A Wireless, Bidirectional Interface for <em>In Vivo</em> Recording and Stimulation of Neural Activity in Freely Behaving Rats

In vivo electrophysiology is a powerful technique to investigate the relationship between brain activity and behavior at a millisecond and micrometer ...

Philipps-Universität Marburg

When studying functional asymmetries in normal laboratory rats, several behavioral tests have been applied and proven their utility, including turning in rotometers or open-fields, handedness in paw usage, T-maze alternation, and others. Here, we analyzed male Wistar rats in two tests, namely the elevated plus-maze and the T-maze. In these tests, behavioral asymmetries are rather likely to occur, since the animals have to show several types of turns towards the left or right when ambulating through these environments. In a first study using the plus-maze, we provide detailed data on (A) the types of turns which the animals showed when changing their direction within arms (i.e., 180 degrees turns), and (B) the types of turns when proceeding from one arm to an adjacent one (i.e., 90 degrees turns). With respect to asymmetry, we found moderate biases in favor of the right. On the 1st day of plus-maze testing, there was a trend for more rightward turns within arms. On the 2nd day of testing, there was a trend for turns towards the right when alternating between arms of the plus-maze. In a 2nd study, we asked for asymmetries in the plus-maze in animals, which had been treated acutely with the psychostimulatory amphetamine analogue 3,4-methylene-dioxymethamphetamine (MDMA). Psychostimulants drugs, especially amphetamine, have repeatedly been used before in work on functional asymmetry, since they can enhance or reveal asymmetries in normal rats. MDMA had dose-dependent effects on activity, which affected turns within arms, and turns between arms; however, there was only sparse evidence with respect to asymmetry. Interestingly, and if at all, asymmetry was in favor of the right. Finally, we present data for behavior in the T-maze, where we used a spontaneous test version, that is, the animals could explore the maze but had no task to solve. Asymmetries were measured as turns within the start arm (180 degrees), and as left- or rightward turns between arms (90 degrees ) at the T-point of the maze. In both measures, we again obtained evidence for asymmetries in favor of the right. This work supports previous studies showing that the T-maze is suitable to analyze behavioral asymmetries in rats. In addition, it provides new evidence with respect to the elevated plus-maze, indicating that this standard tool of anxiety research may also be useful in research on behavioral asymmetries and their underlying brain mechanisms. Behavioral biases in favor of the right, as shown here, have often been reported before, especially with Wistar rats. Such biases should be taken into account, since they can serve as an approach to study brain/behavior relationships, and since they may affect the outcome of physiological manipulations or behavioral trainings.

Analysis of behavioral asymmetries in the elevated plus-maze and in the T-maze.

The fact that rats emit different types of ultrasonic vocalizations in a variety of contexts has received increasing experimental attention, since such calls might serve as indices of the animal's subjective state, and/or as social signals in various types of interactions with other rats. Here, we present two experiments in adult male Wistar rats where we tested several different situations and conditions with respect to the occurrence of high-frequency (50-kHz) and low-frequency (22-kHz) calls. These experiments showed that rats emitted high-frequency calls when tested singly in a housing cage, which was situated in a room with no other rats present. Calling did not habituate with repeated testing, and occurred in the animal's own home cage, or a fresh housing cage, and irrespective of whether the animal's motivational status was high or low, that is, irrespective of whether they were food-deprived or fed ad libitum. Furthermore, high- and low-frequency calls were observed when applying a standardized new tickling procedure, which provided evidence for effective types of tickling. Most, but not all, young adult rats still accepted this stimulation as play. Therefore, this procedure might be a useful method to elicit high-frequency calls in adult rats. Overall, substantial evidence for inter-individual variability and intra-individual stability in vocalization was provided both, within and between housing cage and tickle tests. This variability seems to depend at least partly on dispositions or traits, which can be gauged by specific screening tests, like measuring risk-assessment in the elevated plus-maze, since animals with more risk-assessment were more likely to emit high-frequency calls during cage and tickle tests. These findings are discussed with respect to the major hypotheses concerning the functional significance of ultrasonic vocalizations, namely the social/communicatory and the motivational/emotional hypothesis.

Situational factors, conditions and individual variables which can determine ultrasonic vocalizations in male adult Wistar rats.

