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B D Shivers

Publications and source records attributed to B D Shivers.

At least 37 records · Page 2Linked to original sources
PubMed1989

Two novel GABAA receptor subunits exist in distinct neuronal subpopulations.

Two cDNAs encoding novel GABAA receptor subunits were isolated from a rat brain library. These subunits, gamma 2 and delta, share approximately 35% sequence identity with alpha and beta subunits and form functional GABA-gated chloride channels when expressed alone in vitro. The gamma 2 subunit is the rat homolog of the human gamma 2 subunit recently shown to be important for benzodiazepine pharmacology. Cellular localization of the mRNAs encoding the gamma 2 and delta subunits in rat brain revealed that largely distinct neuronal subpopulations express the two subunits. The delta subunit distribution resembles that of the high affinity GABAA receptor labeled with [3H]muscimol; the gamma 2 subunit distribution resembles that of GABAA/benzodiazepine receptors labeled with [3H]flunitrazepam. These findings have implications for the composition of two different GABAA receptor subtypes and for information processing in networks using GABA for signaling.

Animals↗
PubMed1989

Distribution and partial characterization of immunoreactive prolactin in the rat brain.

Immunoreactive (IR) prolactin was localized immunocytochemically in cell bodies in the mediobasal hypothalamus and in fibers in many regions of the rat brain. The cell bodies were found in the arcuate nuclei and the adjacent areas ventral to the ventromedial nuclei. Fiber projections extended rostrally to and/or through the anterior hypothalamus, preoptic area, nucleus accumbens, septum, diagonal bands of Broca, caudate-putamen, frontal cortex and accessory olfactory bulb; laterally to the amygdala, especially the central nucleus and some parts of the medial nucleus; caudally to and/or through the midbrain central gray, reticular formation, parabrachial region, and several portions of the lower brain stem and spinal cord extending to sacral levels. The system appears to be essentially identical to that containing proopiomelanocortin (POMC) and its processed peptides, as shown by double immunocytochemistry. Preabsorption of the antiprolactin antiserum with either prolactin or the 16,000-dalton N-terminus of POMC eliminated immunoreactivity in the brain. Preabsorption with other POMC-derived peptides, including beta-lipotropic hormone, beta-endorphin, met-enkephalin, adrenocorticotrophic hormone (1-24), corticotropin-like intermediate lobe peptide, alpha- and gamma-melanocyte-stimulating hormones and an octapeptide region of the N-terminus of POMC bearing some homology with prolactin, did not eliminate immunoreactivity in the brain. Similarly, preabsorption with growth hormone, luteinizing hormone, follicle-stimulating hormone, motilin or fetuin did not eliminate immunoreactivity in the brain. The antiprolactin antiserum also recognized all cells in the intermediate lobe and a subset of cells in the anterior lobe of the Snell dwarf mouse pituitary. This immunoreactivity was eliminated by preabsorption of the antiserum with prolactin or with the 16,000-dalton N-terminus of POMC. These results suggest that IR prolactin in the brain may be related to the N-terminus of POMC. Additional results based on one- and two-dimensional gel electrophoresis and immunoblotting indicate that the antiprolactin antiserum used in the majority of the immunocytochemical studies recognized a number of proteins.

Animals↗
PubMed1989

A subset of neurons containing immunoreactive prolactin is a target for estrogen regulation of gene expression in rat hypothalamus.

Cells whose nuclei accumulated 3H-estradiol were identified autoradiographically in fixed, frozen sections of colchicine-treated rat hypothalamus (n = 3 animals). After autoradiogram development, these sections were subjected to immunocytochemistry using rabbit antirat prolactin antiserum and the avidin-biotinylated horseradish peroxidase method. In the hypothalamus, a substantial subset of the neurons containing immunoreactive prolactin accumulated 3H-estradiol in their nuclei: of 3, 642 immunoreactive cells examined, 1,216 had autoradiographically labeled nuclei, or about 33%. The immunoreactive prolactin neurons with autoradiographically labeled nuclei were located in the medial basal hypothalamus intermingled with immunoreactive prolactin neurons whose nuclei were not labeled autoradiographically. Since hypothalamic immunoreactive prolactin neurons have a rich and widely distributed fiber system, the present results suggest that estrogen, acting through a subset of these neurons, can modify directly the neuronal activity of several brain regions which regulate diverse aspects of the reproductive effort. Also, since immunoreactive prolactin and immunoreactive beta-endorphin exist in the same hypothalamic cell population, opioid peptides derived from pro-opiomelanocortin may mediate some effects of estrogen on the neural circuitry regulating reproduction.

Animals↗
PubMed1988

Alzheimer's disease amyloidogenic glycoprotein: expression pattern in rat brain suggests a role in cell contact.

