Meng-Li Tsai

A simple method for fabricating horizontal and vertical microwire arrays

Microwire array electrodes are important in multi-site, multiple single-unit recording experiments. A simple method is described herein for the construction of microwire arrays consisting of evenly spaced insulated microwires in either horizontal or vertical orientations. Several key steps in the fabrication of a good microwire array electrode are made easier with this method. These steps include (1) arranging microwires into a desirable configuration, (2) keeping track of microwire sequences, and (3) soldering microwires to closely packed slots. This method needs only general mechanical tools and is relatively simple even for inexperienced workers.

Differential morphine effects on short- and long-latency laser-evoked cortical responses in the rat.

&NA; Evoked potential and ensemble neuronal activities were used to study the responses of the primary sensorimotor cortex (SmI) to noxious CO2 laser irradiation of the middle part of the tail in conscious behaving rats. The hypothesis that systemic morphine treatment preferentially attenuates the longer‐latency laser‐evoked cortical responses was also tested. Laser‐evoked potentials (LEPs) and multiple single‐unit (SU) activities were, respectively, recorded from chronically implanted stainless‐steel screws and microwire electrodes. When examined individually, many SmI neurons showed either short‐latency (<100 ms) or long‐latency (300–500 ms) responses to laser irradiation. These neurons are widely dispersed in the tail region and hind limb region of the SmI, and also in the forelimb and head regions of the primary motor cortex (MI). Quantitatively, a higher percentage of neurons in the SmI tail region responded with shorter latencies compared to those in the SmI hind limb region or in the MI. When responses of many simultaneously recorded SU were examined together, short‐latency and long‐latency SmI ensemble activities matched the LEP1 and LEP2, respectively. Systemic morphine significantly attenuated the long‐latency but not the short‐latency component in both LEPs as well as ensemble neuronal activity in the tail region of the SmI. These effects were blocked by naloxone pretreatment.

An infrared range camera-based approach for three-dimensional locomotion tracking and pose reconstruction in a rodent.

We herein introduce an automated three-dimensional (3D) locomotion tracking and pose reconstruction system for rodents with superior robustness, rapidity, reliability, resolution, simplicity, and cost. An off-the-shelf composite infrared (IR) range camera was adopted to grab high-resolution depth images (640×480×2048 pixels at 20Hz) in our system for automated behavior analysis. For the inherent 3D structure of the depth images, we developed a compact algorithm to reconstruct the locomotion and body behavior with superior temporal and solid spatial resolution. Since the range camera operates in the IR spectrum, interference from the visible light spectrum did not affect the tracking performance. The accuracy of our system was 98.1±3.2%. We also validated the system, which yielded strong correlation with automated and manual tracking. Meanwhile, the system replicates a detailed dynamic rat model in virtual space, which demonstrates the movements of the extremities of the body and locomotion in detail on varied terrain.

A bundled microwire array for long-term chronic single-unit recording in deep brain regions of behaving rats.

Chronic single-unit recording in subcortical brain regions is increasingly important in neurophysiological studies. However, methods for long-term, stable recording of multiple single-units in deep brain regions and in dura-surrounded ganglion have not yet been established. In the present study, we propose a bundled microwire array design which is capable of long-term recording of the trigeminal ganglion and deep-brain units. This electrode set is easy to construct from common materials and tools found in an electrophysiological laboratory. The salient features of our design include: (1) short and separated tungsten microwires for stable chronic recording; (2) the use of a 30-guage stainless steel guide tube for facilitating penetration and aiming for deep targets as well as electrical grounding; (3) the inclusion of a reference of the same microwire material inside the bundle to enhance common mode rejection of far field noises; and (4) an adjustable connector. In our case, we used a 90° backward bending connector so that implanted rats could perform the same hole-seeking behavior and their faces and the whiskers could be stimulated in the behaving state. It was demonstrated that this multi-channel electrode caused minimal tissue damage at the recording site and we were able to obtain good, stable single-unit recordings from the trigeminal ganglion and ventroposterior medial thalamus areas of freely moving rats for up to 80 days. This methodology is useful for the studies that require long term and high quality unit recording in the deep brain or in the trigeminal system.

