Biomedical subjects

A G Watts

Publications and source records attributed to A G Watts.

44 records · Page 3Linked to original sources

PubMed1984

Indoleamines in the hypothalamus and area of the midbrain raphe nuclei of male and female rats throughout postnatal development.

We have investigated the changes in the concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the hypothalamus-preoptic area (HPOA) and midbrain raphe (MR) region of male and female rats throughout development. No sex differences were found in the concentrations of the indoleamines in either of the areas investigated at any stage of development. The 5-HIAA/5-HT molar ratio was maximal at 4 days of age in both the HPOA and MR. A small but significant sex difference in the 5-HIAA/5-HT ratio occurred in the HPOA (higher in males) but not in the MR at 40 days of age, and the ratio was significantly greater in 80-day-old female rats in the HPOA but not MR. Studies using NSD 1015 to block the conversion of 5-hydroxytryptophan to 5-HT showed that a higher rate of 5-HT synthesis occurred in the HPOA of 80-day-old rats compared with the neonatal HPOA and that in 80-day-old rats the rate of 5-HT synthesis was significantly higher in females. These results show that endogenous steroids do not affect the activity of serotoninergic neurons in the HPOA or MR either during or immediately after the critical period of sexual differentiation. In addition, the results from the NSD 1015 experiments show that the high 5-HIAA/5-HT ratio found in neonates does not involve a higher rate of 5-HT synthesis than that in adult rats.

Animals↗

PubMed1984

Pulsatile luteinizing hormone release, and the inhibitory effect of estradiol-17 beta in gonadectomized male and female rats: effects of neonatal androgen or exposure to constant light.

The characteristics of pulsatile LH release and the acute inhibition of LH release by estradiol-17 beta (E2) were studied in long term (21 days) gonadectomized female and male Wistar rats. Three groups of female rats were examined; animals exposed either to summer lighting (14-h on; 10-h off; LD) or continuous illumination (LL) and animals treated neonatally with testosterone propionate (TP) and exposed to LD. The mean plasma LH concentrations and interpulse intervals were similar in both male and LD female rats. However, treatment of female rats with TP or exposure to LL reduced the mean plasma LH concentration in female rats and increased the interpulse interval when compared with LD female or male rats. The amplitude of the LH pulses was significantly greater in the LD female rats compared with those in the male rats; since pituitary responsiveness to a single iv injection of 50 ng LHRH/100 g BW was similar in the two groups, this suggests that the amount of LHRH released per pulse of LH is greater in the female than in the male. The greater amplitude but similar frequency of LH pulses in the LD female compared with the LD male suggest that the MCR of LH may be greater in the female. The pulse amplitude in the TP-treated rats was similar to that in the rats exposed to LL and since pituitary responsiveness to LHRH was significantly greater in the TP rats, there was probably more LHRH released per pulse of LH in the LL-treated rats. Pituitary responsiveness to LHRH was significantly lower in the LL- and TP-treated rats compared with males and LD females. The timing of the inhibition of LH secretion by E2 was similar in all four groups of animals, and in LD females was not affected by a 92% depletion of serotonin, 100% depletion of 5-hydroxyindoleacetic acid, or a 33% depletion of dopamine in the hypothalamus produced by the administration of parachlorophenylalanine.(ABSTRACT TRUNCATED AT 400 WORDS)

Androgens↗

PubMed1982

Immediate increases in plasma prolactin and neurophysin but not other hormones after electroconvulsive therapy.

Plasma prolactin, growth hormone, cortisol, luteinising-hormone-releasing hormone (LHRH), thyrotropin-releasing hormone (TRH), and nicotine and oestrogen stimulated neurophysin (NSN and ESN) were measured before and for 6 min after electroconvulsive therapy (ECT) in eight women with severe electroconvulsive therapy (ECT) in eight women with severe depression. Plasma concentrations of NSN and ESN had increased significantly (as much as 10-fold for NSN) within 1 min of the seizure, and concentrations of prolactin had increased within 2-4 min after the seizure. Whereas plasma prolactin and ESN either continued to increase or remained raised throughout the 6 min after seizure, the concentrations of NSN fell to reach a value at 6 min that was approximately 50% of the maximum. There were no increases in any of the other hormones or peptides within the 6 min period under study. Thus ECT has selective effects on hormone release which cannot be attributed simply to a generalised release of pituitary or hypothalamic hormones in response to brain stimulation and/or stress.

Adult↗

PubMed1981

Effects of short-term constant light on the proestrous luteinizing hormone surge and pituitary responsiveness in the female rat.

We have investigated the effects of exposure to short-term constant light (LL) on the spontaneous, proestrous luteinizing hormone (LH) surge in the female rat. Exposure to LL during the 3 days preceding proestrus delayed and reduced the magnitude of the LH surge which was measured in blood samples taken from conscious animals through an intra-atrial catheter that had been implanted early on the morning of proestrus. The pituitary responsiveness to synthetic luteinizing hormone-releasing hormone (LHRH) in animals exposed to LL was reduced about 6-fold about the time of the LH surge compared with that in animals on a 14 h light- 10 h dark (LD) regimen. In contrast to animals on LD, treatment of rats on LL with estrogen and progesterone after ovariectomy failed to restore to normal the pituitary responsiveness which is markedly reduced by ovariectomy. The implantation of a silicone-elastomer capsule containing 17 beta-estradiol into rats on LL after ovariectomy did not facilitate pituitary responsiveness. These results suggest that exposure of the female rats to LL for 3 days causes a shift in phase of the LH surge (which may represent a free-running LH rhythm) and reduces the magnitude of the LH surge by a mechanism which may involve a reduction in the sensitivity to estrogen of the centres involved in LHRH release.

