration of stimulus (non-segregated configuration). There was a population of cells, which exhibited significantly stronger suppression with non-segregated configuration than with figure-ground segregated configuration. Such differential modulation of response by the SRF stimulus in the primary visual cortex is a possible basis of perceptual figure-ground segregation.

Physiological and anatomical organization of multiwhisker response interactions in the barrel cortex of rats

To understand the physiological properties and anatomical organization of the spatiotemporal interaction of the responses to multiwhisker stimulation in neurons of the rat barrel cortex, single-unit recordings of 114 neurons were performed across all layers (layer II/III, n = 39; IV, n = 33; V/VI, n = 42) of the posteromedial barrel subfield of the primary somatosensory cortex of anesthetized rats. Two neighboring principal and adjacent whiskers (PW and AW, respectively) in the same row were deflected rostrally or caudally at varying interstimulus intervals (ISIs). In 37% of the neurons, the response to the combined stimulus was significantly larger than the sum of the responses to stimulation of the individual whiskers. In instances in which response facilitation was observed, selectivity was noted for the combination (75%) of the PW with a particular AW or for a particular direction (60%) of whisker deflection. The direction bias of the responses to multiwhisker stimulation was well correlated with that of the sum of the responses to single whisker stimulation (r = 0.83; p < 0.001). The pattern and magnitude of the response interaction in the neurons of the superficial layers were closely related to the location of the recorded cell in the barrel columns. Multiwhisker stimulation at short ISIs (</=3 msec) evoked prominent response facilitation in cells located close to the border between two columns (p < 0.05, one-way ANOVA), where two excitatory inputs were expected to arrive at the same time. Our results suggest that the spatiotemporal patterns of multiwhisker stimulation, such as whisker combination, direction of deflection, and timing, are expressed as different magnitudes of response interaction, which depends on the proximity of cells to home and adjacent barrel columns.

Changes in capillary luminal diameter in rat soleus muscle after hind-limb suspension

This study examined the time course change of the capillary luminal diameter and the number of capillaries in the rat soleus muscle during hind-limb suspension. Male Wistar rats were divided into 1 and 3 weeks of hind-limb suspension (HS) groups (HS-1 and HS-3). The HS groups were compared with age-matched control groups. All morphometric parameters with respect to capillary and muscle fibre cross-sectional area were determined in perfusion-fixed soleus muscles. After 1 and 3 weeks of hind-limb suspension, the mean muscle fibre cross-sectional area was significantly decreased in HS-1 (-32.0%) and HS-3 (-59.3%) compared with age-matched control groups. Despite a lower capillary-to-fibre ratio (HS-1, -19.3%; HS-3, -21.2%), the capillary density was unchanged in HS-1 and significantly increased in HS-3 compared with age-matched control groups. The mean capillary luminal diameter was significantly smaller in HS-1 (-19.9%) and HS-3 (-21.9%) than in the age-matched control groups. The capillary-to-fibre perimeter ratio which indicates the capillary surface area available for gas exchange between blood and tissue did not significantly differ between control groups and HS groups. In conclusion, the morphometrical adaptations in rat soleus with the suspension involved changes in both the capillary luminal diameter and number of capillaries, and the change in capillary surface area was proportional to the degree of muscle atrophy in HS groups.

Temporal characteristics of response integration evoked by multiple whisker stimulations in the barrel cortex of rats

We investigated the responses of 114 cells in the barrel cortex of rats to describe the temporal characteristics of excitatory interactions among neurons serving two vibrissae. To examine these interactions, the principal whisker and one adjacent whisker in the same row were stimulated simultaneously or serially at various interstimulus intervals (ISIs). In 37% of the cells tested, combined stimulation of two whiskers exhibited response facilitation; the response to the combined stimulus was larger than the sum of the responses to stimulation of the individual whiskers. The occurrence and magnitude of the facilitation were strongly dependent on the ISI. The ISI capable of producing facilitation for a particular cell was tuned to a narrow range (mean +/- SD, 5.3 +/- 2.3 msec). The ISI that evoked the maximal facilitation was 1.3 +/- 1.3, 3.4 +/- 2.3, and 2.8 +/- 4.5 msec for neurons in layers II/III, IV, and V/VI, respectively. These ISIs corresponded to the difference in latencies between the responses to the individual stimulations of the principal and adjacent whiskers. A significant response facilitation was observed in the regular-spiking cells but not in the fast-spiking cells. When the ISI was longer than the range that evoked facilitation, a suppression of the response to the second whisker stimulation was observed. Facilitation was observed predominantly in layer II/III cells (69%) and to a lesser extent in cells of layers IV (15%) and V/VI (24%). Our results suggest that, in the barrel cortex, the temporal relationships among tactile stimuli are coded by facilitatory and inhibitory interactions among neurons located in neighboring barrel columns.

