Long-duration insomnia after lesions of the perikaryons of the paramedian preoptic area in cats

The destruction of paramedian preoptic neurons by intra-tissue injection of ibotenic acid induces, in the cat, the disappearance of deep slow wave sleep and paradoxical sleep for 2 to 4 weeks, while light slow wave sleep is slightly disturbed. This insomnia, well tolerated, is not secondarily associated with central temperature disturbance.     

Sterility and delayed vaginal opening following electrolytic lesions placed neonatally in medial preoptic area in female rats.

Electrolytic lesions were placed in the preoptic area or in the middle and posterior hypothalamus of female rats within 48 hrs after birth. Vaginal opening was delayed significantly in rats having the medial preoptic area (mPOA) destructed as compared to sham-operated animals and those given lesions in the other parts of the hypothalamus. Only rats with the mPOA completely destructed developed the anovulatory syndrome. In these animals, unilateral ovariectomy was not followed by enlargement of its fellow. The present results are not in agreement with those of previous workers that electrolytic destructions of the diencephalon induced precocious puberty. The difference may be ascribable to difference in size and locus of lesions.     

Impaired Pressure Natriuresis in Obese Youths

Objective: To compare the response and recovery of blood pressure (BP) and sodium excretion (U_NaV) in response to a behavioral stressor in overweight/obese and lean adolescents. Research Methods and Procedures: Twenty‐five lean (12% to 20% body fat) and 59 overweight/obese (>25% body fat) normotensive adolescents were provided all meals for 3 days (average sodium intake, 4000 ± 200 mg/d), before performing the stressor on the third day. There was a 2‐hour pre‐stress rest, followed by a 1‐hour stress (involving a video game task), and a 2‐hour recovery. Percentage of body fat was obtained from DXA. U_NaV was measured hourly, whereas systolic BP and diastolic BP measurements were obtained at 15‐minute intervals, and averaged for each 1‐hour period. Results: There was no significant difference between the lean and overweight/obese group for the response of systolic BP and diastolic BP (group by time interaction, p = 0.60 and p = 0.64, respectively). However, the lean group had a significantly greater increase in U_NaV in response to the stressor compared with the overweight/obese group (p = 0.02). U_NaV remained elevated compared with baseline in both groups at the 1‐hour (p ≤ 0.0001) and 2‐hour (p ≤ 0.0001) post‐time points. Furthermore, there was a tendency for a larger number of sodium retainers in the overweight/obese group compared with the lean group (39.0% vs. 20.0%; χ² = 2.85, df = 1, p = 0.09). Discussion: This study provided evidence that sodium regulation was impaired during a behavioral stress in overweight/obese individuals compared with lean individuals.     

Persistence of sleep-temperature coupling after suprachiasmatic nuclei lesions in rats

The suprachiasmatic nucleus (SCN) regulates the circadian rhythms of body temperature (T(b)) and vigilance states in mammals. We studied rats in which circadian rhythmicity was abolished after SCN lesions (SCNx rats) to investigate the association between the ultradian rhythms of sleep-wake states and brain temperature (T(br)), which are exposed after lesions. Ultradian rhythms of T(br) (mean period: 3.6 h) and sleep were closely associated in SCNx rats. Within each ultradian cycle, nonrapid eye movement (NREM) sleep was initiated 5 +/- 1 min after T(br) peaks, after which temperature continued a slow decline (0.02 +/- 0.006 degrees C/min) until it reached a minimum. Sleep and slow wave activity (SWA), an index of sleep intensity, were associated with declining temperature. Cross-correlation analysis revealed that the rhythm of T(br) preceded that of SWA by 2-10 min. We also investigated the thermoregulatory and sleep-wake responses of SCNx rats and controls to mild ambient cooling (18 degrees C) and warming (30 degrees C) over 24-h periods. SCNx rats and controls responded similarly to changes in ambient temperature. Cooling decreased REM sleep and increased wake. Warming increased T(br), blunted the amplitude of ultradian T(br) rhythms, and increased the number of transitions into NREM sleep. SCNx rats and controls had similar percentages of NREM sleep, REM sleep, and wake, as well as the same average T(b) within each 24-h period. Our results suggest that, in rats, the SCN modulates the timing but not the amount of sleep or the homeostatic control of sleep-wake states or T(b) during deviations in ambient temperature.     

