Effects of thyroid status on the characteristics of alpha 1-, alpha 2-, beta, imipramine and GABA receptors in the rat brain

Associations of Thyroid Hormones Profile During Normal Pregnancy and Postpartum With Anxiety, Depression, and Obsessive/Compulsive Disorder Scores in Euthyroid Women

Objective

Thyroid dysfunction (overt and subclinical) has been consistently linked to pregnancy adversity and abnormal fetal growth and development. Mood disorders such as anxiety, depression, and obsessive-compulsive disorder (OCD) are frequently diagnosed during pregnancy and at postpartum, and emerging evidence suggests association with impaired offspring neurodevelopment and growth. This study aimed to examine potential associations between thyroid function and mood symptoms during pregnancy and postpartum.

Design

This is a prospective study measuring thyroid hormones and assessing mood symptoms by employing specific questionnaires in the same cohort of 93 healthy pregnant women at the 24th (2nd trimester) and 36th (3rd trimester) gestational weeks and at the 1st postpartum week.

Methods

Serum thyroid hormones, TSH, anti-TPO, and anti-Tg antibodies were measured at the 24th (2nd trimester) and 36th (3rd trimester) gestational weeks and at the 1st postpartum week. Specific validated questionnaires were employed at the same time-points to assess separately symptoms of anxiety [Generalized Anxiety Disorder Inventory (GADI), Penn State Worry Questionnaire (PSWQ), STAI-State Anxiety inventory (STAI-S), STAI-Trait Anxiety Inventory (STAI-T)], depression [Edinburgh Postnatal Depression Scale (EPDS), Stein’s Blues Scale (BLUES), Beck Depression Inventory (BDI)], and obsessive compulsive disorder (OCD) [Yale-Brown Obsessive Compulsive scale (Y-BOCS)].

Results

At the 2nd trimester, GADI score correlated negatively with FT3 (p < 0.010, r = −0.545) and positively with TSH (p < 0.050, r = 0.837) concentrations; GADI, PSWQ, EPDS and Y-BOCS scores correlated negatively with FT4 concentrations (p < 0.010, r = −0.768; p < 0.010, r = −0.384; p < 0.050, r = −0.364; p < 0.010, r = −0.544, respectively). At the 3rd trimester, BLUES score correlated positively with rT3 concentrations (p = 0.00, r = 0.89); GADI, EPDS, and Y-BOCS scores correlated negatively with FT4 concentrations (p = 0.001, r = − 0.468; p = 0.036, r = −0.39; p = 0.001, r = −0.625, respectively); GADI, STAI-S, and Y-BOCS scores correlated positively with TSH concentrations (p = 0.015, r = 0.435; p = 0.024, r = 0.409 p = 0.041, r = 0.389, respectively). At postpartum, PSWQ, STAI-T, EPDS, and BDI scores correlated positively with rT3 concentrations (p = 0.024, r = 0.478; p = 0.014, r = 0.527; p = 0.046, r = 0.44; p = 0.021, r = 0.556, respectively, Y-BOCS score correlated positively with TSH (p = 0.045, r = 0.43), and BLUES score correlated positively with anti-TPO antibody concentrations (p = 0.070, r = 0.586).

Conclusion

The reported findings demonstrate positive associations between low-normal thyroid function at the 2nd and 3rd trimesters of pregnancy and postpartum with anxiety, depression, and OCD scores.

Effects of various antidepressants on serum thyroid hormone levels in patients with major depressive disorder

A total of 62 patients with major depressive disorder were analyzed in the study. Patients were evaluated for 11 weeks in an open label design to investigate the differential effects of reboxetine, sertraline and venlafaxine on thyroid hormones. Serum thyrotrophin (TSH), thyroxine (T4) and free (f)T4 levels were measured before and after treatment. All groups showed significant improvement in HAM-D scores. TSH level significantly reduced and T4 level significantly increased in the reboxetine group, however TSH level significantly increased and T4 level significantly reduced in the sertraline group. Percent changes of TSH (p=0.007) and T4 (p=0.001) were significantly different between the reboxetine and sertraline groups. In the sertraline group, baseline TSH levels were correlated with response to treatment as determined by the change in HAM-D scores (p=0.03, r=0.648). There was a significant association between the percent changes in TSH values and the reduction in HAM-D scores in the reboxetine group (p=0.03, r=-0.434). In the whole study group, female patients had lower values of basal T4 compared with men (p=0.043), however percent changes of T4 did not differ between genders. In the treatment-responders significant increase in the reboxetine group and significant decrease in the sertraline group regarding the T4 values were found. We observed that various antidepressants had different effects on thyroid hormone levels and this could be attributed to the different mechanisms of actions of these antidepressants.

