Postnatal Development of GABAergic Synapses in the Nigral and Entopeduncular Afferent Territory of the Rat Thalamus

Abstract

The time course of the development of GABAergic synapses in the basal ganglion afferent territories of the rat thalamus (the projection zones of the nigro- and entopedunculothalamic afferents) was analyzed at the electron microscopic level. The analysis was carried out in conventionally processed tissue and the tissue was processed for postembedding immunocytochemistry for GABA. It was primarily focused on the development of axosomatic synapses known as the main termination mode of the basal ganglion thalamic afferents. In neonatal rats (P0), small-to-medium-sized axons and large axonal growth cone-like GABA-immunoreactive structures were found engaged in symmetrical synapses with neuronal somata and proximal dendrites. At P7, the size of the axosomatic profiles was considerably increased and synapses appeared more mature. Between P7 and P14, there were numerous degenerating GABA-positive synaptic profiles displaying symmetrical synaptic contacts. Normal-looking GABA-positive terminals were large, extending for several micrometers along the somata and primary dendrites of thalamic neurons. By P21, these boutons acquired the appearance of axosomatic boutons in the adult, i.e., of a large elongated shape, numerous mitochondria, multiple synaptic contacts of pleomorphic vesicles and numerous puncta adherentia. The time course was different from the one described in the somatosensory thalamus by other authors, implying that anatomical and connectional differences between thalamic nuclei are also reflected in the patterns of their synaptogenesis.

Development of the human motor‐related thalamic nuclei during the first half of gestation, with special emphasis on GABAergic circuits

“…In view of the rich GABAergic connectivity in the motor‐related thalamic nuclei, the expression patterns of different GABAergic markers in them during development represent a special interest, as they may reflect the stages of maturation of specific GABAergic connections. To our knowledge, little information is available on the development of the above‐listed GABAergic connections in the motor‐related thalamic nuclei during fetal life and the early postnatal period (Kultas‐Ilinsky and Verney, 2003). Studies on the development of the thalamus have focused almost exclusively on sensory nuclei and mainly in rodents.…”