Retrograde amnesia caused by Met- Leu- and des-Tyr-Met-enkephalin in the rat and its reversal by naloxone

Immediate post-training i.p. injection of Met-enkephalin, Leu-enkephalin or des-Tyr-Met-enkephalin, caused retrograde amnesia for a shuttle avoidance task in rats. The effect was linearly related to the log of the dose between 0.32 and 2.0 μg/kg, and the potency of the three compounds was similar (ED₅₀ 0.35–0.45 μg/kg). Naloxone (0.2 mg/kg) antagonized the amnestic effect of the peptides. Since the log dose-response curves were displaced to the right in quasi-parallel fashion, and Lineweaver-Burk plots of the data showed an intersection very close to the origin of the horizontal axis, the antagonism between naloxone and the three peptides appears to be competitive.     

Cortical projections to the periaqueductal gray in the monkey: A retrograde and orthograde horseradish peroxidase study

Stereotaxic fluid microinjections of horseradish peroxidase (HRP) into the periaqueductal gray (PAG), coupled with cortical HRP gel placements in macaque and cebus monkeys, have provided substantive retrograde and orthograde evidence that the rostral dorsal convexity and rostral medial prefrontal cortex are the principal sources of cortical-PAG projections. The prefrontal cortex projects to the dorsolateral quadrant of the PAG, precisely the area shown to receive spinothalamic inputs in mammals, including monkey. The findings are discussed in terms of a possible affective role in central analgesic mechanisms.     

Nonarrhythmogenicity of therapeutic cryothermic lesions of the myocardium

There is increasing interest in the application of surgical methods to the treatment of refractory ventricular tachyarrhythmias (VT). Cryothermic ablation is one of the more promising techniques. However, there is clinical concern that a cryothermic lesion may lead to later arrhythmias. Previous studies have shown that dogs with nonhomogeneous, transmural infarctions are susceptible to VT initiation using programmed electrical stimulation (PES). The purpose of this study was to compare the incidence of inducing VT in dogs with transepicardial cryothermic myocardial damage (Group A) versus dogs with nonhomogeneous transmural infarctions resulting from 2-hr occlusion of the left anterior descending coronary artery (LAD) and subsequent reperfusion (Group B). Twelve dogs in each group were studied 10-14 days later using PES with unipolar cathodal ventricular pacing and two ventricular extrastimuli. Initiation of VT was attempted from at least six normal intramyocardial sites in each dog along the distribution of the LAD and in close proximity (less than or equal to 1 cm) to areas of chronically cryoablated damaged tissue. All dogs survived the initial procedure. VT was not inducible in any dog in Group A. Histological as well as electrophysiological evaluation, including determination of regional excitability thresholds and refractory periods employing strength-interval curves, revealed that all of the Group A dogs had homogeneous transmural infarcts with variable subendocardial sparing. In conclusion (1) cryothermal injury produces homogeneous damage; and (2) the lesion produced is not arrhythmogenic at 7-14 days.     

Two cases of variant Philadelphia chromosome resulting from translocation (21;22) and (3;19;22)

Two further cases of variant Philadelphia chromosome are presented. The possible presence of a specific oncogene on the long arm of chromosome #22 is discussed.     

Clinical significance of tricyclic antidepressant plasma levels

Review of the literature indicates that measurements of tricyclic antidepressant plasma levels have great potential for clinical application. Their use is currently limited mainly by the difficulty in obtaining quality laboratory determinations in most geographic areas. Plasma levels are most valuable in treatment of patients who have problems with lack of response to the drugs, placebo response, noncompliance, multidrug effects, and changes associated with aging. Clinical application of steady-state plasma level ranges should be limited to patients with endogenous depression, since data are very limited for other varieties of depressive illness.