The cost of delaying rewarding brain stimulation

Six rats trained to press a lever to obtain rewarding electrical stimulation of the brain through chronically implanted, lateral hypothalamic electrodes were used to estimate the rate at which short delays between the response and the reward degraded the rewarding effect of the stimulation. Frequency thresholds rose steadily with delays through to 2.2 s at a rate of 10% per second.

Effects of intramuscular or interpleural administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy

OBJECTIVE

To evaluate effects of interpleural or IM administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy.

DESIGN

Experimental trial.

ANIMALS

18 healthy dogs.

PROCEDURE

Dogs underwent median sternotomy and were randomly assigned to groups of 6 dogs each. Group-A dogs were given morphine (1.0 mg/kg of body weight) i.m.; group-B dogs were given 0.5% bupivacaine (1.5 mg/kg) interpleurally; and group-C dogs were given morphine (1.0 mg/kg) interpleurally. Heart rate; systolic, diastolic, and mean arterial pressures; rectal temperature; pain score; and arterial blood gas partial pressures were measured and pulmonary function testing was performed immediately after extubation (time 0) and up to 48 hours later. Serum cortisol and morphine concentrations were measured at time 0 and up to 12 hours after surgery.

RESULTS

There was a significant decrease in pH, PaO2, mean oxygen saturation of hemoglobin, and dynamic compliance; and a significant increase in PaCO2, alveolar-arterial difference in partial pressure of oxygen, pulmonary resistance, and work of breathing for dogs in all groups after surgery. Serum cortisol concentrations were significantly increased, compared with preoperative values, in all dogs. Serum cortisol concentrations were significantly higher in group-B dogs between 3 and 5 hours after surgery, compared with group-A dogs.

CONCLUSIONS

Median sternotomy was associated with significant alterations in pulmonary function. Effects of interpleural administration of bupivacaine and morphine were similar to effects of i.m. administration of morphine.

Adenosine receptor blockade and hypoxia-tolerance in rainbow trout and Pacific hagfish. I. Effects on anaerobic metabolism

The physiological properties of adenosine may be essential in the control of energy metabolism for the survival of animals exposed to oxygen shortages. Accordingly, we tested the hypothesis that adenosine modulates metabolic regulation in rainbow trout and Pacific hagfish exposed to acute hypoxia. Treatment of hypoxic rainbow trout (PwO2=3.33 or 4.00 kPa) with the adenosine receptor (AR) blocker theophylline was associated with greater increases in plasma [lactate], more rapid and pronounced metabolic acidosis, higher tissue [lactate], and lower heart creatine charge and glycogen content than in the hypoxic controls. The recruitment of anaerobic metabolism in hypoxic trout treated with enprofylline, an AR blocker with very weak affinity, was intermediate to that of the hypoxic theophylline-injected and control groups. In hagfish, plasma [lactate] increased following exposure to a PwO2 of 1.33 kPa but did not increase following exposure to 3.33 kPa and, like plasma acidosis, it was greatest in the animals treated with theophylline. These findings indicate that AR blockade results in a more rapid and pronounced recruitment of anaerobic metabolism following acute hypoxic exposure, and while rainbow trout and Pacific hagfish show marked differences in their responses to hypoxia, adenosine appears to play an important protective role in both species.

Adenosine receptor blockade and hypoxia-tolerance in rainbow trout and Pacific hagfish. II. Effects on plasma catecholamines and erythrocytes

The purpose of this study was to examine the role of adenosine receptors (ARs) in (1) the regulation of catecholamine secretion and (2) the modulation of blood oxygen capacitance by catecholamines. To this end, we assessed the response of rainbow trout and Pacific hagfish treated with either an AR blocker, theophylline, or saline under hypoxic and normoxic conditions. Compared with the control hypoxic rainbow trout, AR blockade resulted in a smaller increase in haematocrit and haemoglobin (Hb) concentration of the blood, smaller red blood cell transmembrane pH differences and mean cellular [Hb] (MCHC), as well as a 16-fold higher plasma adrenaline concentration after only 10 min of acute hypoxic exposure. In hypoxic hagfish, AR blockade had no effect on the [Hb] of the blood, and there was no regulation of red blood cell pH or changes in MCHC. However, whereas plasma [adrenaline] did not change following exposure to a PwO2 of 1.33 kPa in the hypoxic sham group, the concentration increased 3.8-fold within 10 min in the theophylline-injected group. These results suggest that adenosine modulates the circulating level of catecholamines in both hypoxic rainbow trout and hypoxic Pacific hagfish.

Regional distribution of vasoactive intestinal peptide immunoreactivity in the brain of salmon, trout and carp

The content of vasoactive intestinal peptide (VIP) was determined by radioimmunoassay in different brain regions of three fish species, namely salmon, trout and carp. The VIP extracted from salmon brain was shown by reverse-phase high-performance liquid chromatography to coelute with native porcine VIP. Highest VIP levels were measured in the salmon brain with a maximum of 112 pg/mg protein in the hypothalamus, followed by the telencephalon, olfactory bulb and optic tectum. In contrast, in the trout brain highest levels were found in the olfactory bulb (111 pg/mg protein). Lower levels were measured in the hypothalamus, telencephalon and cerebellum. The VIP content of the carp brain was considerably less, with highest values measured in the hypothalamus (12 pg/mg protein). The specificity in regional distribution further stresses the role of VIP in neurotransmission and indicates a function in neuroendocrine mechanisms and in the processing of olfactory stimuli.

