Development of olfactory and thermal responsiveness in hypothyroid and hyperthyroid rat pups

Modified shoe for adjusting hard stuffy and smelly sole: An uncommon accompaniment of hypothyroidism

Disorders of smell and taste are both neglected as well as underreported problems of hypothyroidism. A 35-year-old male presented with intolerance to cold, dryness of skin, and swelling of both feet and some foul smelling odor from his feet. When we examined his feet we found that instead of wearing his shoes properly he had just slipped his feet inside the shoe so that the odor from his feet is not smelled by us. Although this symptom was largely ignored by many doctors, the literature mentions that patients of hypothyroidism may perceive dysosmia (distortion of smell) and hyposmia (elevated threshold for detection of smell).

The effects of thyroid hormone level and action in developing brain: are these targets for the actions of polychlorinated biphenyls and dioxins?

Alterations in thyroid hormone level or responsivity to thyroid hormone have significant neurologic sequelae throughout the life cycle. During fetal and early neonatal periods, disorders of thyroid hormone may lead to the development of motor and cognitive disorders. During childhood and adult life, thyroid hormone is required for neuronal maintenance as well as normal metabolic function. Those with an underlying disorder of thyroid hormone homeostasis or mitochondrial function may be at greater risk for developing cognitive, motor, or metabolic dysfunction upon exposure to substances which alter thyroid hormone economy. Polychlorinated biphenyls (PCBs) and dioxins have been argued to interfere with thyroid hormone action and thus may affect the developing and mature brain. Animal models provide useful tools for studying the effects of thyroid hormone disorders and the effects of environmental endocrine disruptors. The congenitally hypothyroid, hyt/hyt, mouse exhibits abnormalities in both the cognitive and motor systems. In this mouse and other animal models of thyroid hormone disorders, delayed somatic and reflexive development are noted, as are permanent deficits in hearing and locomotor and adaptive motor behavior. This animal's behavioral abnormalities are predicated on anatomic abnormalities in the nervous system. In turn, these abnormalities are correlated with differences in neuronal structural proteins. In normal mice, the expression of mRNAs coding for these proteins occurs temporally with the onset of autonomous thyroid hormone production. The hyt/hyt mouse has a mutation in the thyroid stimulating hormone receptor (TSHr) gene which renders it incapable of transducing the TSH signal in the thyrocyte to produce thyroid hormone. Some behavioral and possibly some biochemical abnormalities in mice exposed to PCBs are similar to those seen in the hyt/hyt mouse. In addition to direct effects on brain development and neuronal maintenance, thyroid hormone is necessary for maintaining metabolic functioning through its influence on mitochondria. Because the brain is particularly sensitive to inadequate energy generation, disorders of thyroid hormone economy also indirectly impair brain functioning. Alterations in thyroid hormone level result in differing expression of mitochondrial genes. Mutations in these mitochondrial genes lead to well-recognized syndromes of encephalomyopathy, myopathy, and multisystem disorder. Hence, PCBs and dioxins, by possibly altering the thyroid hormone milieu, may alter the functioning of mitochondria in the generation of adenosine triphosphate (ATP). The use of animal models of thyroid hormone deficiency for behavioral, anatomic, histologic, and molecular comparison will help elucidate the mechanisms of action of these putative endocrine-disrupting compounds. The study of thyroid hormone disorders provides a template for relating thyroid hormone mediated effects on the brain to these compounds.

Drug-induced taste and smell disorders. Incidence, mechanisms and management related primarily to treatment of sensory receptor dysfunction

Drugs in every major pharmacological category can impair both taste and smell function and do so more commonly than presently appreciated. Impairment usually affects sensory function at a molecular level, causing 2 major behavioural changes--loss of acuity (i.e. hypogeusia and hyposmia) and/or distortion of function (i.e. dysgeusia and dysosmia). These changes can impair appetite, food intake, cause significant lifestyle changes and may require discontinuation of drug administration. Loss of acuity occurs primarily by drug inactivation of receptor function through inhibition of tastant/odorant receptor: (i) binding; (ii) Gs protein function; (iii) inositol trisphosphate function; (iv) channel (Ca++,Na++) activity; (v) other receptor inhibiting effects; or (vi) some combination of these effects. Distortions occur primarily by a drug inducing abnormal persistence of receptor activity (i.e. normal receptor inactivation does not occur) or through failure to activate: (i) various receptor kinases; (ii) Gi protein function; (iii) cytochrome P450 enzymes; or other effects which usually (iv) turn off receptor function; (v) inactivate tastant/odorant receptor binding; or (vi) some combination of these effects. Termination of drug therapy is commonly associated with termination of taste/smell dysfunction, but occasionally effects persist and require specific therapy to alleviate symptoms. Treatment primarily requires restoration of normal sensory receptor growth, development and/or function. Treatment which restores sensory acuity requires correction of steps initiating receptor and other pathology and includes zinc, theophylline, magnesium and fluoride. Treatment which inhibits sensory distortions requires reactivation of biochemical inhibition at the receptor or inactivation of inappropriate stimulus receptor binding and/or correction of other steps initiating pathology including dopaminergic antagonists, gamma-aminobutyric acid (GABA)-ergic agonists, calcium channel blockers and some orally active local anaesthetic, antiarrhythmic drugs.