Effects of perinatal hypothyroidism on rat behavior and its relation with apoptosis of hippocampus neurons

Thyroid hormone is an important factor for proper development of the mammalian brain. Perinatal hypothyroidism leads to long-term behavior and neuromotor competence alterations in humans and animals. Our study aimed to investigate the effects of perinatal hypothyroidism on behavior changes of rat pups and its relation with the apoptosis of hippocampus neurons. Behavior tests were taken to evaluate the effects caused by perinatal hypothyroidism. TUNEL staining was used to analyze the apoptosis of neurons on CA3 region of hippocampus. The study suggested that perinatal hypothyroidism affects behavior development, as well as leading to the decrease in spatial learning and memory capability. This condition can be improved with hormone substitute treatment. Furthermore, the changes of learning and memory capability are closely related to the increasing number of apoptotic neurons in the hippocampus.

Thyroid hormone and γ-aminobutyric acid (GABA) interactions in neuroendocrine systems

Thyroid hormones (THs) have critical roles in brain development and normal brain function in vertebrates. Clinical evidence suggests that some human nervous disorders involving GABA(gamma-aminobutyric acid)-ergic systems are related to thyroid dysfunction (i.e. hyperthyroidism or hypothyroidism). There is experimental evidence from in vivo and in vitro studies on rats and mice indicating that THs have effects on multiple components of the GABA system. These include effects on enzyme activities responsible for synthesis and degradation of GABA, levels of glutamate and GABA, GABA release and reuptake, and GABA(A) receptor expression and function. In developing brain, hypothyroidism generally decreases enzyme activities and GABA levels whereas in adult brain, hypothyroidism generally increases enzyme activities and GABA levels. Hyperthyroidism does not always have the opposite effect. In vitro studies on adult brain have shown that THs enhance GABA release and inhibit GABA-reuptake by rapid, extranuclear actions, suggesting that presence of THs in the synapse could prolong the action of GABA after release. There are conflicting results on effects of long term changes in TH levels on GABA reuptake. Increasing and decreasing circulating TH levels experimentally in vivo alter density of GABA(A) receptor-binding sites for GABA and benzodiazepines in brain, but results vary from study to study, which may reflect important regional differences in the brain. There is substantial evidence that THs also have an extranuclear effect to inhibit GABA-stimulated Cl(-) currents by a non-competitive mechanism in vitro. The thyroid gland exhibits GABA transport mechanisms as well as enzyme activities for GABA synthesis and degradation, all of which are sensitive to thyroidal state. In rats and humans, GABA inhibits thyroid stimulating hormone (TSH) release from the pituitary, possibly by action directly on the pituitary or on hypothalamic thyrotropin-releasing hormone neurons. In mice, GABA inhibits TSH-stimulated TH release from the thyroid gland. Taken together, these studies provide strong support for the hypothesis that there is reciprocal regulation of the thyroid and GABA systems in vertebrates.

Short-Term Effects of Thyroid Hormones on Cytoskeletal Proteins Are Mediated by GABAergic Mechanisms in Slices of Cerebral Cortex from Young Rats

