Knocking-down the NMDAR1 subunit in a limited amount of neurons in the rat hippocampus impairs learning.

Amplicon vectors derived from herpes simplex virus type 1 were built to modify NMDA receptors by expressing antisense RNA for the essential NR1 subunit. Their ability to modify endogenous levels of NR1 was tested in cultures of rat embryo neocortical neurons. We studied behaviour and tested for expression in adult rats injected with those vectors into the dorsal hippocampus to find out which cells and how many appear involved in memory formation. Rats injected with vectors expressing NR1 antisense performed significantly worse than control rats in an inhibitory avoidance task. Immunohistochemistry was performed in brain slices from the same animals. The transduced cells represented 6-7% of pyramidal neurons in CA1, showing that a single gene knockdown of NR1 in a small number of neurons significantly impaired memory formation. Perhaps neurons undergoing synaptic plasticity are more susceptible to NR1 knockdown, and hence NMDAR are particularly required in those neurons undergoing synaptic plasticity during learning, or perhaps, and more likely, there is not a high level of redundancy in the hippocampal circuits involved, leading to the idea that a certain level of NR1 expression/availability appears necessary for memory formation in most of CA1 pyramidal neurons.

Low-threshold, dual-passive mode locking of a large mode area Nd:GdVO(4) laser.

The all solid-state combination of a saturable Bragg mirror for amplitude modulation and a cascaded chi((2)):chi((2)) nonlinearity (phase-mismatched second harmonic crystal) as an axial-mode phase locker for continuous-wave mode locking of large mode area lasers is investigated. The dual-passive mode-locking technique generates extremely stable sub-10ps sech(2) pulses at 76MHz from a ~6W, TEM(00)-mode, diode-pumped, thermal-lens-shaped, Brewster Nd:GdVO(4) laser.

Gonadotropin-releasing hormone receptor microaggregation. Rate monitored by fluorescence resonance energy transfer.

Gonadotropin-releasing hormone (GnRH) regulates pituitary gonadotropin release and is a therapeutic target for human and animal reproductive diseases. In the present study we have utilized the technique of fluorescence resonance energy transfer to monitor the rate of GnRH receptor-receptor interactions. This technique relies on the observation that the degree of physical intimacy of molecules can be assessed by the tendency of proximal fluorophores to exchange energy. Our data indicate that GnRH agonist, but not antagonist, occupancy of the GnRH receptor promotes physical intimacy (microaggregation) between receptors. The time course indicates that this occurs promptly (<1 min) after occupancy and persists for at least 80 min and within the physiologically relevant range of the releasing hormone. The process measured is not inhibited by 0.1 mm vinblastin, 2 microm cytochalasin D, or 3 mm EGTA, an observation that distinguishes it from macroaggregation (patching, capping, and internalization). These observations, along with reports from other laboratories, are consonant with a growing body of evidence that indicates that microaggregation is an early event following agonist occupancy of the receptor and part of the mechanism by which effector regulation occurs.

Femtosecond Ti:Sapphire Oscillator Electro-Optically Cavity Dumped at 50 kHz.

Use of a transverse KD?P Pockels cell and novel low-loss sapphire Rochon polarizer to cavity dump a hard-aperture, Kerr-lens mode-locked, Ti:sapphire oscillator is demonstrated. High-quality 90-fs pulses with energies of ~50 nJ at repetition rates of up to 50 kHz were obtained.

Some hypothalamic hamartomas contain transforming growth factor alpha, a puberty-inducing growth factor, but not luteinizing hormone-releasing hormone neurons.

Activation of LH-releasing hormone (LHRH) secretion, essential for the initiation of puberty, is brought about by the interaction of neurotransmitters and astroglia-derived substances. One of these substances, transforming growth factor alpha (TGFalpha), has been implicated as a facilitatory component of the glia-to-neuron signaling process controlling the onset of female puberty in rodents and nonhuman primates. Hypothalamic hamartomas (HH) are tumors frequently associated with precocious puberty in humans. The detection of LHRH-containing neurons in some hamartomas has led to the concept that hamartomas advance puberty because they contain an ectopic LHRH pulse generator. Examination of two HH associated with female sexual precocity revealed that neither tumor had LHRH neurons, but both contained astroglial cells expressing TGFalpha and its receptor. Thus, some HH may induce precocious puberty, not by secreting LHRH, but via the production of trophic factors--such as TGFalpha--able to activate the normal LHRH neuronal network in the patient's hypothalamus.

