Dynamic and multimodal responses of gustatory cortical neurons in awake rats.

To investigate the dynamic aspects of gustatory activity, we recorded the responses of small ensembles of cortical neurons to tastants administered to awake rats. Multiple trials of each tastant were delivered during recordings made in oral somatosensory (SI) and gustatory cortex (GC). When integrated tastant responses (firing rates averaged across 2.5 sec) were compared with water responses, 14.4% (13/90) of the GC neurons responded in a taste-specific manner. When time was considered as a source of information, however, the incidence of taste-specific firing increased: as many as 41% (37/90) of the recorded GC neurons exhibited taste-specific patterns of response. For 17% of the neurons identified as responding with taste-specific patterns, the stimulus that caused the most significant response was a function of the time since stimulus delivery. That is, a single neuron might respond most strongly to one tastant in the first 500 msec of a response and then respond most strongly to another tastant later in the response. Further analysis of the time courses of GC and SI cortical neural responses revealed that modulations of GC firing rate arose from three separable processes: early somatosensory input (less than approximately 0.2 sec post-stimulus), later chemosensory input ( approximately 0.2-1 sec), and delayed somatosensory input related to orofacial responses (more than approximately 1.0 sec). These data demonstrate that sensory information is available in the time course of GC responses and suggest the viability of views of gustatory processing that treat the temporal structure of cortical responses as an integral part of the neural code.

Rabbit classical eyeblink conditioning is altered by brief cerebellar cortical stimulation.

A pair of studies examined how cortical intracerebellar stimulation (ICS) affects eyeblink conditioning in the rabbit. Rabbits were implanted with chronic bipolar stimulating electrodes in the cell body layers of cerebellar lobule H-VI. Brief (40 ms) trains of intracranial stimulation (100 Hz, 250 microA) were delivered during training trials [forward pairings of a tone-conditioned stimulus (CS) with an air puff unconditioned stimulus (US)]. In Experiment 1, the onset of ICS varied randomly within sessions. US-onset-coincident ICS proved detrimental to the maintenance of conditioning [measured as the percentage of trials on which conditioned responses (CRs) were made] compared to ICS that ended 60 ms before US onset. Based on these findings, a second experiment compared a group trained with ICS consistently delivered at US onset to groups trained with ICS consistently delivered either at CS onset or between the two stimuli, as well as to unstimulated control subjects. Animals receiving CS- or US-coincident ICS learned slowest, whereas animals receiving middle stimulation learned more quickly than all other groups. In both Experiments 1 and 2, highly trained animals produced blinks in direct response to the stimulation. These data are discussed in terms of a new hypothesis concerning interactions between cerebellar cortex and the deep cerebellar nuclei during eyeblink conditioning--a rebound from inhibition hypothesis.

Techniques for long-term multisite neuronal ensemble recordings in behaving animals.

Advances in our understanding of neural systems will go hand in hand with improvements in the experimental techniques used to study these systems. This article describes a series of methodological developments aimed at enhancing the power of the methods needed to record simultaneously from populations of neurons over broad regions of the brain in awake, behaving animals. First, our laboratory has made many advances in electrode design, including movable bundle and array electrodes and smaller electrode assemblies. Second, to perform longer and more complex multielectrode implantation surgeries in primates, we have modified our surgical procedures by employing comprehensive physiological monitoring akin to human neuroanesthesia. We have also developed surgical implantation techniques aimed at minimizing brain tissue damage and facilitating penetration of the cortical surface. Third, we have integrated new technologies into our neural ensemble, stimulus and behavioral recording experiments to provide more detailed measurements of experimental variables. Finally, new data analytical techniques are being used in the laboratory to analyze increasingly large quantities of data.

Nutrient tasting and signaling mechanisms in the gut. IV. There is more to taste than meets the tongue.

The tongue is the principal organ that provides sensory information about the quality and quantity of chemicals in food. Other information about the temperature and texture of food is also transduced on the tongue, via extragemmal receptors that form branches of the trigeminal, glossopharyngeal, and vagal nerves. These systems, together with information from the gastrointestinal (GI) system, interact to determine whether or not food is palatable. In this themes article, emphasis is placed on the integrative aspects of gustatory processing by showing the convergence of gustatory information with somatosensory, nociceptive, and visceral information (from the GI system) on the tongue and in the brain. Our thesis is that gustation should be thought of as an integral part of a distributed, interacting multimodal system in which information from other systems, including the GI system, can modulate the taste of food.

Simultaneous reorganization in thalamocortical ensembles evolves over several hours after perioral capsaicin injections.

Reorganization of the somatosensory system was quantified by simultaneously recording from single-unit neural ensembles in the whisker regions of the ventral posterior medial (VPM) nucleus of the thalamus and the primary somatosensory (SI) cortex in anesthetized rats before, during, and after injecting capsaicin under the skin of the lip. Capsaicin, a compound that excites and then inactivates a subset of peripheral C and Adelta fibers, triggered increases in spontaneous firing of thalamocortical neurons (10-15 min after injection), as well as rapid reorganization of the whisker representations in both the VPM and SI. During the first hour after capsaicin injection, 57% of the 139 recorded neurons either gained or lost at least one whisker response in their receptive fields (RFs). Capsaicin-related changes continued to emerge for >/=6 h after the injection: Fifty percent of the single-neuron RFs changed between 1-2 and 5-6 h after capsaicin injection. Most (79%) of these late changes represented neural responses that had remained unchanged in the first postcapsaicin mapping; just under 20% of these late changes appeared in neurons that had previously shown no plasticity of response. The majority of the changes (55% immediately after injection, 66% 6 h later) involved "unmasking" of new tactile responses. RF change rates were comparable in SI and VPM (57-49%). Population analysis indicated that the reorganization was associated with a lessening of the "spatial coupling" between cortical neurons-a significant reduction in firing covariance that could be related to distances between neurons. This general loss of spatial coupling, in conjunction with increases in spontaneous firing, may create a situation that is favorable for the induction of synaptic plasticity. Our results indicate that the selective inactivation of a peripheral nociceptor subpopulation can induce rapid and long-evolving (>/=6 h) shifts in the balance of inhibition and excitation in the somatosensory system. The time course of these processes suggest that thalamic and cortical plasticity is not a linear reflection of spinal and brainstem changes that occur following the application of capsaicin.

