TRANSIENT EXPRESSION OF ESTROGEN-RECEPTOR IMMUNOREACTIVITY (ER-IR) INTHE LAYER-V OF THE DEVELOPING RAT CEREBRAL-CORTEX

Occurrence of estrogen receptor-immunoreactivity (ER-IR) in the cerebr al cortex was examined in neonatal and adult rats. In newborn rats of postnatal day 1 (= day of birth) and postnatal day 5 (PD1 and PD5, res pectively), ER-IR was not evident in the neocortex. On postnatal days 7, 10 and 13 (PD7, PD10 and PD13 respectively), a group of cells with distinct ER-IR appeared in the layer V of the auditory cortex. At the PD10, weak but specific ER-IR were also appeared in the somatosensory and the visual cortices. Among these areas, the ER-IR positive neurons occurred most frequently in the auditory cortex at PD10 rats. By exam ination of adjacent sections, one stained with Cresyl violet and the a nother stained with acethylcholinesterase (AChE) histochemistry, it wa s revealed that the region with ER-IR at PD7 to PD13 was limited to la yer V of the neocortex. These signals, however, disappeared at PD15. I n layer II of the neocortex, on the other hand, weak ER-IR signals wer e detected throughout the area sporadically at PD21 and in adults. The ER-IR detected transiently in the auditory cortex by the antiserum mi ght contribute to maturation and establishment of the neurons of the r at auditory circuit.