Neuregulins signaling via a glial erbB-2-erbB-4 receptor complex contribute to the neuroendocrine control of mammalian sexual development.

Activation of erbB-1 receptors by glial TGFalpha has been shown to be a component of the developmental program by which the neuroendocrine brain controls mammalian sexual development. The participation of other members of the erbB family may be required, however, for full signaling capacity. Here, we show that activation of astrocytic erbB-2/erbB-4 receptors plays a significant role in the process by which the hypothalamus controls the advent of mammalian sexual maturation. Hypothalamic astrocytes express both the erbB-2 and erbB-4 genes, but no erbB-3, and respond to neuregulins (NRGs) by releasing prostaglandin E(2) (PGE(2)), which acts on neurosecretory neurons to stimulate secretion of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling sexual development. The actions of TGFalpha and NRGs in glia are synergistic and involve recruitment of erbB-2 as a coreceptor, via erbB-1 and erbB-4, respectively. Hypothalamic expression of both erbB-2 and erbB-4 increases first in a gonad-independent manner before the onset of puberty, and then, at the time of puberty, in a sex steroid-dependent manner. Disruption of erbB-2 synthesis in hypothalamic astrocytes by treatment with an antisense oligodeoxynucleotide inhibited the astrocytic response to NRGs and, to a lesser extent, that to TGFalpha and blocked the erbB-dependent, glia-mediated, stimulation of LHRH release. Intracerebral administration of the oligodeoxynucleotide to developing animals delayed the initiation of puberty. Thus, activation of the erbB-2-erbB-4 receptor complex appears to be a critical component of the signaling process by which astrocytes facilitate the acquisition of female reproductive capacity in mammals.

Simultaneous and independent visualization of the gonadotropin-releasing hormone receptor and its ligand: evidence for independent processing and recycling in living cells.

The first step in GnRH signaling is binding by the peptide to its plasma membrane receptor (GnRHR). The receptor is a member of the seven transmembrane G protein-coupled class but lacks the characteristic C-terminal cytoplasmic tail, making it among the smallest receptors in this superfamily. It has been known since 1980 that agonist occupancy of the GnRHR results in patching, capping, and internalization, although it has not been possible to localize the unoccupied GnRHR, because elaboration of receptor antisera has not been easy to achieve. The recent production of a green fluorescent protein (GFP) conjugate of the GnRHR ("rGnRHR-C-tail-GFP") that is expressed in cells, targeted to the plasma membrane, binds GnRH analogs and couples to G proteins has made it possible to monitor movement of the unoccupied receptor by confocal microscopy. In the present study, we used this probe, along with Texas Red conjugates of a GnRH agonist, to examine simultaneous processing of the receptor and its ligands. The preparation of the GFP GnRHR chimera has been described. A Texas Red conjugate was made from the GnRH agonist D-Lys6-Pro9-des-Gly10EA-GnRH by standard procedures. Bioactivity of this conjugate was confirmed. Confocal fluorescence images of living GGH3 cells showed that the agonist binds the GFP-GnRH receptor construct on the cell membrane and causes the internalization of vesicles delimited by a membrane. Shortly after internalization, the agonist separates from receptor inside the vesicle, although it is still enclosed in membranes containing free receptor. As the vesicles approach the perinuclear space, the separation between receptor and agonist is more pronounced. Free receptor appears at the cell membrane after the internalization of agonist has been completed. The protein synthesis inhibitor, cycloheximide (1 mM) did not inhibit this process, suggesting that the free receptor results from the recycling of previously internalized vesicles rather than from newly synthesized receptor. These studies show visual evidence for recycling of the GnRH receptor in cultured cells.

The Oct-2 POU domain gene in the neuroendocrine brain: a transcriptional regulator of mammalian puberty.

