Transcriptional control of adrenal catecholamine and opiate peptide transmitter genes

Expression of alpha3, beta3 and gamma1 GABA(A) receptor subunit messenger RNAs in visual cortex and lateral geniculate nucleus of normal and monocularly deprived monkeys

Complementary RNA probes derived from complementary DNA specifically subcloned from monkey tissue were used to localize, by in situ hybridization histochemistry, the relatively rare alpha3, beta3 and gamma1 subunit transcripts of the GABA(A) receptor in visual cortex and lateral geniculate nucleus of normal monkeys and in monkeys that had been deprived of vision in one eye. Overall, levels of alpha3, beta3 and gamma1 subunit transcripts were very low. In the primary visual cortex (area 17) they were concentrated in layers II and VI and in a stratum of white matter subjacent to layer VI. The localization and density of the three messenger RNAs closely resembled those of other rare (alpha2, alpha5 and beta1) transcripts but their distribution also overlapped that of the predominant alpha1, beta2 and gamma2 subunit transcripts. In area 18, alpha3 and beta3 transcript distribution resembled that in area 17, with the addition of a third band of hybridization in layer IV for beta3. Gamma1 subunit transcript localization in area 18 differed significantly from that in area 17, with increased expression restricted to layer IV. In the dorsal lateral geniculate nucleus, beta3 and gamma1 transcripts were expressed at low levels across all layers while alpha3 transcripts were restricted to the magnocellular layers. Following 15 and 18 day periods of monocular deprivation, induced by intravitreal injections of tetrodotoxin, levels of alpha3 receptor subunit transcripts showed modest reductions in layer VI of area 17 and in deprived geniculate laminae of adult animals. Reductions in alpha3 transcript levels were much more pronounced in layer IVCbeta of a five-month-old monkey deprived for the same time. Levels of beta3 and gamma1 transcripts were unaffected by monocular deprivation in cortex and geniculate at any age. Taken together with studies of other GABA(A) receptor transcripts, these results demonstrate the heterogeneity of GABA(A) receptor messenger RNA expression in the monkey geniculo-striate pathway and the varied response to reduced neuronal activity.

Anesthesia during hormone administration abolishes the estrogen induction of preproenkephalin mRNA in ventromedial hypothalamus of female rats

Estrogen treatment increases preproenkephalin (PPE) mRNA levels in the ventromedial nucleus of the hypothalamus (VMH). Roy et al. (Brain Res., 337 (1985) 163-166) discovered that anesthesia during estrogen priming could reduce female rat sexual receptivity. In the present study we tested whether the action of estrogen to induce PPE gene expression in the VMH could be similarly affected by anesthesia. By quantitative in situ hybridization and slot-blot analysis techniques we found a 1.8-fold increase in PPE mRNA levels in the VMH after 1 hour of estrogen treatment in ovariectomized (OVX) Sprague-Dawley female rats. Anesthetizing the rats with pentobarbital for 1 h during the exposure to estrogen blocked the estrogen induction of PPE mRNA in the VMH. By way of contrast no changes in the PPE mRNA levels were observed in the caudate putamen. A similar trend was seen using chloral hydrate. It appears that neuronal activity is required for the early phase of estrogen induction of PPE mRNA levels in the VMH. This in turn could be correlated with changes in female sociosexual behaviors.

Expression patterns and deprivation effects on GABAA receptor subunit and GAD mRNAs in monkey lateral geniculate nucleus