Since the late eighties of the last century, when the so-called serial reaction time (SRT) task was first presented, analysis of sequential learning and performance has developed into a prosperous area of neurocognitive research in human subjects and non-human primates. In more recent years, rodent implementations of SRT tasks have become available, which will be summarized here and discussed with respect to their advantages, but also to their methodological and theoretical drawbacks. Then, a review of new neurobiological findings with such rodent tasks will be provided, that will be embedded into the existing theoretical framework, originally obtained from the work with primate species. Among others, this review will show that rodent SRT tasks allow actualizing and thus, studying many psychological features of human sequential tasks, for example, cognitive complexity of sequences. Since these rodent tasks can be used for a number of neuronal analyses, it is assumed that they will provide important insights for the neural mechanisms underlying such cognitive functions.

Rodent models of serial reaction time tasks and their implementation in neurobiological research.

In the present review, the phenomenon of ultrasonic vocalization in rats will be outlined, including the three classes of vocalizations, namely 40-kHz calls of pups, and 22- and 50-kHz calls of juvenile and adult rats, their general relevance to behavioral neuroscience, and their special relevance to research on anxiety, fear, and defense mechanisms. Here, the emphasis will be placed on 40- and 22-kHz calls, since they are typical for various situations with aversive properties. Among other topics, we will discuss whether such behavioral signals can index a certain affective state, and how these signals can be used in social neuroscience, especially with respect to communication. Furthermore, we will address the phenomenon of inter-individual variability in ultrasonic calling and what we currently know about the mechanisms, which may determine such variability. Finally, we will address the current knowledge on the neural and pharmacological mechanisms underlying 22-kHz ultrasonic vocalization, which show a substantial overlap with mechanisms known from other research on fear and anxiety, such as those involving the periaqueductal gray or the amygdala.

On the relationships between ultrasonic calling and anxiety-related behavior in rats.

Rats express affective states by visible behaviors (like approach or flight) and through different kinds of ultrasonic vocalizations (USV). 50-kHz calls are thought to reflect positive affective states since they occur during rewarding situations like social play or palatable food. However, the effects of voluntary exercise on USV have not been investigated yet, although such exercise can serve as reward. To this aim, we gave young adult rats restricted daily access to a runway maze, where they could interact with either a movable (experimental group) or locked wheel (sedentary group) for 14days and we tested USV in anticipation of and during subsequent running. We also studied inter-individual differences in running, and relationships with USV, and rat-typical trait measures. The results showed that the experimental rats had to be separated into "runners" and "pseudorunners" since only runners performed true running, whereas pseudorunners hardly entered the wheel and turned it only with their forelimbs. This outcome seems to be related to subject-dependent differences in responding to novelty and in reward sensitivity, as indicated by pertinent screening tests, which we had performed prior to the 14days of wheel access. In the runway, our experimental and control groups did not differ in visible anticipatory behavior, like approach. Yet, only runners and sedentary rats displayed an increasing but similar amount of anticipatory USV, which is suggestive of a state of incentive anticipation of the coming wheel access. During exercise, only runners increased USV, probably indicating a highly positive emotional state. To conclude, voluntary exercise provides a promising tool to induce 50-kHz USV during and in anticipation of exercise. When performing such studies, possible individual differences between subjects have to be taken into account, and the actual wheel performance should carefully be controlled.

Exercise reward induces appetitive 50-kHz calls in rats.

It is widely agreed upon that hippocampal function is linked to episodic-like and spatial memory across various species, for example, rodents. However, the interplay between hippocampal function and other types of learning and memory, like procedural stimulus-response or sequential learning, is less clear. Recently (Eckart et al. in Hippocampus 22:1202-1214, 2012), we showed that excitotoxic hippocampal lesions, which mainly affected its dorsal part, led not only to the expected deficits in a spatial and episodic-like memory task, namely the object place recognition test, but also to substantial improvements in terms of speed and accuracy in a rat adaption of the human sequential reaction time task (SRTT). The design of that experiment, however, which included fixed test durations per training day, led to the fact that lesioned animals gained more instrumental experience, which may partly have accounted for their enhanced performance. In order to rule out such a potential confound, we performed the present experiment on rats with similar ibotenic lesions aiming at the dorsal hippocampus, but we now kept the amount of correct instrumental responses and reinforcements on the same level as in controls. Our data revealed that lesioned animals were still able to complete the SRTT in a substantially smaller amount of time, when compared to control and sham-operated animals, although no differences were observable in terms of speed or accuracy. Also, the animals with lesions showed impaired extinction in a subsequent test where rewards were omitted. The former effect can primarily be attributed to shorter post-reinforcement pauses in the lesioned animals, and the possible mechanisms of this and the extinction effect will be addressed in the discussion.

