David de Wied

The induction of excessive grooming in the rat by intraventricular application of peptides derived from ACTH: structure-activity studies.

Abstract Intraventricular administration of synthetic ACTH-like peptides in the rat induces excessive grooming, stretching and yawning. The present study demonstrates that induction of excessive grooming is dose-dependent and independent of the endocrine system. Structure-activity studies show that ACTH1–24, ACTH1–16-NH2, ACTH1–16, α-MSH and βp-MSH are equipotent. Although the presence of the sequence ACTH5–10 in the peptides studies seems of importance in the induction of excessive grooming, it appeared that C-terminal elongation is necessary for the expression of the activity. Administration of [D-Phe7] ACTH4–10 and [D-Phe7] ACTH1–10 results in appreciable grooming activity of the rat. However, substitution of a D-arginine at the 8 position did not alter the activity of ACTH4–10. The structure-activity relationship of these peptides on grooming activity of the rat is compared to that known for retardation of avoidance extinction. Although some similarities exist, it is concluded that the expression of excessive grooming and retardation of avoidance activity is mediated through different mechanisms.

Effect of oxytocin and vasopressin on memory consolidation: sites of action and catecholaminergic correlates after local microinjection into limbic-midbrain structures

The effects of local postlearning microinjections of arginine-vasopressin (AVP) and oxytocin (OXT) on one-trial learning passive avoidance behavior and the influence of AVP on alpha-MPT-induced disappearance of norepinephrine (NE) and dopamine (DA) in discrete brain regions have been studied in the rat. OXT injected bilaterally in the hippocampal dentate gyrus (25-25 pg) or in the midbrain dorsal raphe nucleus (50 pg) significantly attenuated passive avoidance behavior. Facilitation of passive avoidance behavior was observed when the peptide was injected into the dorsal septal nucleus. AVP facilitated passive avoidance behavior when administered into the hippocampal dentate gyrus, dorsal raphe nucleus or dorsal septal nucleus. Injection of either neuropeptides into the central amygdaloid nucleus appeared to be ineffective. One week after the behavioral experiments a repeated injection of AVP into the hippocampal dentate gyrus increased the disappearance of NE in the dentate gyrus and in the nucleus ruber. An injection into the dorsal septal nuclei decreased the NE disappearance in the dorsal septal nucleus itself and increased it in the nucleus ruber. Injection in the dorsal raphe nucleus led to an increase in the disappearance of DA in the locus coeruleus and in the nucleus ruber. It is concluded that memory consolidation can be oppositely influenced by local application of minute amounts of either OXT or AVP into certain limbic-midbrain structures, suggesting an involvement of these brain regions in the memory effects of these peptides. Modulation of catecholamine turnover in specific brain areas after AVP administration may be related to this behavioral effect.

Oxytocin, vasopressin and memory: opposite effects on consolidation and retrieval processes

The observation that administration of pitressin, a relatively crude extract of the neurohypophysis, during acquisition resulted in a long lasting resistance to extinction of a shuttle-box avoidance response led us to suggest that hypothalamo-neurohypophyseal principles affect memory processes 11. Subsequent studies showed that vasopressin was responsible for the long-term effect on avoidance behavior3, s. Timegradient studies with vasopressin favoured the hypothesis that consolidation processes are facilitated by the peptide s. The consolidation hypothesis has been corroborated by studies on passive avoidance 1 and approach behavior a and by the anti-amnesic effect of vasopressin, analogs and fragmentsla,~4,19,2L Since preretention administration of the peptide also facilitates passive avoidance behaviod, 5, increases resistance to extinction of active avoidance 5,s and approach responses 15 and vasopressin alleviates amnesia, when given prior to the retention test 7,19, the peptide may also enhance retrieval processes. Oxytocin, the other neurosecretory product of the hypothalamo-neurohypophy seal system also affects the maintenance of avoidance responses but it has an effect opposite to that of vasopressin 6,2°. Observations in particular with intracerebroventricular administration of oxytocin suggested that this peptide may be a naturally occurring amnesic neuropeptide 6. This hypothesis is obviously untenable unless timegradient effects which are typical for amnesic treatments are demonstrated. Accordingly, the present experiments were aimed to investigate the effects of oxytocin administered intracerebroventricularly at various intervals after the learning trial on the retention of a passive avoidance response. For comparison, the effects of similarly administered arginine-vasopressin (AVP) were also studied. Male SPF Wistar rats (Cpb, TNO, Zeist, The Netherlands), weighing 160-180 g, were used. The rats had free access to food and water and were kept under controlled light-dark conditions (light on between 5.00 and 19.00 h). For intracerebroventricular treatment a polyethylene cannula was implanted in a lateral ventricle under anesthesia

