No abstract

This study has examined whether circulating estrogens are involved in regulating y-aminobutyric acid (GABA), receptor mRNA expression in regions of the female rat brain known to contain estrogen receptors (ERs). In situ hybridization experiments using 35S-labeled oligonucleotides specific for %, B3, and y, subunit mRNAs of the GABA, receptor demonstrated that all three mRNAs were abundant in only the medial preoptic nucleus (MPN), where they were expressed by the vast majority of cells, and specific regions of the bed nucleus of the stria terminalis including the principle encapsulated nucleus (PrN-BNST) and bed nucleus of the anterior commissure (BNAC). Estrogen treatment of ovariectomized rats for 7 d resulted in significant 30-60% increases in QL~ and Y,, but not p3, subunit mRNA expression in the MPN and PrN-BNST. Estrogen treatment for 24 hr resulted in levels of mRNA expression intermediate between those of controls and animals treated with estrogen for 7 d. No changes in subunit mRNA expression were detected for any subunit in the BNAC or cingulate cortex. Double-labeling immunocytochemistry experiments using antibodies directed against the cll, subunit of the GABA, receptor and the ER, revealed that 67 f 3% of % subunit-immunoreactive cells in the MPN also contained ER immunoreactivity. Cells expressing OL* subunits in the PrN-BNST were also found to possess ERs while those in the BNAC and cingulate cortex did not. These findings suggest the possibility that ER-containing cells in the MPN and PrN-BNST express an c&-y, isoform of the GABA, receptor that has its (II, and y, subunits regulated by circulating estrogen concentrations. Together, our observations indicate that estrogen may regulate GABA,, receptor mRNA expression at a transcriptional level and that this is only likely to occur within regions of the rat brain possessing ERs.

We studied the developmental acquisition of three of the cotransmitters found in the gastropyloric receptor (GPR) neurons of the stomatogastric nervous systems of the lobsters Homarus americanus and Homarus gammarus. By using wholemount immunocytochemistry and confocal microscopy, we examined the distribution of serotonin‐like, allatostatin‐like, and FLRFNH2‐like immunoreactivities within the stomatogastric nervous system of embryonic, larval, juvenile, and adult animals. The GPR neurons are peripheral sensory neurons that send proprioceptive information to the stomatogastric and commissural ganglia. In H. americanus, GPR neurons of the adult contain serotonin‐like, allatostatin‐like, and Phe‐Leu‐Arg‐Phe‐amide (FLRFNH2)‐like immunoreactivities. In the stomatogastric ganglion (STG) of the adult H. americanus and H. gammarus, all of the serotonin‐like and allatostatin‐like immunoreactivity colocalizes in neuropil processes that are derived exclusively from ramifications of the GPR neurons. In both species, FLRFNH2‐like immunoreactivity was detected in the STG neuropil by 50% of embryonic development (E50). Allatostatin‐like immunoreactivity was visible first in the STG at approximately E70–E80. In contrast, serotonin staining was not clearly visible until larval stage I (LI) in H. gammarus and until LII or LIII in H. americanus. These data indicate that there is a sequential acquisition of the cotransmitters of the GPR neurons. J. Comp. Neurol. 408:318–334, 1999. © 1999 Wiley‐Liss, Inc.