Thyroparathyroidectomy produces a progressive escape deficit in rats

Unveiling the nongenomic actions of thyroid hormones in adult mammalian brain: The legacy of Mary B. Dratman

A comprehensive review was conducted to compile the contributions of Mary B. Dratman and studies by other researchers in the field of nongenomic actions of thyroid hormones in adult mammalian brain. Dratman and her collaborators authored roughly half of the papers in this area. It has been almost fifty years since Dratman introduced the novel concept of thyroid hormones as neurotransmitters for the first time. The characterization of unique brain-region specific accumulation of thyroid hormones within the nerve terminals in adult mammals was a remarkable contribution by Dratman. It suggested a neurotransmitter- or neuromodulator-like role of thyroid hormone and/or its derivative, 3-iodothyronamine within adrenergic systems in adult mammalian brain. Several studies by other researchers using synaptosomes as a model system, have contributed to the concept of direct nongenomic actions of thyroid hormones at synaptic regions by establishing that thyroid hormones or their derivatives can bind to synaptosomal membranes, alter membrane functions including enzymatic activities and ion transport, elicit Ca2+/NO-dependent signaling pathways and induce substrate-protein phosphorylation. Such findings can help to explain the physiological and pathophysiological roles of thyroid hormone in psychobehavioral control in adult mammalian brain. However, the exact mode of nongenomic actions of thyroid hormones at nerve terminals in adult mammalian brain awaits further study.

Effects of thyroid hormone deficiency on behavior in rat strains with different predisposition to catalepsy

The effects of thyroidectomy on anxiety-related behavior in the elevated plus-maze test, locomotor activity, and defecation in the open-field test and duration of cataleptic freezing were studied in rats of two strains differing in predisposition to catalepsy: cataleptic strain GC and its ancestor strain Wistar. Total thyroxine level was significantly decreased in control GC rats compared to that in control Wistar rats. Control Wistar and GC rats did not differ either in the percentages of open-arm entries or the time spent therein in the elevated plus-maze test or in defecation score in the open-field test. At the same time, control Wistar rats showed more locomotor activity compared to control GC rats in the open-field test. Thyroid hormone deficiency did not affect the percentages of open-arm entries and the time spent therein in the elevated plus-maze test as well as defecation score in both strains. Thyroidectomy did not alter significantly locomotor activity in Wistar rats, but produced a nearly twofold increase in locomotor activity in GC rats. The most important finding is that thyroidectomy significantly increased the expression of catalepsy in Wistar rats, which points to a role of thyroid hormones in the regulation of predisposition to cataleptic reaction.

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.