: Thyroid hormones play important roles in brain function. However, few information is available about the effect of 3,5,3'-triiodo-L-thyronine (T(3)) or thyroxine (T(4)) on the in vitro phosphorylation of intermediate filament (IF) proteins from cerebral cortex of rats. In this study we investigated the involvement of GABAergic mechanisms mediating the effects of T(3) and T(4) on the in vitro incorporation of (32)P into IF proteins from cerebral cortex of 10-day-old male rats. Tissue slices were incubated with or without T(3), T(4), gamma-aminobutiric acid (GABA), kinase inhibitors or specific GABA antagonists and (32)P-orthophosphate for 30 min. The IF-enriched cytoskeletal fraction was extracted in a high salt Triton-containing buffer and the in vitro (32)P incorporation into IF proteins was measured. We first observed that 1 microM T(3) and 0.1 microM T(4) significantly increased the in vitro incorporation of (32)P into the IF proteins studied through the PKA and PKCaMII activities. A similar effect on IF phosphorylation was achieved by incubating cortical slices with GABA. Furthermore, by using specific GABA antagonists, we verified that T(3) induced a stimulatory effect on IF phosphorylation through noncompetitive mechanisms involving GABA(A), beyond GABA(B) receptors. In contrast, T(4) effects were mediated mainly by GABA(B) mechanisms. In conclusion, our results demonstrate a rapid nongenomic action of T(3) and T(4) on the phosphorylating system associated to the IF proteins in slices of cerebral cortex of 10 day-old male rats and point to GABAergic mechanisms mediating such effects.

Elevated thyroid indices in children and adolescents with obsessive-compulsive disorder: effects of clomipramine treatment

OBJECTIVE

To examine the basal thyroid function in pediatric Obsessive Compulsive Disorder (OCD) versus controls, and to explore the relation between baseline thyroid measures and response to clomipramine treatment, and the effects of treatment on thyroid hormones.

METHODS

Sixteen children and adolescents with DSM-III-R OCE and 13 control children and adolescents without psychiatric illness were compared on basal measures of thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4). For the OCD subjects, samples were compared pre- and post- 4 weeks of treatment with clomipramine. Response of OCD symptoms was measured by the Children's Yale-Brown Obsessive Compulsive Scale (CY-BOCS).

RESULTS

OCD subjects demonstrated subtle but significant elevations of TSH, T3, and T4 pre-treatment compared to controls. Clomipramine treatment was associated with significant decreases in TSH and T3 concentrations. Pre-treatment TSH and T4 concentrations correlated with reductions in CY-BOCS following 8 weeks of clomipramine.

CONCLUSION

Elevated thyroid function at baseline may be a biomarker of OCD improvement, and may reflect aspects of the underlying pathophysiology of OCD.

Mild thyroid hormones deficiency modifies benzodiazepine and mu-opioid receptor binding in rats

The effects of a mild hypothyroidism condition on benzodiazepine (BDZ) and mu opioid receptor levels was investigated. Female Wistar rats were randomly divided into two groups: 1) hypothyroid rats (n=7), which received methimazole (60 mg/kg per day) in drinking water for four weeks, and 2) euthyroid rats (n=8), which drank only tap water. Animals were sacrificed and their brains were used for autoradiography experiments. When compared to the euthyroid group, the hypothyroid group presented reduced benzodiazepine receptor binding in medial amygdala (24%) and high mu-receptor levels in frontal (25%), sensorimotor (65%) and temporal (29%) cortices, basolateral amygdala (50%) and ventroposterior thalamic nucleus (49%). The present data suggest that alterations in BDZ and mu-receptor binding could be associated with the higher excitability observed in animals with triiodothyronine (T(3)) deficiency.

Effects of dysthyroidism in plus maze and social interaction tests

The aim of the present study was to determine the influence of thyroid hormones on the anxiety of male Wistar rats. Dysthyroidism was induced by adding 20 mg of methimazole (100 ml) to their drinking water or by adding 0.3 mg of L-thyroxine (100 ml) to their drinking water from the ninth day of gestation. After weaning, the drugs were administered to young rats until the end of the experiment. Anxious behavior was measured using the elevated plus maze and social interaction tests when the animals were 85 days old. Chronic methimazole administration produced a significant anxiolytic pattern in both tests. In the plus maze test, the methimazole-treated animals entered and remained more time in the open arms than the control animals. In the social interaction test, they spent more time in bodily contact, and did this more frequently than those in the control group did. Results from this experiment suggest that chronic thyroid deficiency produces an anxiolytic-like effect in both tests.

