Effects of aging on cholinergic neuromuscular transmission in isolated small intestine of ad libitum fed and calorically-restricted rats.

BACKGROUND: Age-associated losses of enteric neurons have been described. In rat ileum, myenteric neurons lost during aging have been reported to be predominantly cholinergic, and caloric restriction (CR) has been shown to protect against these losses. Cholinergic myenteric neurons include excitatory motor neurons, so the aim of this work was to determine whether neuronal loss in ad libitum (AL)-fed animals is reflected in dysfunctional cholinergic neuromuscular transmission, and if CR reduces any such dysfunction. METHODS: Effects of electrical field stimulation (EFS) and applied acetylcholine (ACh) were examined in the longitudinal muscle of isolated ileal segments from 6-month-old rats and from 13- and 24-month-old rats fed either AL or CR diets. KEY RESULTS: Contractile responses to EFS were abolished by atropine and potentiated by the acetylcholinesterase inhibitor, eserine. Frequency-response relationships were not significantly different amongst the three age-groups. Sensitivity to applied ACh, however, was three-fold lower in the oldest animals (P < 0.05). Eserine potentiated responses to ACh; there were no statistically significant differences amongst the sensitivities to ACh in its presence. No significant differences between AL- and CR-fed animals were measured, although variability was less in CR-fed than in AL-fed groups. CONCLUSIONS & INFERENCES: The cholinergic system supplying the rat ileum longitudinal muscle did not appear to be impaired in old age. Decreased sensitivity to applied ACh in old tissues may have been due to increased acetylcholinesterase activity. Caloric restriction had no significant effect on responses to EFS or applied ACh. The implications of these results are discussed.

Diadenosine tetraphosphate protects sympathetic terminals from 6-hydroxydopamine-induced degeneration in the eye.

AIMS: To examine diadenosine tetraphosphate (Ap(4)A) for its ability to protect the eye from neurodegeneration induced by subconjunctival application of 6-hydroxydopamine (6-OHDA). METHODS: Intraocular neurodegeneration of anterior structures was induced by subconjunctival injections of 6-OHDA. Animals were pre-treated with topical corneal applications of Ap(4)A or saline. RESULTS: 6-OHDA caused miosis, abnormal pupillary light reflexes, a precipitous drop in intraocular pressure and loss of VMAT2-labelled (vesicle monoamine transporter-2, a marker for sympathetic neurones) intraocular neurones. Pre-treatment with Ap(4)A prevented all of these changes from being induced by 6-OHDA, demonstrably preserving the sympathetic innervation of the ciliary processes. This neuroprotective action of Ap(4)A was not shared with the related compounds adenosine, ATP or diadenosine pentaphosphate. P2-receptor antagonists showed that the effects of Ap(4)A were mediated via a P2-receptor. CONCLUSION: Ap4A is a natural component of tears and aqueous humour, and its neuroprotective effect indicates that one of its physiological roles is to maintain neurones within the eye. Ap(4)A can prevent the degeneration of intraocular nerves, and it is suggested that this compound may provide the basis for a therapeutic intervention aimed at preventing or ameliorating the development of glaucoma associated with neurodegenerative diseases. Furthermore, subconjunctival application of 6-OHDA provides a useful model for studying diseases that cause ocular sympathetic dysautonomia.

Analysis of pancreatic polypeptide cDNA from the house musk shrew, Suncus murinus, suggests a phylogenetically closer relationship with humans than for other small laboratory animal species.

Pancreatic polypeptide was isolated and sequenced from endocrine cells of the pancreas from an insectivore, the house musk shrew, Suncus murinus. The primary sequence was APLEPAYPGD(10)NATPEQMAQY(20)AAELRKYINM(30)VTRPRYamide. This is the first polypeptide hormone to be characterised from this species and is typical of the primary sequences of pancreatic polypeptide of other animals, being a C-terminal-amidated peptide with 36 residues. Comparison with several vertebrate sequences shows that it has more in common with the human form than do the forms from common laboratory animals such as rabbits, rats, mice and guinea-pigs.

Effects of diadenosine polyphosphates on tear secretion in New Zealand white rabbits.

Extracellular diadenosine polyphosphates play important signaling functions in a number of physiological responses. Here we show that diadenosine polyphosphates are normal constituents of tear fluid and are potent stimulators of tear secretion through their interaction with P2Y receptors. Diadenosine tetraphosphate (Ap(4)A) and Ap(5)A were found in rabbit tears under basal conditions at concentrations of 2.92 and 0.58 microM, respectively. Single applications of UTP, ATP, and Ap(4)A increased tear secretion to 160 +/- 8% (n = 16) (P < 0.001), 131 +/- 6% (P < 0.05), and 162 +/- 11% (P < 0.05) of placebo values, respectively. Ap(4)A, Ap(5)A, and Ap(6)A, but not Ap(2)A and Ap(3)A, were able to stimulate tear secretion in a dose-dependent manner. Concentration-response studies produced pD(2) values of 5.56 +/- 0.03, 5.75 +/- 0.12, and 5.50 +/- 0.09 for Ap(4)A, Ap(5)A, and Ap(6)A, respectively, with Ap(4)A showing the greatest efficacy. Diadenosine polyphosphates also stimulated P2Y(1) and P2Y(2) receptors expressed in 1321N1 cells with no apparent effect on the other P2Y receptors tested. Nonselective P2 antagonists did not modify the tear secretion induced by UTP or Ap(4)A in rabbit eyes in vivo or in cloned receptors, except for a weak but significant reduction in stimulated tear secretion by reactive blue 2. These results suggest that diadenosine polyphosphates stimulate tear secretion via a P2Y receptor-mediated mechanism. Comparing the effects of diadenosine polyphosphates applied to the rabbit eye and to cloned P2Y receptors, it appears that the P2Y(2) receptor subtype is responsible for the prosecretory effects of these compounds.