Effects of hypoxia on rainbow trout (Oncorhynchus mykiss): intraerythrocytic phosphates

Intraerythrocytic levels of guanosine and adenosine phosphates were estimated in normoxic and hypoxic rainbow trout after intra-arterial injection with either saline or carbonic anhydrase. A significant reduction of the total pool of adenosine and guanosine was observed in hypoxic animals. Similarly, a decrease in both ATP and GTP levels occurred in hypoxic animals injected either with saline or with carbonic anhydrase. Interestingly, there was a highly significant relationship between ATP and GTP levels, indicating that they are under similar control. In addition, a significant positive relationship between nucleoside triphosphate (NTP) and Mg2+ levels was observed. It is possible that the availability of ATP and GTP to hemoglobin (Hb) may be proportionally smaller than their intraerythrocytic absolute levels. No clear relationship between intraerythrocytic NTP levels and plasma carbonic anhydrase infusion was observed, despite the significant effect of carbonic anhydrase on acid­base balance. There was a significant relationship between red blood cell pH and [NTP]:[Hb] in fish exposed to hypoxia for 48 h. No such relationship existed during the first 6 h of hypoxic exposure. Possible mechanisms accounting for the reduction in NTP levels during the initial phases of hypoxia are discussed.

Why is there no carbonic anhydrase activity available to fish plasma?

Carbonic anhydrase (CA) is absent from the plasma of vertebrates. In vitro, CA in fish plasma will short-circuit the effect of catecholamines, which is to increase red blood cell (RBC) pH and volume, both of which enhance the affinity of hemoglobin for O2. CA was infused into trout for a period of 6 h and injected after 48 h, during which the animal was submitted to deep hypoxia (PO2=30­35 mmHg; 4.0­4.7 kPa). O2 content, lactate content, catecholamine levels, hematocrit, hemoglobin concentration and pHi were similar to those in the saline-infused control group. In contrast, cell volume was significantly higher and pHe, total CO2 content and organic phosphate levels were significantly lower than in the control group. The concentration of CA was not high enough completely to short-circuit the increase in pHi and red blood cell volume caused by catecholamines. The lower pHe in the CA-infused animals could enhance the activity of the Na+/H+ pump, which would keep the nucleotide triphosphate levels low. pH is a balance between acid loading at the muscle and acid excretion at the gills or the kidneys; we cannot distinguish between which of these resulted in a decrease of plasma pH. In conclusion, CA in plasma did not cause the expected reduction in blood oxygen content but did have a marked effect on plasma total CO2 content.

IMMUNOLOCALIZATION OF H+-ATPase IN THE GILL EPITHELIA OF RAINBOW TROUT

The localization of proton pumps (H+-ATPase) in gill epithelia of rainbow trout [Oncorhynchus mykiss (Walbaum)] was elucidated by immunofluorescence microscopy, using rabbit polyclonal antibodies against the 70 kDa subunit of H+-ATPase purified from clathrin-coated vesicles of bovine brain. In the gill epithelia of freshwater trout, the immunostaining was uniformly distributed along the lamellae and generally concentrated in apical regions. It is concluded, therefore, that H+-ATPase is located in the apex of both chloride cells and epithelial cells of freshwater fish. Hypercapnic treatment resulted in a non-polarized and restrictive distribution of H+-ATPase in the chloride cell. No fluorescent staining was observed in the gill epithelium of seawater-adapted rainbow trout, except in some unidentified anucleate surface material. The presence of the 70 kDa subunit in fish gill epithelia was confirmed by Western blot. These results support the proposed role of a proton pump in sodium uptake in freshwater fish and demonstrate that the H+-ATPase in fish gills is of the vacuolar type, antigenically similar to the H+-ATPase in mammalian brain and kidney.

Adenoid cystic carcinoma of the trachea--a cause of pseudo-angina pectoris

Primary tracheal tumors are rare. Typically slow growing, they present late in the course of disease, with obstructive respiratory symptoms. A 25-year-old man developed external substernal chest pain and pressure with dyspnea that were relieved with rest. Noninvasive evaluation identified a tracheal tumor, adenoid cystic carcinoma by biopsy, which was previously undescribed as a cause of pseudo-angina pectoris. The patient's evaluation, management, and 20-month follow-up are presented. A mechanism for the patient's noncardiac exertional chest pain is proposed. Previous experience with adenoid cystic carcinomas of the trachea is reviewed.

Advocacy and delivery of community mental health services--do they mix? A Saskatchewan perspective

It is typical of the Provincial Divisions of the Canadian Mental Health Association to provide or oversee direct services for mentally disordered persons and for high-risk groups, and also to act socially and politically as advocates on their behalf. In Saskatchewan the relationship between the CMHA Division and the provincial government is described as one of "quiet negotiation and occasional publicly conducted conflict resolution". Some of the accomplishments of this effective working relationship are described.