Mitogenic action of adenosine on osteoblast-like cells, MC3T3-E1

The purpose of this study was to investigate the mechanisms by which adenosine stimulates proliferation of osteoblast-like cells, MC3T3-E1. Adenosine by itself induces the stimulation of cell proliferation and accentuates the mitogenecity of PDGFs (AA and BB homodimers) for the cells. 8-Cyclopentyl-1,3-dimethylxanthine (CPX), a nonselective adenosine receptor antagonist, partially inhibited adenosine-induced DNA synthesis in a competitive manner, suggesting that the mitogenic action of adenosine is, at least in part, mediated by xanthine-sensitive receptors. In pertussis-toxin (PTX)-pretreated cells, adenosine- but not PDGF-BB-stimulated DNA synthesis was partially inhibited, and CPX did not exert a further inhibitory effect, suggesting an involvement of PTX-sensitive G-protein downstream of CPX-sensitive receptor. When adenosine uptake was prevented with dipyridamole, the stimulation of proliferation by adenosine was not decreased at all, indicating that the CPX-insensitive part of adenosine action is not associated with the uptake of adenosine and subsequent incorporation into the nucleotide pool. Adenosine did not influence the basal level or the PDGF-BB-induced increase in [Ca2+]i. Since it is known that the cAMP pathway acts in inhibiting osteoblast proliferation, the mitogenic action of adenosine would be dependent on neither the cAMP pathway nor the phospholipase C/Ca2+ pathway. It has been concluded that adenosine exerts a mitogenic effect via two pathways at least, one mediated by xanthine-sensitive receptor and PTX-sensitive G-protein and the other through an unknown xanthine- and PTX-insensitive process.

Effects of different intensity endurance training on the capillary network in rat skeletal muscle

Effects of low- and high-intensity endurance training on the capillary luminal diameter and number were studied morphometrically in the rat plantaris muscle. Male Wistar-Imamichi rats were divided into three groups: sedentary control group (Cont, n = 9), low-intensity (running speed of 20 m/min) training group (T-20, n = 8) and high-intensity (running speed of 40 m/min) training group (T-40, n = 7). Rats in both training groups were subjected to each treadmill running program for 60 min/day, 5 days/week for 9 weeks. After 9 weeks of training, citrate synthase activity significantly increased in T-40 compared with Cont, but did not change in T-20. All morphometric parameters with respect to capillary and muscle fiber area were determined in the perfusion-fixed plantaris muscle. The mean muscle fiber areas in both T-20 and T-40 were similar to that in Cont. The capillary-to-fiber ratios were significantly higher in T-20 (2.28 +/- 0.06) and T-40 (2.29 +/- 0.06) than in Cont (2.00 +/- 0.07). The number of capillaries with a small luminal diameter (2-4 microns) was significantly higher in T-20 than in Cont. In contrast, T-40 had a significantly higher number of capillaries with a large luminal diameter (8-10 microns) compared with Cont. This study indicates that endurance training induces changes in the capillary luminal diameter as well as capillary number, and that the adaptive response of the capillary luminal diameter to endurance training depends on the training intensity.

Morphological adaptation of capillary network in compensatory hypertrophied rat plantaris muscle

The aim of this study was to examine the morphological adaptation of the capillary network in hypertrophied plantaris muscles by examining both capillary numbers and luminal circumferences. Hypertrophy of the plantaris muscle was induced by myectomy of the gastrocnemius muscle. This hypertrophy was characterised by increases in muscle mass and fibre cross-sectional area. All capillary parameters were determined using morphometric methods in perfusion-fixed plantaris muscle. Increased capillary-to-fibre ratio was observed in the overloaded plantaris muscle while no change was observed in the capillary luminal circumference. No differences were observed in the capillary density and the capillary-to-fibre perimeter ratio of the normal and the hypertrophied plantaris muscle. These results indicated that chronic overload-induced neocapillarization, but not enlargement of capillary luminal circumference, contributed to the prevention of decreases in the capillary-to-fibre perimeter ratio in the plantaris muscle in the hypertrophied process.

