Biomedical subjects

Howard C Cromwell

Publications and source records attributed to Howard C Cromwell.

5 recordsLinked to original sources

PubMed2006

Inhibitory gating of single unit activity in amygdala: effects of ketamine, haloperidol, or nicotine.

BACKGROUND: Inhibitory gating is thought to be a basic process for filtering incoming stimuli to the brain. Little information is currently available concerning local neural networks of inhibitory gating or the intrinsic neurochemical substrates involved in the process. METHODS: The goal of the present study was to examine the pharmacological aspects of inhibitory gating from single units in the amygdala. We tested the effects of ketamine (80 mg/kg) and haloperidol (1 mg/kg) on inhibitory gating. Additionally, we examined the effect of nicotine (1.2 mg/kg) on single unit gating in this same brain structure. RESULTS: We found that in one subset of neurons, ketamine administration significantly reduced tone responsiveness with a subsequent loss of inhibitory gating, whereas the other subset persisted in both auditory responding and gating albeit at a weaker level. Haloperidol and nicotine had very similar effects, exemplified by a dramatic increase in the response to the initial "conditioning" tone with a subsequent improvement in inhibitory gating. CONCLUSIONS: Tone responsiveness and inhibitory gating persists in a subset of neurons after glutamate N-methyl-D-aspartate receptor blockade. Dopamine and nicotine modulate gating in these normal animals and have similar effects of enhancing responsiveness to auditory stimulation at the single unit and evoked potential level.

Acoustic Stimulation↗

PubMed2005

Auditory inhibitory gating in the amygdala: single-unit analysis in the behaving rat.

Inhibitory sensory gating has been proposed to be a fundamental physiological process that filters neural input. Its temporal properties could allow for a rapid influence on vigilance and attention processes. Inhibitory mechanisms are reflected by reductions in neural responsiveness to repeated and well-predicted stimuli; for auditory gating, this translates into an inhibition of the neural activation to subsequent tone stimuli embedded within sequential and identical tone presentations. Here we expand previous neurophysiological data on inhibitory gating by examining gating in the amygdala using single-unit recording in freely moving animals. Previous data have shown the amygdala to be important in mediating rapid auditory sensory processing involved in emotional conditioning. We measured inhibitory gating with two matching auditory tones presented in a repetitive fashion (10 ms tones, ISI = 500 ms and 10 s between pairs) for 1 h (360 pairs). The majority of the tone responsive units showed inhibitory gating (78/95 units) located in both the medial and lateral subnuclei of the amygdala. Different types of tone responses were gated, including both shorter- and longer-duration excitatory tone responses as well as inhibitory tone responses. Different degrees of gating were found ranging from 100% inhibition (complete gating category) to 25% inhibition (graded gating category). The degree of gating varied over short-term and long-term time intervals. These findings demonstrate the existence of inhibitory gating in the amygdala and provide a detailed description of the basic properties of this rapid neural inhibition that could play an important role in filtering stimulus input.

Acoustic Stimulation↗

PubMed2005

Relative reward processing in primate striatum.

Rewards are often not only valued according to their physical characteristics but also relative to other available rewards. The striatum (caudate nucleus, putamen, ventral striatum including nucleus accumbens) is involved in the organization of movement and the processing of reward information. We studied the activity of single striatal neurons in macaques that were presented with different combinations of two rewards. We found in nearly half of the investigated neurons that the processing for one reward shifted, relative to the other rewards that were available in a given trial block. The relative reward processing concerned all forms of striatal activity related to reward-predicting visual stimuli, arm movements and reception of rewards. The observed changes may provide a neural basis for the known shifts in valuation of rewarding outcomes relative to known references.

Animals↗

PubMed2003

Effects of expectations for different reward magnitudes on neuronal activity in primate striatum.

In behavioral science, it is well known that humans and nonhuman animals are highly sensitive to differences in reward magnitude when choosing an outcome from a set of alternatives. We know that a realm of behavioral reactions is altered when animals begin to expect different levels of reward outcome. Our present aim was to investigate how the expectation for different magnitudes of reward influences behavior-related neurophysiology in the anterior striatum. In a spatial delayed response task, different instruction pictures are presented to the monkey. Each image represents a different magnitude of juice. By reaching to the spatial location where an instruction picture was presented, animals could receive the particular liquid amount designated by the stimulus. Reliable preferences in reward choice trials and differences in anticipatory licks, performance errors, and reaction times indicated that animals differentially expected the various reward amounts predicted by the instruction cues. A total of 374 of 2,000 neurons in the anterior parts of the caudate nucleus, putamen, and ventral striatum showed five forms of task-related activation during the preparation or execution of movement and activations preceding or following the liquid drop delivery. Approximately one-half of these striatal neurons showed differing response levels dependent on the magnitude of liquid to be received. Results of a linear regression analysis showed that reward magnitude and single cell discharge rate were related in a subset of neurons by a monotonic positive or negative relationship. Overall, these data support the idea that the striatum utilizes expectancies that contain precise information concerning the predicted, forthcoming level of reward in directing general behavioral reactions.

Animals↗

PubMed2003

Effect of baclofen on alcohol and sucrose self-administration in rats.

BACKGROUND: Baclofen, a gamma-aminobutyric acid type B agonist, has been proposed as a pharmacotherapeutic agent in the treatment of addictive disorders such as alcoholism. Preclinical studies documenting the effect of baclofen on alcohol intake have provided conflicting results. The goal of this study was to determine the effect of baclofen pretreatment on ethanol- and sucrose-reinforced responding. METHODS: Animals were trained to self-administer a 10% ethanol in water solution on a fixed ratio 1 schedule of reinforcement by using the sucrose-fade method. With a within-subject design, the effect of three doses of baclofen (1.8, 3.2, and 5.6 mg/kg intraperitoneally) was examined on 10% ethanol- and 2% sucrose-reinforced responding. Dose-dependent effects on responding and on drinking-pattern microstructure were examined. RESULTS: Under a fixed ratio 1 schedule, baclofen reduced responding for alcohol and sucrose reinforcement in a similar, dose-dependent manner. A dose-dependent response attenuation was seen during the initial segment of an operant session when highly repetitive response patterns were generated. Further analysis of drinking ultrastructure revealed that baclofen altered the patterns of these repetitive responses by lengthening the self-initiated intertrial intervals. CONCLUSIONS: Systemic baclofen administration attenuates responding for alcohol and sucrose reinforcement in a dose-dependent manner. If the reinforcing efficacy and response requirement for sucrose and alcohol are matched, then baclofen has similar effects on responding and patterns of drinking microstructure. We conclude that the neural mechanisms that support both ethanol and sucrose self-administration behavior are sensitive to gamma-aminobutyric acid type B modulation.

Alcohol Drinking↗