Hypothyroidism brain

The most significant of the abnormalities observed in a hypothyroid brain is a hypoplastic neuropile, i.e., a marked reduction in the number of connections between neurons [102], This has been observed both in the cerebrum and the cerebellum. For instance a permanent and dramatic reduction in the arborization of the dendritic tree of the Purkinje cell is observed in the hypothyroid cerebellum [103]. The length of the primary dendritic trunk is increased and a deficit in the number, density and branching of the dendritic spines is noticed. In contrast neonatal hyperthyroidism accelerates development of spines. Similar findings have been reported for the cerebrum, i.e., reduction in length and branching of pyramidal neurons, of the density of axonal terminals and of the number of spines [102],... 

Dementia due to other general medical condition (e.g, normal-pressure hydrocephalus, hypothyroidism, brain tumor, vitamin B12 deficiency, intracranial radiation)... 

In neonates with congenital hypothyroidism, brain metabolite changes may be detected by MRS. 

Rodriguez-Pena A, Ibarrola N, Iniguez MA, Munoz A, Bernal J 1993 Neonatal hypothyroidism affects the timely expression of myelin-associated glycoprotein in the rat brain. J Clin Invest 91 812-818... 

The adult brain is endowed with nuclear as well as cytosolic and membrane T3 receptors that have been visualized by autoradiography and studied biochemically [30-33]. Both neurons and neuropil are labeled by [ 1251]T3, and the labeling is selective across brain regions. Functionally, one of the most prominent features of neural action of thyroid hormone in adulthood is subsensitivity to norepinephrine as a result of a hypothyroid state [27], These changes may be reflections of loss of dendritic spines in at least some neurons of the adultbrain. Clinically, thyroid hormone deficiency increases the probability of depressive illness, whereas thyroid excess increases the probability of mania (Ch. 52) in susceptible individuals [27],... 

Triiodothyronine (Cytomel, T3). T3 is also an effective augmenting agent. It is important to use the T3 thyroid hormone instead of thyroxine (T4). T4 is the form most often used to treat hypothyroidism, but T3 crosses from the bloodstream to the brain more easily and thus is better for treating depression. T3 is usually tolerated well and is taken at 25-50 pg/day in split doses. When taking T3, laboratory tests to check thyroid function should be performed periodically. 

Of particular importance in the geriatric patient Case reports of organic brain syndrome, cognitive impairment, ataxia, cerebellar dysfunction, AV block, edema, tremor, renal impairment, nephrogenic diabetes insipidus, urinary frequency, hypothyroidism, leukocytosis, weight gain... 

Hypothyroid women frequently have anovulatory cycles and are therefore relatively infertile until restoration of the euthyroid state. This has led to the widespread use of thyroid hormone for infertility, although there is no evidence for its usefulness in infertile euthyroid patients. In a pregnant hypothyroid patient receiving thyroxine, it is extremely important that the daily dose of thyroxine be adequate because early development of the fetal brain depends on maternal thyroxine. In many hypothyroid patients, an increase in the thyroxine dose (about 30-50%) is required to normalize the serum TSH level during pregnancy. Because of the elevated maternal TBG levels and, therefore, elevated total T4 levels, adequate maternal thyroxine dosages warrant maintenance of TSH between 0.5 and 3.0 mll/L and the total T4 at or above the upper range of normal. 

Table III gives the results of an experiment in which the effect of serum manipulation on sulfolipid synthesis by dissociated brain cells was examined. The cells isolated from the embryonic mouse brain were grown on the medium containing calf serum (20%) for 3 days by which time most of the cells would have attached to the substratum. On the 4th day, the medium was replaced by fresh medium containing calf serum, calf serum + 13(2 x 10 8m), hypothyroid calf serum, or hypothyroid calf serum + 13(13 ng/ml). Cultures were grown for another week and then labeled with 400 pCi for 16 h. The lipids...

Hrdina PD, Ghosh PK, Rastogi RB, Singhal RL. Ontogenic pattern of dopamine, acetylcholine, and acetylcholinesterase in the brains of normal and hypothyroid rats. Can J Physiol Pharm 1975 53 709-715. 

In contrast to the type I deiodinase which shows a high preference for rT4 over T4 as the substrate (Table II), the type II enzyme is somewhat more effective in the deiodination of T4 than of rT3 (Table III). Under the conditions tested, the Km value of T4 for the type II enzyme is three orders of magnitude lower than the Km of T4 for the type I deiodinase. The Km of rT3 for the type II deiodinase is somewhat greater than that of T4 and differs less from the Km of rT3 for the type I enzyme. The Umax of the conversion of T4 to T3 by the type II enzyme depends on the tissue and the thyroid status of the animal (see below). In cerebral cortex of hypothyroid rats [82] it is roughly one-thousandth of the maximum T3 production by the hepatic type I deiodinase of euthyroid animals determined under similar conditions [32]. The VmiJKm ratio of this reaction is, therefore, similar for the type II deiodinase of hypothyroid rat brain and the type I deiodinase of euthyroid rat liver and much greater than that for the hepatic enzyme of hypothyroid rats [86], In view of the reaction kinetics of the type II deiodinase (see below), it is questionable if the Vm,JKm ratios estimated in vitro also apply to physiological conditions with unknown cofactor availability. 

Use with caution in patients with respiratory disease, Lewy Body dementia, narrow angle-closure glaucoma (including family history), alcohol withdrawal syndrome, brain damage, epilepsy, hypothyroidism, myaesthenia gravis, prostatic hypertrophy, thyrotoxicosis... 

Salvati S, Cambegei LY, Sorcinni M, Olivieri A, DiBase A. Effects of propylthiouracial induced hypothyroidism on membranes of adult rat brain. Lipids 1993 28 1075-1078. 

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