Vasoactive intestinal polypeptide in the chicken anterior pituitary gland

In birds, prolactin secretion is stimulated by a hypothalamic prolactin releasing hormone, vasoactive intestinal polypeptide (VIP). Active immunization against VIP suppresses both prolactin and LH secretion. Since VIP in physiological doses, does not stimulate LH release, it is suggested that it might act to regulate the function of LHproducing cells in a paracrine manner. The aim of this thesis is to provide biochemical, molecular and anatomical evidence to support this hypothesis.Vasoactive intestinal polypeptide was shown to be present in the chicken anterior pituitary gland using high performance liquid chromatography (HPLC), radioimmunoassay (RIA) and immunocytochemistry. The VIP antibodies used for both RIA and immunocytochemistry showed no cross reaction with any known VIP-like peptides, including pituitary adenylate cyclase activating polypeptide (PACAP). VIP mRNA was also shown to be present in anterior pituitary gland, using reversetranscription polymerase chain reaction (RT-PCR) and primers designed from the chicken VIP cDNA sequence, and by solution hybridization RNAse protection assay.Two VIP-immunoreactive cell (VIP-ir) types were found throughout the cephalic and caudal lobes of the anterior pituitary gland. The morphological features of the VIP-ir cell types were similar to that of the folliculo-stellate cell type (FS-cell). One VIP-cell type contained the Ca 2+ binding protein S-100 protein, a specific marker of FS-cells, while the S-100 protein was not detected in the second VIP-cell type. The VIP-cells were closely associated with gonadotrophs, lactotrophs and unidentified cell types, but VIP-ir was not colocalised with LH or PRL. The VIP-cell characteristically enveloped several adjacent gonadotrophs with cytoplasmic projections, which suggests that intra-pituitary VIP may regulate the gonadotroph in a paracrine manner.VIP receptors were localised immunocytochemically, in the anterior pituitary gland and hypothalamus, using antibodies raised the peptide sequence of the human subtype-I (VIP-RI) and the subtype-II VIP receptors (VIP-RII). The VIP-RI was not present in PRL-, LH- or GH-cells, but was found exclusively in ACTH-cells. The VIP-RII was diffusely distributed through both lobes of the chicken anterior pituitary gland, but the cell type containing VIP-RII immunoreactivity was not identified.The effects of VIP and PACAP on pituitary hormone secretion were determined in vitro using cultured hemi-pituitaries. VIP and PACAP stimulated PRL secretion in a dose dependent manner. High concentrations of VIP and PACAP stimulated GH and LH secretion but did not affect ACTH secretion.In conclusion, VIP is produced in the anterior pituitary gland and occurs in a FS-cell type which is closely associated with gonadotrophs. These observations are consistent with the view that intra-pituitary VIP may act in a paracrine manner to regulate the function of gonadotrophs

Unitary evolution in Gowdy cosmology

Recent results on the non-unitary character of quantum time evolution in the family of Gowdy T**3 spacetimes bring the question of whether one should renounce in cosmology to the most sacred principle of unitary evolution. In this work we show that the answer is in the negative. We put forward a full nonperturbative canonical quantization of the polarized Gowdy T**3 model that implements the dynamics while preserving unitarity. We discuss possible implications of this result.Comment: 5 pages, no figures. V2 discussion expanded, references added. Final version to appear in PR

A unique Fock quantization for fields in non-stationary spacetimes

In curved spacetimes, the lack of criteria for the construction of a unique quantization is a fundamental problem undermining the significance of the predictions of quantum field theory. Inequivalent quantizations lead to different physics. Recently, however, some uniqueness results have been obtained for fields in non-stationary settings. In particular, for vacua that are invariant under the background symmetries, a unitary implementation of the classical evolution suffices to pick up a unique Fock quantization in the case of Klein-Gordon fields with time-dependent mass, propagating in a static spacetime whose spatial sections are three-spheres. In fact, the field equation can be reinterpreted as describing the propagation in a Friedmann-Robertson-Walker spacetime after a suitable scaling of the field by a function of time. For this class of fields, we prove here an even stronger result about the Fock quantization: the uniqueness persists when one allows for linear time-dependent transformations of the field in order to account for a scaling by background functions. In total, paying attention to the dynamics, there exists a preferred choice of quantum field, and only one $SO(4)$-invariant Fock representation for it that respects the standard probabilistic interpretation along the evolution. The result has relevant implications e.g. in cosmology.Comment: Typos correcte

Kakutani Dichotomy on Free States

Two quasi-free states on a CAR or CCR algebra are shown to generate quasi-equivalent representations unless they are disjoint.Comment: 12 page