The expression and regulation of seven GABAA receptor subunit gene transcripts were examined in the adult monkey lateral geniculate nucleus. In situ hybridization histochemistry was used to localize mRNAs of the genes encoding monkey-specific alpha 1, alpha 2, alpha 4, alpha 5, beta 1, beta 2, and gamma 2 subunits. The highest levels of expression in the nucleus were for alpha 1, beta 2, and gamma 2 subunit transcripts. The levels were substantially higher in the magnocellular than in the parvocellular layers. Alpha-2, alpha 4, alpha 5, and beta 1 subunit mRNAs were expressed at much lower levels, and magno- and parvocellular layers had approximately equal levels of expression. Following 4- or 21-day periods of monocular deprivation induced by intravitreal injections of tetrodotoxin, levels of the alpha 1, alpha 2, alpha 4, alpha 5, beta 1, and beta 2 mRNAs were decreased in the deprived geniculate laminae. Adjacent sections hybridized with probes specific for 67-kDa glutamic acid decarboxylase (GAD) mRNA also showed decreased levels of expression in deprived laminae after the 21-day deprivation period. Levels of gamma 2 receptor subunit mRNA were unaffected by monocular deprivation. In our previous studies, a clearly significant downregulation is observed for this subunit transcript in the visual cortex of monkeys deprived for equivalent times. The differential expression and responses to deprivation in the lateral geniculate nucleus suggest region-specific regulation of GABAA receptor subunit genes.

Estrogen regulates preproenkephalin-A mRNA levels in the rat ventromedial nucleus: temporal and cellular aspects

Numerous studies suggest that the ventromedial nucleus of the hypothalamus is a primary locus of control for reproductive behavior in the female rat. The display of lordosis behavior is estrogen dependent and its regulation appears to involve the activity of endogenous opioid circuits in the mediobasal hypothalamus and brainstem. Hypothalamic levels of preproenkephalin-A mRNA and the neuropeptide which it encodes, methionine-enkephalin, are dramatically up-regulated by estrogen. To characterize the temporal and cellular aspects of the effect of an acute exposure to estrogen on preproenkephalin-A mRNA levels in the ventromedial nucleus and arcuate nucleus of the hypothalamus, ovariectomized female rats were injected with 50 micrograms estradiol benzoate and used for quantitative in situ hybridization histochemistry of preproenkephalin-A mRNA. In the ventromedial nucleus, estrogen treatment caused a biphasic increase in the number of preproenkephalin-A mRNA cells. Maximal numbers of cells expressing preproenkephalin-A mRNA were observed at 1 and 48 h after estrogen injection. At 4 and 96 h after estrogen injection, the numbers of preproenkephalin-A mRNA cells were similar to that which was seen in the ovariectomized female. The induction of preproenkephalin-A mRNA expression in cells of the arcuate nucleus followed a similar pattern that peaked 48 h after exposure to estrogen. Levels of preproenkephalin-A mRNA per cell did not change in either nucleus as a function of estrogen treatment. Thus, acute estrogen treatment induces expression of preproenkephalin-A mRNA in populations of cells in the ventromedial hypothalamus and arcuate nucleus in which preproenkephalin-A mRNA expression is undetectable by in situ hybridization in the absence of circulating estrogen.

Pentylenetetrazole-induced seizures stimulate transcription of early and late response genes

Cellular immediate early gene and neuropeptide gene expression have each been demonstrated to be modulated in hippocampus in response to a variety of seizure-inducing stimuli. In this study, gene transcription for three immediate early genes, c-fos, c-jun and NGFI-A, and three neuropeptide genes, enkephalin, dynorphin and neuropeptide Y, was investigated using nuclear run-on assays following a single injection of the convulsant pentylenetetrazole (PTZ). At 15 min following PTZ injection, only transcription for c-fos was increased. By 6 h following PTZ treatment, transcription for all immediate early genes and for dynorphin and neuropeptide Y was increased; however, this increase was transient in that transcription of all genes returned to control values by 48 h following PTZ treatment. Thus, regulation of immediate early and neuropeptide gene mRNA levels and immunoreactivity occurs, at least in part, at the level of transcription for the genes encoding neuropeptide Y, dynorphin, c-fos, c-jun, and NGFI-A. Moreover, the difference between increased transcription rates reported here and increased mRNA levels reported here and elsewhere suggests that additional post-transcriptional regulation of gene expression occurs in hippocampal neurons.