Involvement of the Cav3.2 T-type calcium channel in thalamic neuron discharge patterns

BackgroundMice that have defects in their low-threshold T-type calcium channel (T-channel) genes show altered pain behaviors. The changes in the ratio of nociceptive neurons and the burst firing property of reticular thalamic (RT) and ventroposterior (VP) neurons in Cav3.2 knockout (KO) mice were studied to test the involvement of thalamic T-channel and burst firing activity in pain function.ResultsUnder pentobarbital or urethane anesthesia, the patterns of tonic and burst firings were recorded in functionally characterized RT and VPL neurons of Cav3.2 KO mice. Many RT neurons were nociceptive (64% under pentobarbital anesthesia and 50% under urethane anesthesia). Compared to their wild-type (WT) controls, fewer nociceptive RT neurons were found in Cav3.2 KO mice. Both nociceptive and tactile RT neurons showed fewer bursts in Cav3.2 KO mice. Within a burst, RT neurons of Cav3.2 KO mice had a lower spike frequency and less-prominent accelerando-decelerando change. In contrast, VP neurons of Cav3.2 KO mice showed a higher ratio of bursts and a higher discharge rate within a burst than those of the WT control. In addition, the long-lasting tonic firing episodes in RT neurons of the Cav3.2 KO had less stereotypic regularity than their counterparts in WT mice.ConclusionsRT might be important in nociception of the mouse. In addition, we showed an important role of Cav3.2 subtype of T-channel in RT burst firing pattern. The decreased occurrence and slowing of the bursts in RT neurons might cause the increased VP bursts. These changes would be factors contributing to alternation of pain behavior in the Cav3.2 KO mice.

Wavelet-based analysis of low-frequency fluctuations of blood pressure and sympathetic nerve activity in rats

Biorthogonal wavelets were employed to quantify the relationship of fluctuations between blood pressure (BP) and sympathetic nerve activity (SNA). We forced the SNA to fluctuate by electrical stimulation the medulla in anesthetized, paralyzed, vagotomized, cardiac sympathetic-blocked, baroreceptor-denervated, and angiotensin II-converting enzyme-inhibited rats. Although spectral analysis showed a close coupling between fluctuations of BP and SNA at the stimulating frequencies, only the fluctuations of SNA in frequencies of 0.25 to approximately 0.4 Hz were proportional to BP fluctuations over the course of time. The results suggest that fluctuations transmitted from SNA to BP were uniform without shifting due to the nature of vasculature or the lagging of sympathetic action in frequencies of 0.25 to approximately 0.4 Hz, and support the possibility of using low-frequency variabilities of BP to quantitatively estimate fluctuations of SNA at time domain.

Correlation of discharges of rostral ventrolateral medullary neurons with the low-frequency sympathetic rhythm in rats.

The rostral ventrolateral medulla (RVLM) is critically important in the generation of sympathetic activity. The purpose of this study was to investigate whether discharges of RVLM neurons contribute to low-frequency (LF) sympathetic rhythms. Blood pressure (BP), renal sympathetic nerve activity (SNA), and neuronal activity in the RVLM were simultaneously recorded in seven anesthetized, paralyzed, and artificially ventilated rats. Fifty-one RVLM neurons were recorded and classified into three differential functional groups according to their activities related to baroreceptor input. Those in the category of spike firing inhibited by a BP increase (BP(I)) and which excited sympathetic discharges was the most abundant (24%). Coherence analysis was used to examine the relationship of the firing frequency of RVLM neurons with the LF (0.2-0.8Hz) rhythm of SNA. Forty-one percent of RVLM neurons showed a significant correlation to LF rhythms, and BP(I) neurons with sympathoexcitatory properties were the major contributors. In another 4 baroreceptor-denervated rats, 36 RVLM neurons were recorded. In these rats, RVLM neuronal activities no longer changed with BP fluctuations. Nevertheless, more than 40% of RVLM neurons were sympathoexcitatory, and 36% of RVLM neurons were still correlated with the LF SNA rhythm. Our results suggest that there are RVLM neurons involved in generating the LF rhythm in SNA and that the baroreflex can induce the participation of more neurons in LF rhythm generation.

