Recently, five members of the somatostatin receptor family have been cloned. However, little is known about their cellular and subcellular localization in the central nervous system. Using specific ...anti-peptide antisera, we observed somatostatin receptor 3-like immunoreactivity in many brain regions, including the cerebral cortex, hippocampus, hypothalamus, amygdala and cerebellum. In all of these regions (except for the cerebellar cortex), somatostatin receptor 3-like immunoreactivity was selectively targeted to 4–8-
μm-long rod-shaped profiles which did not co-localize with axonal or dendritic markers. One immunoreactive profile was always associated with one neuronal cell body. This staining pattern was resistant to colchicine treatment and showed a closely overlapping distribution with somatostatin receptor 3 messenger RNA, suggesting that the receptor protein is not transported over long distances. Electron microscopic analysis revealed that somatostatin receptor 3-like immunoreactivity is localized to the plasma membrane of neuronal cilia which extended into an intercellular pocket and showed a 9+0 filament pattern in their basal body and proximal segments.
Thus, somatostatin receptor 3 demonstrates a unique example of a G-protein-coupled receptor not localized to “classical” pre- or postsynaptic sites, but selectively targeted to neuronal cilia. The presence of the somatostatin receptor 3 receptor on neuronal cilia suggests that these presumably non-motile cilia may not merely represent developmental remnants, but rather function as chemical sensors of the immediate milieu.
Background and aims: Recently, novel somatostatin receptor (sstr) subtype specific ligand analogues have been developed for medical treatment of neuroendocrine tumours expressing different sstrs ...(sstr1–5). At present, individual expression patterns of sstr subtypes are based on methods such as in situ hybridisation and polymerase chain reaction at the transcriptional level. Therefore, we generated subtype specific antibodies against sstr1, 2A, 3, and 5 and analysed their presence, cellular localisation, distribution, and expression pattern in 33 gastrinomas, 36 insulinomas, and 35 tumours associated with a carcinoid syndrome by immunohistochemistry at the translational level. Methods: Western blotting experiments were performed in the normal human pancreas used as a reference organ and in tumour tissues; at the cellular level, sstrs were localised by immunohistochemistry in tissue paraffin sections. Results: In western blot analyses, the antibodies identified the respective receptors in their correct molecular range in extracts of the pancreas and neuroendocrine tumours. Using immunohistochemistry and immunofluorescence, the antibodies specifically detected the receptors in islet cells of the normal pancreas. Immunohistochemistry in the tumours revealed that all investigated sstr subtypes were highly expressed in the different tumour types. The frequency and expression pattern of the individual sstr subtypes varied considerably not only between the different tumour types but also in each patient. Conclusions: We conclude that immunohistochemistry with subtype specific antibodies can be used in clinical routine work to analyse sstr expression patterns for each patient before treatment and to facilitate well directed individual medical therapy by administering subtype specific somatostatin analogues.
People with a genetic predisposition for substance abuse have defects in genes for the opioid peptides and receptors. A high number of polymorphisms have been detected in the μ-opioid receptor, some ...of which result in pharmacological alterations. The opioid peptide proopiomelanocortin proved extraordinarily rich in mutations that often lead to severe phenotypical consequences. Prodynorphin displays a polymorphic regulation of transcription. Variants of the μ- and the δ-opioid receptor showed positive associations with opiate and/or alcohol addiction in some studies. However, these associations were weak, indicating a small contribution of the opioid system to these disorders.
The potential neuroleptic-like effect of ampullosporin A, a new peptaibol, isolated from the fungus
Sepedonium ampullosporum HKI-0053, was characterized using specific behavioural models and methods.
...Ampullosporin A (amp) disrupted the retrieval of a well-trained conditioned reaction and normalized the behavioural effects of subchronic ketamine treatment in the social interaction test in a dose which showed only inconsiderable side effects. The experiments demonstrated that the substance did not antagonize the apomorphine (apo) induced hyperactivity. On the other hand, the locomotor stimulation induced by the NMDA receptor antagonist MK-801 was nearly completely suppressed by ampullosporin A, supposing interactions with the glutamatergic system. Binding studies demonstrated no interaction with dopaminergic D
1 and D
2 receptors. However, amp can alter the activity of glutamate receptors.
The results resemble characteristics of an atypical neuroleptic drug. But further experiments are necessary to validate the suggested neuroleptic-like activity.
The influence of opioid antagonists and of morphine on rat hippocampal slices in a model of reversible hypoxia/hypoglycemia was investigated by assessment of evoked field potentials (population spike ...amplitude). In control slices, a brief hypoxia/hypoglycemia led to a loss of field potentials followed by an impaired recovery (40–50% of baseline) during reperfusion. In contrast, restoration was significantly improved when the opioid receptor antagonists funaltrexamine (μ) or naltrindole (δ) were administered prior to and during hypoxia/hypoglycemia. In addition, recovery was improved in brain slices derived from μ-opioid receptor-deficient mice as compared to wild-type mice, indicating a deleterious role of endogenous opioids in hypoxia/hypoglycemia.
Exogenous opiate exposure with morphine (0.1, 1.0, 10
μM) prior to hypoxia/hypoglycemia caused a slight concentration dependent increase of evoked field potentials. When morphine exposure was terminated after 1
h and immediately followed by hypoxia/hypoglycemia, an impaired recovery of population spike amplitude was obtained, dependent on morphine concentration during preincubation. These results demonstrate that morphine aggravates neurotoxic effects of hypoxia/hypoglycemia.
