Whole-cell recordings in freely moving rats

Intracellular recording, which allows direct measurement of the membrane potential and currents of individual neurons, requires a very mechanically stable preparation and has thus been limited to in vitro and head-immobilized in vivo experiments. This restriction constitutes a major obstacle for linking cellular and synaptic physiology with animal behavior. To overcome this limitation we have developed a method for performing whole-cell recordings in freely moving rats. We constructed a miniature head-mountable recording device, with mechanical stabilization achieved by anchoring the recording pipette rigidly in place after the whole-cell configuration is established. We obtain long-duration recordings (mean of approximately 20 min, maximum 60 min) in freely moving animals that are remarkably insensitive to mechanical disturbances, then reconstruct the anatomy of the recorded cells. This head-anchored whole-cell recording technique will enable a wide range of new studies involving detailed measurement and manipulation of the physiological properties of identified cells during natural behaviors.     

Oscillatory entrainment of striatal neurons in freely moving rats

Oscillations and synchrony in basal ganglia circuits may play a key role in the organization of voluntary actions and habits. We recorded single units and local field potentials from multiple striatal and cortical locations simultaneously, over a range of behavioral states. We observed opposite gradients of oscillatory entrainment, with dorsal/lateral striatal neurons entrained to high-voltage spindle oscillations ("spike wave discharges") and ventral/medial striatal neurons entrained to the hippocampal theta rhythm. While the majority of units were likely medium-spiny projection neurons, a second neuronal population showed characteristic features of fast-spiking GABAergic interneurons, including tonic activity, brief waveforms, and high-frequency bursts. These fired at an earlier spindle phase than the main neuronal population, and their density within striatum corresponded closely to the intensity of spindle oscillations. The orchestration of oscillatory activity by networks of striatal interneurons may be an important mechanism in the pathophysiology of neurological disorders such as Parkinson's disease.     

The determination of the nociceptive thresholds in freely moving rats

A simple method for determination of nociceptive thresholds in free-moving rats is put forward. The method is based on the registration of vocalization reaction caused by the feed through the lungs connected with the stimulator by thin wires electrodes of gradually increasing impulses of constant electric current. The examples of effect of morphin and naloxone on the nociceptive thresholds as well the alteration of thresholds during predatory aggression are given.     

Circadian rhythms of urinary electrolyte excretion in freely moving rats

In 8 freely moving rats the circadian variation in the eletrolyte excretion was studied. Food was available during either the dark or the light period. The lights were on from 0800–2000 hr. Potassium, phosphate and magnesium showed peak excretion values during the dark period under both feeding conditions, although the maxima occurred 2.5 hr earlier when the rats were fed during the light period; minimum excretion was recorded just prior to feeding. Sodium excretion followed a different pattern; for animals fed during the night, maximum excretion occurred almost at the end of the dark period and minimum excretion at the start of the feeding period. For day-fed animals these values were recorded 5 and 4 hours earlier, respectively. Calcium excretion reached a maximum after the feeding period and a minimum shortly after the onset of feeding. From this study it can be concluded that the peak excretions of potassium, phosphate and magnesium are only slightly influenced by the feeding regimen, indicating that they depend mainly on an endogenous rhythm. In contrast, the minimum excretion of these ions is determined by feeding. For calcium maximum as well as minimum excretion is correlated with the feeding regimen. The excretion pattern of sodium differs from that of calcium, as well as potassium, phosphate and magnesium, indicating that it is controlled by a different mechanism.     

Respiratory sinus arrhythmia in freely moving and anesthetized rats.

