Serological investigation of protozoan pathogens (Trypanosoma cruzi, Toxoplasma gondii and Neospora caninum) in opossums from southern Brazil.

South American opossums of the order Didelphimorphia are considered sentinels for zoonotic infections and environmental diseases, such as for Chagas disease caused by Trypanosoma cruzi. Nevertheless, there is a paucity of data regarding protozoan diseases such Toxoplasma gondii and Neospora caninum in Neotropical marsupials; despite these pathogens have been considered threats to some marsupial species. The aim of this study was to determine whether Didelphis albiventris and Philander frenatus opossums from southern Brazil had been previously exposed to T. cruzi, T. gondii or N. caninum. Opossum samples were obtained by live-trapping of free-ranging animals and collection at wildlife rehabilitation centers in Rio Grande do Sul (RS) state, Brazil. The detection of anti-T. cruzi and anti-T. gondii antibodies was performed by indirect hemagglutination and anti-N. caninum antibodies by competitive enzyme-linked immunosorbent assay. In total, samples were collected from 76 marsupials from nine municipalities in RS state, including 69 D. albiventris (white-eared opossum), and seven were P. frenatus (southern four-eyed opossum). For T. cruzi, 11% were seropositive, and for T. gondii 26% were seropositive. None of the marsupials sampled here were seropositive for N. caninum. Risk factor analysis showed that free-living animals were about five-fold more likely to be infected by T. gondii than were rescued animals. Our study showed the exposure of Neotropical marsupials (D. albiventris and P. frenatus) to protozoan pathogens T. cruzi and T. gondii, while no evidence of N. caninum exposure was found. The set of results presented here may have an effect on ecology and conservation of the studied species and may also indicate possible sentinels of these pathogen circulation.

Rat hippocampal theta rhythm during sensory mismatch.

It has been suggested that sensory mismatch induces motion sickness, but its neural mechanisms remain unclear. To investigate this issue, theta waves in the hippocampal formation (HF) were studied during sensory mismatch by backward translocation in awake rats. A monopolar electrode was implanted into the dentate gyrus in the HF, from which local field potentials were recorded. The rats were placed on a treadmill affixed to a motion stage translocated along a figure 8-shaped track. The rats were trained to run forward on the treadmill at the same speed as that of forward translocation of the motion stage (a forward condition) before the experimental (recording) sessions. In the experimental sessions, the rats were initially tested in the forward condition, and then tested in a backward (mismatch) condition, in which the motion stage was turned around by 180 degrees before translocation. That is, the rats were moved backward by translocation of the stage although the rats ran forward on the treadmill. The theta (6-9 Hz) power was significantly increased in the backward condition compared with the forward condition. However, the theta power gradually decreased by repeated testing in the backward condition. Furthermore, backward translocation of the stage without locomotion did not increase theta power. These results suggest that the HF might function as a comparator to detect sensory mismatch, and that alteration in HF theta activity might induce motion sickness.

Hippocampal place cell activity during chasing of a moving object associated with reward in rats.

Hippocampal place cells encode location of animals in the environment. However, it remains unknown whether the hippocampal place cells encode a continuously moving object in the environment. To investigate this topic, we analyzed the place cell activity of freely moving rats when a toy car was introduced into an arena. First, in a freely moving task without the car, the rats freely navigated inside the arena to earn an intracranial stimulation (ICS) reward for each 150 cm traveled. Second, they were divided into two groups and tested using two different tasks. In the car-dependent navigation (CDN) task, the car was placed inside the arena, and the rat received ICS if it chased and came within 20 cm of the car. In the car-independent navigation (CIN) task, the rat acquired ICS rewards if it traveled 150 cm regardless of its relation to the car. Place fields remapped more frequently in the CDN than the CIN tasks. In both the CDN and CIN tasks, the place cell activity inside the place fields displayed moderate tuning to the movement parameters of the rats and car, and the distance between the car and rats. However, tuning of the place cells to movement variables of the car was more selective in the CDN than the CIN tasks, while information regarding movement variables of the car represented by the place cell activity was larger in the CDN than the CIN task. These results indicated that place cell activity within the place fields represents not only an animal's own location but also the movement variables of another moving object if that object is associated with rewards. The present results provide new evidence that place cell activity conveys relevant information in a task even if this information is derived from other moving objects.

