Vasopressin-deficient rats show a reduced amplitude of the circadian sleep rhythm

The hypothalamic suprachiasmatic nuclei are responsible for the generation of many circadian rhythms, including the rhythm of arginine vasopressin (AVP) in the cerebrospinal fluid (CSF). We used cortical EEG recordings taken from AVP-deficient (Brattleboro strain) rats to investigate the possible role of AVP in the generation of circadian sleep/arousal rhythms. When housed either in a light-dark cycle or in constant light, Brattleboro rats showed circadian rhythms of arousal, slow-wave sleep, and paradoxical sleep. However, the amplitudes of the slow-wave and paradoxical sleep (but not arousal) rhythms in these animals were significantly lower than in controls. The results indicate that hypothalamic synthesis of AVP is not necessary for the generation of circadian sleep rhythms, but the amplitude of the rhythms may be modulated by the circadian release of AVP into CSF.

Paraventricular nucleus injections of noradrenaline: cardiovascular effects in conscious Long-Evans and Brattleboro rats

The cardiovascular effects of noradrenaline injected into the hypothalamic paraventricular nucleus (PVN) were investigated in conscious Long-Evans (control) rats and homozygous vasopressin (AVP)-deficient Brattleboro rats. Unilateral microinjection of noradrenaline (3-30 nmol) into the PVN produced dose-dependent increases in systolic and diastolic blood pressure of Long-Evans rats, and a concomitant decrease in heart rate. Only the highest dose of noradrenaline tested (30 nmol) caused a significant pressor response in Brattleboro rats (9 +/- 4/9 +/- 4 mm Hg, systolic/diastolic, n = 7) which was significantly smaller than the response produced by the same dose of noradrenaline in Long-Evans rats (32 +/- 8/27 +/- 6 mm Hg, n = 7). Intravenous pretreatment of Long-Evans rats with the V1-receptor antagonist, d(CH2)5Tyr[Et]DAVP, almost completely abolished the pressor effect of noradrenaline (10 nmol) without significantly attenuating the bradycardia. The alpha 2-adrenoceptor antagonist, idazoxan (4 nmol), injected into the PVN abolished the pressor response produced by noradrenaline (10 nmol) in Long-Evans rats but had no significant effect on the bradycardia. Pretreatment with the alpha 1-adrenoceptor antagonist, prazosin (0.7 nmol), significantly attenuated both the pressor and bradycardic effects of noradrenaline in Long-Evans rats. These results suggest that the pressor response produced by microinjection of noradrenaline into the hypothalamic PVN of conscious Long-Evans rats is mediated largely through stimulation of alpha 2-adrenoceptors and is dependent, in part, on release of AVP into the circulation. A component of the bradycardia seen with this intervention may be mediated through stimulation of alpha 1-adrenoceptors in the PVN.

The vasopressin-associated glycopeptide is not a prolactin-releasing factor: studies with lactating Brattleboro rats

We have recently reported that the posterior pituitary contains PRL-releasing factor (PRF), a small (less than 5000 mol wt) peptide which induces a rapid, hormone-specific, and concentration-dependent stimulation of PRL secretion. Although the identity of posterior pituitary PRF is yet unknown, it is distinct from known PRL secretagogues. Recently, the vasopressin-associated glycopeptide (VAG), which is concentrated in the posterior pituitary, was suggested as a PRF. To investigate whether VAG functions as a PRF, we used Brattleboro rats, which are deficient in arginine vasopressin (AVP), AVP-associated neurophysin, and VAG. Homozygous (DI) and heterozygous (HZ) lactating Brattleboro rats were used. The water consumption of pregnant DI rats (greater than 300 ml/day) was 6-fold higher than that of HZ rats. To correct their water imbalance, DI rats were implanted with osmotic minipumps containing the vasopressin analog 1-desamino-8-D-arginine vasopressin. On days 7-8 of lactation, pups were separated for 6 h, and blood was collected from the dams via a jugular cannula. Upon introduction of the pups, plasma PRL levels increased 100-fold in both DI and HZ rats and remained elevated for the duration of suckling. The suckling-induced rises in plasma oxytocin in DI and HZ rats were also superimposable. The weight gains of the pups of DI and HZ mothers were similar. PRF activity was determined using perifused anterior pituitary cells. Posterior pituitaries from DI and HZ rats contained equivalent amounts of PRF activity. Moreover, purified rat VAG (1.5 and 6.0 micrograms) failed to stimulate PRL release from pituitary cells. The posterior pituitary content of immunoreactive AVP was 2500-fold higher in HZ rats, but the contents of dopamine and oxytocin were similar. It is concluded that VAG neither mediates the suckling-induced rise of plasma PRL, nor stimulates PRL secretion from perifused anterior pituitary cells. Furthermore, posterior pituitaries from DI and HZ rats contain equivalent amounts of PRF activity. Collectively, these data indicate that VAG is not the posterior pituitary PRF.