The cloned cDNA encoding the rat cognate of the human A4 amyloid precursor protein was isolated from a rat brain library. The predicted primary structure of the 695-amino acid-long protein displays 97% identity to its human homologue shown previously to resemble an integral membrane protein. The protein was detected in rodent brain and muscle by Western blot analysis. Using in situ hybridization and immunocytochemistry on rat brain sections, we discovered that rat amyloidogenic glycoprotein (rAG) and its mRNA are ubiquitously and abundantly expressed in neurons indicating a neuronal original for the amyloid deposits observed in humans with Alzheimer's disease (AD). The protein appears in patches on or near the plasma membranes of neurons suggesting a role for this protein in cell contact. Highest expression was seen in rat brain regions where amyloid is deposited in AD but also in areas which do not contain deposits in AD. Since amyloid deposits are rarely observed in rat brain, we conclude that high expression of AG is not the sole cause of amyloidosis.

Alzheimer Disease↗
PubMed1988

Estrogen increases proenkephalin messenger ribonucleic acid levels in the ventromedial hypothalamus of the rat.

The effects of estrogen on proenkephalin (PE) gene expression were measured in neurons of the ventromedial hypothalamus. Slot blot hybridization analysis indicates that the levels of PE mRNA in the ventromedial hypothalamus of ovariectomized rats increase 3.1-fold after 2 weeks of estrogen replacement. In situ hybridization reveals that the estrogen-inducible enkephalinergic neurons are located in the ventrolateral aspect of the ventromedial nucleus, a subnucleus known to contain many estrogen-concentrating neurons. The increase in PE mRNA levels is due to both a 63% increase in the number of detectable PE mRNA-containing neurons and a 2.0-fold increase in the levels of PE mRNA per enkephalinergic neuron (1.63 x 2.0 = 3.3-fold overall induction). This estrogen-regulated enkephalinergic cell group may represent part of the neural network mediating estrogen's effects on reproductive behavior and/or other neuroendocrine processes.

Animals↗
PubMed1987

A novel subtype of muscarinic receptor identified by homology screening.

A new member of the protein superfamily of G-protein coupled receptors has been isolated by homology screening. By virtue of its homology with other muscarinic acetylcholine receptors and its ability to bind muscarinic specific antagonists, this muscarinic receptor subtype is designated M4. The M4 mRNA is preferentially expressed in certain brain regions. The existence of multiple receptor subtypes encoded by distinct genes in the brain has functional implications for the molecular mechanisms underlying information transmission in neuronal networks.

Amino Acid Sequence↗
PubMed1987

Localization of preproenkephalin mRNA in the rat brain and spinal cord by in situ hybridization.

To determine the localization in rat brain and spinal cord of individual neurons that contain the messenger RNA coding for the opioid peptide precursor preproenkephalin, we performed in situ hybridization with a tritiated cDNA probe complementary to a protion of preproenkephalin mRNA. We observed autoradiographic signal over the cytoplasm of neurons of many regions of the central nervous system. Several types of controls indicated specificity of the labeling. Neurons containing preproenkephalin mRNA were found in the piriform cortex, ventral tenia tecta, several regions of the neocortex, nucleus accumbens, olfactory tubercle, caudate-putamen, lateral septum, bed nucleus of the stria terminalis, diagonal band of Broca, preoptic area, amygdala (especially central nucleus, with fewer labeled neurons in all other nuclei), hippocampal formation, anterior hypothalamic nucleus, perifornical region, lateral hypothalamus, paraventricular nucleus, dorsomedial and ventromedial hypothalamic nuclei, arcuate nucleus, dorsal and ventral premamillary nuclei, medial mamillary nucleus, lateral geniculate nucleus, zona incerta, periaqueductal gray, midbrain reticular formation, ventral tegmental area of Tsai, inferior colliculus, dorsal and ventral tegmental nuclei of Gudden, dorsal and ventral parabrachial nuclei, pontine and medullary reticular formation, several portions of the raphe nuclei, nucleus of the solitary tract, nucleus of the spinal trigeminal tract (especially substantia gelatinosa), ventral and dorsal cochlear nuclei, medial and spinal vestibular nuclei, cuneate and external cuneate nuclei, gracile nucleus, superior olive, nucleus of the trapezoid body, some deep cerebellar nuclei, Golgi neurons in the cerebellum, and most laminae of the spinal cord. In most of these brain regions, the present results indicate that many more neurons contain preproenkephalin mRNA than have been appreciated previously on the basis of immunocytochemistry.

Animals↗
PubMed1987

Haloperidol increases proenkephalin mRNA levels in the caudate-putamen of the rat: a quantitative study at the cellular level using in situ hybridization.

