Inferior quality of RSA during paradoxical sleep in rats with hereditary diabetes insipidus

Effects of vasopressin and related peptides on neurons of the rat lateral septum and ventral hippocampus

The effects of vasopressin (VP), VP fragments and propressophysin glycopeptide on neuronal activities in the septum-hippocampus complex of rats were studied in vitro and in vivo. The frequency of the hippocampus theta rhythm in Brattleboro rats homozygous for diabetes insipidus was significantly slower than that of heterozygous litter mates and normal rats. Intracerebroventricular micro-injection of des-glycine-amide vasopressin corrected for several hours the frequency deficit of the theta rhythm in the homozygous Brattleboro rats and the centrally administered VP slowed down theta rhythm in normal rats. Microinotophoretically administered VP excited single neurons in the lateral septum of ventral hippocampus, and/or facilitated the responses of these neurons to glutamate and to stimulation of the glutamatergic afferent fibers in the fimbria bundle. The excitatory effects of VP vanished within seconds after termination of the peptide administration, however, the peptide-induced enhancement of glutamate and syntatically induced excitations were sustained for up to 60 min after the peptide administration. In vitro, pM concentrations of VP, VP 4-8 and C-terminus glycopeptide of propresophysin facilitated for 30-60 min the glutamate-mediated EPSPs in neurons of the lateral septum or the ventral hippocampus. The EPSPs increase in the lateral septum neurons was not prevented by pretreatment with antagonist of the V1a type of the vasopressin receptor. The resting membrane potential and input resistance were not affected by the peptides. A low-frequency electrical stimulation in the diagonal Band of Broca or in the Bed nucleus of the stria terminals, sources of the vasopressinergic innervation of the septum, facilitated the negative wave of the filed potentials responses evoked in the lateral septum by stimulating the fimbria bundle fibers in control Long-Evans and Brattleboro rats heterozygous for diabetes insipidus. The field potential increase was sustained for several hours after the stimulation, and it was not occluded by long-term potentiation elicited by high frequency stimulation of the fimbria bundle afferent fibers. Brattleboro rats homozygous for diabetes insipidus failed to show the filed potential increase after the diagonal band stimulation. It is suggested that the long-lasting facilitation of glutamate-mediated excitations might be a physiological action of the propressophysin-derived peptides in the septum-hippocampus complex which, in concert with other forms of synaptic plasticity like the long-term potentiation, facilitates the hippocampus-mediated forms of learning and memory. This action is presumably related to the memory enhancing effect of the propressophysin-derived peptides.

Vasopressin regulates human sleep by reducing rapid-eye-movement sleep

In two double-blind experiments, effects of intravenous infusion of arginine vasopressin (AVP) on sleep were evaluated in 2 groups of 10 men (20-35 yr). In experiment I, subjects were tested on two occasions, during which they received either placebo or 0.33 IU/h AVP. In experiment II, on three different occasions, subjects received either placebo or 0.66 or 0.99 IU/h AVP. Infusions were administered between 2200 and 0700 h. Nocturnal plasma AVP concentrations were close to the upper limit of the normal physiological range during 0.66 IU/h AVP (16.6 +/- 2.2 pg/ml) but markedly exceeded this range during 0.99 IU/h AVP (25.0 +/- 1.6 pg/ml). Results indicate primary effects of AVP on rapid-eye-movement (REM) sleep, with moderate reductions in REM sleep during 0.33 IU/h AVP (averaging -10.5%) and with substantial reductions in REM sleep (-24.0%) during 0.66 IU/h AVP. During 0.99 IU/h AVP the effect did not further increase (-24.4%). Less consistent effects of AVP were an increase in stage 2 sleep and in time awake. Effects of AVP were not mediated by changes in cortisol or blood pressure. Results suggest AVP to participate in REM sleep regulation under normal physiological conditions.

Hippocampal electrical activity in the diabetes insipidus (Brattleboro) rat

Theta rhythm was recorded from the hippocampus in normal male and female rats, and from female rats with homozygous alleles (HODI) and heterozygous alleles of diabetes insipidus (HEDI). Second-by-second spectral analysis of the complete period of rapid eye-movement sleep indicated that HODI and HEDI rats had the same theta frequency range as normals, but the mean theta frequency (6.4 cycles c/s) was lower than normal (6.8 c/s), mainly in having a smaller proportion of frequencies greater than or equal to 7.8 c/s. Pharmacological studies in the waking rat demonstrated a theta rhythm in the HODI and normal rats after atropine or after urethane and eserine, indicating the presence of both atropine-sensitive and atropine-resistant pathways. However, after eserine, a huge increase in hippocampal fast waves (30 to 55 c/s) accompanying struggling (as compared with immobility) was found in the HODI rat, which was double that in the normal rat. An enhanced cholinergic input or response at the septal or hippocampal level may account for the large fast wave as well as the lower mean theta frequency in the HODI rat.