Vasopressin V1-receptor blockade lowers arterial blood pressure in young conscious Long-Evans rats

Young, conscious Long-Evans rats had significantly higher basal mean arterial blood pressure than age-matched Brattleboro rats with hereditary hypothalamic diabetes insipidus, and an intravenous injection of a specific vasopressin V1-receptor blocker significantly decreased the mean arterial pressure in the former animals only. The basal heart rate, which was significantly higher in the Brattleboro rats than in the Long-Evans rats, was unaffected by the vasopressin antagonist in either strain. These results indicate that vasopressin may be important in maintaining normal blood pressure in young rats.

Blunted pressure natriuresis in the Brattleboro diabetes insipidus rat

Antidiuretic hormone is known to stimulate the renal synthesis of prostaglandins. These autacoids, in turn, modulate the pressure natriuresis phenomenon. Accordingly, the present study was done to test the hypothesis that, in the absence of antidiuretic hormone and antidiuretic hormone-dependent prostaglandin synthesis, the pressure natriuresis response is blunted. Experiments were performed on Brattleboro diabetes insipidus rats (n = 7) and Long Evans control rats (n = 14). A change in perfusion pressure in the Long Evans rats from 89.3 +/- 1.0 to 108.7 +/- 1.1 mm Hg (p less than 0.05) was associated with significant increases in the fractional excretion of sodium (1.1 +/- 0.2 to 2.3 +/- 0.3%) and the urinary prostaglandin excretion (32.6 +/- 6.8 to 56.6 +/- 10.0 pg/min). In contrast, a similar change in perfusion pressure in the diabetes insipidus rat from 88.6 +/- 1.4 to 106.2 +/- 1.5 mm Hg (p less than 0.05) resulted in no significant increases in either sodium or prostaglandin excretions. Treatment of a third group of diabetes insipidus rats (n = 9) with 1-desamino-8-D-arginine vasopressin (1 microgram/day) restored the natriuretic response to increases in renal perfusion pressure. Treated diabetes insipidus and Long Evans control rats had comparable natriuretic responses to increases in renal perfusion pressure. Untreated diabetes insipidus rats, on the other hand, had blunted responses. In summary, the pressure natriuresis response in diabetes insipidus rats is blunted compared with Long Evans control rats. We conclude that antidiuretic hormone is necessary for the complete expression of the pressure natriuresis response.

Anterior neocortical kindling in vasopressin-deficient rats

Kindling of seizures with stimulation of anterior neocortex was examined in control rats and in Brattleboro rats deficient in arginine-vasopressin (AVP). There were no significant differences between control rats, homozygous Brattleboro rats, and heterozygous Brattleboro rats in the rate and pattern of kindling of generalized seizures. Thus AVP is not critically involved in anterior neocortical kindling.

