μL Normal Saline Research Articles

The Effectiveness of Hering’s Nerve Stimulation in Controlling Penicillin-Induced Seizures in the Rat Is Dependent on the Amygdala

Objective: This study tests the hypothesis that the ability of Hering’s nerve stimulation (HNS) to blunt seizure activity is dependent on the availability of dopamine in the amygdala. Methods: In 10 rats, Hering’s nerve (HN) on the right side was isolated and placed on an electrode and penicillin was locally placed on each rat’s left frontoparietal region to induce seizures. After the initiation of seizures, HN was stimulated. After the recurrence of seizure activity, the left basolateral amygdala was injected with 1.0 µl of normal saline, dopamine, haloperidol or 1% lidocaine in sequential tests. HN was stimulated after each injection and the latency and amplitude of the seizure activity were assessed. Results: Focal cortical penicillin induced seizures that resulted in tonic-clonic movement of the limbs and face that lasted 35–45 min. Tonic-clonic movements of the limbs and face of similar latency and amplitude were induced by repeated reapplication of penicillin in untreated rats. HNS decreased seizure activity, but infusion of haloperidol or lidocaine into the basolateral amygdala blocked this antiseizure effect of HNS. In contrast, infusion of saline or dopamine had no effect on the ability of HNS to blunt seizure activity. None of the amygdala injections altered the latency or amplitude of seizure activity. Conclusion: These results demonstrate that the ability of HNS to blunt seizure activity in the rat is dependent on an intact dopamine system in the basolateral amygdala. These data will hopefully be useful in furthering our understanding of the circuitry that allows peripheral nerve stimulation to alter seizure activity.

Acute changes in cochlear potentials due to cisplatin

The purpose of this study was to investigate how the hair cells and stria vascularis are affected at the onset of cisplatin ototoxicity. The effects on the endocochlear potential (EP) and the cochlear microphonics (CM) were observed simultaneously in two groups of adult chinchillas receiving as follows: (1) 5 μl of cisplatin (1 mg/ml) in normal saline, and (2) 5 μl of normal saline on the round window. The EP and the CM were recorded for 12–14 h after cisplatin application, and morphological changes were assessed using scanning electron microscopy. Both the EP and the CM amplitude demonstrated a profound reduction, and a very strong correlation was observed between these two values during this time period. Although the reduction of the EP and the CM was observed by 12–14 h, only very slight degeneration of outer hair cells was seen at that time. These data suggested that a reduction of the EP which was caused by the alteration of the stria vascularis might be primarily responsible for very early changes in cochlear function after topical cisplatin application, while later changes were the direct result of hair cell damage.

Does Thoracic Epidural Anesthesia Affect Gut Mucosal Blood Flow in Rats?

Does Thoracic Epidural Anesthesia Affect Gut Mucosal Blood Flow in Rats? Sielenkämper et al.(page 844)Thoracic epidural anesthesia has been shown to attenuate surgery-related injury to the gastrointestinal system, possibly by preventing a decrease in gastric intramucosal pH, a surrogate marker for adequate intestinal perfusion. After equipping 19 rats with epidural catheters, Sielenkamper et al. randomized the animals to receive epidural infusion of either 20 μl bupivacaine, 0.4%, or normal saline. Videomicroscopy of the ileal mucosa was performed before and after epidural infusion, and the images captured for off-line analysis of microvascular blood flow.Epidural bupivacaine infusion induced a complete block of hind limb motility in conscious rats in less than 2 min. In all animals, motility was restored within 18–22 min after infusion. During intravital microscopy, the epidural infusion of bupivacaine in anesthetized rats resulted in a decrease in mean arterial pressure (MAP) from 108 ± 9 to 62 ± 10 mmHg within 60 s. Video recordings to assess effects of epidural bupivacaine began after hemodynamics stabilized (approximately 1–4 min).Epidural bupivacaine increased erythrocyte velocity (VRBC) in terminal arterioles. The total intercapillary area size (ICATOT) was unchanged, but for the group receiving thoracic epidural anesthesia, there was indication of a possible decrease (stop and go) blood flow in the villus microcirculation. The observed increase in gut mucosal blood flow, said the authors, was likely the result of sympathetic nerve blockade, followed by a beneficial interorgan or within-organ redistribution of blood flow.