Synaptic regulation of glial protein expression in vivo

We investigated signaling between individual nerve terminals and perisynaptic Schwann cells, the teloglial cells that cover neuromuscular junctions. When deprived of neuronal activity in vivo, either by motor nerve transection or tetrodotoxin injection, perisynaptic Schwann cells rapidly up-regulated glial fibrillary acidic protein. Addition of transcription or translation inhibitors to excised muscles prevented this increase. Stimulation of cut nerves prevented glial fibrillary acidic protein increases even when postsynaptic nicotinic receptors were blocked, but not when neurotransmitter release was blocked with omega-conotoxin GVIA. We conclude that there is a nerve terminal to glial signal, requiring presynaptic neurotransmitter release, which regulates perisynaptic Schwann cell genes. This may be a general principle since many types of glial are sensitive to transmitters applied in vitro or released in situ.

Time course of enkephalin mRNA and peptides in cultured rat adrenal medulla

Explantation of rat adrenal medullae to organ culture results in dramatic changes in enkephalins and catecholamines that are similar to the changes seen in vivo in response to denervation, which eliminates transsynaptic impulse activity. We have used rapid and sensitive solution hybridization methods to measure preproenkephalin (PPenk) mRNA and total cellular RNA in samples from rat tissues and adrenal medullary explants. The profiles of adrenal medullary PPenk mRNA, enkephalin-containing (EC) peptides, total cellular RNA and catecholamines [epinephrine (epi) and norepinephrine (norepi)] were measured during 14 days of organ culture. After 8 h in culture, total RNA had declined by 60%, epi and norepi declined 80 to 85% and EC peptides by 50% while the amount of PPenk mRNA per gland increased by 400%. Between 8 h and 14 days total RNA and catecholamine levels remained constant while PPenk mRNA increased to a peak of 85 +/- 10 (S.E.M.) pg/gland at 2-4 days, a value that was 80 times greater than the zero time (preculture) values. EC peptide levels lagged behind the increase in PPenk mRNA and reached a peak of 25 +/- 4 (S.E.M.) pmol Met-enkephalin equivalents/gland at 4 days that was 80 times greater than zero time values. Both PPenk mRNA and EC peptides declined in parallel between 4 and 14 days. The ratio of the copies of proenkephalin (Penk) peptide to PPenk mRNA was estimated to be 25,000 at the time of explantation and after 4 days in culture. From steady-state kinetics half-life estimates of 9.6 h for PPenk mRNA and 14.7 h for Penk peptide were obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

The emergence of architectonic field structure and areal borders in developing monkey sensorimotor cortex

Adult monkey sensorimotor cortex consists of several structurally and functionally distinct areas. The developmental sequence through which the characteristic architectonic features and the borders of these areas become resolved was examined in a series of fetal, postnatal and adult monkeys by using Nissl staining, cytochrome oxidase and acetylcholinesterase histochemistry, and immunocytochemistry for GABA and the neuropeptides somatostatin, neuropeptide Y, substance P and cholecystokinin. At the youngest fetal age examined (E110), the pre- and postcentral gyri possess six clearly delineated cellular layers; populations of GABA- and neuropeptide-immunoreactive cells can be identified, but their somatic sensory cortex at E110 lacks areal cytoarchitectonic parcellation. Despite the apparent homogeneity in the cytoarchitecture of the somatic sensory cortex, incipient areal borders are revealed by staining for cytochrome oxidase and acetylcholinesterase activity, and by staining immunocytochemically for several neuropeptides. The motor cortex at E110 differs from that in adults by the presence of a prominent layer IV; a clear cytoarchitectonic border between areas 3a and 4 is detectable at E110, which is also revealed by chemoarchitectonic markers. With increasing age, the characteristic architectonic features gradually emerge and areal cytoarchitectonic borders appear, becoming adult-like by early postnatal ages. The gradual changes in cytoarchitecture are paralleled by redistributions of GABA- and neuropeptide-immunoreactive cells and fiber plexuses. The data demonstrate that the progressive refinement in cytoarchitectonic features and in the distributions of neurotransmitter- and peptide-containing cells occurs primarily during the latter third of gestation. The major changes are temporally coincident with the ingrowth of afferent axonal systems, suggesting that the establishment of connectivity may be capable of modulating finer details of structural or molecular phenotype, particularly intra-areal cytoarchitectonic features and neurotransmitter or peptide expression.