Adrenoceptors and cardiovascular regulation in conscious, unrestrained, Long Evans and Brattleboro rats

In conscious rats, in the presence of prazosin and idazoxan (alpha 1- and alpha 2-adrenoceptor antagonists, respectively), blood pressure (BP) and heart rate (HR) become unstable, due to the occurrence of 'spontaneous' depressor and tachycardic episodes. These events could be triggered also by auditory stimuli, and were blocked by antagonism of beta 2-adrenoceptors. In adrenal-demedullated animals treated with prazosin and idazoxan, BP was less variable than in sham-operated animals, but bolus injections of adrenaline or salbutamol could simulate the 'spontaneous' depressor events seen in the latter. The marked swings in HR were not explained by sensitization of the cardiac baroreflex in the presence of idazoxan, but were probably due to blockade of prejunctional autoinhibitory alpha 2-adrenoceptors, amplifying the effects of intermittent sympatho-adrenal activation.

Cardiovascular consequences of water deprivation in female Long Evans and Brattleboro rats

Female Long Evans and Brattleboro rats were studied while water-replete and after water deprivation sufficient to cause hypovolaemia of similar degree in the two strains. A comparison was made of the blood chemistry and cardiovascular status in the two conditions, and the ability of the renin-angiotensin system, sympathoadrenal activity and (in Long Evans rats) vasopressin to influence blood pressure were assessed by pharmacological blockade of these systems. Under water-replete conditions there were significant differences between plasma variables in the two strains (Long Evans: vol., 3.67 +/- 0.07 ml/100 g b. wt., sodium, 142 +/- 0.3 mmol/l; osmolality, 290 +/- 1 mosmol/kg; Brattleboro: vol., 3.89 +/- 0.07 ml/100 g b. wt.; sodium 148 +/- 0.4 mmol/l; osmolality 304 +/- 2 mosmol/kg). Inhibition of the renin-angiotensin system (with captopril) had a slightly greater hypotensive effect in Brattleboro than in Long Evans rats. In both strains the hypotensive effects of captopril were enhanced markedly in the presence of pentolinium, and, under those conditions there was a vasopressin-dependent recovery of blood pressure in Long Evans rats that was absent in Brattleboro rats. Water deprivation caused a greater proportional reduction in body weight, and increase in plasma sodium and osmolality in Brattleboro than in Long Evans rats, although resting cardiovascular statuses were not markedly different. Despite Brattleboro rats having substantial hypernatraemia (156 +/- 1.0 mmol/l), that should have acted to inhibit renin release, they showed a profound hypotensive response to captopril that was not apparent in Long Evans rats. Thus, the absence of vasopressin in female Brattleboro rats severely affects cardiovascular adaptation to water deprivation. Comparison of the present results with published data obtained from male Long Evans and Brattleboro rats shows marked sex differences in the response to the same water deprivation protocol, and indicates that data obtained from males and females should not be cumulated.

Twenty-four-hour pineal melatonin synthesis in the vasopressin-deficient Brattleboro rat

The diurnal time course of pineal melatonin synthesis was analyzed simultaneously in the arginine vasopressin (AVP)-deficient Brattleboro rat (BB), the Long-Evans (LE) and Sprague-Dawley (SD) rat by means of radioenzymatic determination of the rate-limiting enzyme serotonin-N-acetyltransferase (NAT) and the melatonin content over a period of 24 h. While all 3 strains displayed a distinct day-night rhythm of melatonin synthesis (low day-time, high night-time values), BB rats generally exhibited lower NAT values as compared to LE and SD rats, though reaching a significant difference at 02.99 h only. Twenty-four-hour melatonin content was characterized by distinct nocturnal maxima in LE and SD rats, while BB rats showed a plateau-like nocturnal time course. Electrophysiological and pharmacological findings in SD rats point to an inhibitory influence of AVP upon pineal melatonin synthesis. The lack of AVP obviously does not result in disinhibition of pineal melatonin synthesis but rather in a different time course of pineal melatonin content. This might either be due to strain differences or to yet unknown compensatory mechanisms in BB rats.

