Interaction between metabotropic receptors and purinergic transmission in rat hippocampal slices

Determinants for further wishes for cosmetic and reconstructive interventions in 1652 patients with surgical treated carcinomas of the oral cavity

Background

The impairment of the appearance is a major problem for patients with carcinomas of the oral cavity. These patients want to recover their preoperative facial appearance. Some do not realize that this is not always possible and hence develop a desire for further cosmetic and reconstructive surgery (CRS) which often causes psychological problems.

Method

The desire of patients for CRS (N = 410; 26%) has been acquired in this DÖSAK rehab study including multiple reasons such as medical, functional, aesthetic and psychosocial aspects. They relate to the parameters of diagnosis, treatment and postoperative rehabilitation. Patients without the wish for CRS (N = 1155; 74%) served as control group. For the surgeons, knowledge of the patient’s views is relevant in the wish for CRS. Nevertheless, it has hardly been investigated for patients postoperatively to complete resection of oral cancer. In this retrospective cross-sectional study, questionnaires with 147 variables were completed during control appointments. Thirty-eight departments of Oral and Maxillofacial Surgery took part, and 1652 German patients at least 6 months after complete cancer resection answered the questions. Additionally, a physician’s questionnaire (N = 1489) was available. Statistical analysis was performed with SPSS vers. 22.

Results

The patient’s assessment of their appearance and scarring are the most important criteria resulting in wishes for CRS. Furthermore, functional limitations such as eating/swallowing, pain of the facial muscles, numb regions in the operating field, dealing with the social environment, return to work, tumour size and location, removal and reconstruction are closely related.

Conclusion

The wish for CRS depends on diverse functional psychosocial and psychological parameters. Hence, it has to be issued during conversation to improve rehabilitation. A decision on the medical treatment can be of greater satisfaction if the surgeon knows the patients’ needs and is able to compare them with the medical capabilities. The informed consent between doctor and patient in regard to these findings is necessary.

Interactions between adenosine and metabotropic glutamate receptors in the rat hippocampal slice

1. We have examined excitatory postsynaptic potentials and paired-pulse interactions in rat hippocampal slices to obtain more information about the site and mechanism of interactions between metabotropic glutamate receptors and adenosine receptors. 2. The results show that the suppression of adenosine sensitivity is explained by a selectively reduced responsiveness to A(1) receptor stimulation, and does not involve any facilitation of A(2A) adenosine receptors, since it can be obtained in the absence of endogenous adenosine and is not prevented by the A(2A) receptor blocker ZM241385. 3. The glutamate receptors involved are of the group I class since the suppression of adenosine sensitivity is produced by ACPD and the group I selective compound DHPG. Furthermore, the effects of DHPG could be prevented by LY367385, a selective antagonist at the mGlu(1a) subtype of group I receptors. The selective antagonist at mGlu(5) receptors, SIB1893, did not prevent the suppression of adenosine sensitivity by DHPG. Blockade of the DHPG/adenosine interaction was also obtained by superfusion with the protein kinasae C inhibitor chelerythrine. 4. Since the suppression of adenosine responses by metabotropic receptor agonists was seen in the paired-pulse paradigm, we conclude that the observed interactions occur at the level of the presynaptic terminals. 5. The interaction with adenosine receptors is not specific, but applies also to a suppression of responses mediated by the GABA(B) receptor agonist baclofen. 6. We conclude that activation of the mGlu1a subtype of receptor can suppress responses mediated via adenosine A1 receptors, probably by activating protein kinase C. Since the changes induced by metabotropic glutamate receptor agonists last for at least 60 min, the data also imply that these interactions could play an important role in changes of synaptic function long after even transient increases of glutamate release in the CNS.