Effects of thyroxine and naloxone administration on metabolism and ventilation in hamsters

This study examined the interaction between hyperthyroidism and opioid receptor function on control of ventilation and metabolism in male Harlan hamsters 4 and 8 weeks after implanting thyroxine (T(4)) or placebo pellets. Metabolism, but not body temperature, increased in T(4)-treated hamsters relative to placebo-treated animals. After 4 weeks, body weights were greater in the T(4)-treated hamsters, but comparable to controls after 8 weeks. At that time, body length was greater in T(4)-treated hamsters than in controls. Thyroxine did not affect ventilation in air or in response to CO(2). Naloxone, an opioid receptor antagonist, decreased metabolism in T(4)-treated, but not in placebo-treated hamsters without affecting ventilation in air in either group. In the placebo group naloxone augmented the ventilatory response to hypercapnia by increasing frequency. These results negate our hypotheses that: (1) hyperthyroid hamsters exhibit greater ventilation in air and in response to hypercapnia than controls; and (2) that naloxone augments these effects.

Administration of L-thyroxine does not improve the response of the hypothalamo-pituitary-ovarian axis to clomiphene citrate in functional hypothalamic amenorrhea

OBJECTIVE

To investigate the hypothalamo-pituitary-ovarian axis in women with functional hypothalamic amenorrhea to determine whether the combination of L-thyroxine and clomiphene citrate produces a qualitative and quantitative increase in induced ovulatory cycles.

SETTING

Gynecological Endocrinology Research Center, University of Siena (Italy).

PATIENTS

16 young women with functional hypothalamic amenorrhea and 15 women with normal cycles in early follicular phase.

DESIGN

Administration of 50 microgram GnRH and 200 microgram TRH. The women with functional hypothalamic amenorrhea were divided into groups A (n=8) and B (n=8). Both groups were given 100 mg/day clomiphene for 5 days/month for 3 months. Women in group A were also given 75 mcg/day thyroid hormone (L-thyroxine) for 3 months.

MAIN OUTCOME MEASURES

Comparison of basal and stimulated levels of gonadotropins, TSH and Prl, in groups A and B. Qualitative and quantitative comparison of ovulatory cycles induced in the groups.

RESULTS

Administration of clomiphene and clomiphene plus L-thyroxine was evaluated in the second and third months of treatment and was followed by a total of 11 ovulatory cycles, six in group A and five in group B. No significant difference was found between groups. Mean progesterone concentrations measured 16 days after the last clomiphene tablet were 5.5+/-1.2 ng/ml in group A and 5.1+/-1.3 ngl/ml in group B.

CONCLUSIONS

Administration of L-thyroxine with clomiphene does not improve the response of the hypothalamo-pituitary-ovarian axis to clomiphene citrate or the number of ovulatory cycles and does not reduce luteal phase defects.

Low levels of transthyretin in the CSF of depressed patients

OBJECTIVE

Transthyretin plays an important role in the transport and distribution of thyroid hormone in the central nervous system (CNS). This study replicated and extended to patients with nonrefractory depressive illness a pilot study indicating that patients with refractory major depression have significantly lower levels of CSF transthyretin than do healthy comparison subjects.

METHOD

Lumbar punctures were performed in drug-free subjects with DSM-III-R major depression (N = 18), DSM-III-R bipolar disorder, depressed phase (N = 1), and healthy comparison subjects (N = 24). CSF concentrations of transthyretin, determined by a quantitative dot-immunobinding assay, of the depressed patients and comparison subjects were compared by analysis of covariance (ANCOVA). The relationship between CSF transthyretin levels and Hamilton Depression Rating Scale scores was determined in a subset of the depressed patients.

RESULTS

CSF concentrations of transthyretin were significantly lower in the depressed patients than in the comparison subjects by ANCOVA. Within the depressed group there was no significant overall correlation between CSF transthyretin levels and Hamilton depression scale scores, but there was a significant inverse correlation in male depressed patients (N = 8) between CSF transthyretin concentrations and Hamilton depression scores.

CONCLUSIONS

Lower CSF transthyretin concentrations in depressed patients may reflect either a stable trait in this population or a state change secondary to depression or other factors. Lower CSF transthyretin concentrations may result in altered CNS thyroid hormone homeostasis. Such alteration could account for certain mood and neurovegetative symptoms of depression and might contribute to failure of standard antidepressant treatment.