Cardiac baroreflex sensitivities in conscious, unrestrained, Long Evans and Brattleboro rats

Cardiac baroreflex sensitivity (BRS; i.e. the slope of the line relating change in pulse interval to change in systemic arterial pressure) was assessed in response to an increase in mean blood pressure (MBP) evoked by methoxamine or a decrease evoked by sodium nitroprusside. Measurements were made in Long Evans (i.e. control) and in Brattleboro (i.e. vasopressin (AVP)-deficient) rats, following acute and chronic intravascular catheterization, and in water-replete and water-deprived states (the latter designed to reduce plasma volume and activate AVP-dependent mechanisms (in Long Evans rats]. There were no differences between the corresponding values for cardiac BRS in Long Evans and Brattleboro rats. Furthermore, water deprivation caused no significant changes in cardiac BRS in either strain. These results do not support the claim that absence of endogenous AVP in Brattleboro rats is associated with marked impairment of cardiac BRS, and indicate that chronic changes in circulating AVP do not cause systematic changes in cardiac BRS.

Thirst in Brattleboro rats

Thirst mechanisms in Brattleboro rats are activated because of a deficiency in circulating vasopressin. Plasma osmolality, renin, and angiotensin II (ANG II) are increased. We measured the responsiveness of Brattleboro rats and appropriate control strains to cellular and extracellular thirst stimuli taking the spontaneous base-line water intake into account. Brattleboro rats drank more in response to intraperitoneal hypertonic NaCl than controls, but when their fluid losses were prevented by nephrectomy they did not overdrink. Despite low urinary concentration, Brattleboro rats excreted the sodium load at least as rapidly as the controls. Brattleboro rats drank after intracranial injection of renin, renin substrate, and ANG I and II. The dose-response curves were similar to controls, although the Nottingham Long-Evans control strain drank significantly less in response to some doses of the peptides. Intracranial captopril inhibited renin- and ANG I-induced but not ANG II-induced drinking. Isoproterenol reduced spontaneous drinking of Brattleboro rats but increased drinking in controls. However, when urinary losses were prevented by ureteric ligation, isoproterenol caused markedly greater water intake in Brattleboro rats than in controls. Subcutaneous captopril in moderate, thirst-enhancing doses also caused a larger increase in water intake in Brattleboro rats than in controls. Therefore the renin-angiotensin system of Brattleboro rats is more responsive to renin-dependent thirst challenges than that of normal controls.

Reactions to vesical foreign bodies in two strains of rats

Foreign bodies in the urinary tract induce uroliths. This study examined reactions to vesical foreign bodies in Brattleboro rats manifesting diabetes insipidus and Sprague-Dawley rats. A silk suture was placed in the bladder of these rats and the occurrence of vesical uroliths, stone composition, and mucosal morphology were examined. Sprague-Dawley rats readily formed bladder stones in addition to a urolith formed over the suture, but there was little evidence that Brattleboro rats developed similar stones. Stone composition was primarily ammonium magnesium phosphate. The mucosal reactive hyperplasia was pronounced in the Sprague-Dawley, but was negligible in the Brattleboro rats. In conclusion, vesical foreign bodies readily induced uroliths in Sprague-Dawley rats, but there was no similar evidence in Brattleboro rats. It is suggested that the excessive diuresis of the latter may play a major role for this resistance to form stones, but the precise mechanisms of it are complex and remain to be explored.

Effects of naloxone and cholecystokinin on food and water intake in vasopressin-deficient rats (Brattleboro strain)

