Transmission to interneurons is via slow excitatory synaptic potentials mediated by P2Y(1) receptors during descending inhibition in guinea-pig ileum.

BACKGROUND: The nature of synaptic transmission at functionally distinct synapses in intestinal reflex pathways has not been fully identified. In this study, we investigated whether transmission between interneurons in the descending inhibitory pathway is mediated by a purine acting at P2Y receptors to produce slow excitatory synaptic potentials (EPSPs). METHODOLOGY/PRINCIPAL FINDINGS: Myenteric neurons from guinea-pig ileum in vitro were impaled with intracellular microelectrodes. Responses to distension 15 mm oral to the recording site, in a separately perfused stimulation chamber and to electrical stimulation of local nerve trunks were recorded. A subset of neurons, previously identified as nitric oxide synthase immunoreactive descending interneurons, responded to both stimuli with slow EPSPs that were reversibly abolished by a high concentration of PPADS (30 µM, P2 receptor antagonist). When added to the central chamber of a three chambered organ bath, PPADS concentration-dependently depressed transmission through that chamber of descending inhibitory reflexes, measured as inhibitory junction potentials in the circular muscle of the anal chamber. Reflexes evoked by distension in the central chamber were unaffected. A similar depression of transmission was seen when the specific P2Y(1) receptor antagonist MRS 2179 (10 µM) was in the central chamber. Blocking either nicotinic receptors (hexamethonium 200 µM) or 5-HT(3) receptors (granisetron 1 µM) together with P2 receptors had no greater effect than blocking P2 receptors alone. CONCLUSIONS/SIGNIFICANCE: Slow EPSPs mediated by P2Y(1) receptors, play a primary role in transmission between descending interneurons of the inhibitory reflexes in the guinea-pig ileum. This is the first demonstration for a primary role of excitatory metabotropic receptors in physiological transmission at a functionally identified synapse.

The use and assessment of ketamine-medetomidine-butorphanol combinations for field anaesthesia in wild European badgers (Meles meles).

OBJECTIVE: To evaluate the effectiveness of four ketamine-based anaesthetics in badgers using a quantitative anaesthesia assessment technique. STUDY DESIGN: Prospective randomized 'blinded' experimental trial. METHODS: The quality of induction, of anaesthesia (at 5-minute intervals) and of recovery were assessed in 93 badgers, given either one of three ketamine (K)-medetomidine (M)-butorphanol (B) combinations: group A - M K B at 20/40/80 microg kg(-1); group B - M K B at 20/40/60 microg kg(-1); and group C - M K B at 20/60/40 microg kg(-1), or ketamine (K) alone at 2 mg kg(-1) (group D). The assessor was ignorant of the combination administered. Physiological variables (heart and respiratory rates and rectal temperature) were measured at 5-minute intervals during anaesthesia. Gingival mucus membrane colour was also recorded. RESULTS: Induction to anaesthesia was most rapid with ketamine (2 mg kg(-1)) although induction quality did not differ between techniques. Ketamine used alone gave the poorest score for anaesthesia quality. Heart rate (HR) and scores for gingival mucus membrane colour were higher in animals anaesthetized with ketamine alone. Rectal temperature did not differ significantly between the techniques at any time during anaesthesia. Ketamine used alone produced the poorest quality of recovery. CONCLUSION AND CLINICAL RELEVANCE: The M-K-B combinations investigated overcame several side effects associated with ketamine anaesthesia, but at the expense of more variable induction times, lower HRs, and poorer mucus membrane coloration.

Histochemical localisation of a galactose-containing glycoconjugate expressed by sensory neurones innervating different peripheral tissues in the rat.

The plant lectin Bandeiraea simplicifolia I-isolectin B4 (BSI-B4) identifies a galactose-containing, membrane-associated glycoconjugate expressed by a discrete subpopulation of unmyelinated primary sensory neurones in the rat. We have previously suggested that BSI-B4 selectively binds to primary sensory neurones that innervate the skin. However, in that study, the tracer diamidino yellow was applied to the cut ends of peripheral nerves to identify neurones innervating particular target tissues. In this study, we have avoided axotomy by retrogradely labelling primary sensory neurones from peripheral tissues using the carbocyanine dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbacyanine perchlorate (DiI). DiI was injected into the plantar skin, gastrocnemius muscle, and pyloric region of the stomach in rats. Corresponding ganglia were sectioned, incubated in BSI-B4 conjugated to fluorescein isothiocyanate, and examined with a fluorescence microscope. DiI-labelled cells were identified by red fluorescence within the cytoplasm, whereas cells binding BSI-B4 displayed green fluorescence associated with the plasma membrane and Golgi apparatus. Quantitative analysis revealed that 36.2% of cutaneous neurones, 7.6% of muscle neurones, and 6.8% of visceral neurones expressed the BSI-B4-binding site, indicating that a small but significant proportion of small-diameter primary sensory neurones innervating muscle and viscera also express BSI-B4-binding sites.

Preliminary comparison of four anaesthetic techniques in badgers (Meles meles).

OBJECTIVE: To investigate the use of four ketamine-based anaesthetic combinations in wild badgers. STUDY DESIGN: Prospective, randomized, clinical trial. ANIMALS: Twenty-four adult badgers. MATERIALS AND METHODS: Animals were divided into four groups of six and were anaesthetized using either intramuscular (IM) ketamine alone (20 mg kg(-1)), ketamine (15 mg kg(-1) IM) and midazolam (0.4 mg kg(-1) IM), ketamine (10 mg kg(-1) IM) and midazolam (1 mg kg(-1) IM) or ketamine (5 mg kg(-1) IM) and medetomidine (80 microg kg(-1) IM) antagonized with atipamezole (0.8 mg kg(-1); IM). Features of each technique, i.e. quality of induction, maintenance and recovery, and the need for additional doses, were assessed using a simple descriptive scale. Physiological variables, i.e. rectal temperature, respiratory rate, heart rate and blood pressure, were also recorded. RESULTS: Combinations of ketamine and midazolam did not produce adequate anaesthesia. The combination of medetomidine and ketamine had few advantages over ketamine alone. CONCLUSIONS AND CLINICAL RELEVANCE: These data will contribute to a wider study attempting to refine anaesthetic techniques in badgers.

High rectal temperature indicates an increased risk of unexpected recovery in anaesthetized badgers.

OBJECTIVE: To identify factors associated with sudden early recovery (SER) from anaesthesia in badgers (Meles meles). STUDY DESIGN: Experimental trial. ANIMALS: Ninety-three adult wild badgers. METHODS: Animals were randomly assigned to receive one of four anaesthetics based on medetomidine (M) ketamine (K) and butorphanol (B) combined in different ratios: (i) MKB 20:40:80 microg kg(-1); (ii) MKB 20:40:60 microg kg(-1); (iii) MKB 20:60:40 microg kg(-1); and (iv) ketamine alone 0.2 mg kg(-1). For each animal, induction time was measured and physiological variables (heart rate, respiratory rate and rectal temperature) were recorded at 5-minute intervals during anaesthesia. Cases of SER were recorded and binary logistic regression applied to identify predictive factors. RESULTS: Fourteen animals (15%) exhibited SER. Rectal temperature was the only variable that was a significant predictor of SER. Animals showing SER had significantly higher rectal temperatures which, in contrast to other cases, did not fall during the first 10 minutes of anaesthesia, which was when most SERs occurred. CONCLUSION AND CLINICAL RELEVANCE: We recommend that (i) rectal temperature is closely monitored during wild badger anaesthesia and (ii) that animals with higher than expected temperatures are treated with additional caution.