Endogenous vasopressin and the weaning period in Brattleboro rats

Vasopressin, which is important for behavior and brain development, begins to influence osmoregulation with the onset of weaning. We studied the role of vasopressin in the development of feeding behavior since its mechanisms might be essential for the age determination of the suckling and weaning periods. Radionuclide methods were employed to follow maternal milk, solid food and water consumption in developing Brattleboro rats. The appearance of solid food intake and the spontaneous extinction of maternal milk intake indicated the onset and the end of weaning. The absence of endogenous vasopressin did not influence the onset and/or the duration of the weaning period. Both vasopressin-deficient homozygous Brattleboro rats and their heterozygous littermates (with preserved vasopressin synthesis) began to consume solid food and water at the age of 16 days and their intake of maternal milk was terminated about the 27th day of age. Thus, the maturation of feeding behavior in the suckling and weaning periods is vasopressin-independent.

Hypothalamic neuropeptides and memory

Vasopressin and oxytocin exert pronounced effects on behavior by a direct action on the brain. A single injection of vasopressin results in a long-term inhibition of extinction of a conditioned avoidance response suggesting that vasopressin triggers a long-term effect on the maintenance of a learned response, probably by facilitation of memory processes. In addition vasopressin improves passive avoidance behavior, facilitates retention of sexually motivated T-maze choice behavior in male rats, delays extinction of an appetitive discrimination task, affects approach behavior to an imprinting stimulus in ducklings, delays the postcastration decline in copulatory behavior in male rats, prevents or reverses amnesia induced by electroconvulsive shock, CO2 inhalation, pentylenetetrazol or puromycin. The majority of these effects may be explained by stimulatory influences of vasopressin on memory processes. Generally oxytocin exerts effects which are opposite to those of vasopressin and it has been suggested that oxytocin may be an amnesic neuropeptide. Evidence has been obtained that endogenous vasopressin and oxytocin play a physiological role in brain processes related to memory. Various limbic system structures seem to act as the anatomical substrate for the behavioral effects of vasopressin and different neurotransmitter systems seem to be involved. It is postulated that in case vasopressin affects retrieval processes the site of action is located in the amygdala and the dentate gyrus of the hippocampal complex with dopamine and serotonin as the respective neurotransmitter systems involved.(ABSTRACT TRUNCATED AT 250 WORDS)

EEG effects of subcutaneous and intracerebroventricular injections of arginine vasopressin in the rat

Several studies have suggested that arginine vasopressin (AVP) may act centrally as a neurohormone or neuromodulator to produce electrophysiological and behavioral effects. However, there are few reports of EEG effects of AVP in unanesthetized, behaving animals. In the present study the EEG effects of "behaviorally relevant" subcutaneous (SC) doses of AVP (6 micrograms/kg) known to raise blood pressure were compared to "behaviorally relevant" intracerebroventricular (ICV) doses (0.1-1.0 ng) and multiple "toxic" ICV doses (1.0 microgram) of AVP. Central injections of toxic doses of AVP produced behavioral arrest, bodily barrel rolling, and EEG slowing, but did not induce electrographic signs of seizure activity. Comparison of the spectral characteristics of the EEG revealed some similarities in the distribution of power between SC and the 1.0 ng ICV dose; whereas ICV doses of 0.1 and 0.5 ng produced power distributions that were different from those seen following saline or SC doses of AVP. The similarities in EEG activity between SC injections and the 1.0 ng ICV dose suggest a common brain state may be induced by the two routes of administration in those dose ranges.

Centrally mediated effects of neurohypophyseal hormones

The neurohypophyseal hormones oxytocin and vasopressin cause a variety of biological effects in animals which are mediated by central nervous system mechanisms. Among the best studied of these effects is the modulation of both memory processes and the development of drug tolerance and dependence. Neurohypophyseal hormones have also been shown to alter various physiological parameters such as heart rate and body temperature following central administration. In addition, these peptides can profoundly alter spontaneous, unlearned behavior in several rodent species. Many of the centrally mediated effects of neurohypophyseal hormones have been shown to be elicited at sites within the brain stem and the limbic system where vasopressin and oxytocin occur in cell bodies, axons and nerve terminals, suggesting a physiological role for these peptide effects. The various central effects of neurohypophyseal hormones involve different mechanisms which can be distinguished from one another on the basis of required dose, time-course of action, and structure-activity relationships. Thus, alterations of spontaneous behavior are mediated by putative receptors closely related to vasopressin receptors in blood vessels responsible for the peripheral pressor response while the effects on memory processes are mediated by a mechanism which is not closely related to those involved in the peripheral hormonal effects of the peptides. The influence of neurohypophyseal hormones on memory and attention may be useful clinically. A potential role for these peptides in mental disorders is discussed.