Trophic effects of purines in neurons and glial cells

In addition to their well known roles within cells, purine nucleotides such as adenosine 5' triphosphate (ATP) and guanosine 5' triphosphate (GTP), nucleosides such as adenosine and guanosine and bases, such as adenine and guanine and their metabolic products xanthine and hypoxanthine are released into the extracellular space where they act as intercellular signaling molecules. In the nervous system they mediate both immediate effects, such as neurotransmission, and trophic effects which induce changes in cell metabolism, structure and function and therefore have a longer time course. Some trophic effects of purines are mediated via purinergic cell surface receptors, whereas others require uptake of purines by the target cells. Purine nucleosides and nucleotides, especially guanosine, ATP and GTP stimulate incorporation of [3H]thymidine into DNA of astrocytes and microglia and concomitant mitosis in vitro. High concentrations of adenosine also induce apoptosis, through both activation of cell-surface A3 receptors and through a mechanism requiring uptake into the cells. Extracellular purines also stimulate the synthesis and release of protein trophic factors by astrocytes, including bFGF (basic fibroblast growth factor), nerve growth factor (NGF), neurotrophin-3, ciliary neurotrophic factor and S-100beta protein. In vivo infusion into brain of adenosine analogs stimulates reactive gliosis. Purine nucleosides and nucleotides also stimulate the differentiation and process outgrowth from various neurons including primary cultures of hippocampal neurons and pheochromocytoma cells. A tonic release of ATP from neurons, its hydrolysis by ecto-nucleotidases and subsequent re-uptake by axons appears crucial for normal axonal growth. Guanosine and GTP, through apparently different mechanisms, are also potent stimulators of axonal growth in vitro. In vivo the extracellular concentration of purines depends on a balance between the release of purines from cells and their re-uptake and extracellular metabolism. Purine nucleosides and nucleotides are released from neurons by exocytosis and from both neurons and glia by non-exocytotic mechanisms. Nucleosides are principally released through the equilibratory nucleoside transmembrane transporters whereas nucleotides may be transported through the ATP binding cassette family of proteins, including the multidrug resistance protein. The extracellular purine nucleotides are rapidly metabolized by ectonucleotidases. Adenosine is deaminated by adenosine deaminase (ADA) and guanosine is converted to guanine and deaminated by guanase. Nucleosides are also removed from the extracellular space into neurons and glia by transporter systems. Large quantities of purines, particularly guanosine and, to a lesser extent adenosine, are released extracellularly following ischemia or trauma. Thus purines are likely to exert trophic effects in vivo following trauma. The extracellular purine nucleotide GTP enhances the tonic release of adenine nucleotides, whereas the nucleoside guanosine stimulates tonic release of adenosine and its metabolic products. The trophic effects of guanosine and GTP may depend on this process. Guanosine is likely to be an important trophic effector in vivo because high concentrations remain extracellularly for up to a week after focal brain injury. Purine derivatives are now in clinical trials in humans as memory-enhancing agents in Alzheimer's disease. Two of these, propentofylline and AIT-082, are trophic effectors in animals, increasing production of neurotrophic factors in brain and spinal cord. Likely more clinical uses for purine derivatives will be found; purines interact at the level of signal-transduction pathways with other transmitters, for example, glutamate. They can beneficially modify the actions of these other transmitters.

Acute heat stress induces edema and nitric oxide synthase upregulation and down-regulates mRNA levels of the NMDAR1, NMDAR2A and NMDAR2B subunits in the rat hippocampus

The influence of heat stress on constitutive isoform of neuronal nitric oxide synthase (cNOS) and NMDA receptor gene expression in hippocampus was examined in a rat model. Subjection of animals to 4 h heat stress at 38 degrees C resulted in a marked upregulation of cNOS in the hippocampus accompanied with a marked general expansion and edematous cell changes. On the other hand NMDA receptor messenger RNA encoding NMDAR1, NMDAR2A and NMDAR2B subunits showed a marked downregulation in the hippocampus of heat stressed rats compared to the controls. Our results show that upregulation of cNOS is instrumental in heat stress associated edema and cell injury. Furthermore, an increased production of NO as evident with upregulation of cNOS appears to be a key factor in the downregulation of NMDA receptor gene expression in heat stress.