Central Nervous System Effects of the Neurohypophyseal Hormones and Related Peptides

This review of the CNS effects of the neurohypophyseal hormones and related neuropeptides discusses recent data illustrating the significance of these principles in brain function, synthesis, distribution, in particular in extrahypothalamic brain structures, binding sites, and signal transduction. Binding sites for vasopressin of the vascular V1a type have been found in the CNS and there is evidence for the existence of a subtype of the antidiuretic V2 receptor in the brain. Also two types of oxytocin binding sites have been detected. One widely distributed throughout the CNS is comparable to the uterine type receptor and a sexually dimorphic slightly different type is found in the ventromedial nucleus. Vasopressin and oxytocin can be converted to highly selective C-terminal fragments as AVP-(4-9) and OXT-(4-9) and shorter fragments. Conversely they can be acetylated. This almost completely blocks intrinsic activity in bioassays for central and peripheral effects. Such modifications are a good example of the plasticity of a neuropeptide system. For a number of CNS effects of the neurohypophyseal hormones, the whole molecule is required, as it is for their endocrine effects. This is the case for the influence of vasopressin on social communication, temperature regulation, epilepsy, and barrel rotation which may be an animal model of febrile convulsions, and some aspects of the central regulation of the cardiovascular system and for oxytocin on sexual behavior, social communication, and grooming. Nonendocrine C-terminal conversion products seem to exert their effects exclusively on the brain. These neuropeptides modulate learning and memory processes, social recognition, and rewarded behavior. The neuroendocrine and neuropeptide effect of vasopressin and oxytocin and related neuropeptides often exert their CNS effects in an opposite way. Neurochemical and electrophysiological studies suggest that norepinephrine, dopamine, serotonin, and glutamate are the neurotransmitters involved in the influence of the neurohypophyseal hormones and related neuropeptides on brain function. It appears that adequate amounts of vasopressin and oxytocin to induce these effects are released at the appropriate sites of action. It is postulated that the mix of neuropeptides released in the brain in response to environmental changes qualifies the behavioral, neuroendocrine, and immune response and the response of the autonomic nervous and vegetative systems of the organism. Although various other neuropeptides, such as those colocalized in vasopressinergic and oxytocinergic neurons, those produced in pro-opiomelanocortin (POMC) systems, and others, play a role in the modulation of adaptive responses, the neurohypophyseal hormones are unique in that their production sites in the hypothalamus serve the periphery, the pituitary, and the brain.

Neuroleptic activity of the neuropeptide β-LPH62–77 ([Des-Tyr1]γ-endorphin; DTγE)

In contrast to β-endorphin, α-endorphin, β-LPH61–69 and Met-enkephalin which delay extinction of pole-jumping avoidance behavior (De Wied et al., 1978), γ-endorphin given either subcutaneously (30 ng/rat) or intraventricularly (0.3 ng/rat) facilitated extinction. Removal of the N-terminal amino acid residue tyrosine — yielding the neuropeptide [Des-Tyr1]γ-endorphin (DTγE) — which destroys the opiate-like activity as determined on the electrically driven guinea pig ileum, potentiated the facilitating effect of γ-endorphin on pole-jumping avoidance behavior. Observations on passive avoidance behavior gave essentially the same results. Whereas α-endorphin facilitated this behavior. DTγE attenuated passive avoidance behavior. Amounts of γ-endorphin and DTγE which were highly active on extinction of pole-jumping avoidance behavior (0.3 μg s.c. per rat) were without effect on gross behavior in an open field. Much higher amounts (10–50 μg s.c. per rat) also failed to affect the rate of ambulation in an open field. In relatively high doses (20 μg i.v.t. or 50 μg s.c. per rat), γ-endorphin and in particular DTγE were positive in the various “grip tests”. Haloperidol given s.c. (0.03–0.1 μg/rat) facilitated extinction of pole-jumping avoidance behavior and attenuated passive avoidance behavior. The same amounts decreased ambulation in an open field. In higher doses haloperidol was active in the “grip tests” but in addition caused severe immobility, ptosis and extension of the lower limbs. Intraventricularly administered morphine or β-endorphin induced wide open eyes, exophthalmus, rigidity and reduced reflexes, in contrast to γ-endorphin and DTγE which did not produce such effects. These results are interpreted to indicate that DTγE or a closely related peptide is an endogenous neuroleptic. It may be that a reduced availability as a result of an inborn error in the generation of DTγE is an etiological factor in psychopathological states for which neuroleptic drugs are beneficial.

