Visualization of neuropeptide-binding sites on individual telencephalic neurons of the rat

Preparation and high-resolution microscopy of gold cluster labeled nucleic acid conjugates and nanodevices

Nanogold and undecagold are covalently linked gold cluster labels which enable the identification and localization of biological components with molecular precision and resolution. They can be prepared with different reactivities, which means they can be conjugated to a wide variety of molecules, including nucleic acids, at specific, unique sites. The location of these sites can be synthetically programmed in order to preserve the binding affinity of the conjugate and impart novel characteristics and useful functionality. Methods for the conjugation of undecagold and Nanogold to DNA and RNA are discussed, and applications of labeled conjugates to the high-resolution microscopic identification of binding sites and characterization of biological macromolecular assemblies are described. In addition to providing insights into their molecular structure and function, high-resolution microscopic methods also show how Nanogold and undecagold conjugates can be synthetically assembled, or self-assemble, into supramolecular materials to which the gold cluster labels impart useful functionality.

Labelling of peptides with 1.4-nm gold particles to demonstrate their binding sites in the rat spinal cord

Recently we presented a method to label the neuropeptide substance P with a 1.4-nm gold particle covalently bound at the N-terminus that can be used for demonstrating its binding sites in histological sections. In this study we examined whether the peptides neuropeptide Y, somatostatin, calcitonin gene-related peptide and bradykinin can be labelled in the same way. Polyacrylamide gel electrophoresis revealed a reduction in mobility for peptide-gold conjugates over gold particles alone consistent with peptide binding. In cryostat sections of the rat lumbar spinal cord, the peptides showed a distinct binding pattern in the grey matter corresponding to data of studies using autoradiographic methods. Therefore, we conclude that this simple and fast method can be used for labelling peptides in general to demonstrate their binding sites in histological sections, provided the peptide binds by its C-terminus.

Astrocytic neurotransmitter receptors in situ and in vivo

In the brain, astrocytes are associated intimately with neurons and surround synapses. Due to their close proximity to synaptic clefts, astrocytes are in a prime location for receiving synaptic information from released neurotransmitters. Cultured astrocytes express a wide range of neurotransmitter receptors, but do astrocytes in vivo also express neurotransmitter receptors and, if so, are the receptors activated by synaptically released neurotransmitters? In recent years, considerable efforts has gone into addressing these issues. The experimental results of this effort have been compiled and are presented in this review. Although there are many different receptors which have not been identified on astrocytes in situ, it is clear that astrocytes in situ express a number of different receptors. There is evidence of glutamatergic, GABAergic, adrenergic, purinergic, serotonergic, muscarinic, and peptidergic receptors on protoplasmic, fibrous, or specialized (Bergmann glia, pituicytes, Müller glia) astrocytes in situ and in vivo. These receptors are functionally coupled to changes in membrane potential or to intracellular signaling pathways such as activation of phospholipase C or adenylate cyclase. The expression of neurotransmitter receptors by astrocytes in situ exhibits regional and intraregional heterogeneity and changes during development and in response to injury. There is also evidence that receptors on astrocytes in situ can be activated by neurotransmitter(s) released from synaptic terminals. Given the evidence of extra-synaptic signaling and the expression of neurotransmitter receptors by astrocytes in situ, direct communication between neurons and astrocytes via neurotransmitters could be a widespread form of communication in the brain which may affect many different aspects of brain function, such as glutamate uptake and the modulation of extracellular space.