On the Coherent State Path Integral for Linear Systems

We present a computation of the coherent state path integral for a generic linear system using ``functional methods'' (as opposed to discrete time approaches). The Gaussian phase space path integral is formally given by a determinant built from a first-order differential operator with coherent state boundary conditions. We show how this determinant can be expressed in terms of the symplectic transformation generated by the (in general, time-dependent) quadratic Hamiltonian for the system. We briefly discuss the conditions under which the coherent state path integral for a linear system actually exists. A necessary -- but not sufficient -- condition for existence of the path integral is that the symplectic transformation generated by the Hamiltonian is (unitarily) implementable on the Fock space for the system.Comment: 15 pages, plain Te

A Community Based Model of Environmental Resource Conservation and Livelihoods: Non-Governmental Organisation Supported Tšenekeng Botanical Garden in Semonkong, Lesotho.

Environmental degradation in Lesotho has resulted in decreasing arable land that has adversely affected agricultural productivity and food security. As a response to the declining food production, many people are making a living out of their environmental resources. Some people harvest the medicinal plants from the communal land for sale. As a result, some of the valuable environmental resources and particularly the medicinal plants are now depleted due to over-harvesting. As a response to protecting the depleting environmental resources, governments and Non-Governmental Organisations (NGOs) have implemented community based resources conservation projects. On the one hand, many government conservation programmes have followed an autocratic approach that imposes projects on the community. On the other hand, NGOs are complimented for including the affected communities in decision making process through different participatory methods. In this regard, this research paper assesses the contribution of local NGO’s (Serumula Development Association) community based environmental resources conservation programme, Tšenekeng Botanical Garden to environmental conservation and livelihood making

Quantum Gowdy T3T^3 model: A unitary description

The quantization of the family of linearly polarized Gowdy $T^3$ spacetimes is discussed in detail, starting with a canonical analysis in which the true degrees of freedom are described by a scalar field that satisfies a Klein-Gordon type equation in a fiducial time dependent background. A time dependent canonical transformation, which amounts to a change of the basic (scalar) field of the model, brings the system to a description in terms of a Klein-Gordon equation on a background that is now static, although subject to a time dependent potential. The system is quantized by means of a natural choice of annihilation and creation operators. The quantum time evolution is considered and shown to be unitary, allowing both the Schr\"odinger and Heisenberg pictures to be consistently constructed. This has to be contrasted with previous treatments for which time evolution failed to be implementable as a unitary transformation. Possible implications for both canonical quantum gravity and quantum field theory in curved spacetime are commented

An infinite genus mapping class group and stable cohomology

We exhibit a finitely generated group \M whose rational homology is isomorphic to the rational stable homology of the mapping class group. It is defined as a mapping class group associated to a surface \su of infinite genus, and contains all the pure mapping class groups of compact surfaces of genus $g$ with $n$ boundary components, for any $g\geq 0$ and $n>0$. We construct a representation of \M into the restricted symplectic group ${\rm Sp_{res}}({\cal H}_r)$ of the real Hilbert space generated by the homology classes of non-separating circles on \su, which generalizes the classical symplectic representation of the mapping class groups. Moreover, we show that the first universal Chern class in H^2(\M,\Z) is the pull-back of the Pressley-Segal class on the restricted linear group ${\rm GL_{res}}({\cal H})$ via the inclusion ${\rm Sp_{res}}({\cal H}_r)\subset {\rm GL_{res}}({\cal H})$.Comment: 14p., 8 figures, to appear in Commun.Math.Phy

Non-perturbative embedding of local defects in crystalline materials

We present a new variational model for computing the electronic first-order density matrix of a crystalline material in presence of a local defect. A natural way to obtain variational discretizations of this model is to expand the difference Q between the density matrix of the defective crystal and the density matrix of the perfect crystal, in a basis of precomputed maximally localized Wannier functions of the reference perfect crystal. This approach can be used within any semi-empirical or Density Functional Theory framework.Comment: 13 pages, 4 figure

Time Evolution of the External Field Problem in QED

We construct the time-evolution for the second quantized Dirac equation subject to a smooth, compactly supported, time dependent electromagnetic potential and identify the degrees of freedom involved. Earlier works on this (e.g. Ruijsenaars) observed the Shale-Stinespring condition and showed that the one-particle time-evolution can be lifted to Fock space if and only if the external field had zero magnetic components. We scrutinize the idea, observed earlier by Fierz and Scharf, that the time-evolution can be implemented between time varying Fock spaces. In order to define these Fock spaces we are led to consider classes of reference vacua and polarizations. We show that this implementation is up to a phase independent of the chosen reference vacuum or polarization and that all induced transition probabilities are well-defined and unique.Comment: 60 pages, 1 figure, revised introduction, summary of results added, typos correcte