Arginine8-vasopressin affects catecholamine metabolism in specific brain nuclei.

Abstract Following the i.c.v. administration of arginine8-vasopressin (30 ng in 1 μl saline) to rats that had been injected i.p with α-MPT 30 min prior to the administration of the peptide catecholamine metabolism was altered in a restricted number of brain nuclei. Noradrenaline disappearance was accelerated as compared to saline treated controls in the dorsal septal nucleus, the anterior hypothalamic nucleus, the medial forebrain bundle, the parafascicular nucleus, the dorsal raphe nucleus, the locus coeruleus, the nucleus tractus solitarii and the Al-region. In the supraoptic nucleus and the nucleus ruber a decreased noradrenaline disappearnce was observed after the administration of the peptide. Dopamine disappearance was accelerated in the caudate nucleus, the median eminence, the dorsal raphe nucleus and the A8-region. These results support the view that vasopressin is participating in the regulation of a variety of physiological processes by modulating neurotransmission in specific brain nuclei.

ACTH-like peptides and opiate receptors in the rat brain: Structure-activity studies

The present study aims at further identifying the interaction of ACTH-like peptides and rat brain opiate receptors in vitro. The sequence ACTH4-10 is crucial with respect to affinity since it is the shortest sequence to inhibit the binding of [3H]-dihydromorphine and [3H]-naltrexone to these receptors. A second active site seems to be localized in the N-terminal part of ACTH11-24. This structure-activity relationship is compared to that observed for these peptides on the adrenal cortex and behavior.

Effect of catecholamine-receptor stimulating agents on blood pressure after local application in the nucleus tractus solitarii of the medulla oblongata

The effect of various catecholamines and alpha-mimetics, given by microinjection in the A2-region of the nucleus tractus solitarii (NTS), on blood pressure was investigated in anesthetized male rats. A dose-dependent decrease of blood pressure and heart rate was induced by adrenaline as the most effective drug, followed by noradrenaline, dopamine, alpha-methylnoradrenaline and octopamine. Ablation of the rostral or caudal part of the NTS, or removal of the area postrema did not diminish the effect of alpha-methylnoradrenaline. Higher doses of noradrenaline and alpha-methylnoradrenaline caused an initial rise of blood pressure, while the blood pressure lowering effect of noradrenaline was diminished, and that of alpha-methylnoradrenaline and dopamine delayed. Isoprenaline and the (+)-stereoisomers of noradrenaline and alpha-methylnoradrenaline were ineffective. The hypotensive effect of dopamine was not prevented by systemic injection of the dopamine beta-hydroxylase inhibitor FLA 63. Prior application of haloperidol, yohimbine and phentolamine antagonized the hypotensive response to dopamine and alpha-methylnoradrenaline. Application of peripherally effective alpha-mimetics into the A2-region had no or little effect, while high doses increased blood pressure. Tyramine and clonidine caused some decrease of blood pressure. Clonidine also decreased blood pressure when it was applied in the area of the locus coeruleus. Application of isoprenaline in the locus coeruleus also decreased blood pressure while in contrast adrenaline, noradrenaline, dopamine and alpha-methylnoradrenaline increased blood pressure. The present data suggest that the catecholaminergic receptors in the A2-region of the NTS differ from the classic vascular alpha-receptor and that the NTS also may contain structures which can antagonize the decrease in blood pressure.

Interaction between acth fragments, brain opiate receptors and morphine-induced analgesia

The present study confirms that N-terminal fragments of ACTH have an affinity for rat brain opiate receptors in vitro. Such peptides, devoid of corticotrophic activity, were found to inhibit morphine-induced analgesia if they also possessed affinity for opiate receptors in vitro. The structure-activity relationship for these two parameters is comparable to that observed for the same peptides on the induction of excessive grooming.

Differential Responses to Osmotic Stress of Vasopressin-Neurophysin mRNA in Hypothalamic Nuclei

mRNA encoding the vasopressin-neurophysin precursor was quantitated in individual hypothalamic nuclei of rats by a liquid hybridization assay. Drinking of 2% saline for 14 days, a treatment that increased the plasma vasopressin concentration 9-fold, resulted in a 5- and 2-fold increase in mRNA levels in the supraoptic and paraventricular nucleus, respectively. This osmotic stimulus had no effect on vasopressin-neurophysin mRNA content of the suprachiasmatic nucleus. This dissociation in regulation of vasopressin-neurophysin mRNA in hypothalamic nuclei indicates the existence of two separate vasopressin systems that are independently activated.