Opioid peptides and cholecystokinin (CCK) have been shown to play a role in regulation of feeding behavior. Another neuropeptide that has recently been suggested to be involved in feeding is vasopressin. We explored possible interactions between opiates, CCK and vasopressin in feeding regulation by studying feeding suppression produced by naloxone and CCK in Brattleboro (DI) rats, which are homozygous for diabetes insipidus and lack the ability to synthesize vasopressin. Ten DI and 15 age-matched Long Evans (LE) rats were food deprived for 14 hours on two different days and then injected with naloxone (2.5 mg/kg) on one day or saline on the other. Thirty minutes later the food was returned and food and water consumption were measured after 1, 3 and 4 hr. Naloxone suppressed the food consumption of both DI and LE rats but the suppression was greater for the DI rats. This result was specific to feeding as water consumption was suppressed in LE more than in DI rats. Two weeks later, the same rats were food deprived for 6 hours on two different days and then injected with CCK-8 (2.5 micrograms/kg) on one day and with saline on the other. Food was returned one minute after the injection and food and water consumption were measured 30 and 60 minutes later. Food intake was reduced equally for both DI and LE rats. Water intake was not reduced. The results suggest that the suppression of feeding by CCK does not require an intact vasopressinergic system. The greater feeding suppression by naloxone in DI rats may suggest that opiates are interacting with vasopressin in producing their effects on food intake.

A comparison of the febrile responses of the Brattleboro and Sprague-Dawley strains of rats to endotoxin and endogenous pyrogens

The febrile responses of homozygous (di/di) Brattleboro rats, to both intravenous endogenous pyrogen and to a lipopolysaccharide endotoxin, were compared with those of normal Sprague-Dawley rats. There were no detectable differences between the fever curves of the two strains in response to endogenous pyrogen. Brattleboro rats, which are deficient in the neuropeptide arginine vasopressin (AVP), displayed fevers that were both qualitatively and quantitatively indistinguishable from those of normal Sprague-Dawley rats that do not suffer from congenital diabetes insipidus. It is concluded that the absence of AVP-containing cells in Brattleboro rats is not an important factor in determining the nature of their febrile responses to endogenous pyrogen. More remarkable, however, were the divergent febrile responses of the two strains to intravenously injected endotoxin. Normal rats displayed hypothermic responses, whereas the Brattleboro rats became febrile. By 2 h after the injection of endotoxin, body temperatures in both strains had returned to normal. Three hours after the rats had been exposed to endotoxin, both strains were found to be totally refractory to endogenous pyrogen. However, when both strains of rats were tested to endogenous pyrogen 3 days later, their febrile responses were more than double the magnitude of their initial control responses. These alterations in the febrile responsiveness of rats occurring at different times after the injection of endotoxin appear to be related to the effects that endotoxin has on the cells of the reticuloendothelial system, over the same time course.

Correction of genetic diabetes insipidus by adult hypothalamic grafts

Brattleboro rats manifest chronic diabetes insipidus as a result of the genetic deficiency of hypothalamic vasopressin. When basal hypothalamic tissue derived from adult F344 rats was implanted as cell suspensions or tissue blocks in the supraoptic regions of these animals, concentration of urine together with reduced urine output and water intake was observed in some animals. Histologic examination of the grafted brains from the responding animals revealed neuronal cells at the implant sites and vasopressin-staining fibers in the median eminence. This study demonstrates the feasibility of the grafting of adult cerebral tissues to correct a genetic hormonal deficiency.

Insulin binding and action in isolated cardiocytes from spontaneously diabetic BB rats

Isolated cardiac myocytes from control and insulin treated diabetic BB rats were used to study cellular alterations related to partly controlled diabetes. Scatchard analysis of equilibrium binding data showed an unaltered affinity and number of insulin receptors in cardiocytes from both groups of animals. Moreover, insulin internalization was found to be identical under these conditions. Insulin action was determined by measuring the effect of the hormone on initial velocities of 3-0-methylglucose influx. Basal activity of the glucose transporter and maximal transport stimulation by insulin remained unaffected. In contrast, the sensitivity of the carrier towards stimulation by insulin was markedly reduced in cardiocytes from diabetic rats with a half-maximal action occurring at an insulin concentration of 3 X 10(-10) mol/l and 9 X 10(-9) mol/l in control and diabetic animals, respectively. The onset of insulin action was much slower in cells from diabetic BB rats exhibiting an increase in the coupling time by 400% from 5 to 20 min, respectively. The data suggest an association of partly controlled diabetes with myocardial alterations located at the postreceptor level.