Regional expression of the type 3 iodothyronine deiodinase messenger ribonucleic acid in the rat central nervous system and its regulation by thyroid hormone

Type 3 iodothyronine deiodinase (D3) is a selenoenzyme that inactivates thyroid hormone. It is necessary for T3 homeostasis in the central nervous system. D3 activity has been identified in many regions of the brain and parallels thyroid status, but the level at which it is regulated and its specific cellular locations are not known. We evaluated the effect of thyroid status on the expression of the D3 gene within the central nervous system using in situ hybridization histochemistry. D3 messenger RNA (mRNA) was identified throughout, but with high focal expression in the hippocampal pyramidal neurons, granule cells of the dentate nucleus, and layers II-VI of the cerebral cortex. In every region, D3 mRNA abundance was correlated with thyroid status. Four different D3 transcripts were identified by Northern analyses, with evidence for region-specific processing, and D3 mRNA increased 4- to 50-fold from the euthyroid to the hyperthyroid state. D3 mRNA was not detectable in hypothyroid brain. In the central nervous system, the D3 gene is highly T3 responsive, and its focal localization within the hippocampus and cerebral cortex suggests an important role for T3 homeostasis in memory and cognitive functions.

Thyroid hormones and the treatment of depression: an examination of basic hormonal actions in the mature mammalian brain

Numerous clinical reports indicate that thyroid hormones can influence mood, and a change in thyroid status is an important correlate of depression. Moreover, thyroid hormones have been shown to be effective as adjuncts for traditional antidepressant medications in treatment-resistant patients. In spite of a large clinical literature, little is known about the mechanism by which thyroid hormones elevate mood. The lack of mechanistic insight reflects, in large part, a longstanding bias that the mature mammalian central nervous system is not an important target site for thyroid hormones. Biochemical, physiological, and behavioral evidence is reviewed that provides a clear picture of their importance for neuronal function. This paper offers the hypothesis that the thyroid hormones influence affective state via postreceptor mechanisms that facilitate signal transduction pathways in the adult mammalian brain. This influence is generalizable to widely recognized targets of antidepressant therapies such as noradrenergic and serotonergic neurotransmission.

Propranolol blocks the stimulatory effects of naloxone on ventilation and oxygen consumption in hamsters

The purposes of these studies were: 1) to determine the effects of various doses of propranolol, a nonspecific beta-adrenergic antagonist, on ventilation, oxygen consumption, and body temperature in hamsters, and 2) to test the hypothesis that in hamsters the stimulatory effects of naloxone, an opioid receptor antagonist, on ventilation and oxygen consumption occur, at least in part, through the release of catecholamines that act via beta-adrenergic receptors. Propranolol, a non-specific beta adrenergic receptor antagonist, at a 20 mg/kg depressed body temperature, oxygen consumption, tidal volume, and ventilation relative to saline. The lower dose of 10 mg/kg had only transitory effects on tidal volume at 60 min and ventilation at 30 min post-injection-Naloxone (1 mg/kg) relative to saline stimulated ventilation and oxygen consumption. These effects were blocked by propranolol pretreatment. The results of these experiments demonstrate that in the hamster, 1) body temperature, oxygen consumption, and ventilation appear to be modulated by beta-adrenergic receptors, and 2) the stimulatory effects of naloxone on oxygen consumption and ventilation may occur through the interaction of endogenous opioids and beta-adrenergic receptor systems.

Novel uses of thyroid hormones in patients with affective disorders

Hormones of the thyroid axis have been used to treat patients with any of several mental illnesses. However, in recent decades interest has focused almost exclusively on depression, though thyroid hormones, mainly thyroxine (T4), are used with lithium in rapid cycling bipolar disorder, a condition in which depression and mania rapidly alternate. In depression L-triiodothyronine (T3) has been used in preference to T4 because of its rapid onset and offset of action. In women starting treatment, T3 hastens the onset of therapeutic action of standard antidepressant drugs. It fails to do so in depressed men, who anyway respond faster than women to standard antidepressants. Standard drugs fail to produce satisfactory improvement in one-quarter to one-third of depressed patients. Then, in both men and women, T3 converts about two-thirds of drug failures to successes in rapid fashion. Lithium, which has antithyroid properties, produces a similar conversion rate. The majority of depressed patients are grossly euthyroid, but many show one or another subtle change in thyroid axis activity. However, the thyroid state of patients has not been matched systematically with their response to thyroid hormone augmentation. It seems likely that a tendency toward hypothyroidism can predispose to depression, but when depression occurs in a euthyroid patient, the thyroid axis is often invoked in the process of restitution.