Conjunctive effects of reward and behavioral episodes on hippocampal place-differential neurons of rats on a mobile treadmill.

Previous studies reported context (or behavior)-dependent activities of hippocampal place cells, which are suggested to be the neural basis of episodic memory. However, it remains unclear what distinctive items these context-dependent activities encode. We investigated separately the effects of space, locomotion, and episodes with positive/negative reinforcements on activity of place-differential neurons in the hippocampal CA1 area. Rats were placed on a treadmill affixed to a motion stage translocated along a figure 8-shaped track. The track could be navigated by two different routes that shared a common central stem. The stage was paused at the start and end of the routes, where conditioned response tasks with different reinforcements were imposed. As the rats passed the common central stem, some neurons fired differently depending on the route. Comparison of hippocampal spatial firing patterns across different conditions with and without treadmill operation and/or the tasks indicated that these route-dependent spatial firing patterns were sensitive to locomotion, the tasks, and vestibular sensation or visual cues such as optic flow. The results suggest that external sensory inputs, path integration, and reinforcement context are all integrated in the hippocampus, which might provide the neural basis of episodic memory.

Unambiguous representation of overlapping serial events in the rat hippocampal formation.

The hippocampal formation is suggested to be crucial in unambiguous representation of overlapping temporal sequences in episodic memory. We hypothesized that, if this was true, the hippocampal formation neurons would differentially respond to the same elements even in different temporal sequences. The present study was designed to investigate hippocampal formation CA1 neuronal activity of rats during performance of a conditional delayed stimulus-response association task in which three stimuli were conditionally and serially presented with a delay. In the task, the pairs of the second and third stimuli were overlapped across the trials, but separated by the preceding first stimuli. Conditioned tones coming from one of three possible directions were followed, after a short delay, by one of three pairs of reinforcement series. The pairs consisted of air puff (aversive sensory stimuli) and tube protrusion (which allowed licking sucrose behavior) in the following combinations: air puff-tube protrusion, tube protrusion-tube protrusion and tube protrusion-air puff. The pairs were interposed by a 2 s delay. The three conditioned tone directions were associated with these three pairs in a one-to-one correspondence, and its association was conditional to three possible conditioned tone frequencies (300, 530, and 1,200 Hz). The responses of 107 neurons to the air puff and tube protrusion were analyzed by two-way ANOVA (task condition x reinforcement situation). Of 42 air puff-responsive and 64 tube protrusion-responsive neurons, 36 and 53 displayed significant main effects and/or significant interaction, respectively. Furthermore, neural responses during the delay periods were dependent on the task conditions. The results indicated that the majority of the hippocampal formation neurons showed task condition- and/or reinforcement situation-dependent responses, suggesting a crucial role of the hippocampal formation in representation of overlapping serial events in episodic memory.

Differential activation in the medial temporal lobe during a sound-sequence discrimination task across age in human subjects.

To elucidate the brain mechanisms to encode sequential events, event-related potentials (ERPs) were recorded during a sound-sequence discrimination task using young and middle-aged adult subjects. In the task, a series of six or 12 kinds of natural sounds were sequentially presented; 70-80% of the stimuli were presented in a fixed order (Non-target), but the remaining stimuli, in a random order (Target). The subjects were instructed to detect the Targets and press a button at the end of each Target. In a control task, the same sounds were randomly presented (Control), and they were instructed to press the button at the end of each sound. Behavioral results indicated that the young subjects learned the task faster than did the middle-aged subjects. Positive ERP waves were evoked by Targets and Non-targets in the parieto-occipital area around 300-700 ms after stimulus onset. The mean amplitudes during this period in the young subjects were larger in Target than Control conditions, and those in Target condition were larger in the young than middle-aged subjects. Furthermore, the mean amplitudes in the Target condition were significantly correlated with behavioral performance. Equivalent dipoles for the ERPs evoked by Targets were estimated in the medial temporal lobe including the hippocampal formation and parahippocampal gyrus. The results suggest that the ERPs around 300-700 ms latency are involved in sound-sequence information processing. Furthermore, decrease in amplitudes of this positivity in the middle-aged subjects suggests that age-related memory decline is associated with deficits in encoding and retrieval of unfamiliar sequence.