Release of aldosterone and corticosterone from the adrenal cortex of the Brattleboro rat in response to administration of ACTH

The time-course and dose-response of the in-vivo secretion of aldosterone and corticosterone after administration of ACTH(1-24) were measured in adrenal venous blood from female Brattleboro rats, homozygous for hypothalamic diabetes insipidus and lacking arginine vasopressin (AVP). Female Long-Evans rats were used as controls. All animals were pretreated with dexamethasone and anaesthetized with pentobarbital. Basal secretions of aldosterone and corticosterone were four- to sixfold lower in Brattleboro than in Long-Evans rats. Administration of ACTH consistently increased the secretion of aldosterone and corticosterone similarly in the two groups of rats; maximum values were observed 20-30 min after ACTH injection. However, for all the doses of ACTH (0.05, 0.5 and 5.0 mi.u./100 g body wt) and at every stage of response the secretion rates of aldosterone and corticosterone were twofold lower in Brattleboro than in Long-Evans rats. Furthermore the absolute increase in steroid secretion induced by ACTH was reduced by half in Brattleboro rats. These results show that the impairment of adrenal activity is largely due to a reduced capacity for corticosteroidogenesis in the adrenal cortex of Brattleboro rats. The mechanisms of action of AVP are discussed.

Role of ADH in ethylketocyclazocine-induced diuresis: studies in the Brattleboro rat

Kappa opioids produce diuresis presumably through ADH. We investigated further the role of ADH in kappa-induced diuresis by utilizing the Brattleboro rat, a strain lacking endogenous ADH. Ethylketocyclazocine (EKC), a kappa opioid prototype, increased urine formation in Sprague-Dawley, but not in Brattleboro rats. Furthermore, EKC pretreatment abolished the antidiuretic response to ADH administered exogenously to Brattleboro rats. Our study suggests that, in addition to a fall in plasma ADH reported previously, kappa opioids have direct effects on the renal response to ADH.

Enhanced noradrenergic activity in kidney of Brattleboro rats with diabetes insipidus

The possibility that sympathetic nervous system activity may be altered in Brattleboro rats with diabetes insipidus (DI) was studied using the norepinephrine (NE) turnover technique. Female DI and Long-Evans rats were used. NE turnover in peripheral organs was calculated by measuring the decline in tissue [NE] after inhibition of tyrosine hydroxylase with alpha-methyltyrosine. NE turnover was increased significantly in the kidney of DI rats but was not significantly altered in other peripheral organs examined (heart, duodenum, skeletal muscle). Both NE and epinephrine concentrations in the adrenal gland were significantly higher in the DI rats. Treatment of DI rats for 7 days with vasopressin tannate (Pitressin, 100 mU/100 g) or 1-deamino-[8-D-arginine] vasopressin (DDAVP, 250 ng X kg-1 X day-1) reversed the changes in renal NE turnover and also decreased the turnover in other tissues. The results of these studies suggest that, compared with Long-Evans rats, DI rats have a selective increase in NE turnover in the kidney and the potential to release more catecholamines from the adrenal glands. The apparently nonspecific effect of antidiuretic therapy on NE turnover in DI rats is probably mediated by the epithelial receptor for vasopressin, because both Pitressin and DDAVP produced similar results.

