Contribution of amino acid transmitters to epileptiform activity and reflex suppression in electrically head stunned sheep.

In sheep, administration of a combination of zolazepam and tiletamine hydrochloride resulted in a dose dependent reduction in the duration of epileptic activity induced by an electric stun applied to the head. The compound also lengthened the normal period of reflex suppression that occurs after a stun. Excitatory amino acid receptor antagonists (2-amino-7-phosphonoheptanoic and 2-amino-5-phosphonovaleric acids) also reduced the duration of epileptic activity following an electric stun. These drugs did not alter the time of pedal and ear pinch reflex suppression. Administration of bicuculline (a gamma amino-4-butyric acid [GABA] receptor antagonist) reduced the period of stun induced reflex suppression and increased seizure duration. Administration of a GABA receptor agonist, baclofen, increased the duration of reflex suppression. The results suggest that the development of epileptiform-like activity following application of an electric current to the head is dependent upon excitatory amino acid receptors. The reflex suppression that also arises following an electric stun is contributed to by the activation of GABA receptor mechanisms.     

Effect of pre-anesthetic meperidine on gastro-esophageal reflux in anesthetized dogs

Meperidine has been shown to decrease lower esophageal sphincter tone in monkeys and people, to have little effect in cats, and to physically increase it in dogs. We hypothesized that administration of meperidine to dogs before anesthesia would decrease the probability of GER during the subsequent anesthetic. In this randomized, prospective clinical trial we aimed to determine the incidence of GER in dogs undergoing elective orthopedic surgery and receiving either meperidine or morphine prior to anesthesia. Dogs were admitted to the study, if they were healthy, with no history of vomiting or dysphagia. Dogs were fasted overnight. Dogs were received either morphine (0.66 mg kg^–1 IM) or meperidine (8.8 mg kg^–1 IM) with acepromazine. Anesthesia in all dogs included thiopental and isoflurane in oxygen. To measure esophageal pH a sensor-tipped catheter was placed with the tip 5–7 cm cranial to the lower esophageal sphincter, and connected to a computer for continual data collection. Dogs were observed for vomiting after pre-medication, and the pH of any fluid running from the mouth or nose during anesthesia was measured. Gastro-esophageal reflux was defined as a decrease in esophageal pH below 4 or an increase above 7.5 for greater than 15 seconds. One-way anova was used to test significance of differences between groups in parametric variables. Fisher's Exact test was used to test significance of differences in incidence between groups. In dogs receiving meperidine the incidence of vomiting was 0, and of GER was 31% (4/13), compared to 60% (6/10) and 60% (6/10), respectively in dogs receiving morphine. In this preliminary study, the administration of pre-anesthetic meperidine was associated with a 29% reduction in the absolute risk of GER compared to morphine.     

Changes in the release of amino acid neurotransmitters in the brains of calves and sheep after head-only electrical stunning and throat cutting

In calves aged two to five months, throat cutting resulted in an increase in the concentration of the amino acid neurotransmitters glutamate and aspartate in the brain. Electrical head-only stunning by itself also increased the concentrations of these two neurotransmitters. The levels induced by stunning resulted in a seizure state characterised by epileptiform-like activity in the electroencephalograph. Combing head-only stunning with throat cutting within 10 seconds of the stun had a synergistic effect upon glutamate and aspartate, increasing their concentration by a greater amount and more quickly than either procedure on its own. An irreversible loss of brain function also occurred more quickly than after throat cutting alone. The administration of glutamate and aspartate receptor antagonists before the throat cutting lengthened the time to the loss of brain function in a dose dependent manner. Similar changes were observed in sheep but they occurred much more quickly than in cattle.     

METI-acaricide resistance in Tetranychus urticae does not confer resistance to the naphthoquinones

The naphthoquinones and the METI group of compounds act on sites associated with mitochondrial respiration, but METI-resistant strains of two-spotted spider mite from Japan and the UK exhibited no cross-resistance to the naphthoquinones. The potential for developing commercial naphthoquinones therefore remains high.     

Characterisation of Neonicotinoid and Pymetrozine Resistance in Strains of Bemisia tabaci (Hemiptera: Aleyrodidae) from China

Four strains of the Q biotype and one of the B biotype of the whitefly Bemisia tabaci collected from China were characterised for resistance to four neonicotinoid insecticides and pymetrozine. Q biotype strains showed moderate to strong resistance to imidacloprid, thiamethoxam and acetamiprid, but little or no cross-resistance to dinotefuron. Resistance to neonicotinoids was consistently associated with resistance to pymetrozine, despite the latter having a distinct (though unresolved) mode of action. The single B biotype strain proved largely susceptible to all the insecticides investigated. Resistance in the Q biotype strains was associated with over-expression of a cytochrome P450 monooxygenase gene, CYP6CM1, whose substrate specificity presumably accounts for the observed cross-resistance profiles.     

Atypical presentation of caecal perforation in two horses

This case report describes retroperitoneal and subserosal emphysema as the primary indication of a caecal perforation associated with an episode of colic. Feed contamination was not noted on repeated peritoneal fluid samples or within the peritoneal cavity at the time of surgery; however, subserosal and retroperitoneal emphysema at the base of the caecum was identified during surgical exploration, which later corresponded to retroperitoneal caecal perforation at necropsy examination.     

Gait abnormalities caused by selective anesthesia of the suprascapular nerve in horses

OBJECTIVE: To assess gait abnormalities associated with selective anesthesia of the suprascapular nerve (SSN) achieved by use of perineural catheterization and thereby determine the function of that nerve as it relates to gait in horses. ANIMALS: 3 adult horses with no preexisting clinically apparent lameness at a walk. PROCEDURE: Each horse was anesthetized; the right SSN was exposed surgically for placement of a perineural catheter to permit delivery of 1 mL of 2% mepivacaine hydrochloride. Six hours after recovery from anesthesia, each horse was videotaped while walking (50-step data acquisition period) before and after administration of mepivacaine. Videotapes were reviewed and the proportion of abnormal steps before and after selective SSN anesthesia was assessed. A step was considered abnormal if a marked amount of scapulohumeral joint instability (ie, lateral luxation of the proximal portion of the humerus) was observed during the weight-bearing phase of the stride. RESULTS: Clinically apparent gait dysfunction was detected in all 3 horses following perineural administration of the local anesthetic agent. Anesthesia of the SSN resulted in scapulohumeral joint instability as evidenced by consistent lateral excursion of the shoulder region during the weight-bearing phase of gait at a walk. The proportion of abnormal steps before and after SSN anesthesia was significantly different in all 3 horses. CONCLUSIONS AND CLINICAL RELEVANCE: These data support the role of the SSN in shoulder joint stability in horses and define SSN dysfunction as 1 mechanism by which the syndrome and gait dysfunction clinically referred to as sweeny may develop.