Biomedical subjects

Marshall G Shuler

Publications and source records attributed to Marshall G Shuler.

5 recordsLinked to original sources

PubMed2006

Learning induces long-term potentiation in the hippocampus.

Years of intensive investigation have yielded a sophisticated understanding of long-term potentiation (LTP) induced in hippocampal area CA1 by high-frequency stimulation (HFS). These efforts have been motivated by the belief that similar synaptic modifications occur during memory formation, but it has never been shown that learning actually induces LTP in CA1. We found that one-trial inhibitory avoidance learning in rats produced the same changes in hippocampal glutamate receptors as induction of LTP with HFS and caused a spatially restricted increase in the amplitude of evoked synaptic transmission in CA1 in vivo. Because the learning-induced synaptic potentiation occluded HFS-induced LTP, we conclude that inhibitory avoidance training induces LTP in CA1.

Animals↗

PubMed2006

Reward timing in the primary visual cortex.

We discovered that when adult rats experience an association between visual stimuli and subsequent rewards, the responses of a substantial fraction of neurons in the primary visual cortex evolve from those that relate solely to the physical attributes of the stimuli to those that accurately predict the timing of reward. In addition to revealing a remarkable type of response plasticity in adult V1, these data demonstrate that reward-timing activity-a "higher" brain function-can occur very early in sensory-processing paths. These findings challenge the traditional interpretation of activity in the primary visual cortex.

Action Potentials↗

PubMed2004

Layer-specific somatosensory cortical activation during active tactile discrimination.

Ensemble neuronal activity was recorded in each layer of the whisker area of the primary somatosensory cortex (SI) while rats performed a whisker-dependent tactile discrimination task. Comparison of this activity with SI activity evoked by similar passive whisker stimulation revealed fundamental differences in tactile signal processing during active and passive stimulation. Moreover, significant layer-specific functional differences in SI activity were observed during active discrimination. These differences could not be explained solely by variations in ascending thalamocortical input to SI. Instead, these results suggest that top-down influences during active discrimination may alter the overall functional nature of SI as well as layer-specific mechanisms of tactile processing.

Afferent Pathways↗

PubMed2004

Neuron/target plasticity in the peripheral gustatory system.

Taste bud volume on the anterior tongue in adult rats is matched by an appropriate number of innervating geniculate ganglion cells. The larger the taste bud, the more geniculate ganglion cells that innervate it. To determine if such a match is perturbed in the regenerated gustatory system under different dietary conditions, taste bud volumes and numbers of innervating neurons were quantified in adult rats after unilateral axotomy of the chorda tympani nerve and/or maintenance on a sodium-restricted diet. The relationship between taste bud size and innervation was eliminated in rats merely fed a sodium-restricted diet; individual taste bud volumes were smaller than predicted by the corresponding number of innervating neurons. Surprisingly, the relationship was disrupted in a similar way on the intact side of the tongue in unilaterally sectioned rats, with no diet-related differences. The mismatch in these groups was due to a decrease in average taste bud volumes and not to a change in numbers of innervating ganglion cells. In contrast, individual taste bud volumes were larger than predicted by the corresponding number of innervating neurons on the regenerated side of the tongue; again, with no diet-related differences. However, the primary variable responsible for disrupting the function on the regenerated side was an approximate 20% decrease in geniculate ganglion cells available to innervate taste buds. Therefore, the neuron/target match in the peripheral gustatory system is susceptible to surgical and/or dietary manipulations that act through multiple mechanisms. This system is ideally suited to model sensory plasticity in adults.

Animals↗

PubMed2002

Integration of bilateral whisker stimuli in rats: role of the whisker barrel cortices.

Recently, we demonstrated that neural responses within the whisker region of the primary somatosensory cortex (SIw) of rats are profoundly influenced by the spatiotemporal attributes of ipsilateral, as well as contralateral, whisker stimuli. As inactivation of one SIw eliminates in the intact SIw both ipsilaterally evoked responses and the influence of ipsilateral stimulation on contralaterally evoked activity, we proposed that interhemispheric interactions between the SIws may be important for integrating bilateral whisker information. To test whether rats can recognize the bilateral nature of a whisker stimulus, we developed a tactile discrimination task that required rats to conjointly determine distances to a left and a right discriminandum as equidistant or non-equidistant using only their facial whiskers. All rats trained in this task achieved performance levels indicative of an ability to integrate bilateral whisker information. Testing during unilateral, as well as bilateral, inactivation of the SIws indicated that rats rely on both SIws for detecting the bilateral nature of a whisker stimulus. Rats were unable to perform the task without both sets of whiskers, a fact that indicates that the whiskers (and not other modalities) were used to perform this task. The findings presented here indicate that rats can solve a task that requires the conjoint detection of left and right whisker-mediated distance information and implicate the SIws as central to this ability.

Animals↗