Development of rotorod performance in normal and congenitally hypothyroid mutant mice

Balancing behavior on a rotating cylinder was measured in genetically hypothyroid (hyt/hyt) mutant mice and their phenotypically normal littermates (hyt/+) at 10 different ages between Day 12 and Day 55. Normal mice showed competent balancing behavior in this task by 23 days of age, but mutant hypothyroid mice were incapable of balancing throughout the period of testing. Similar results were found with animals initially tested as adults, indicating that the developmental effects are probably not attributable to different rates of learning. These results are discussed in terms of documented central nervous system abnormalities in animals deprived of thyroid hormone early in life.

The development of aversive responses to quinine in hyperthyroid rats

Normal and hyperthyroid rat pups received intraoral infusions of 0.25% quinine hydrochloride at 8, 10, 12, 14, or 16 days of age. Chin scraping and paw treading, aversive behaviors that adult rats show to quinine, emerged at 12 to 14 days in normal animals and were accelerated in hyperthyroid animals. Once these behaviors emerged, the hyperthyroid pups showed levels of both paw treading and chin scraping that were typical of controls several days older. Hyperthyroid and control pups did not differ in their intake of quinine at ages at which there were marked differences in chin scraping and paw treading. Other types of responses that pups show to aversive stimuli, such as paw treading. Other types of responses were not affected by the thyroid treatment. These findings suggest that the appearance of chin scraping and paw treading at 12-14 days of age in normal animals results from maturation of motor systems underlying these behaviors, and that this maturation can be accelerated by treatment with thyroid hormones.

Olfactory granule cell development in normal and hyperthyroid rats

Dendritic development was examined in olfactory bulbs of both normal 7-, 14-, 21- and 60-day-old rats and littermates treated on postnatal days 1-4 with 1 microgram/g body weight of L-thyroxine sodium. Tissue was processed via the Golgi-Cox technique and subjected to quantitative analyses of mitral and internal layer granule cell development. These populations of granule cells were selected because their pattern of late proliferation suggested potentially greater susceptibility to postnatal hormonal alterations. Although neonatal hyperthyroidism induces widespread acceleration of maturation, including precocious chemosensitivity, granule cell development was unaffected relative to littermate controls. Both normal and hyperthyroid groups exhibited an inverted U-shaped pattern of cellular development, with rapid dendritic dendritic growth and expansion occurring during the earliest ages tested, but with loss of processes and dendritic field size occurring after day 21.

Development of home orientation in hypothyroid and hyperthyroid rat pups

In order to assess the effects of perinatal hypothyroidism or hyperthyroidism on the development of an integrated behavioral response, we tested hypothyroid, hyperthyroid, and control pups, as well as pups receiving thyroxine replacement therapy, for the development of the home orientation response. Hypothyroidism was induced in the pups by feeding the pregnant or lactating female a diet of .2% propylthiouracil from Day 15 of gestation to Day 22 postpartum. Pups receiving replacement therapy and pups made hyperthyroid were injected daily with thyroxine, starting at birth. The ability of the pups to initiate and maintain locomotion toward the nest was assessed between Days 4 and 22. Hyperthyroid, control, and replacement therapy pups behaved very similarly on the task, showing a peak in the percentage of pups homing between Days 12 and 16. Hypothyroid pups showed a delay in the peak percentage until Day 20, although the percentage of pups was similar to that found in other treatments. An integrated behavioral response can be delayed by hypothyroidism and still emerge apparently intact at a later age.

Thermotaxis in neonatal rat pups

Deprived and nondeprived 3- and 6-day-old rat pups were tested on a thermal gradient for thermotaxis. Deprived 3-day olds demonstrated a marked thermotaxic responsiveness that was not observed in nondeprived 3-day olds or in deprived and nondeprived 6-day olds. Deprived 3-day olds did not show a strong thermal orientation immediately, but the distance moved by pups increased with repeated trials on the gradient. These findings demonstrate that neonatal rats are capable of thermotaxis, but that factors of age, deprivation and repeated handling determine pups' responsiveness to thermal gradients.