Vitamin D and bone mineral homeostasis during pregnancy in the diabetic BB rat

Vitamin D and bone mineral metabolism during pregnancy were studied in 17 diabetic and 13 control BB rats. On day 21 of pregnancy, reduced mean levels of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3; 56.9 vs. 97.9 pg/ml; P less than 0.0001] and vitamin D-binding protein (304 vs. 482 micrograms/ml; P less than 0.0001) were found in the diabetic rats, while the free 1,25-(OH)2D3 concentration was not different from the control level. Total plasma calcium and total plasma protein concentrations were also significantly decreased in the diabetic group, but the calculated diffusible calcium was not significantly lower. Calcium and phosphorus urinary excretion were increased in the diabetic rats. There was no difference in bone mineral content. The fetuses of the diabetic BB rat had a lower body weight and were hypoinsulinemic. Both 1,25-(OH)2D3 (41.3 vs. 54.7 pg/ml; P less than 0.01) and vitamin D-binding protein (80 vs. 123 micrograms/ml; P less than 0.001) were decreased in the fetuses of diabetic rats, but the free 1,25-(OH)2D3 concentration was slightly but significantly (6.96 vs. 5.54; P less than 0.05) increased. We observed that the fetuses of diabetic rats had fewer ossification centers, counted with the Alizarin Red S staining method. The fetal ash weight was lower in the diabetic group (16.7 vs. 26.9 mg; P less than 0.0001). In addition, the relative calcium and phosphorus, but not magnesium, content of ash was lower in the fetuses of diabetic rats. This reduced mineral content in fetuses of diabetic mothers could be implicated in the pathogenesis of early neonatal hypocalcemia in infants of diabetic mothers.

Behavioral variability within the Brattleboro and Long-Evans rat strains

Samples of genetically diabetes insipidus (DI) and normal (NO) rats were obtained from American suppliers (Rochester (RO)/DI and NO) and from the colony maintained at Charing Cross Hospital in London (Charing Cross (CC)/DI and NO) to test the hypothesis that the behavior of vasopressin-deficient Brattleboro (DI) and possibly normal Long-Evans rats may vary significantly between different colonies. DI rats of both colonies exhibit longer latencies to emerge into an open field than do NO rats. RO/DI and CC/DI rats acquire goal-approach behavior in a straight runway at similar rates. Following shock in the runway goal box, however, RO/DI rats exhibit marked recovery of running behavior relative to CC/DI rats over the ten post-shock sessions. All DI animals show reductions in goal-approach speed on the first post-shock trial, indicating that the aversive experience is remembered. CC/NO rats acquire goal-approach behavior more slowly than RO/NO rats, but neither NO group shows substantial recovery of goal approach behavior following shock. CC/DI rats showed impaired acquisition of a delayed non-match to sample task relative to RO/DI rats. All groups demonstrated the ability to utilize representational memory to solve the delayed non-match to sample problem once the contingency was learned. The results indicate that DI and normal Long-Evans rats from different colonies show marked differences in behavior. Since differences between DI and normal rats on tests indicating memory are not consistent across colonies, it is unlikely that vasopressin deficit is solely responsible for memory deficiencies. However, vasopressin deficiency may result in changes in temperament.

Functional involvement of vasopressin in the maintenance of systemic arterial blood pressures after phenoxybenzamine or phentolamine administration: studies in Long-Evans and Brattleboro rats

The alpha adrenoceptor antagonists phenoxybenzamine and phentolamine are reported to have opposite effects on vasopressin release, the former inhibiting and the latter enhancing it. In this study we have assessed the functional involvement of vasopressin in the maintenance of blood pressure in conscious rats after administration of either phenoxybenzamine or phentolamine. In normal (Long-Evans) rats, phenoxybenzamine caused a small fall in arterial blood pressure, whereas phentolamine initially caused a profound hypotension which was followed by a fluctuating recovery back to normotensive levels. Similar effects were seen in rats deficient in hypothalamic vasopressin (Brattleboro strain). Administration of an antagonist of the cardiovascular actions of vasopressin [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid)-8-D-arginine vasopressin] in the presence of either alpha adrenoceptor antagonist alone was without effect in Long-Evans or Brattleboro rats, but, under these conditions, subsequent administration of captopril caused a profound and sustained hypotension in both strains. Administration of captopril in the presence of either alpha adrenoceptor antagonist alone caused a prompt fall in blood pressure which was sustained for the duration of the experiment in the Brattleboro rats. However, under these conditions, the blood pressure of the Long-Evans rats showed some recovery over the subsequent 45 min; this recovery was antagonized by [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid)-8-D-argine vasopressin]. It is concluded that after alpha adrenoceptor antagonism with either phenoxybenzamine or phentolamine, the renin-angiotensin system exerts a major pressor influence. However, after captopril administration in the presence of phenoxybenzamine or phentolamine, vasopressin contributes to the maintenance of arterial blood pressure in Long-Evans rats; the magnitude of this contribution is similar irrespective of the alpha adrenoceptor antagonist used.