Respiratory modulation of muscle sympathetic nerve activity in patients with chronic heart failure.

BACKGROUND: Sympathoexcitation and respiratory instability are closely related to worsening of chronic heart failure. To elucidate the dynamic nature of respiratory modulation of sympathetic activity in patients with heart failure, we studied within-breath variation of muscle sympathetic nerve activity (MSNA) under various ventilatory volumes. METHODS AND RESULTS: MSNA, blood pressure, and respiratory flow were recorded in 23 patients with left ventricular ejection fraction

Time-varying spectral analysis of heart rate and left ventricular pressure variability during balloon coronary occlusion in humans: a sympathoexicitatory response to myocardial ischemia.

OBJECTIVES: We assessed time-varying spectral components of heart rate and left ventricular (LV) pressure variability during coronary angioplasty to elucidate dynamic autonomic responses to transient myocardial ischemia. BACKGROUND: Sympathoexcitatory reflexes elicited by acute coronary occlusion are rarely addressed in the clinical settings because of a lack of technique to monitor transient changes in sympathetic activation. METHODS: RR interval and LV pressure and volume were serially recorded in 14 patients with effort angina during balloon coronary angioplasty. Wavelet analysis was applied for determination of nonstationary spectral components of RR interval and LV peak pressure variability. RESULTS: The wavelet analysis revealed that coronary occlusion provoked low-frequency (LF) fluctuations of RR interval (seven patients) and LV peak pressure (six patients) at 0.06 +/- 0.01 Hz, but not in the remaining patients. Following the balloon inflation, the LF component of RR interval began to increase after the onset of myocardial ischemia, peaked at about 80 s, and then declined in the late phase of inflation. Consequently, the ratio of low to high frequency component rose to be significantly greater in the LF augmentation group than in the no LF augmentation group in the middle phase of coronary occlusion. The patients with no LF augmentation had little evidence of myocardial ischemia as reflected by changes in ST segment and LV systolic function during coronary occlusion. CONCLUSIONS: The wavelet analysis of RR interval and LV pressure variability clearly showed a dynamic profile of spectral components in response to transient coronary artery occlusion. The resultant regional myocardial ischemia elicited a profound sympathoexcitatory response followed by a gradual suppression. This method provides a useful tool to gain a new insight into the nonstationary autonomic influence on the cardiovascular system.

Time course of sympathovagal imbalance and left ventricular dysfunction in conscious dogs with heart failure.

To elucidate the time course of sympathovagal balance and its relationship to left ventricular function in heart failure, we serially evaluated left ventricular contractility and relaxation and autonomic tone in 11 conscious dogs with tachycardia-induced heart failure. We determined a dynamic map of sympathetic and parasympathetic modulation by power spectral analysis of heart rate variability. The left ventricular peak +dP/dt substantially fell from 3,364 +/- 338 to 1,959 +/- 318 mmHg/s (P < 0.05) on the third day and declined gradually to 1,783 +/- 312 mmHg/s at 2 wk of rapid ventricular pacing. In contrast, the time constant of left ventricular pressure decay and end-diastolic pressure increased gradually from 25 +/- 4 to 47 +/- 5 ms (P < 0.05) and from 10 +/- 2 to 21 +/- 3 mmHg (P < 0.05), respectively, at 2 wk of pacing. The high-frequency component (0.15-1.0 Hz), a marker of parasympathetic modulation, decreased from 1,928 +/- 1,914 to 62 +/- 68 x 10(3) ms2 (P < 0.05) on the third day and further to 9 +/- 12 x 10(3) ms2 (P < 0.05) at 2 wk. Similar to the time course of left ventricular diastolic dysfunction, plasma norepinephrine levels and the ratio of low (0.05- to 0.15-Hz)- to high-frequency component increased progressively from 135 +/- 50 to 532 +/- 186 pg/ml (P < 0.05) and from 0.06 +/- 0.06 to 1.12 +/- 1.01 (P < 0.05), respectively, at 2 wk of pacing. These cardiac and autonomic dysfunctions recovered gradually toward the normal values at 2 wk after cessation of pacing. Thus a parallel decline in left ventricular contractility with parasympathetic influence and a parallel progression in left ventricular diastolic dysfunction with sympathoexcitation suggest a close relationship between cardiac dysfunction and autonomic dysregulation during development of heart failure.