Creatine kinase release from regenerated muscles after eccentric contractions in rats

The purpose of this study was to test the hypothesis that an increase in plasma creatine kinase (CK) activity after eccentric contractions (ECC) would be attenuated in regenerated muscle fibres. Adult male Wistar rats (aged 12-14 weeks) were randomly assigned to a treatment group (n = 14) or a control group (n = 10). In the treatment group, 1.2% barium chloride solution (BaCl2) was injected into the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles to induce degeneration and subsequent regeneration. The same amount of isotonic saline solution was injected into TA and EDL for the control group. Histological observation showed that approximately 50% of the fibres in the transverse sections of both muscles underwent necrosis 2 days after BaCl2 injection. The CK activity increased about tenfold at 2-4 h after BaCl2 injection. At 4 weeks after BaCl2 injection, when the regeneration process was almost complete, the TA and EDL of anaesthetized rats from both groups were subjected to ECC in which maximal dorsiflexion was caused by nerve electrical stimulation and the flexed foot was forcibly extended by a lever arm connected to a motor. This action was performed in 2 sets of 30 repetitions. Maximal isometric torque of the dorsiflexors decreased to about 15% (P < 0.01) of the pre-ECC value immediately after the exercise. Blood samples were collected before and 2, 4, 12, 24, 48 h after ECC. The CK activity increased significantly (P < 0.01) and peaked at 2-4 h after ECC, and there was no significant difference in the amount of CK increase between the treatment [1007 (SEM 120) IU.l-1] and the control [1064 (SEM 120) IU.l-1] group. Contrary to the hypothesis, CK release after ECC was not attenuated in muscle regenerated from BaCl2-induced myonecrosis.

ATP and adenosine act as a mitogen for osteoblast-like cells (MC3T3-E1)

Extracellular ATP, and to a lesser extent adenosine, an ATP metabolite, stimulated cell proliferation in osteoblast-like cells (MC3T3-E1). ATP increased cytosolic Ca2+ due to Ca2+ mobilization from intracellular storage in the same concentration range of the nucleotide as that effective for DNA synthesis, suggesting the mediation of the phospholipase C/Ca2+ system in the mitogenic action. Since adenosine induced no Ca2+ mobilization, P2-purinergic receptor appears to be associated with ATP actions. The growth-promoting effect of ATP was not inhibited by H7, a protein kinase C inhibitor, and indomethacin, a cyclooxygenase inhibitor, indicating no involvement of activation of protein kinase C and production of prostaglandins in ATP-induced mitogenic signals. Either ATP or adenosine remarkably and synergistically potentiated platelet derived growth factor-induced DNA synthesis. These findings suggest that extracellular ATP and adenosine may play a physiological role in the regulation of bone formation.

Muscle contractile activity modulates GLUT4 protein content in the absence of insulin

We examined whether muscle contractile activity directly modulates GLUT4 protein content in rat skeletal muscle without the participation of insulin action or via amplified insulin action. To attain this purpose, the effects of increased, by training, or eliminated, by denervation, muscle contractile activity on muscle GLUT4 protein concentration were investigated in severely insulin-deficient diabetic rats. For the first set of experiments, insulin-deficient diabetic rats (induced by injection of 80 mg/kg B.W. streptozotocin) were trained for three weeks by treadmill running (90 min/day, 19 m/min, 10%, 6 days/week). GLUT4 protein concentration in soleus muscle was increased by 48% (p < 0.01) as compared with diabetic sedentary animals. For the second set of experiments, rats were injected with streptozotocin (100 mg/kg). The muscles innervated by the sciatic nerve of one leg were denervated four days after injection of streptozotocin. Three days after denervation, soleus muscles in both legs were excised. Insulin deficiency decreased GLUT4 protein concentration in innervated soleus muscle. In insulin-deficient diabetic rats, denervation also decreased soleus GLUT4 protein concentration by 50% (p < 0.01) as compared with the contralateral innervated muscle. Furthermore, the effects of insulin-deficiency and denervation on GLUT4 protein concentration were additive. These results provide evidence that muscle contractile activity directly modulates skeletal muscle GLUT4 protein concentration independent of insulin action.