Natriuresis induced by mild hypernatremia in humans

The hypothesis that increases in plasma sodium induce natriuresis independently of changes in body fluid volume was tested in six slightly dehydrated seated subjects on controlled sodium intake (150 mmol/day). NaCl (3.85 mmol/kg) was infused intravenously over 90 min as isotonic (Iso) or as hypertonic saline (Hyper, 855 mmol/l). After Hyper, plasma sodium increased by 3% (142.0 +/- 0.6 to 146.2 +/- 0.5 mmol/l). During Iso a small decrease occurred (142.3 +/- 0.6 to 140.3 +/- 0.7 mmol/l). Iso increased estimates of plasma volume significantly more than Hyper. However, renal sodium excretion increased significantly more with Hyper (291 +/- 25 vs. 199 +/- 24 micromol/min). This excess was not mediated by arterial pressure, which actually decreased slightly. Creatinine clearance did not change measurably. Plasma renin activity, ANG II, and aldosterone decreased very similarly in Iso and Hyper. Plasma atrial natriuretic peptide remained unchanged, whereas plasma vasopressin increased with Hyper (1.4 +/- 0.4 to 3.1 +/- 0.5 pg/ml) and decreased (1.3 +/- 0.4 to 0.6 +/- 0.1 pg/ml) after Iso. In conclusion, the natriuretic response to Hyper was 50% larger than to Iso, indicating that renal sodium excretion may be determined partly by plasma sodium concentration. The mechanism is uncertain but appears independent of changes in blood pressure, glomerular filtration rate, the renin system, and atrial natriuretic peptide.     

Bombesin acts in preoptic area to produce hypothermia in rats

To determine a neuroanatomic location where bombesin produces hypothermia, bombesin or an inactive bombesin analog, [D-Trp⁸]-bombesin, were microinjected in nanogram quantities into various regions of the brain of unanesthetized, unrestrained, cold-exposed rats. Bombesin, but not [D-Trp⁸]-bombesin, produced hypothermia when injected into or near the preoptic area, whereas injections into other forebrain and midbrain areas failed to lower body temperature. These results support a possible involvement of a bombesin-like peptide in thermoregulation.     

Susceptibility of rats to corneal lesions after injectable anesthesia

Corneal injury is not a commonly reported side effect after injectable or inhalation anesthesia in rats, but a number of surgery studies at our facility resulted in a high incidence of these injuries. To explore the potential association of various anesthetic protocols with the development of corneal lesions in rats, we retrospectively evaluated clinical records and sections of eyes from 215 male and 187 female Wistar rats used in eight intravenous infusion toxicology studies. None of the studied compounds was associated with eye toxicity. For placement of jugular vein vascular access ports, rats were anesthetized with enflurane, isoflurane, ketamine-xylazine, or Hypnorm-midazolam. Histologically, corneal changes were scored from 0 to 4 in light of degree of mineralization, leukocytic infiltrates, neovascularization, fibrosis, and ulceration. Prestudy (postsurgical) ophthalmic examination findings of corneal opacities were correlated with mineralization of the anterior limiting membrane and corneal ulceration. Corneal lesions were more severe in animals anesthetized with ketamine-xylazine, and minimal changes occurred after anesthesia with either enflurane or isoflurane. The results of further analysis suggest that corneal lesions can be observed within 24 h after injectable anesthetic administration and are not reversible. The severity of corneal changes was reduced when ketamine-xylazine anesthesia was reversed with yohimbine. Compared with Sprague-Dawley and Lewis rats, Wistar, Long-Evans, and Fischer 344 rats had increased incidence and severity of corneal lesions after anesthesia with ketamine-xylazine, suggesting that these three strains are at increased risk for developing postanesthetic corneal lesions with this regimen.     

Transition from precopulatory to copulatory behaviour in male rats with lesions in medial preoptic area: dependence on precopulatory pattern of female

In the present study, both the precopulatory behaviour and the copulatory readiness of male rats following the bilateral medial preoptic area lesions was compared with their intact states. In behavioural testing, the intensity of female precopulatory behaviour was used as an experimental variable. The results showed that the natural threshold of copulatory readiness of males was increased in the lesioned state, the animals were more dependent on the soliciting patterns of the female. However, all the males exhibited conspicuous precopulatory behaviour towards the stimulus females used. Apparently, further brain structures participate in the regulation of sexual behaviour of males, above all, in activation or maintenance of precopulatory activity.     

Effects of preoptic – suprachiasmatic lesions on renal excretion of electrolytes

Rats sustaining lesions of the posteroventral portion of the medial preoptic nucleus and the anterior portion of the suprachiasmatic nucleus exhibited decreased cumulative urine volumes, as well as lower sodium and potassium excretion following hypertonic saline injections. Circadian rhythms and mean levels of these variables during the steady state were unchanged. The lesioned area may participate in central regulation of water and electrolyte balance.     