Influences of hypothyroidism on lipid composition and inositol lipid-linked receptors responsiveness and protein kinase C (PKC) activity in the cerebral cortex of Lewis rats

The influence of hypothyroidism (HO) induced by treatment with propylthiouracil on lipid composition, receptor responsiveness of M1-muscarinic receptors (M1AChRs) and metabotropic glutamate receptors (mGluRs) as well as on protein kinase C (PKC) activity was investigated in the cerebral cortex of Lewis rats. HO did not influence the lipid composition. There was a significant 2-fold increase of efficacy and 6-fold decrease of potency of carbachol-induced inositol phosphate (IP) accumulation in HO, with respect to control rats. The efficacy of trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD)-induced IP accumulation was also higher in HO (by 50%), without differences in EC50 values. The activities of soluble calcium-dependent and calcium-independent PKC were higher in HO than in control rats (both roughly 30%); membrane-associated PKCs were not modified. The data indicate that HO induces an increased responsiveness of M1AChRs and mGluRs and a rise in the soluble PKC activity that could be available and ready for translocation.

Effect of acute and chronic treatment with triiodothyronine on serotonin levels and serotonergic receptor subtypes in the rat brain

Hyperthyroidism is often associated with behavioral disorders, and thyroid hormones modify receptor sensitivity as well as the synthesis and/or turnover rate of many neurotransmitters. We evaluated the influence in adult rats of triiodothyronine (T3), administered s.c. (100 micrograms/kg) acutely (once only) or chronically (once a day for 3 or 7 consecutive days), on brain serotonin concentration and on the density and affinity of two brain serotonin (5-HT) receptor subtypes mainly involved in behavioral effects. After both acute and chronic T3 treatment, serotonin levels increased in the cerebral cortex but not in the hippocampus. The density and affinity of 5-HT1A receptors (using [3H]-8-OH-DPAT as ligand) were not affected, while there was a significant decrease in the number of 5-HT2 receptors in the cerebral cortex (using [3H]ketanserin as ligand). This observation might indicate that thyroid hormones enhance 5-HT concentration in certain brain areas, thus causing a down-regulation of 5-HT2 receptors. The serotonergic system could be involved in the complex brain-neurotransmitter imbalance underlying hyperthyroidism-linked behavioral changes.

Perinatal alterations of thyroid hormones and behaviour in adult rats

Several studies have shown the relevance of the neuroendocrinological system in the development and function of the nervous system. In order to observe the influence of thyroid hormones during development on the behaviour of adult rats we induced dysthyroid states during the perinatal period. Results indicate that some behaviours are more susceptible to the action of thyroid hormones than others. We observed that the thyroid hormone deficiency causes an increase of activity in animals in spite of a large period of rehabilitation. Thyroxine-treated rats showed an anxiogenic behavioural pattern in the elevated plus-maze, while animals rehabilitated from perinatal deficit of thyroid hormones showed an anxiolitic pattern. These findings suggest that an excess of thyroid hormones has less effect on behaviour than a deficiency of these hormones.

Naloxone stimulates oxygen consumption but not ventilation in hypothyroid hamsters

Male golden Syrian hamsters made hypothyroid by 5 wk of propylthiouracil (PTU) treatment and control hamsters given tap water were studied. Both groups of nine animals demonstrated increased oxygen consumption after SC naloxone administration relative to saline treatment. Naloxone stimulated ventilation and ventilation in response to hypoxic (10% O2) and hyperoxic, hypercapnic (7% CO2 in oxygen) challenges in control hamsters. Relative to their responses to saline, PTU-treated hamsters exhibited no stimulation of ventilation nor of ventilation in response to the gas challenges after naloxone treatment. These results suggest that (a) the stimulation of oxygen consumption by naloxone does not directly increase ventilation; and (b) thyroid hormone status in the hamster affects opioid modulation of ventilation.