Permissive stimulation of Ca(2+)-induced phospholipase A2 by an adenosine receptor agonist in a pertussis toxin-sensitive manner in FRTL-5 thyroid cells: a new 'cross-talk' mechanism in Ca2+ signalling

We have described the pertussis toxin (PTX)-sensitive potentiation of P2-purinergic agonist-induced phospholipase C activation, Ca2+ mobilization and arachidonic acid release by an adenosine receptor agonist, N6-(L-2-phenylisopropyl)adenosine (PIA), which alone cannot influence any of these cellular activities [Okajima, Sato, Nazarea, Sho and Kondo (1989) J. Biol. Chem. 264, 13029-13037]. In the present study we have found that arachidonic acid release was associated with lysophosphatidylcholine production, and conclude that arachidonic acid is produced by phospholipase A2 in FRTL-5 thyroid cells. This led us to assume that PIA augments P2-purinergic arachidonic acid release by increasing [Ca2+]i which, in turn, activates Ca(2+)-sensitive phospholipase A2. The arachidonic acid-releasing response to PIA was, however, always considerably higher (3.1-fold increase) than the Ca2+ response (1.3-fold increase) to the adenosine derivative. In addition, arachidonic acid release induced by the [Ca2+]i increase caused by thapsigargin, an endoplasmic-reticulum Ca(2+)-ATPase inhibitor, or calcium ionophores was also potentiated by PIA without any effect on [Ca2+]i and phospholipase C activity. This action of PIA was also PTX-sensitive, but not affected by the forskolin- or cholera toxin-induced increase in the cellular cyclic AMP (cAMP), suggesting that a PTX-sensitive G-protein(s) and not cAMP mediates the PIA-induced potentiation of Ca(2+)-generated phospholipase A2 activation. Although acute phorbol ester activation of protein kinase C induced arachidonic acid release, P2-purinergic and alpha 1-adrenergic stimulation of arachidonic acid release was markedly increased by the protein kinase C down-regulation caused by the phorbol ester. This suggests a suppressive role for protein kinase C in the agonist-induced activation of arachidonic acid release. We conclude that PIA (and perhaps any of the G1-activating agonists) augments an agonist (maybe any of the Ca(2+)-mobilizing agents)-induced arachidonic acid release by activation of Ca(2+)-dependent phospholipase A2 in addition to enhancement of agonist-induced phospholipase C followed by an increase in [Ca2+]i.

A single species of A1 adenosine receptor expressed in Chinese hamster ovary cells not only inhibits cAMP accumulation but also stimulates phospholipase C and arachidonate release

Chinese hamster ovary cells were transfected with both A1 adenosine receptor and muscarinic type 3 acetylcholine receptor cDNAs. The muscarinic receptor agonist carbachol stimulated phospholipase C activity, resulting in Ca2+ mobilization and arachidonate release. N6-Cyclopentyladenosine (CPA), an A1 receptor agonist, did not activate Ca(2+)-related signal transduction systems by itself but instead inhibited cAMP accumulation. In the presence of carbachol, however, the A1 receptor agonist enhanced muscarinic receptor agonist-induced phospholipase C/Ca2+ responses. In addition, the arachidonate release caused by Ca2+ ionophores or thapsigargin was also amplified by CPA, without a change in phospholipase C activity. Thus, CPA augments Ca(2+)-mediated phospholipase A2 activation in addition to and separate from its ability to amplify phospholipase C-mediated Ca2+ mobilization. Because the permissive actions of CPA on phospholipase C and phospholipase A2 activation were each reversed by pertussis toxin treatment, in a manner similar to that of the CPA-induced inhibition of cAMP accumulation, we conclude that a single species of A1 receptor expressed in Chinese hamster ovary cells can couple to multiple signal transduction systems stemming from phospholipase C stimulation, phospholipase A2-mediated and Ca(2+)-dependent arachidonate release, and inhibition of cAMP accumulation. A pertussis toxin-sensitive G protein (or proteins) mediates the permissive actions of the A1 receptor in the stimulation of phospholipase C- and phospholipase A2-mediated arachidonate release.