Previous immunocytochemical studies have shown that the opioid peptides, Met-enkephalin and Leu-enkephalin, are present in medium-sized, spiny projection neurons of the caudate-putamen. It has also been demonstrated that chronic treatment of rats with the dopamine receptor blocker, haloperidol, results in an increase in the levels of enkephalin peptides and proenkephalin mRNA in this brain region. To determine whether this increase in proenkephalin mRNA content is exhibited by all enkephalinergic neurons of the caudate-putamen or by only a subpopulation, we have used in situ nucleic acid hybridization to examine the haloperidol-induced increase in proenkephalin mRNA levels at the cellular level. Results of in situ hybridization suggest that all enkephalinergic neurons in the caudate-putamen can respond to haloperidol treatment with an increase in steady state levels of proenkephalin mRNA, and that the mean induction is an approximate 3-fold increase in the message levels. This suggests that dopamine exerts a tonic inhibitory effect on the expression of the proenkephalin gene in all of the enkephalinergic neurons of the caudate-putamen. Dot blot analysis indicated a 2.4-fold increase in the tissue levels of this mRNA. The agreement between the in situ hybridization results and dot blot analysis supports in situ hybridization as a reliable method for quantitative studies of alterations in neuropeptide precursor mRNAs in the brain.

Animals↗
PubMed1986

Reversible disruption of lordosis via midbrain infusions of procaine and tetrodotoxin.

Behavioral effects of bilateral intracranial infusions of tetrodotoxin (1, 3.3 or 10 ng/rat), 50% procaine (2 microliters/rat) or phosphate-buffered saline (PBS-2 microliters/rat) into the dorsal midbrain of conscious, lightly-restrained female rats were evaluated. High levels of lordotic responsiveness were induced in ovariectomized animals treated with estradiol (E2) capsules or subcutaneous injections of estradiol benzoate (EB) followed by progesterone (P). The effect of each of the 3 infusates on lordosis was determined using manual stimulation and lordosis quotient determinations. In addition, the vocalization by an animal during lordosis measurements, paw withdrawal to pinch, righting reflex latency and recognition of a platform edge were also monitored. Within 2 minutes following procaine or tetrodotoxin (TTX) infusions in E2 implanted rats, lordotic responsiveness declined sharply. Whereas procaine-treated animals returned to control levels of responsiveness within 20 minutes, TTX infusions induced a more prolonged depression of lordosis lasting up to 8 hours. Infusions of PBS had no effect on any of the behaviors. In a separate group of animals treated with either E2 or EB + P and infused with 10 ng TTX the time course of the decline in lordotic responsiveness was identical for both steroid treatments. Paw withdrawal was unaffected by TTX while all other measured behaviors were disrupted along the same time course as lordosis. Collectively the above results implicate the requirement of sodium-dependent neuronal activity within dorsal midbrain for the maintenance of the lordosis reflex, along with other behavioral responses influenced by this brain region.

Animals↗
PubMed1986

Cellular localization of proenkephalin mRNA in rat brain: gene expression in the caudate-putamen and cerebellar cortex.

The cellular locations of proenkephalin mRNA have been determined for the caudate-putamen and cerebellar cortex of the rat brain by in situ hybridization. In the caudate-putamen, more than half of the neurons express the proenkephalin gene. Morphologically, they are medium-sized cells that may represent projection neurons. In the cerebellar cortex, proenkephalin mRNA is present in a subpopulation of neurons in the granule layer that appear to be Golgi cells--i.e., inhibitory interneurons. The presence of [Met]enkephalin, a pentapeptide derived from proenkephalin, in these two brain areas is consistent with a synthetic role for this mRNA and implicates proenkephalin gene expression in the control of motor function.

Animals↗
PubMed1986

Combination of immunocytochemistry and in situ hybridization in the same tissue section of rat pituitary.

A procedure is described for combining avidin-biotinylated horseradish peroxidase immunocytochemistry, for localizing peptides or proteins, with in situ hybridization for localizing mRNA autoradiographically in the same cryostat section of paraformaldehyde-fixed rat pituitary. Protection against enzymatic degradation of target mRNAs during the immunocytochemical step was necessary and was accomplished by including an RNase inhibitor, 0.04% diethylpyrocarbonate, in primary and secondary antisera. This combination of methods may be useful in other tissues, as well, for (a) determining the relation of protein content to the concentration of its encoding mRNA, (b) proving the synthetic capacity of a cell in which a protein has been localized, (c) determining immunological or nucleic acid probe specificity, or (d) as an alternative to double-labeling immunocytochemical methods.