Heart rate increases during inspiration and slows during postinspiration; this respiratory sinus arrhythmia helps match pulmonary blood flow to lung inflation and maintain an appropriate diffusion gradient of oxygen in the lungs. This cardiorespiratory pattern is found in neonatal and adult humans, baboons, dogs, rabbits, and seals. Respiratory sinus arrhythmia occurs mainly due to inhibition of cardioinhibitory parasympathetic cardiac vagal neurons during inspiration. Surprisingly, however, a recent study in anesthetized rats paradoxically found an enhancement of cardiac vagal activity during inspiration, suggesting that rats have an inverted respiratory sinus arrhythmia (Rentero N, Cividjian A, Trevaks D, Pequignot JM, Quintin L, and McAllen RM. Am J Physiol Regul Integr Comp Physiol 283: R1327-R1334, 2002). To address this controversy, this study examined respiratory sinus arrhythmia in conscious freely moving rats and tested whether the commonly used experimental anesthetics urethane, pentobarbital sodium, or ketamine-xylazine alter respiratory sinus arrhythmia. Heart rate significantly increased 21 beats/min during inspiration in conscious rats, a pattern similar to the respiratory sinus arrhythmia that occurs in other species. However, anesthetics altered normal respiratory sinus arrhythmia. Ketamine-xylazine (87 mg/kg and 13 mg/kg) depressed and pentobarbital sodium (60 mg/kg) abolished normal respiratory sinus arrhythmia. Urethane (1 g/kg) inverted the cardiorespiratory pattern so that heart rate significantly decreased during inspiration. Our study demonstrates that heart rate normally increases during inspiration in conscious, freely moving rats, similar to the respiratory sinus arrhythmia pattern that occurs in other species but that this pattern is disrupted in the presence of general anesthetics, including inversion in the case of urethane. The presence and consequences of anesthetics need to be considered in studying the parasympathetic control of heart rate.     

Gluconeogenesis activation after intravenous angiotensin II in freely moving rats.

Intravenous (IV) administration of angiotensin II (0.95 nmol/100 g body weight) produced a marked increase in plasma glucose of 20 h fasted rats. To investigate the possibility of a stimulation of gluconeogenesis, conscious unrestrained rats were continuously infused with [14C]bicarbonate, 60 microl/min (0.18 microCi/min), and label incorporation into circulating glucose was determined before and after angiotensin injection. The rate of 14C incorporation into blood glucose of fed rats increased significantly after angiotensin II administration, a 279% increase after 20 min (P < 0.01). In conclusion, the results of the present study show that the hyperglycemia induced by intravenous (IV) administration of angiotensin II is accompanied by an activation of gluconeogenesis, as evidenced by a rapid and marked increase in the rate of 14CO2 incorporation into circulating glucose.     

Firing properties of substantia nigra dopaminergic neurons in freely moving rats

Single unit recordings were obtained from putative dopaminergic neurons in the substantia nigra of awake, freely moving rats. The cells exhibited waveforms, range of firing rates and types of firing patterns identical to those of identified DA neurons of anesthetized or paralyzed rats. Two firing patterns were observed: single spike activity and a bursting mode with spikes of progressively diminished amplitude and increased duration within each burst. The degree of burst firing varied considerably among the cells and individual cells sometimes switched from one pattern of firing (e.g. predominantly single spike) to another (e.g. bursting), although the determinants of these transitions are, at this time, unclear. Putative DA neurons were inhibited by i.v. apomorphine and excited by i.v. haloperidol. Haloperidol also reversed the apomorphine-induced inhibition of firing. Inhibitions and excitations were associated with a reduction and elevation, respectively, in burst firing. The effects of the two drugs were identical to their effects in immobilized rats. In several cases, a putative DA neuron was observed to fire all of its spikes in near coincidence with at least one other cell with identical electrophysiological characteristics. This form of interaction (i.e. presumed electrical coupling) between DA cells is only rarely observed in anesthetized or paralyzed rats and may play a significant role in the normal functioning of the nigrostriatal DA system.     

3D pose estimation enables virtual head fixation in freely moving rats

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A lightweight microdrive for single-unit recording in freely moving rats and pigeons

A design for an inexpensive and reliable subminiature microdrive for recording single neurons in the freely moving animal is presented. The Scribe microdrive is small and lightweight and has been used successfully to record in freely moving rats and pigeons. It would also be suitable for recording in mice. The device is simple and inexpensive yet allows for stable and precise manipulation of the recording electrodes. As a result it supports stable recordings conducted over long periods. Because the Scribe microdrive is a small-diameter device it is also suitable for multisite, multielectrode applications. Here we discuss the construction of the device and comment on its use in recording from freely moving rats and pigeons.     

Neurophysiological recordings in freely moving monkeys

Recordings of neuronal activity in freely moving rats are common in experiments where electrical signals are transmitted using cables. Such techniques are not common in monkeys because their prehensile abilities are thought to preclude such techniques. However, analysis of brain mechanisms underlying spatial navigation and cognition require the subject to walk. We have developed techniques for recordings in freely moving monkeys in two different situations: a 5 x 5 m testing laboratory and in a 50 m2 open field environment. Neuronal signals are sent to amplifiers and data acquisition systems using cables or telemetry. These techniques provide high quality recordings of single neurons during behaviors such as foraging, walking, and the performance of memory tasks and thus provide a unique opportunity to study primate behavior in a semi-natural situation.     