Effect of propylthiouracil-induced hypothyroidism on cerebral cortex of young and aged rats: lipid composition of synaptosomes, muscarinic receptor sites, and acetylcholinesterase activity

The effect of hypothyroidism on the lipid composition of synaptosomes, density and affinity of muscarinic receptor sites, and acetylcholinesterase activity in the cerebral cortex of young and aged rats was investigated. The animals were made hypothyroid by adding 0.05% propyl-2-thiouracil to their drinking water for four weeks. This pathological state induced an increase in the relative percentage of sphingomyelin in young rats. In aged rats hypothyroidism induced a decrease of sphingomyelin and glycerophosphocholine and an increase of cholesterol. The effect of hypothyroid state on cerebral cortex resulted in an increase of acethylcholinesterase activity both in young and aged rats and was also reflected in an increase of density of M1-AChRs but only in the former.

Effect of propylthiouracil-induced hypothyroidism on membranes of adult rat brain

The effect of hypothyroidism on the lipid composition of myelin and synaptosomes isolated from adult rat brain was investigated. The animals were made hypothyroid by adding 0.05% propyl-2-thiouracil to their drinking water for four weeks. This pathological state resulted in a significant increase in the relative percentage of choline glycerophospholipids in synaptosomes with a concomitant decrease in ethanolamine glycerophospholipids as compared to controls. In myelin, hypothyroidism significantly influenced only the relative percentage of sulfatides. The effect of the hypothyroid state on mature brain was also reflected in changes in the membrane fatty acid composition. Myelin and synaptosomes showed an increase in arachidonic (20:4) and eicosatrienoic (20:3) acids and an increase in the fatty acid unsaturation index. Furthermore, the 20:4/20:3 and 20:3/18:2 ratios were lower and higher, respectively, in treated animals. The data indicate that hypothyroidism affects the lipid composition of synaptosomes and myelin even though the effects were less pronounced in myelin. The lipid changes observed in hypothyroidism may be of physiological significance, as it is well known that lipid composition modulates various membrane-bound enzymes, transporters and receptors.

Organization of auditory callosal connections in hypothyroid adult rats

Callosal connections were studied with tracers (horseradish peroxidase (HRP) and wheat germ agglutinin-horseradish peroxidase (WGA-HRP)) in normal rats and rats deprived of thyroid hormones with methimazole (Sigma) since embryonic day 14 and thyroidectomized at postnatal day 6. In hypothyroid rats, the auditory areas, in particular the primary auditory area, showed cytoarchitectonic changes including blurred lamination and decrease in the size of layer V pyramidal neurons. In control rats, callosally-projecting neurons were found between layers II and VI with a peak in layer III and upper layer IV. In hypothyroid rats, labelled neurons were found between layers IV and VI with two peaks corresponding to layer IV and upper layer V, and in upper layer VI. Quantitative analysis of radial distribution of callosally-projecting neurons confirmed their shift to infragranular layers in hypothyroid rats. Three-dimensional reconstructions showed a more continuous tangential distribution of callosally-projecting neurons in hypothyroid rats which may be due to the maintenance of a juvenile 'exuberant' pattern of projections. These changes in cortical connectivity may be relevant for understanding epilepsy and mental retardation associated with early hypothyroidism in humans and to clarify basic mechanisms of cortical development.

Repeated administration of triiodothyronine enhances the susceptibility of rats to isoniazid- and picrotoxin-induced seizures

In an experimental condition of hyperthyroidism, obtained by repeated administration of triiodothyronine in adult rats (100 micrograms/kg/day, sc for 7 consecutive days), there is an increased susceptibility to the convulsant effect of isoniazid (300 mg/kg, ip) and picrotoxin (4 mg/kg, ip). On the other hand, the characteristics of brain [3H] flunitrazepam binding sites are not modified. These data afford further experimental evidence of the influence of thyroid hormones on brain function.