POU homeodomain genes are transcriptional regulators that control development of the mammalian forebrain. Although they are mostly active during embryonic life, some of them remain expressed in the postnatal hypothalamus, suggesting their involvement in regulating differentiated functions of the neuroendocrine brain. We show here that Oct-2, a POU domain gene originally described in cells of the immune system, is one of the controlling components of the cell-cell signaling process underlying the hypothalamic regulation of female puberty. Lesions of the anterior hypothalamus cause sexual precocity and recapitulate some of the events leading to the normal initiation of puberty. Prominent among these events is an increased astrocytic expression of the gene encoding transforming growth factor-alpha (TGF alpha), a tropic polypeptide involved in the stimulatory control of LHRH secretion. The present study shows that such lesions result in the rapid and selective increase in Oct-2 transcripts in TGF alpha-containing astrocytes surrounding the lesion site. In both lesion-induced and normal puberty, there is a preferential increase in hypothalamic expression of the Oct-2a and Oct-2c alternatively spliced messenger RNA forms of the Oct-2 gene, with an increase in 2a messenger RNA levels preceding that in 2c and antedating the peripubertal activation of gonadal steroid secretion. Both Oct-2a and 2c trans-activate the TGF alpha gene via recognition motifs contained in the TGF alpha gene promoter. Inhibition of Oct-2 synthesis reduces TGF alpha expression in astroglial cells and delays the initiation of puberty. These results suggest that the Oct-2 gene is one of the upstream components of the glia to neuron signaling process that controls the onset of female puberty in mammals.

Redistribution of G(q/11)alpha in the pituitary gonadotrope in response to a gonadotropin-releasing hormone agonist.

In the present study, we took advantage of high-resolution multilaser confocal microscopy to examine the distribution of the alpha-subunit of the guanyl nucleotide binding protein subfamily G(q/11) (G(q/11)alpha). Dispersed cultures of pituitary cells were prepared from female weanling rats, fixed, permeabilized, and then stained with monoclonal antiserum (mouse) to the gonadotrope-specific form of secretogranin (SIIp), which was then tagged with Texas Red. Accordingly, the subpopulation of gonadotropes (approximately 15% of total cells) could be identified against a background of other pituitary cell types. G(q/11)alpha was localized with antiserum made in rabbit, then tagged with fluorescein. Hoechst 33258 nuclear stain was also used in some experiments for topological reference. The data indicate localization of the G(q/11)alpha in a cellular region near the plasma membrane and external to the border of the layer occupied by secretory granules. In the absence of activation, there were an average of six clusters of G(q/11)alpha in a section 1 microm thick and through the center of the cell. This corresponds to an average of 60 clusters per cell, assuming a mean gonadotrope diameter of 10 microm. Following continuous treatment with 0.1 microg/ml Buserelin, a metabolically stable GnRH agonist, the average number of clusters increased to 200/cell after 40 min and remained approximately constant for 120 min. This increase was blocked by the protein synthesis inhibitor, cycloheximide. In response to Buserelin, there was an additional increase in the number of clusters inside the cell in the area occupied by the secretory granules and in the perinuclear area. Prolonged (24 h) treatment with Buserelin, sufficient to provoke the onset of desensitization, did not significantly change total numbers of G(q/11)alpha clusters, although more were located in the peripheral compartment, an increase that occurred at the expense of the cytoplasmic compartment. Redistribution of the G(q/11)alpha family may be functionally significant, because this moiety may be rate limiting at the site of regulation of signal transduction.

Visualization of unoccupied and occupied gonadotropin-releasing hormone receptors in living cells.

Three chimeras of the rat GnRH receptor (rGnRHR) and an enhanced green fluorescent protein (GFP) were assessed to examine their suitability as probes of the receptor in transfected GH3 cells. Direct fusion of GFP to the N or C terminus of the rGnRHR abolished the receptor ligand binding affinity and the chimeric receptors were intracellularly localized. In contrast, rGnRHR-Ctail-GFP, a fusion of the N-terminus of the GFP to the C-terminus of the rGnRHR with the intracellular C-terminal tail of the catfish GnRHR as an intermediate spacer, was functional in terms of plasma membrane localization, ligand binding ability, receptor-mediated signal transduction and pattern of homologous down-regulation. The functional chimera of GnRHR and GFP provided a useful model for observation of GnRHR distribution and agonist-stimulated trafficking in living cells.