Bimodal regulation of adrenal opiate peptides by cholinergic mechanisms

Physiologic stressors increase trans-synaptic impulse activity and result in adrenal catecholamine release and biosynthesis. To determine the effects of stress on the co-localized opiate peptide system, rats were cold stressed at 4 degrees C. While cold stress slightly decreased enkephalin levels, a more severe stress (wetting and cold) increased enkephalin levels by 95%. Examining trans-synaptic-cholinergic mechanisms, treatment with either nicotinic or muscarinic agonists alone resulted in no change in adrenal enkephalin content. However, treatment with both nicotinic and muscarinic agonists together resulted in a three-fold rise in enkephalin levels. To further examine cellular mechanisms, medullae were explanted in the presence of agents that increase second messenger cyclic nucleotide levels. Treatments that increase the levels of cAMP, the cyclic nucleotide associated with nicotinic receptor activation, prevented the rise in medullary enkephalin relative to control explants. In contrast, treatments that increased cGMP levels, the cyclic nucleotide associated with muscarinic receptor activation, had no effect on enkephalin content compared to control explants. However, in the presence of both forskolin (10 microM) plus db-cGMP (5 mM), enkephalin content rose three-fold over control explants. These data suggest that, distinct from catecholamine pathways, enkephalin levels can be positively or negatively regulated by the severity of a stressful stimulus, by cholinergic receptor mechanisms and by an interaction of cyclic nucleotide second-messenger pathways.

Preproenkephalin DNA-binding proteins in the rat: 5' flanking region

Various extracellular signals (i.e. transmitters, hormones, growth factors, etc.), together with their respective second-messenger pathways, regulate transmitter biosynthesis and neuronal function by altering gene expression. In this study we validated a protocol for isolating rat striatum and adrenal medullary nuclei for the purpose of extracting, identifying, and characterizing, nuclear regulatory factors which may serve a functional role in signal-transduction processes. Through gel retardation studies using a 299 base pair (bp) XmnI-SacI 32P-labeled probe (derived from the 5' untranslated region of the rat preproenkephalin gene), we show that different patterns of retained bands result from nuclear extracts derived from rat adrenal medulla and striatum (as well as from other tissue). These tissue differences may have biological significance since rat adrenal medullae have low basal enkephalin levels while the striatum has high levels of this peptide and its respective mRNA. Additionally, certain retained bands were common to both cytosolic and nuclear compartments, suggesting binding factors may be located in either cell space. An initial biochemical characterization of these factors was also undertaken. Generally, salt levels of 100 mM or more reduced factor binding while 10-50 mM sodium ion levels showed preferentially enhanced bands. Binding activity appeared optimal at pH 6.8. As all retained bands were abrogated by proteinase K treatment, these factors appear to have a significant protein component. Finally, of particular interest is that this 299 bp region contains many sequences showing over 80% sequence identity with several previously characterized transcriptional control elements (i.e. cAMP and phorbol ester inducible enhancers, GCN4, AP1, Sp1, CCAAT binding factor, ATF, and AP2). If binding is confirmed (footprint analysis) and function validated (transfection studies), the evolutionary significance of the apparent presence of gene regulatory sequences and functional element divergence of the DNA region between different species can be evaluated.

Ontogeny of the opiate phenotype: an approach to defining transsynaptic mechanisms at the molecular level in the rat adrenal medulla

Transmitter phenotypic expressions is a dynamic cellular process governed by multiple interactions with the neuronal environment. During sympathoadrenal development the arrival of presynaptic nerve terminals at the adrenal chromaffin cell (in the immediate postnatal period), coincides with the acquisition and subsequent development of a variety of transmitter biosynthetic capacities. Data discussed herein supports the contention that synaptic connections serve a central role in triggering the ontological cascade. Disruption of the normal timing of innervation events is detrimental to subsequent function and results in permanent deficiencies in development. In addition, alteration of transmitter biosynthetic regulatory mechanisms appears to reside at the level of gene expression. In view of this, additional molecular approaches are necessary to further elucidate the fundamental basis of neuronal transmitter phenotypic plasticity. Our approach to this problem represents a logical extension of previous research in this area and ultimately, will involve characterizing transcription activator molecules important in transmitter gene expression at various ontological ages.