Implantable cannula

The drug is administered either intravenously into a cannulated vein or directly into the brain through an implanted cannula placed in the lateral ventricle or into a Um-bic structure such as the nucleus accumbens (43). 

Vapor Pressure. The Shiley Infusaid implantable infusion pump utilizes energy stored in a two-phase fluorinated hydrocarbon fluid. The pump consists of a refillable chamber that holds the dmg and a chamber that holds the fluid. The equiUbrium vapor pressure of the fluid, a constant 60 kPa (450 mm Hg), compresses the bellows, pumping the dmg through a bacterial filter, a capillary flow restrictor, and an infusion cannula to the target body site (56,116). 

Rats were implanted with indwelling jugular cannulae for intravenous (IV) administration of drugs (Weeks and Davis 1964). To monitor cortical EEG and electromyographic (EMG) activity, respectively, they were also prepared with chronic cerebrocortical electrodes and temporalis muscle electrodes (Khazan 1975). One week was allowed for recovery from surgery before experimentation. 

In another series of experiments, rats trained to discriminate LSD (96 pg/kg i.p.) from saline were implanted stereotactically with cannulae aimed at the DRN (59). The ability of the peripherally elicited LSD cue to generalize to LSD injected directly into the DRN was then evaluated over a wide range of doses (2-60 jtg/kg). The results are shown in Fig. 2. Interestingly, the dose of LSD injected via the cannulae required to produce DS control was extremely high,... 

FIG. 2. Comparison of the discriminative stimulus properties of LSD, morphine, and methadone when injected into the DRN of the rat. Rats were trained to discriminate LSD (120 ng/kg s.c.), cannulae implanted, and generalization from peripheral to central administration determined over a variety of doses of each drug. (Redrawn from the research of Rosecrans and Glennon, ref. 59.) A, I.C. saline, , I.C. morphine in morphine trained rats, O, I.C. saline, , I.C. LSD in LSD trained rats, , I.C. saline, , I.C. methadone in methadone trained rats. 

Rats represent an excellent model for EEGs as they are cheap, resist infection during chronic electrode and cannulae implantation, and are relatively easy to train so that behavioral assessments can be made concurrently. 

We attempted to prevent li -overdose death with intracerebroventricularly administered inositol. Sprague-Dawley rats were implanted with guide cannulae in the lateral ventricle. Rats were injected intracerebroventricularly... 

Most of the sensors implanted in the subcutaneous tissue are 200-250 jam (33-31 ga) in diameter. They are usually implanted using a guide cannula whose outside diameter is 21-23 ga (813-635 jam). This insertion process will cause some tissue injury including breaking of capillaries. Experience in our laboratories has shown, however, that the damage is very slight and an edema around the implant, typically the size of a mosquito bite, disappears after about 24 h. 

Male Sprague-Dawley rats weighing 250-300 g are used for these studies. When drugs are to be administered intracerebroventricularly, rats are anesthetized with 60 mg/kg i.p. sodium hexobarbital and 23 gauge guide cannulae aimed at the lateral ventricle (AP = -0.9 mm, L = +1.5 mm, DV = 3.5 mm) (Paxinos and Watson 1982) are stereotaxically implanted conditioning commences one week later. 

Besides the basic apparatus for microdialysis perfusions, fraction collection, and HPLC analysis, several additional instruments and devices are needed, depending on where the microdialysis probe is to be implanted. The most complicated instrumental setup is probably that required for brain dialysis. A stereotaxtic instrument and a stereomicroscope are necessary for precise positioning of microdialysis cannulae into various brain structures. Inhalation anesthesia is preferable and more convenient than injections. However, this type of anesthesia calls for additional equipment, such as air lines, valves, and mixing chamber for halothane or other anesthetic gases, as well as good ventilation of the operation theater. 

For this application, a sterile microdialysis catheter is implanted percutane-ously into the subcutaneous adipose tissue in the periumbilical region using a special stainless steel guide cannula (Rosdahl et al., 1993). The membrane length of 2 to 3 cm and flow rates of 0.1 to 0.5 piL/min should guarantee sufficiently long dialysis time to achieve 100% recovery. Another approach is to use a flat dialysis probe for transcutaneous applications (DeBoer et al., 1993 Korf et al., 1993). Here the skin of newborn babies is first partially removed by stripping with medical tape. Then a microdialysis probe is placed directly onto the exposed skin, usually on the abdomen lateral to the umbilicus (DeBoer et al., 1994). 

Central venous catheters are reluctantly used as blood access for hemodialysis because of safety concerns and frequent complications, for example sepsis, thrombosis, and vessel stenosis. Nevertheless, 20% or more of all patients rely on atrial catheters for chronic dialysis because of lack of other access. Potentially fatal risks related to central venous catheters include air embolism (1), severe blood loss (2), and electric shock (3). These specific risks have been substantially eliminated by the inherent design and implantation of Dialock (Biolink Corporation, USA). Dialock is a subcutaneous device consisting of a titanium housing with two passages with integrated valves connected to two silicone catheters. The system is implanted subcutaneously below the clavicle. The tips of the catheters are placed in the right atrium. The port is accessed percutaneously with needle cannulas. 

Problems with recovery are avoided when sampling the extracellular brain tissue by means of a push-pull cannula. A push-pull cannula consists of two coaxial assembled hollow needles (cannulae) which are implanted into the brain. Artihdal cerebrospinal fluid is infused through the inner cannula and withdrawn through the outer cannula [5-8],... 

The experiments were performed in conscious rats 17-48 h after implantation of the cannula. The striatum was perfused with a Ringer solution (147 mmol/l NaCl, 4 mmol/1 KC1, 1.2 mmol/1 CaCl2, 1.1 mmol/1 MgCl2) at 2 pl/min (CMA/102 microdialysis pump, Sweden). 

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