Conversely, when onset of hypoxia/hypoglycemia was delayed for 3
h after morphine termination, a significantly improved recovery was observed. Similarly, in vivo administration of morphine 12
h prior to slice preparation resulted in a dose dependent improved recovery of field potentials after hypoxia/hypoglycemia. These results provide evidence that preconditioning with morphine is able to induce neuroprotective effects.
Immunohistochemistry for delta-opioid receptor (DOR) was performed on the rat cranial sensory ganglia. The immunoreactivity was detected in 16%, 19% and 11% of neurons in the trigeminal, jugular and ...petrosal ganglia, respectively. The nodose ganglion was devoid of such neurons. DOR-immunoreactive (IR) neurons were mostly small to medium-sized (trigeminal, range = 62–851 μm
2, mean ± SD = 359 ± 175 μm
2; jugular, range = 120–854 μm
2, mean ± SD = 409 ± 196 μm
2; petrosal, range = 167–1146 μm
2, mean ± SD = 423 ± 233 μm
2). Double immunofluorescence method revealed that all DOR-IR neurons were also immunoreactive for calcitonin gene-related peptide. The cutaneous and mucosal epithelia in the oro-facial region, tooth pulp, taste bud and carotid body were innervated by DOR-IR nerve fibers. In the brainstem, IR nerve terminals were located in the superficial medullary dorsal horn and dorsomedial part of the subnucleus oralis as well as the solitary tract nucleus. The present study suggests that DOR-IR neurons may be associated with nociceptive and/or chemoreceptive function in the cranial sensory ganglia.
Immunohistochemistry for the somatostatin sst2A receptor was performed on the rat trigeminal ganglion to know its function in the trigeminal nervous system. The immunoreactivity was detected in 9.4% ...of primary sensory neurons in the ganglion. These neurons were small to medium-sized (range=106.5–1123.2 μm
2; mean±S.D.=506.3±213.2 μm
2) and predominantly located in the rostromedial part of the ophthalmo-maxillary division. They were also immunoreactive for calcitonin gene-related peptide and the vanilloid receptor subtype 1. In addition, 13.7% of trigeminal neurons which were retrogradely traced with fluorogold from the nasal mucosa exhibited sst2A receptor-immmunoreactivity. Trigeminal neurons which innervated the facial skin and tooth pulp were devoid of the immunoreactivity. In the brainstem trigeminal sensory nuclear complex, both the neuronal cell body and the neuropil exhibited sst2A receptor-immunoreactivity in the superficial medullary dorsal horn.
The present study indicates that sst2A receptor-immunoreactive trigeminal nociceptors innervate the nasal mucosa. They may project to the superficial laminae of the medullary dorsal horn.
Disruption of latent inhibition has been proposed as a possible model of cognitive abnormalities that underlie positive symptoms of a schizophrenia. We tested neonatal hippocampal lesioned rats in a ...latent inhibition paradigm. Lesions of the ventral hippocampus were induced by bilateral injections of ibotenic acid in 7 days old rats. The behavior of lesioned rats was tested postpubertally. We found a hyperresponsiveness to dopaminergic stimulation by apomorphine in locomotion tests. Latent inhibition was tested using the acquisition of a conditioned reaction in a two-way shuttle box. Sham operated control animals showed after preexposure of the to-be-conditioned stimulus (combined tone and light stimulus) a low acquisition. Ibotenic acid lesioned animals learned the conditioned reaction with and without preexposure in the same way, indicating disturbed latent inhibition. These results demonstrate disturbances in early postnatal hippocampal lesioned rats comparable with those seen in schizophrenic patients, thus further validating this procedure as a useful animal model of some aspects of schizophrenia.
We have recently shown that the cytoplasmic tail of the rat mu-opioid receptor undergoes alternative splicing giving rise to two isoforms, rMOR1 and rMOR1B. These isoforms exhibit similar ...pharmacological profiles, however, differ in agonist-induced desensitization of coupling to adenylate cyclase. In the present study, we have raised polyclonal antibodies that specifically detect either rMOR1 or rMOR1B and used these antisera for immunocytochemical localization of the receptor proteins in the rat central nervous system. Prominent MOR1B-like immunoreactivity was found in the external plexiform layer of the main olfactory bulb localized to a dense plexus of dendrites mostly originating from mitral cells and extending into the glomerular layer. MOR1-like immunoreactivity was restricted to the perikarya of mitral cells and to distinct juxtaglomerular cells as well as their processes. While MOR1-, DOR1- and KOR1-like immunoreactivity was absent from the external plexiform layer, high densities of opioid peptides were found in this layer suggesting that MOR1B may be a targeted receptor of these peptides. MOR1-like immunoreactivity was observed in many pain-controlling brain areas including the spinal cord dorsal horn, sensory trigeminal complex, raphe nuclei and periaqueductal gray while MOR1B-like immunoreactivity was not detectable in these regions.
Taken together, we provide evidence that the mu receptor isoforms, MOR1 and MOR1B, exhibit a strikingly different distribution in that MOR1 appears to be the major isoform widely distributed throughout the central nervous system and MOR1B being predominantly localized to the olfactory bulb.
Two allelic variants of the delta opioid receptor gene, distinguished by a single base exchange T to C in codon 307 of the translated region, were detected in humans. The amino acid sequence was ...thereby not changed. The resulting C and T alleles combined to give the three genotypes CC, CT and TT. Allele C was more frequent in a sample of 103 German Caucasian heroin addicts (53.4%) than in a control group (39.1%, n = 115). The proportion of CC homozygotes was much greater among the drug-dependent subjects (26.2%) than in controls (9.6%). Although the reasons for this association remain to be explained, our results argue for a participation of the delta type of opioid receptors in the pathophysiology of heroin dependence.
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