3,3'-Diaminobenzidine↗
PubMed1985

Inhibition of the lordosis reflex in rats by intrahypothalamic infusion of neural excitatory agents: evidence that the hypothalamus contains separate inhibitory and facilitatory elements.

In attempts to activate lordosis-facilitating neural mechanisms in the ventromedial hypothalamus (VMH), neural excitatory agents were infused into the medial hypothalamus, and the effects of the infusions on the lordosis reflex and on the electrical activity of VMH neurons were studied. Surprisingly, bilateral intrahypothalamic infusion of glutamate (10 mM, 1.0 microliter/side) into behaving, ovariectomized, estrogen-treated rats displaying moderate lordotic responsiveness did not facilitate lordosis, but instead, resulted in a rapid (within a few minutes) and transient (recovery in about 20 min) inhibition of lordosis. Further experiments showed that this lordosis-inhibiting effect of glutamate was dose-related, and was completely blocked by prior infusion of a local anesthetic, procaine. Infusion of KC1 (1.5 or 15%, 1.0 microliter/side) also induced a dose-related, rapid and transient inhibition of lordosis, that was essentially identical to that induced by glutamate. Kainic acid (0.25 micrograms/0.5 microliter/side) also caused a rapid inhibition of lordosis, but the effect was long-lasting (days). The inhibition of lordosis by these agents was dissociated in time course, presence, and/or severity from effects on non-lordotic behaviors. Electrophysiological studies showed that all three agents tested could excite multiunit activity of the VMH, and that the time courses of these excitations were closely comparable to those of the inhibition of lordosis induced by the respective agents. Altogether, these studies indicated that the excitation of certain medial hypothalamic neurons can inhibit the lordosis reflex. The implied lordosis-inhibiting neural mechanisms are separate from facilitatory mechanism(s), according to differences in latency, duration, and procaine-sensitivity of response.

Animals↗
PubMed1984

Prolactin mRNA exists in rat hypothalamus.

Using radiolabeled DNA complementary to rat pituitary prolactin mRNA, we probed RNA gel blots from three rat tissues: pituitary, hypothalamus, and liver. Poly (A)-enriched RNA from male and female hypothalami contained a hybridizable RNA which was the same size as, though less abundant than, mature pituitary PRL mRNA. These results support the proposal that the rat brain synthesizes PRL.

Animals↗
PubMed1983

Estrogenic maintenance of lordotic responsiveness: requirement for hypothalamic action potentials.

Studies were conducted to determine the requirement for hypothalamic, sodium current-based action potentials in the performance of a stereotypic, estrogen-dependent reflex, the lordosis response. Intrahypothalamic infusion of local anesthetics (50% procaine or 0.5% bupivacaine) into conscious rats had no effect on lordotic responsiveness, and, in a separate group of urethane-anesthetized rats, depressed multiunit electrical activity temporarily. Intrahypothalamic infusion of tetrodotoxin into conscious rats, however, resulted in a dose-dependent, reversible decline in lordotic responsiveness. The first significant drop in lordotic responsiveness occurred 40 min after infusion; the minimum was reached 2-4 h after infusion. Recovery of lordotic responsiveness to preinfusion levels was complete by 12-24 h after infusion. Electrophysiological studies in a separate group of urethane-anesthetized rats revealed that intrahypothalamic tetrodotoxin infusion in most cases suppressed multiunit activity completely usually within 6 min, and this suppression lasted for at least several hours. These data indicate that large, prolonged decreases in electrical activity in the hypothalamus, where estrogenic action is necessary and sufficient to induce lordosis, result in a gradual, reversible decline in lordotic responsiveness. These data are consistent with a 'tonic' rather than a 'mount-by-mount' role of hypothalamic neurons in lordosis. Furthermore, since lordotic responsiveness declined only when hypothalamic electrical activity had been disrupted severely for at least 40 min, it is postulated that the neuroactive products released by lordosis-relevant, hypothalamic neurons may have a duration of action of at least several minutes.

Action Potentials↗
PubMed1983

Midbrain microinfusions of prolactin increase the estrogen-dependent behavior, lordosis.

Microinfusions of rat prolactin into the dorsal midbrain of estrogen-treated, ovariectomized rats increased lordosis behavior. Midbrain microinfusions of antiserum to prolactin into rats displaying maximum lordosis had the opposite effect. The distribution of a prolactin-like substance in the brain was studied immunocytochemically. The results suggest that a hypothalamic neuronal system projecting to the midbrain contains a prolactin-like substance that plays a role in facilitating this behavior and therefore may mediate some of the effects of estrogen on the brain. These data, together with others from studies of the prolactin gene and its regulation, indicate that it may be possible to analyze a sequence of molecular events in the brain that facilitate a behavioral response.

Adrenalectomy↗