Bradykinin receptors in cultured rat dorsal root ganglion cells: influence of length of time in culture

The endogenous nonapeptide bradykinin is a powerful substance which activates nociceptors, resulting in the sensation of pain in man. We used a newly developed non-radioactive method to detect bradykinin binding sites in isolated dorsal root ganglion cells with gold-labelled bradykinin. In a subpopulation of cells, gold-labelled bradykinin was bound in different quantities. The proportion of somata with bradykinin binding markedly depended on the length of time in culture. After 0.75 days, bradykinin was bound to 43% of somata. This proportion increased to 85% after 1.75 days and then decreased to 27% after 5.75 days. Bradykinin was bound to cells of all sizes, ranging from 40 to 2000 microns2 with a maximum of 200-300 microns2. In some cells, binding was also seen along the processes. No correlation was found between the soma size and the density of bradykinin binding. Blocking the bradykinin binding at the B1 receptor with (Des-Arg10)-Lys-bradykinin and at the B2 receptor with D-Arg(Hyp3-Thi5.8-D-Phe7)-bradykinin, respectively, revealed that in 0.75-day-old cultures no or only a very small amount of B1 receptors are present. In 1.75-day-old cultures, the marked increase in the proportion of cells with positive bradykinin binding is due to a de novo expression of the B1 receptor subtype and an up-regulation of the B2 receptor subtype. The selective or combined addition of specific B1 and B2 receptor ligands revealed that both receptor subtypes are co-localized. These data show that cultured sensory neurons express not only B2, but during a short period of time in culture also B1 receptors. The data allow us to hypothesize that a transient increase in bradykinin receptor expression might be caused by cell injury due to disruption of the axon. The injury-induced up-regulation of the receptor in vivo could cause physiological reactions.

High sensitivity of the in vivo detection of somatostatin receptors by 111indium (DTPA-octreotide)-scintigraphy in meningioma patients

The recent availability of isotope-labelled somatostatin analogues has allowed one to detect somatostatin receptors in normal tissue as well as in endocrine or non-endocrine cranial tumours. The purpose of the present study was to establish the value of somatostatin receptor scintigraphy using an 111Indium-labelled somatostatin analogue, octreotide, in the diagnostic work-up of meningioma patients. Twenty-two patients (16 women, 6 men, aged from 19-70 years) with newly diagnosed, residual or recurrent cranial meningiomas were examined. 111Indium-labelled DTPA-octreotide was injected i.v.. Planar and tomographic images were obtained with a gamma camera 4-6, and 24 hours after injection. In all of the meningiomas studied a high density of somatostatin receptors was detected by scintigraphy. No false negative test result was found. Due to this, a 100% predictive value of a negative test was calculated. However, when the tumours were taken in culture differing staining intensity could be seen in the light- and electron microscopic level even on individual cells of a single culture when silver intensified somatostatin-gold was used as ligand. We conclude, that in vivo somatostatin receptor scintigraphy may aid in the pre-operative differential diagnosis of skull base tumours.

111Indium (DTPA-octreotide) scintigraphy in patients with cerebral gliomas

Somatostatin receptors (SR) have been identified in vitro in normal brain tissue, in neuro-endocrine tumours and in cerebral gliomas WHO grade 1 or 2 by autoradiography or using somatostatin-gold conjugates. In vivo, SR detection has become possible by scintigraphy applying the somatostatin analogue octreotide, radio-labelled with 111Indium. It was supposed that expression of SR in cerebral gliomas corresponds to low grade tumour malignancy and that, in vivo, somatostatin receptor scintigraphy (SRS) could refine and improve the WHO grading system for cerebral gliomas. Nineteen patients with cerebral gliomas (grade 2: n = 8, grade 3: n = 3, grade 4: n = 8) were examined with 111In (DTPA-octreotide) to evaluate, whether SRS could improve the pre-operative estimation of tumour biology and the postoperative management. The results of SRS were related with the histological findings and with the in vitro demonstration of somatostatin-binding sites on cultured tumour cells incubated with a somatostatin-gold conjugate. In vivo, none of the patients with glioma grade 2 showed enhanced tracer uptake in the SRS, whereas in vitro SR were detected in cultured tumour tissue in 5 out of 5 cases. Every patient with glioma grade 3 or 4 demonstrated a high focal uptake of 111In (DTPA-octreotide), as shown by SRS. Three patients with glioma grade 4, additionally examined with 99mTc-DTPA, showed an increased tracer uptake within the tumour area when compared with results of SRS.(ABSTRACT TRUNCATED AT 250 WORDS)