Experimental model of cisplatin ototoxicity in chinchillas

Cisplatin is an important antineoplastic agent. Its ototoxicity has been well defined, both in human and animal studies. However, animal models of systemic cisplatin administration have been complicated by multiple toxic effects. We studied cisplatin ototoxicity in an animal model involving topical application of cisplatin to the round-window membrane. Adult chinchillas were anesthetized with ketamine and pentobarbital, and auditory function was tested with the use of auditory brain-stem responses to various stimuli (clicks and 8-and 16-kHz tone bursts). Each animal was used as its own control. The middle-ear cavity was exposed through the bulla. In the experimental ear, a 25-μl solution of 0.25 mg cisplatin/1.0 ml normal saline solution was applied to the round-window membrane. In the control ear, 25 μl normal saline solution was applied to the round-window membrane. Follow-up auditory brain-stem response testing was conducted 7 days after treatment. A significant increase in threshold in the experimental ears was seen on comparison with the control ears. This finding suggests that application of cisplatin to the round-window membrane is a useful animal model in which to study cisplatin ototoxicity. (Otolaryngol Head Neck Surg 1998;119:574-80.)

Central administration of two 5-HT receptor agonists: Effect on REM sleep initiation and PGO waves

Cholinergic neurons in the pedunculopontine tegmental (PPT) and the laterodorsal tegmental (LDT) nuclei are implicated in the generation of rapid eye movement sleep (REM) and ponto-geniculo-occipital (PGO) waves. Serotonin (5-HT) has a role in sleep-wake regulation and appears to inhibit PGO wave generation. We studied the effects of the central infusion of the relatively specific 5-HT 1A receptor agonist 8-hydroxy-2-(n-dipropylamino)tetralin (DPAT) and the less specific 5-HT 1 receptor agonist 1(3-chlorophenyl)piperazine (mCPP) on the regulation of REM and on PGO wave generation. DPAT (0.0, 0.002, 0.01, 0.08, and 0.8 μg/0.5 μl normal saline) and mCPP (0.0, 0.02, 0.2, 2.0, and 20.0 μg/0.5 μl normal saline) were infused unilaterally into the peribrachial region of PPT (PB) in cats. Additionally, DPAT (0.01 μg/0.5 μl) was infused bilaterally into PB in a separate experiment. Low dosages of DPAT (unilateral or bilateral) decreased successful entrances into REM (0.01 μg) and time spent asleep (0.002 μg and 0.01 μg) without affecting outward behavior. No dosage of mCPP significantly decreased the number of REM episodes, and neither drug decreased REM episode duration once REM had been entered. Neither drug affected the rate of PGO waves independently of modulating behavioral state. We propose that 5-HT 1A receptor mechanisms have an inhibitory role in actual REM initiation, possibly by facilitating endogenously generated excitation of brainstem startle mechanisms at the onset of REM.

Inhibition of implantation of hamster embryos by lectins

In order to test their effects on implantation, lectins (Con A and WGA) were infused into one horn of the uterus of each female hamster aged between 10 to 14 weeks at day 3 of pregnancy (D 3). Con A was given to three groups of 10 animals each at dosages of 100, 200 and 400 μg/10 μl normal saline (NS)/animal, and WGA to four groups of animals at dosages of 20, 50, 100 and 200/10 μl NS/animal. Control groups consisted of untreated animals and animals treated with saline. On D 8, laparotomy was performed and the number of fetuses were counted. In untreated and NS-treated groups the number of fetuses were 6.9 and 6.8 per horn, which were not significantly different. In Con A-treated groups, at dosages of 100, 200 and 400 μg the number of fetuses were 2.2, 2.5 and 2.1 per horn, respectively. By contrast, in WGA-treated groups no implantation was detected, except at the dosage of 20 μg, in which 1.1 fetuses per horn was observed. To study the mechanism of inhibition, another three groups of animals were similarly treated with NS, 100 μg Con A and 50 μg WGA/10 μl NS/animal, respectively. On D 4 at 1300–1400 h, uterine lumens were flushed to collect unimplanted blastocysts. No blastocyst was found in NS-and Con A-treated groups, whereas 6.2 blastocysts with complete zona pellucida were collected per horn in WGA-treated group. Histologically, Con A caused vacuolization in epithelium and edema in the stromal layer of endometrium. However, such changes were not observed in WGA-treated uteri.

Methodological aspects of tear flow determination by means of a radioactive tracer.

Theoretical considerations on a simplified biological system representing the tear pathways lead to the assumption of an exponential pattern of elimination of tracer substances from the conjunctival sac. The tracer used in the present study was technetium, Tc99m, as sodium pertechnetate. The detection system consisted of a gamma camera coupled to a digital system, a minicomputer and a magnetic tape unit. After instillation of 10 microliter normal saline solution containing Tc99m the decay of activity was followed by means of an activity-time function curve to which exponential curves were approximated by the computer. As a parameter for tear flow the fractional turnover rate was calculated from 7 to 15 min after instillation. An initial faster elimination was found in the first 7 min following instillation. Corrections for background radiation, evaporation of water and transconjunctival transport of Tc99m were estimated.