Heterotypic sexual behavior in male rats after lesions in different amygdaloid nuclei

Previous studies showed that different amygdaloid nuclei are involved in the control of lordosis behavior in female rats. The objective of the present study was to determine whether these nuclei played a role in the control of lordosis behavior in the male rat. Lesions were placed into different amygdaloid nuclei in male rats castrated as adults and primed with ovarian hormones. Lesions in the corticomedial amygdaloid nucleus completely suppressed lordosis behavior as expressed by the number of animals displaying lordosis responses to male mounts. By contrast extended lesions placed into the lateral amygdaloid nucleus (LN) remained without effects. Lesions placed in the very posterior part of the LN produced "hypersexuality" with a rise in the number of animals displaying lordosis responses and high LQ values. Lesions in the anterior part of the LN induced a decrease in the number of animals showing lordosis responses. The amygdala was then concluded to represent a functionally heterogeneous structure with different regions exerting opposite effects on the display of lordosis behavior in the male rat.     

Mating call phonotaxis in female American toad: lesions of anterior preoptic nucleus

Lesions of the preoptic area and immediately adjacent septal area were made in female American toads, Bufo americanus. The ability to show mating call phonotaxis (MCP) was then tested for. The intensity of MCP was found to decrease as the degree of damage to the anterior tip of the anterior preoptic nucleus (APON) increased. The APON is known to concentrate androgens and to be essential for mating calling by male anurans. Perhaps the APON is involved also in the detection of the elevated levels of prostaglandin associated with MCP. Even in lesioned toads in which phonotaxis was nearly absent, there was an occasional MCP response that seemed entirely normal. Therefore, the APON is not involved in generating or guiding the motor mechanisms of phonotaxis.     

Effects of preoptic and hypothalamic lesions in female turkeys during a photoinduced reproductive cycle

Prolactin (Prl) is released by electrical stimulation in the turkey hypothalamus and preoptic area (POA). Possible trajectories for POA efferents to the median eminence (ME) were tested by placing lesions in the POA, the lateral hypothalamus (LHy), or the ventromedial nucleus of the hypothalamus (VMN) of reproductively quiescent turkey hens, then subjecting them to long photoperiods while monitoring their blood Prl levels and nesting activities. In addition, lesions were made in the VMN of a group of incubating hens to learn whether the lesions would cause the elevated Prl levels to fall or interfere with incubation behavior. Lesions in medial POA, LHy, or VMN prevented the onset of incubation and prevented the large rise in Prl associated with it. However, these lesions did not interfere with the initial, more gradual Prl rise caused by increasing daylengths. Lesions in LHy or VMN appeared to interfere with a pathway lying laterally from POA to ME. Electrical stimulation in medial POA, which caused an increase in circulating Prl, failed to do so in hens with LHy or VMN lesions. Lesions in the VMN of incubating hens caused them to leave the nest and suffer a large decline in Prl, both within 48 h. It is tentatively suggested that incubation behavior and its associated elevated Prl are prevented by the POA lesions and that lesions in LHy or VMN, which mimic POA lesion effects, interfere with POA efferents projecting to ME.     

Effects of lesions in the medial preoptic region on precocial copulation in the male chick

Chicks showing androgen-induced precocial copulation to a prone hand were given bilateral electrolytic lesions in the medial preoptic region. Symmetrical lesions in the medial preoptic area disrupted copulatory behavior over the 10-day postoperative test period. Asymmetrical or sham lesions did not differentially affect copulatory activity. Postoperative records indicated that all animals showed similar increases in weight gain and comb size.     

Late occurring lesions in the skin of rats after repeated doses of X-rays

Late radiation damage, characterized by atrophy and necrosis in the skin and subcutaneous tissues, has been demonstrated in both the tail and feet of rats. The incidence of necrosis increased with total dose. These total doses, in the range 72-144 Gy, were given as 4-8 treatments of 18 Gy, each dose separated from the next by an interval of 28 days. This treatment protocol minimized acute epithelial skin reactions. The same regime applied to the skin on the back of rats resulted in a very severe acute reaction occurring after the second to fifth dose of 18 Gy. This was surprising since back skin, like tail skin, is less sensitive to large single doses of radiation than that of the foot. The late radiation reaction in the foot and tail of rats are compared and contrasted with other attempts to assess late effects in rodent skin and with late changes seen in pig skin.