The development of a multimedia teaching program for fiberoptic intubation.

Current training methods in fiberoptic intubation entail a trial and error process in which trainees acquire skills by practicing this technique in mannequins or patients. These training methods are not efficient and may expose patients to unnecessary instrumentation. An interactive software program is described which uses Director, a commercially available multimedia authoring tool, to (1) familiarize trainees with video images of the upper airway, (2) permit operator controlled progress through a normal fiberoptic intubation, (3) simultaneously display (side by side) two-dimensional or three-dimensional computer tomographic images with a fiberscope in place and the corresponding endoscopic video images, and (4) demonstrate some of the obstacles which occur in clinical practice (e.g. "white-out" and saliva). The intent of this package is to simulate fiberoptic intubation techniques as well as help one create a mental image of the path a fiberscope takes within the lumen of the upper airway. The potential for improving operator immersion (virtual reality) by using a more sophisticated input device is discussed.

Single-unit evidence for eye-blink conditioning in cerebellar cortex is altered, but not eliminated, by interpositus nucleus lesions.

Many theories of motor learning explain learning-related changes in motor behavior in terms of plasticity in the cerebellar cortex. Empirical evidence, however, does not always appear to be consistent with such formulations. It is the anterior cerebellar interpositus nucleus (aINP) that seems to be essential for acquisition and retention of conditioned eye-blink responses under most circumstances and it has been therefore suggested that the aINP is the critical site of learning-related plasticity during eye-blink conditioning. Supporting this conclusion are studies demonstrating that multiple-unit conditioning-related neural activity patterns observed in many brain regions disappear after aINP lesion. The possibility that the cerebellar cortex may be involved in forming these patterns has not been assessed adequately, however. In the current study, trained rabbits received kainic acid lesions of the INP. After recovery, the animals underwent additional sessions of conditioning during which single-unit activity was recorded from the cerebellar cortex. Our results suggest that the aINP is not the sole site of plasticity during eye-blink conditioning, as a subset of the neurons recorded from lesioned animals demonstrated conditioning-related firing patterns. The lesions did change the character of these firing patterns from those observed in saline controls, however, in ways that can be generally described as a loss of organization. The normal tendency for the population of cortical cells to change firing rate together, for instance, was significantly less noticeable in lesioned animals. These results suggest that the aINP may be involved in the production of important features of conditioned responding, such as system timing function, therefore suggesting the need for more models that incorporate aINP and brain stem feedback as integral to the production of organized neural and behavioral responses.

Cytochemical localization of ATPase activity in oat roots localizes a plasma membrane-associated soluble phosphatase, not the proton pump.

Cytochemical techniques employing lead-precipitation of enzymically released inorganic phosphate have been widely used in attempts to localize the plasma membrane proton pump (H(+)-ATPase) in electron micrographs. Using Avena sativa root tissue we have performed a side-by-side comparison of ATPase activity observed in electron micrographs with that observed in in vitro assays using ATPases found in the soluble and plasma membrane fractions of homogenates. Cytochemical analysis of oat roots, which had been fixed in glutaraldehyde in order to preserve subcellular structures, identifies an ATPase located at or near the plasma membrane. However, the substrate specificity and inhibitor sensitivity of the in situ localized ATPase appear identical to those of an in vitro ATPase activity found in the soluble fraction, and are completely unlike those of the plasma membrane proton pump. Further studies demonstrated that the plasma membrane H(+)-ATPase is particularly sensitive to inactivation by the fixatives glutaraldehyde and formaldehyde and by lead. In contrast, the predominant soluble ATPase activity in oat root homogenates is less sensitive to fixation and is completely insensitive to lead. Based on these results, we propose a set of criteria for evaluating whether a cytochemically localized ATPase activity is, in fact, due to the plasma membrane proton pump.

Inhibition and Labeling of the Plant Plasma Membrane H-ATPase with N-Ethylmaleimide.

H(+)-ATPase activity in plasma membranes isolated from Avena sativa root cells is inhibited by N-ethylmaleimide, a covalent modifier of protein sulfhydryl groups. The rate of inhibition is reduced by ADP, MgADP, and MgATP, but even at 40 millimolar ADP the enzyme is only partially protected against inactivation. When plasma membranes are treated wth N-[2-(3)H]ethylmaleimide and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, prominent radioactive bands appear at M(r)=100,000 and several other positions. However, only radioactivity in the M(r)=100,000 protein is reduced by the presence of MgADP. These results provide independent evidence that the M(r)=100,000 polypeptide which is observed in purified preparations of the enzyme is the catalytic subunit of the H(+)-ATPase. When tryptic peptides are produced from N-[2-(3)H]ethylmaleimide labeled M(r)=100,000 protein and separated by reverse phase high performance liquid chromatography, two radioactive peaks are observed for which N-[2-(3)H]ethylmaleimide incorporation is reduced in the presence of MgADP.

Rifampin, oral contraceptives, and pregnancy.

Rifampin is a drug used in the treatment of tuberculosis. In the literature, there are reports of seven patients who became pregnant while taking a combination of rifampin and oral contraceptives. We report an eighth case involving a woman who became pregnant twice on this drug combination.