Available online at www.sciencedirect.com Behavioural Brain Research 188 (2008) 348–354 Research report Effects of adult dysthyroidism on the morphology of hippocampal neurons Josefina Sala-Roca c,∗ , Eva Estebanez-Perpina d , Ferran Balada a , Adriana Garau b , Maria Assumpci ´ o Mart´ ı-Carbonell a a Department of Psychobiology, Universitat Aut` onoma de Barcelona, Spain b Department of Basic Psychology, Universitat Aut` onoma de Barcelona, Spain c Department of Pedagogy, Universitat Aut` onoma de Barcelona, Spain d Department of Biochemistry and Molecular Biology, Institut of Biomedicina, Universitat de Barcelona, Spain Received 14 June 2007; received in revised form 6 November 2007; accepted 24 November 2007 Available online 3 December 2007 Abstract This study investigates the effect of thyroid hormones on the morphology of hippocampal neurons in adult rats. Hypo- and hyperthyroidism were induced by adding 0.02% methimazole and 1% l-thyroxine, in drinking water from 40 days of age, respectively. When the rats were 89 days old their brains were removed and stained by a modified Golgi method and blood samples were collected in order to measure T4 serum levels. Neurons were selected and drawn using a camera lucida. Our results show that methimazole administration reduces the dendritic branching of the apical shafts of CA3 and CA1 pyramidal neurons mainly by increasing the distance to the first branch point in both types of neurons, and reducing branch points in the radius of 50 m from the soma in CA1 neurons. Nevertheless, it was observed an increase of apical spine density in CA3 neurons from this group. Thyroxine reduces apical and basal tree of CA3 pyramidal neurons increasing the distance to the first branch point, reducing branch points in the radius of 50 m from the soma and increases their apical and basal spine density. In CA1 field, thyroxine reduces the number of basal branch points. Both treatments seems to provoke alterations in the same direction reducing the dendritic branching and increasing spine density, although no significances appeared in some of the parameters analyzed. The effects are more evident in thyroxine than methimazole group; and in CA3 neurons than in CA1 neurons. In discussion it is pointed that the increase of spine density could be a mechanism to compensate the functionality reduction that can be provoke by the treatment effect on dendritic branching. © 2007 Elsevier B.V. All rights reserved. Keywords: Hypothyroidism; Hyperthyroidism; Hippocampus; Pyramidal neurons; Spine; Rats 1. Introduction Thyroid hormones are essential for normal brain function. The hippocampus is a neural structure highly sensitive to the actions of thyroid hormones due to its high content of thyroid hormone receptors [29,41]. The most significant and specific regions of the hippocampus are: dentate gyrus, CA3 and CA1. Cells of dentate gyrus project, via mossy fibbers, upon den- drites of pyramidal cells of CA3. At the same time these cells ∗ Corresponding author at: Dep. Pedagogia Sistem` atica i Social, Univ. Aut` onoma de Barcelona, 08193 Bellaterra, Catalonia, Spain. Tel.: +34 93 581 31 88; fax: +34 93 581 14 19. E-mail address: fina.sala@uab.es (J. Sala-Roca). contribute to major input system to CA1 (the Schaffer collat- erals). This circuit is implicated in different functions, i.e. in learning process and stress [4,23,34,40]. Different studies have analyzed the effect of hypothyroidism in the development of the hippocampus. These studies have indi- cated that neonatal hypothyroidism decreases the weight of the hippocampus [25], decreases the volume and structure of gran- ular and pyramidal neurons [24,32,33], delays synaptogenesis [31], affects neuroblast migration [30], increases neuronal death [25] and reduces the number of synapses between mossy fib- ber and CA3 pyramidal neurons and the excrescences of CA3 pyramidal neurons [24]. In adulthood, hypothyroidism also decreases the weight of the hippocampus [25,26] and the volume of the pyramidal 0166-4328/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2007.11.019