Procedural Performance Benefits after Excitotoxic Hippocampal Lesions in the Rat Sequential Reaction Time Task.

When parts of the brain suffer from damage, certain functional deficits or impairments are the expected and typical outcome. A myriad of examples show such negative consequences, which afford the daily tasks of neurologists, neuropsychologists, and also behavioral neuroscientists working with experimental brain lesions. Compared to lesion-induced deficits, examples for functional enhancements or facilitation after brain lesions are rather rare and usually not well studied. Here, the mammalian hippocampus seems to provide an exception, since substantial evidence shows that its damage can have facilitatory behavioral effects under certain conditions. This review will address these effects and their possible mechanisms. It will show that facilitatory effects of hippocampal lesions, although mostly studied in rats, can be found in many mammalian species, that is, they are apparently not species-specific. Furthermore, they can be found with various lesion techniques, from tissue ablation, to neurotoxic damage, and from damage of hippocampal structure itself to damage of fiber systems innervating it. The major emphasis of this review, however, lies on the behavioral effects and their interpretations. Thus, facilitatory effects can be found in several learning paradigms, especially active avoidance, and some forms of Pavlovian and instrumental conditioning. These will be discussed in light of pertinent theories of hippocampal function, such as inhibition, spatial cognition, and multiple memory systems theories, which state that facilitatory effects of hippocampal lesions may reflect the loss of interference between hippocampal spatial and striatal procedural cognition. Using the example of the rat sequential reaction time task, it will also be discussed how such lesions can have direct and indirect consequences on certain behavioral readouts. A final note will advocate considering possible functional facilitation also in neurologic patients, especially those with hippocampal damage, since such a strategy might provide new avenues for therapeutic treatments.

Behavioral facilitation after hippocampal lesion: A review.

Paradoxical kinesia refers to a sudden transient ability of akinetic patients to perform motor tasks they are otherwise unable to perform. The mechanisms underlying this phenomenon are unknown due a paucity of valid animal models that faithfully reproduce paradoxical kinesia. Here, in a first experiment, we present a new method to study paradoxical kinesia by "awakening" cataleptic rats through presenting appetitive 50-kHz ultrasonic vocalizations (USV), which are typical for social situations with positive valence, like juvenile play or sexual encounters ("rat laughter"). Rats received systemic haloperidol to induce catalepsy, which was assessed by means of the bar test. During that test, 50-kHz USV, time- and amplitude-matched white noise (NOISE), or background noise (BACKGROUND) were played back and compared to SILENCE. Every animal was exposed to all four acoustic stimuli in random order, with four independent groups of rats being tested. Only when exposed to playback of appetitive 50-kHz USV, the otherwise akinetic rats rapidly started to move efficiently. The acoustic control stimuli, in contrast, did not release rats from catalepsy, despite eliciting the auditory pinna reflex and head movements towards the sound source. Moreover, in a second experiment, playback of aversive 22-kHz USV and relevant acoustic control stimuli did also not significantly affect catalepsy time. Together, our animal model provides a completely new approach to study mechanisms of paradoxical kinesia, which might help to improve behavioral therapies for Parkinson's disease and other disorders, where akinetic or cataleptic states occur.

Rainer K.W. Schwarting

Behavioral Neuroscience,
Experimental and Biological Psychology,
Behavioral Neuroscience, Experimental and Biological Psychology

Philipps-Universität Marburg

A Wireless, Bidirectional Interface for In Vivo Recording and Stimulation of Neural Activity in Freely Behaving Rats

Rainer K.W. Schwarting

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Behavioral Neuroscience,Experimental and Biological Psychology,Behavioral Neuroscience, Experimental and Biological Psychology

Philipps-Universität Marburg

A Wireless, Bidirectional Interface for In Vivo Recording and Stimulation of Neural Activity in Freely Behaving Rats

Behavioral Neuroscience,
Experimental and Biological Psychology,
Behavioral Neuroscience, Experimental and Biological Psychology