The responses of skin blood flow, mean arterial pressure and R-R interval induced by cold stimulation with cold wind and ice water.

This study was designed to evaluate the peripheral circulation response to cold wind stimulation. Skin blood flow (SBF), ECG R-R intervals (RRs) and mean arterial pressure (MAP) were measured in ten healthy men under strictly controlled conditions. Cold wind flow and ice water bath were prepared as cold stimulations. The subjects were exposed to each cold stimulation and the values of the responses were simultaneously recorded. The cold wind stimulation reduced SBF (maximally 40.4 +/- 3.2%) and increased MAP (maximally 106.9 +/- 1.3%), but did not affect RRs. On the other hand, all parameters were affected by the ice water stimulation, which reduced SBF to 16.4 +/- 1.2% and RRs to 85.1 +/- 3.0%, and increased MAP to 130.6 +/- 2.4% compared with the control state. All subjects suffered from intense pain during the ice water but not the cold wind stimulation, and two of them were eliminated from this study because of vagotonia. After phentolamine iontophoresis was used to block the receptor of peripheral alpha-adrenergic nerve terminals, the cold wind stimulation did not affect SBF. These results suggest that cold wind stimulation is a useful test for evaluating peripheral alpha-adrenergic nerve function in relation to cold sensation, without increase of RRs and noxious pain.

Effects of water ingestion on gastric electrical activity and heart-rate variability in healthy human subjects.

Electrogastrography (EGG) is a method to record electrical activity of the stomach using cutaneous electrodes. Power ratio (PR) is one of the parameters and means the relative change of EGG power of gastric activity from before to after certain stimulations (e.g., meals, water or drugs). Autonomic nervous function is an important modulator of gastric activity, but its relation with the EGG parameters has not been well clarified. We recorded EGG and the R-R interval simultaneously both before and after drinking 150 ml water for 400 s, and spectrally analyzed them using the maximum entropy method in 12 healthy volunteers. We calculated PR from before to after water ingestion, and the power of the high-frequency component of R-R interval variability before (pre-HF) and after water ingestion (post-HF), and their ratio (rHF = post-HF/pre-HF). PR was positively correlated with rHR (r = 0.727; P < 0.05) and negatively correlated with pre-HF (r = 0.706; P < 0.05), and rHF was negatively correlated with pre-HF (r = 0.776; P < 0.05). These results suggest that simultaneous recording of EGG and ECG for frequency domain analysis is necessary to estimate the vagal nervous activity.

The number of noradrenergic and adrenergic neurons in the brain stem does not change with age in male Sprague-Dawley rats.

We examined whether or not the number of noradrenergic and adrenergic neurons changes with age, using peroxidase antiperoxidase (PAP) immunohistochemistry with specific antisera against tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT). TH- and PNMT-immunoreactive neurons were counted in every noradrenergic and adrenergic neuron group of young (3-month-old) and old (24-month-old) rats. The differences in the counted number of TH- and PNMT-immunoreactive neurons did not reach statistical significance between the young and old rats.

Effect of physical training on exercise-induced sweating in women.

The effect of physical training on the time course of sweat rate in women has been examined. Physically untrained and trained young female subjects pedaled a bicycle ergometer at work rates of 483 and 981 kgm.min-1, for 2 h in summer and winter in an ambient environment of 30 degrees C db and 60% rh. The trained women also worked at 1,070 kgm.min-1 and the untrained at 391 kgm.min-1. Rectal temperature was measured, and capsule sweat samples were collected from the back every 5 min. Sweating was initiated more rapidly in the trained group than in the untrained group. The trained group working at a load of 981 kgm.min-1 exhibited a progressive decrease in sweat rate. This was not observed at a work load of 483 kgm.min-1. Hidromeiosis was rarely seen in the untrained group. However, in the untrained women who underwent 60 days of physical training, initiation of sweating occurred more quickly and hidromeiosis was observed. It was concluded that previous physical training improved women's capacity for useful sweating during exercise in a hot environment.