Immortalized hypothalamic neurons express metabotropic glutamate receptors positively coupled to cyclic AMP formation

We have characterized the expression pattern and pharmacological profile of activation of metabotropic glutamate receptors (mGluRs) in immortalized, gonadotropin releasing hormone (GnRH)-secreting GT1-7 cells, which represent a homogeneous cellular population of hypothalamic origin. These cells are known to respond to the mGluR agonist (1S,3R)-cyclopentanedicarboxylic acid (1S,3R-ACPD) with increased GnRH release. To establish which specific mGluR subtypes are expressed by GT1-7 cells, we used polyclonal antibodies raised against non-conserved regions of the carboxy-terminal domains of individual subtypes. The selectivity of these antibodies was tested in HEK 293 cells transiently transfected with each mGluR subtype. GT1-7 cells stained positively for the subtypes mGluR1a, -1b and -5 (belonging to group I mGluR2/3 (group II) and mGluR7 (group III). Agonists of group I mGluRs, including 1S,3R-ACPD, activated phosphoinositide hydrolysis in GT1-7 cells. This effect, however, was manifested only when cell density was low, and it disappeared when cells reached confluence. Stimulation of phosphoinositide hydrolysis could not therefore have been related to hormone secretion because 1S,3R-ACPD effectively released GnRH in confluent cultures. We then focused on group II and III mGluRs, which in transfected cells are negatively linked to adenylate cyclase activity. Unexpectedly, however, agonist which preferentially activate group II and III mGluRs increased both basal and forskolin-stimulated cAMP accumulation in GT1-7 cells. Stimulation of cAMP accumulation by mGluR agonists was not prevented by enzymatic depletion of endogenous adenosine, but was obliterated when cells were incubated with agonists of receptors positively coupled to adenylate cyclase, such as beta-adrenergic and prostaglandin E2 receptors. These results suggest that GT1-7 cells express a novel mGluR subtype positively coupled to adenylate cyclase, which shares the same transduction pathway of other classical receptors coupled with a Gs-type of GTP-binding protein.

Differentiation of group 2 and group 3 metabotropic glutamate receptor cAMP responses in the rat hippocampus

The effects of group 2- versus group 3-selective metabotropic glutamate (mGlu) receptor agonists were examined against forskolin (10 microM)-, vasoactive intestinal peptide (VIP; 1 microM)- and 5'-N-ethylcarboxamidoadenosine (NECA; 10 microM)-stimulated cAMP accumulations in adult rat hippocampal slices (in the presence of adenosine deaminase). Group 2 mGlu receptor-selective ((1S,3R)-1-aminocyclopentane-1, 3-dicarboxylic acid (1S,3R-ACPD) and (2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine (L-CCG I)) and group 3 mGlu receptor-selective (L-2-amino-4-phosphonobutyric acid (L-AP4) and L-serine-O-phosphate) agonists greatly inhibited forskolin-stimulated cAMP formation ( > 80% at maximally effective concentrations). In contrast, stimulation of cAMP by VIP or NECA was inhibited by group 3, but not by group 2, mGlu receptor agonists. In fact, group 2 mGlu receptor agonists greatly potentiated cAMP accumulation evoked by NECA. Both the inhibitory effects of 1S,3R-ACPD on forskolin-stimulated cAMP and the potentiating effects on NECA-stimulated cAMP accumulation were reversed by the competitive group 1/2 mGlu receptor antagonist (+)-alpha-methyl-4-carboxyphenylglycine ((+)-MCPG). However, (+)-MCPG had no effects on L-AP4 inhibition of cAMP. Thus, the effects of group 2 versus group 3 mGlu receptor agonists on cAMP coupling can be pharmacologically as well as functionally differentiated in the rat hippocampus.