Effects of the autonomic system on insulin release in response to exogenous glucose in weaned lambs

Trapped fractional charges at bulk defects in topological insulators

Topological crystalline insulators (TCIs) can exhibit unusual, quantized electric phenomena such as fractional electric polarization and boundary-localized fractional charge^1-6. This quantized fractional charge is the generic observable for identification of TCIs that lack clear spectral features^5-7, including ones with higher-order topology^8-11. It has been predicted that fractional charges can also manifest where crystallographic defects disrupt the lattice structure of TCIs, potentially providing a bulk probe of crystalline topology^10,12-14. However, this capability has not yet been confirmed in experiments, given that measurements of charge distributions in TCIs have not been accessible until recently¹¹. Here we experimentally demonstrate that disclination defects can robustly trap fractional charges in TCI metamaterials, and show that this trapped charge can indicate non-trivial, higher-order crystalline topology even in the absence of any spectral signatures. Furthermore, we uncover a connection between the trapped charge and the existence of topological bound states localized at these defects. We test the robustness of these topological features when the protective crystalline symmetry is broken, and find that a single robust bound state can be localized at each disclination alongside the fractional charge. Our results conclusively show that disclination defects in TCIs can strongly trap fractional charges as well as topological bound states, and demonstrate the primacy of fractional charge as a probe of crystalline topology.

Pancreatic neuroendocrine responses to butyrate in conscious sheep

The role of the autonomic innervation in the control of pancreatic endocrine responses to I.V. infusions of butyrate (0.02 mmol kg-1 min-1 for 10 min) has been investigated in conscious 4-6 month old weaned lambs. Intravenous butyrate produced a small rise in mean arterial plasma pancreatic glucagon concentration which was unlikely to have had any physiological effect and produced no consistent or statistically significant changes in mean plasma pancreatic polypeptide concentration in any of the groups studied. In contrast, butyrate produced an abrupt and substantial rise in mean plasma insulin concentration, which rose to a peak incremental value of about 300 pmol l-1 in normal control lambs. This response was unaffected by pre-treatment with either phentolamine or propranolol alone, but was significantly reduced by simultaneous administration of these drugs, as it was either by pre-treatment with atropine or prior section of the splanchnic nerves. The rise in mean plasma insulin concentration was inhibited most effectively by combined treatment with propranolol, phentolamine and atropine, which was significantly more effective than administration of atropine to lambs with cut splanchnic nerves (P less than 0.01). It is concluded that both divisions of the autonomic nervous system are likely to be involved in mediating the release of insulin from the pancreas, in response to butyrate, in this species under these experimental conditions and also in the resting state.

The role of the sympathetic system in the control of insulin release in response to hyperglycaemia in conscious calves

The effects of the adrenoceptor blocking agents, phentolamine and propranolol, on the release of pancreatic glucagon and insulin in response to exogenous glucose have been investigated in conscious 2--6-week-old calves. There were no significant differences between the changes in mean plasma glucagon or insulin concentration, which occurred in response to hyperglycaemia, in calves pre-treated with both propranolol and phentolamine, phentolamine alone and normal calves. However, the rise in mean plasma insulin concentration was effectively abolished by pre-treatment with propranolol alone and there was a small but significant fall in mean plasma glucagon concentration which was not observed in any of the other groups. The results are discussed in relation to previous studies of the role of the autonomic innervation to the endocrine pancreas in the control of insulin release during hyperglycaemia in conscious calves and weaned lambs.