Functional imaging in freely moving animals

Uncovering the relationships between animal behavior and cellular activity in the brain has been one of the key aims of neuroscience research for decades, and still remains so. Electrophysiological approaches have enabled sparse sampling from electrically excitable cells in freely moving animals that has led to the identification of important phenomena such as place, grid and head-direction cells. Optical imaging in combination with newly developed labeling approaches now allows minimally invasive and comprehensive sampling from dense networks of electrically and chemically excitable cells such as neurons and glia during self-determined behavior. To achieve this two main imaging avenues have been followed: Optical recordings in head-restrained, mobile animals and miniature microscope-bearing freely moving animals. Here we review progress made toward functional cellular imaging in freely moving rodents, focusing on developments over the past few years. We discuss related challenges and biological applications.     

自由活动大鼠睡眠状态和呼吸节律的同步监测方法

目的:设计一种睡眠呼吸暂停综合征动物模型的监测方法.方法:通过多导生理仪同步监测自由活动大鼠6 h生理睡眠时间的皮层脑电、颈部肌电,以及呼吸波形.并用人机交互的方法进行数据处理.结果:监测信号稳定、清晰易辨,根据记录到的信号可进行不同清醒-睡眠状态分期,并判断大鼠的呼吸暂停情况.结论:该法操作简便,是小动物睡眠和呼吸监测的可靠方法.     

自由活动大鼠睡眠呼吸监测技术改进

目的：改进大鼠睡眠呼吸监测技术,解决既往模型中咬线、脱落、信号不稳定问题。方法：改进监测电极、信号接入线路及动物手术。结果：改进后手术时间缩短,创面暴露时间减少,大鼠术后易恢复。且电极稳固性好,脑电和肌电信号更稳定清晰,信号接入线路传导性好,耐用。实现连续长时间监测,成功率高。便于根据信号进行不同清醒一睡眠状态分期,并判断大鼠睡眠呼吸暂停情况。结论：改进后的操作技术操作更简单、信号更稳定,是一项更加实用可靠的小动物睡眠呼吸监测技术。     

Local blood flow in the emotiogenic structures of the brain in freely moving rats

The speed of local blood flow (SLBF) in positive emotiogenic hypothalamic zones was recorded in free-moving white rats, by the method of hydrogen clearance, in states of passive and active alertness, in conditions of artificial (local) activation (by cathode) and inactivation (by DC anode) and also during stimulation of other positive and negative emotiogenic structures. It was established that the natural or artificial activation of the emotiogenic brain zones elicits an increase of SLBF and the inactivation evokes its reduction. Blood flow of the positive emotiogenic brain zones is intensified by stimulation of other positive emotiogenic structures, is reduced by stimulation of the negative emotiogenic zones and does not change at stimulation of emotionally neutral zones. It is suggested, that the mechanism of vascular reactions elicited by activation of positive and negative emotiogenic brain structures has a neurogenic basis and is performed in the type of "axon-reflex" by collaterals of ascending and descending fibers of the forebrain medial bundle.     

Long-term potentiation and unit evoked responses in the cingulate cortex of freely moving rats

Long-term potentiation (LTP) of synaptic efficacy is considered to be the most probable physiological mechanism of long-term memory. However, lack of understanding of cellular and subcellular mechanisms of LTP induction in freely behaving animals does not correspond to the importance of the problem. It was tested whether the characteristics of potentiation in the cingulate cortex after tetanization of the subiculocingulate tract (SCT) meet the criteria of true LTP (that passes all known stages in its development and lasts for more than a day in freely-behaving animals). Additionally, characteristics of spike responses to SCT stimulation and the effects of application of different glutamate receptor blockers were studied. Without application of GABA receptor blockers, the LTP lasted for more than 24 hours. Application of NMDA glutamate receptor blockers significantly inhibited field potentials evoke by testing stimulation. Short-latency spike responses to SCT stimulation were recorded with low probability that increased with stimulation intensity. The obtained data reveal the possibility to compare the involvement of cingulate neurons in acquisition of adaptive behavior and changes in their spike responses during the LTP development in freely-moving rats.