Intrathyroidal carotid artery and nonrecurring right recurrent laryngeal nerve: A case report.

BACKGROUND: When performing thyroidectomy, knowledge of normal anatomy and variants is vital to avoid injuring nearby structures. Typically, the bilateral carotids course posterolateral to the thyroid gland. We describe a rare variant of an intrathyroidal carotid artery, not previously described in the literature. METHODS: A 23-year-old woman with a strong family history of thyroid cancer presented with a left thyroid nodule, and a fine-needle aspiration biopsy revealing papillary thyroid carcinoma. She underwent total thyroidectomy. RESULTS: Intraoperatively, the carotid was found coursing centrally through the right lobe parenchyma, associated with an ipsilateral nonrecurrent recurrent laryngeal nerve (NRLN) entering the cricothyroid joint superolaterally. CONCLUSION: This is, to our knowledge, the first report of such an anatomic variant in the medical literature. Aberrant carotid artery anatomy may potentially cause life-threatening surgical complications and should be considered preoperatively. Furthermore, recognition of concurrent recurrent laryngeal nerve (RLN) anomalies with vascular variations allows identification of nonrecurrent nerves.

Characterizing olfactory binary mixture interactions in Fischer 344 rats using behavioral reaction times.

Response times provide essential subthreshold perceptual data that extend beyond accuracy alone. Behavioral reaction times (RTs) were used to characterize rats' ability to detect individual odorants in a series of complimentary binary odorant mixture ratios. We employed an automated, liquid-dilution olfactometer to train Fischer 344 rats (N = 8) on an odor identification task using nonreinforced probe trials. Binary mixture ratios composed of aliphatic odorants (citral and octanol) were arranged such that relative contributions of the 2 components varied systematically by a factor of 1% (v/v). Odorant concentrations for the target (S+), control (S-), and mixture (S+:S-) odorants were presented relative to threshold for each rat. Rats were initially trained to respond by licking at a spout to obtain liquid reward for either citral or octanol as the reinforced target (S+) odorant. After achieving 100% accuracy, rats were transferred to variable ratio (VR 2) reinforcement for correct responding. Nonreinforced probe trials (2 per block of 22 trials) were tested for each mixture ratio and recorded as either S+ (rats lick-responded in the presence of the mixture) or S- (rats refrained from licking), thereby indicating detection of the trained, S+ odorant. To determine the perceived salience for each ratio, RTs (latency from odorant onset to lick response) were recorded for each trial. Consistent with previous studies, RTs for both odorants were shortest (~150-200ms) when the probe trials consisted of a single, monomolecular component. Binary mixtures that contained as little as 1% of the S-, nontarget odorant, however, were sufficiently different perceptually to increase behavioral RTs (i.e., rats hesitated longer before responding); RTs changed systematically as a function of the binary ratio. Interestingly, the rate of RT change was dependent on which odorant served as the S+, suggesting an asymmetric interaction between the 2 odorants. The data demonstrate the value of behavioral RT as a sensitive measure of suprathreshold perceptual responding.

A technique for characterizing the time course of odor adaptation in mice.

Although numerous studies have analyzed the temporal characteristics underlying olfactory adaptation at the level of the olfactory receptor neuron, to date, there have been no comparable behavioral measures in an animal model. In this study, odor adaptation was estimated in a group of mice employing a psychophysical technique recently developed for use in humans. The premise of this technique is that extended presentation of an odorant will produce odor adaptation, decreasing the sensitivity of the receptors and increasing thresholds for a brief, simultaneous target odorant presented at different time points on the adaptation contour; adaptation is estimated as the increase in threshold for a target odorant presented simultaneously with an adapting odorant, across varying adapting-to-target odorant onset delays. Previous research from our laboratory suggests that this method provides a reliable estimate of the onset time course of rapid adaptation in human subjects. Consistent with physiological and behavioral data from human subjects, the present findings demonstrate that measurable olfactory adaptive effects can be observed for odorant exposures as brief as 50-100ms, with asymptotic levels evident 400-600ms following adapting odorant onset. When compared with the adaptation contour in humans using the same odorant and stimulus paradigm, some differences in the onset characteristics are evident and may be related to sniffing behavior and to relative differences in thresholds. These data show that this psychophysical paradigm can be adapted for use in animal models, where experimental and genetic manipulations can be used to characterize the different mechanisms underlying odor adaptation.