Neurohypophysial hormones and brain function: the neurophysiological effects of oxytocin and vasopressin

An increasing body of evidence suggests that the neurohypophysial hormones, in addition to their classical actions, may also act as neurotransmitters. They have a widespread but discontinuous distribution in the CNS; apart from their presence in the magnocellular nuclei they may be found in the hippocampus, amygdala, septum, substantia nigra, brainstem and spinal cord. They exert profound effects on behavior, particularly on memory, a function frequently ascribed to the hippocampus, amygdala and septum; on memory consolidation, internal reward and self stimulation functions frequently ascribed to brainstem and diencephalic aminergic systems including the substantia nigra and on sensory and autonomic responses which involve the medulla and spinal cord. When applied to the CNS they alter multiple unit activity in certain regions, particularly the hippocampus and cells which contain neural lobe hormones appear to be able to drive other cells synaptically. Finally application of the hormones can profoundly affect the activity of single nerve cells in just those parts of the CNS where, on the basis of their behavioral actions, they might be expected to act.

ACTH4-10 and memory in ECT-treated and untreated patients. I. Effect on consolidation

The aim of the study was to investigate the possible effect of a single dose of ACTH4-10 (30 mg subcutaneously) on memory as measured with a test battery appropriate for the study of "consolidation". Twenty depressive inpatients participated in the intraindividual double-blind cross-over comparison between ACTH4-10 and placebo in connection with the second and third treatment in the ECT series. ACTH4-10 (or placebo) was administered subcutaneously 30 min after unilateral ECT. Memory functions were examined 90 min before and 150 min after the administration of the drug. A similar design was used in a study of 20 inpatients with neurotic depression not treated with ECT. The results of both studies give no evidence of a positive influence of a single dose of ACTH4-10 on consolidation of memory. Possible sources of error are discussed.

Hippocampal rhythmic slow activity (RSA; theta): a critical analysis of selected studies and discussion of possible species-differences

The literature concerning the correlates of hippocampal RSA (theta) has seen a wealth of hypotheses generated from seemingly contradictory data. Two possible reasons for this are examined here. (1) An analysis of the maximum published RSA amplitudes in over 70 papers shows that there is enormous variation in how effective various research groups have been in tapping the hippocampal RSA generator zones. It is suggested that this variation is a major source of 'contradictory data'. The enormous variability is probably due to the fact that the laminar structure of the hippocampus, and the location of two seemingly independent 180 degrees out-of-phase RSA generators, results in very disparate signals being recorded by electrodes of different configurations. Electrodes which are not optimally placed result in records which may provide misinformation as to whether or not the hippocampus is in the RSA 'mode'. The results of studies with less than adequate records must therefore be viewed with great caution. (2) An explanation often evoked to account for much of the controversy is that of species differences. This idea is examined and it is suggested that there are probably not major species differences in that all of the species appropriately examined thus far have neural systems capable of producing both an atropine-sensitive and an atropine-resistant form of RSA. All species (with the exception of primates) also show relations of RSA to ongoing motor behavior. However, there are definitely species differences in the neural mechanisms underlying the production of atropine-sensitive, immobility-related RSA. Although all species appear to be capable of producing immobility-related RSA some do so only rarely (e.g. rats), while others do so frequently, particularly in response to sensory stimulation (e.g. rabbits, cats, guinea pigs). Therefore, the answer to the question as to whether there are species differences in the occurrence of RSA may be yes, or not, depending upon how specifically the question is posed.

Action of posterior pituitary neuropeptides on the nigrostriatal dopaminergic system

The effect of vasopressin, oxytocin and the C-terminal tripeptide of oxytocin, prolyl-leucyl-glycinamide (PLG), were tested on rotational behavior, following unilateral 6-OHDA-enduced lesion of the dopaminergic cell bodies in the substantia nigra. Intraventricular injection of lysine8-vasopressin, oxytocin or PLG caused ipsilateral (towards the lesioned side) rotation, as did peripheral administration of amphetamine. Direct local microinjection of the peptides into the substantia nigra on the intact side was without effect. The data suggest that posterior pituitary neuropeptides (vasopressin and oxytocin) caused presynaptic activation of the nigrostriatal dopaminergic terminals.