Spontaneous activity of primary afferent neurons in diabetic BB/Wistar rats. A possible mechanism of chronic diabetic neuropathic pain

The mechanism of painful diabetic neuropathy remains unknown. Spontaneous activity in nociceptive primary afferents has been implicated in the genesis of chronic pain due to peripheral nerve injury, and diabetic axonopathy shares some histologic features with traumatic neuropathy. We hypothesized that spontaneous hyperactivity of nociceptive neurons might represent the neurophysiologic mechanism of diabetic neuropathic pain. To test this, we examined the spontaneous activity of primary afferent axons from diabetic BB/Wistar and normal Wistar rat saphenous nerves isolated from central and peripheral connections. Microfilament recordings from diabetic nerves showed a significantly higher incidence of spontaneous discharges in comparison to normal nerves. Furthermore, this spontaneous hyperactivity occurred almost exclusively in potentially nociceptive C-fibers. We conclude that in the diabetic BB/Wistar rat, spontaneous impulses are generated in potential nociceptive primary afferent neurons, and that this may represent the mechanism of chronic diabetic neuropathic pain.

Effect of potassium loading on prostaglandin E2 and F2 alpha excretion in the Brattleboro rat

In order to assess the relative roles played by potassium (K) and the antidiuretic hormone (ADH) on the renal production of prostaglandins (PG) E2 and F2 alpha, the 24 hour urinary excretion of these substances was measured in Brattleboro rats (devoid of ADH) and in control Long Evans heterozygote rats. Rats of each strain received either a normal K intake or a K load for 8 days. Urinary PGE2 and PGF2 alpha were measured by radioimmunoassay in three consecutive 24 h urine collections obtained after the above periods. K loading induced an increase in PGF2 alpha (p less than 0.01), PGE2 showing a non significant trend to decrease. The E/F ratio was decreased in K loaded animals. The changes were qualitatively similar in presence or absence of ADH, but animals with diabetes insipidus had lower levels of PGs than control animals. The results suggest the possibility that K loading induces an increase in the activity of the renal enzyme PGE2-9-ketoreductase. The resulting increase in PGF2 alpha could play a role in K excretion and this response is probably independent of ADH.

Hypothalamo-pituitary regulation of thyrotrophin secretion in chronically catheterized Brattleboro rats

Plasma TSH rhythms were measured in Brattleboro (DI) and control Long-Evans (LE) rats with an intracardiac catheter allowing repeated sampling in conscious unstressed animals. The TSH response to thyrotrophin-releasing hormone (TRH; 500 ng/100 g body weight) was also determined. Finally, hypothalamic and pancreatic TRH concentrations and TRH-degrading activity (TRH-DA) were measured by specific radioimmunoassay. Long-Evans rats had a 24-h rhythm with a major modulatory 8-h component. In DI rats, only the 24-h rhythm was detected. The mean 24-h rhythm-adjusted mean TSH level was higher in DI than in LE rats (1.38 +/- 0.05 and 1.14 +/- 0.06 micrograms/l respectively, P less than 0.01). The peak TSH response to TRH was significantly increased in DI rats while the pituitary concentration of TSH was also higher (0.93 +/- 0.09 vs 0.39 +/- 0.06 micrograms/mg wet weight in LE, P less than 0.001). Hypothalamic TRH and TRH-DA were similar in both strains. The response to propylthiouracil-induced hypothyroidism was identical in both strains. We conclude that DI rats have a normal pituitary sensitivity to tri-iodothyronine but a central dysfunction in the pituitary environment leading to some alterations of TSH secretion.