Neuronal Oscillations in Golgi Cells and Purkinje Cells are Accompanied by Decreases in Shannon Information Entropy

Neuronal oscillations have been shown to contribute to the function of the cerebral cortex by coordinating the neuronal activities of distant cortical regions via a temporal synchronization of neuronal discharge patterns. This can occur regardless whether these regions are linked by cortico-cortical pathways or not. Less is known concerning the role of neuronal oscillations in the cerebellum. Golgi cells and Purkinje cells are both principal cell types in the cerebellum. Purkinje cells are the sole output cells of the cerebellar cortex while Golgi cells contribute to information processing at the input stage of the cerebellar cortex. Both cell types have large cell bodies, as well as dendritic structures, that can generate large currents. The discharge patterns of both these cell types also exhibit oscillations. In view of the massive afferent information conveyed by the mossy fiber–granule cell system to different and distant areas of the cerebellar cortex, it is relevant to inquire the role of cerebellar neuronal oscillations in information processing. In this study, we compared the discharge patterns of Golgi cells and Purkinje cells in conscious rats and in rats anesthetized with urethane. We assessed neuronal oscillations by analyzing the regularity in the timing of individual spikes within a spike train by using autocorrelograms and fast-Fourier transform. We measured the differences in neuronal oscillations and the amount of information content in a spike train (defined by Shannon entropy processed per unit time) in rats under anesthesia and in conscious, awake rats. Our findings indicated that anesthesia caused more prominent neuronal oscillations in both Golgi cells and Purkinje cells accompanied by decreases in Shannon information entropy in their spike trains.

Long-Term Changes in Trigeminal Ganglionic and Thalamic Neuronal Activities following Inferior Alveolar Nerve Transection in Behaving Rats

The transection of the inferior alveolar nerve (IANx) produces allodynia in the whisker pad (V2 division) of rats. Ectopic discharges from injured trigeminal ganglion (TG) neurons and thalamocortical reorganization are possible contributors to the sensitization of uninjured V2 primary and CNS neurons. To test which factor is more important, TG and ventroposterior medial nucleus (VPM) neurons were longitudinally followed before, during, and after IANx for up to 80 d. Spontaneous discharges and mechanical stimulation-evoked responses were recorded in conscious and in anesthetized states. Results show (1) a sequential increase in spontaneous activities, first in the injured TG neurons of the IAN (2–30 d), followed by uninjured V2 ganglion neurons (6–30 d), and then VPM V2 neurons (7–30 d) after IANx; (2) ectopic discharges included burst and regular firing patterns in the IAN and V2 branches of the TG neurons; and (3) the receptive field expanded, the modality shifted, and long-lasting after-discharges occurred only in VPM V2 neurons. All of these changes appeared in the late or maintenance phase (7–30 d) and disappeared during the recovery phase (40–60 d). These observations suggest that ectopic barrages in the injured IAN contribute more to the development of sensitization, whereas the modality shift and evoked after-discharges in the VPM thalamic neurons contribute more to the maintenance phase of allodynia by redirecting tactile information to the cortex as nociceptive.

Frequency Ranges of Heart Rate Variability Related to Autonomic Nerve Activity in the Mouse

Mice have gained more and more attention in recent years and been widely used in transgenic experiments. Although the number of researches on the heart rate variability (HRV) of mice has been gradually increasing, a consensus on the frequency ranges of autonomic modulation has not been established. Therefore, the main purpose of this study was to find a HRV “prototype” for conscious mice in the state of being motionless and breathing regularly (called “genuinely resting”), and to determine the frequency ranges corresponding to the autonomic modulation. Further, whether these frequencies will change when the mice move freely was studied to evaluate the feasibility of the HRV spectrum as an index of the autonomic modulation of mice. The recording sites were specially arranged to simultaneously obtain the electrocardiography and electromyography data to be provided for the use of HRV analysis and motion monitoring, respectively. The states of being motionless and breathing regularly as judged from the electromyography results were selected as a genuine resting state of a conscious mouse. The frequencies related to autonomic modulation of HRV were determined by comparing the spectrum changes before and after blockades of the autonomic tone by different pharmaceutical agents in both the genuine resting state and freely moving states. Our results showed that the HRV of mice is not suitable for indexing sympathetic modulation; however, it is possible to use the spectral power in the frequency range between 0.1 and 1 Hz as an index of parasympathetic modulation.