Animals↗

PubMed1981

Oestradiol-17 beta increases pituitary responsiveness by a mechanism that involves the release and the priming effect of luteinizing hormone releasing factor.

We have investigated the mechanism by which oestradiol-17 beta augments pituitary responsiveness to luteinizing hormone releasing factor (LH-RF). Adult rats were ovariectomized on the morning of dioestrus and implanted with either an empty silicone elastomer capsule or a capsule containing oestradiol-17 beta. Twelve hours later the LH response, tested by injecting 50 ng LH-RF/100 g i.v., was significantly greater in animals implanted with an oestradiol capsule compared with that in animals implanted with an empty capsule. The effect of oestradiol was blocked by sodium pentobarbitone administered 4 h before the test, and this block was overcome by infusing LH-RF during the 4 h period at doses which by themselves were not sufficient to evoke a large release of LH. We also measured LH-RF in pituitary stalk blood collected under Althesin anaesthesia between 4-6 and 12-13 h after ovariectomy and capsule implantation. The concentration of LH-RF in stalk plasma fell between these two collection periods in animals implanted with empty but not with oestradiol-filled capsules. The concentrations of LH-RF in stalk plasma, although relatively low, were significantly higher in animals bearing an oestradiol-containing capsule than the concentrations in peripheral plasma from similarly treated animals, and, by comparison with the LH-RF concentrations in peripheral plasma from animals infused with LH-RF, were sufficiently high to increase significantly the responsiveness of the pituitary gland. These data show that as well as acting directly on the pituitary gonadotrophs, oestradiol-17 beta increases the responsiveness of the anterior pituitary gland by a mechanism that involves the release and the priming effect of LH-RF.

Animals↗

PubMed1981

Constant light blocks diurnal but not pulsatile release of luteinizing hormone in the ovariectomized rat.

We have investigated the effects of constant light on the patterns of LH release in long-term ovariectomized rats. Some animals were implanted with a silicone elastomer capsule containing oestradiol-17 beta. Plasma samples in anaesthetized animals were taken from the external jugular vein and in conscious animals from an indwelling intra-atrial catheter. The pulsatile release of LH that occurred in animals not treated with oestrogen was unaffected by constant light or the steroid anaesthetic alphaxalone plus alphadolone acetate (Althesin), but was abolished by sodium pentobarbitone. However, the diurnal release of LH produced by increasing the concentrations of plasma oestradiol in conscious animals was blocked by constant light. Thus, these two rhythms of LH release are controlled by different neural pathways; the one concerned with diurnal LH release being suppressed by exposure to constant light.

Alfaxalone Alfadolone Mixture↗

PubMedDate not supplied

Dehydration-associated anorexia: development and rapid reversal.

Dehydration in rats results in anorexia that is proportional to the degree of dehydration. The aims of this study were first, to determine when anorexia develops in response to drinking hypertonic (2.5%) saline for 4 days; and second, to determine the organization of ingestive behaviors after access to water is resumed. Body weights, food, and fluid intake were measured morning and evening before, during, and after a 4-day period of dehydration caused by drinking hypertonic saline. A profile of the behaviors expressed immediately after rehydration was determined. The data make three points. First, dehydration-associated anorexia does not emerge until the second night of dehydration when the composition of the fluid compartments can no longer be homeostatically buffered. Second, dehydration reduces the amount food eaten nocturnally, but leaves diurnal food consumption largely unaffected. Animals very rapidly return to predehydration nocturnal ingestion patterns, whereas the amounts of food and water ingested during the day are significantly increased. Increased diurnal food intake may play a significant role in normalizing metabolism after dehydration. Finally, anorexia is reversed within minutes of rehydration. The data suggest a model where dehydration simultaneously activates two sets of circuits within the brain that will independently stimulate or inhibit feeding. Eating is inhibited during dehydration through the action of a set of inhibitory circuits, which masks the output of circuits that stimulate eating. However, when drinking water resumes, sensory inputs to these circuits rapidly release the inhibition and allow eating to proceed freely.

Animals↗

PubMedDate not supplied

Congo red birefringent structures in the hypothalamus in senile dementia of the Alzheimer type.

Serial cryostat sections of hypothalamus from four cases of Alzheimer-type dementia and four controls were stained with Congo red and examined for birefringence. Green birefringence and dichroism was associated with (a) neurofibrillary tangles, which were most numerous at the level of the tuberomammillary nucleus where they were found in large acetylcholinesterase-positive neurons; (b) neuropil processes within tangle fields; (c) a few plaque cores in the mammillary body; (d) spicules at the ependyma of the third ventricle, and (e) blood vessels. Birefringence (e) had different properties from (a) to (d) and was considered to be due to collagen. The ependymal spicules did not react with an antibody which recognized the tangles and neuropil processes. Each Alzheimer case had many more tangles than the control cases. Birefringence in (b)-(d) tended to be greater in the Alzheimer than in the control cases. This study confirms previous reports of large numbers of tangles in circumscribed areas of caudal hypothalamus in Alzheimer-type dementia and demonstrates that Congo red staining reveals abnormalities in hypothalamic structures (neuropil processes and ependyma) not demonstrated by other staining techniques.

Aged↗