Tjeerd B. van Wimersma Greidanus

Penetration of neurohypophyseal hormones from plasma into cerebrospinal fluid (CSF): Half-times of disappearance of these neuropeptides from CSF

The penetration of neurohypophyseal peptides after peripheral administration into the cerebrospinal fluid (CSF) was studied in freely moving rats. In addition, the clearance of these peptides from CSF was investigated. Increased concentrations of vasopressin (AVP) in CSF were detectable 2 min after s.c. injection of 5.0 micrograms of this peptide. Peak concentration was reached at 5 min after administration and this level declined slowly over the next hour. Administration of 5.0 micrograms oxytocin (OXT) s.c. or i.v. resulted in increased OXT levels in CSF within 10 min after application. After 60 min a significant elevation of OXT in CSF was no longer present. These data reveal that approximately 0.002% of the peripherally applied amount of AVP or OXT reached the central nervous system at 10 min after injection. AVP (2.5 ng) and OXT (5.0 ng) applied into one of the lateral brain ventricles reached the cisternal cavity within 2 min after administration. Both neuropeptides were cleared from the CSF with terminal half-times of 26 and 19 min for AVP and OXT, respectively. The present data demonstrate that neurohypophyseal hormones do cross the blood-brain barrier in amounts obviously sufficient to induce central actions.

Effects of morphine and β-endorphin on basal and elevated plasma levels of α-MSH and vasopressin

Morphine induced an increase of plasma α-MSH levels and a decrease of AVP levels after peripheral or intracerebroventricular administration. This increase of α-MSH levels and decrease of AVP levels after morphine treatment was observed in non-stimulated animals as well as in rats in which the hormone levels were elevated by water deprivation or by administration of hypertonic saline. These latter effects of morphine on plasma levels of α-MSH and AVP could be blocked by simultaneous administration of naltrexone. β-Endorphin also increased plasma α-MSH levels and lowered plasma AVP levels. From these effects only the increase of the plasma α-MSH level and not the decrease of plasma AVP could be blocked by naltrexone. Moreover PLG treatment was ineffective with respect to the endorphin-induced decrease in plasma AVP, but it partly blocked the increase of plasma α-MSH when this tripeptide was given in combination with β-endorphin.

Modulation of passive-avoidance behavior of rats by intracerebroventricular administration of antivasopressin serum

Intracerebroventricular administration of antivasopressin serum induces a severe disturbance in passive-avoidance behavior, due to an interference in memory processes by selective binding of vasopressin in the brain. Injection of antivasopressin serum immediately after the single learning trial induces almost complete inhibition of the passive-avoidance response when the animals were tested for retention 24 hr later. If injection of the antivasopressin serum is postponed for maximally 2 hr after the learning trial, the treatment still results in a marked disturbance in passive-avoidance behavior, indicating that storage processes involved in memory consolidation last for several hours. Moreover, administration of antivasopressin serum 1 hr prior to the retention session also results in passive-avoidance deficits. This suggests that vasopressin is also involved in retrieval processes.

A rapid and simple cannulation technique for repeated sampling of cerebrospinal fluid in freely moving rats

A cannulation technique for frequent sampling of cerebrospinal fluid (CSF) in unanaesthetized freely moving rats is described. A permanent stainless steel cannula, constructed in such a way that no loss of CSF occurs, is placed into the rats cisterna magna and fixed to the skull by anchoring screws and dental cement. A special CSF outflow opening of the cannula is connected to polyethylene tubing for CSF sampling. Amounts of 50-150 microliters CSF can be collected repeatedly without any sign of disturbing the animal. The technique lends itself not only to pilot studies in which within a short period of time a large amount of CSF is wanted, but also to experiments in which physiological conditions are required.

Vasopressin modulates the activity of catecholamine containing neurons in specific brain regions

Following the i.c.v. administration of antivasopressin serum the alpha-MPT-induced disappearance of noradrenaline was decreased in the dorsal septal nucleus, parafascicular nucleus and the rostral part of the nucleus tractus solitarii, whereas that of dopamine was lowered in the caudate nucleus and in the A2 region of the medulla oblongata. In general the effects are opposite to those previously found following the i.c.v. administration of vasopressin. The results support the hypothesis that vasopressin modulates catecholamine neurotransmission in specific brain regions of the rat.

Behavioral profile of ψ-MSH: Relationship with acta and β-endorphin action

Abstract In view of the close structural similarity of the pro-opiocortin fragment γ-MSH and of ACTH/MSH type peptides, the behavioral profile of γ-MSH was explored. Attention was first focussed on behavioral procedures in which ACTH/MSH related neuropeptides have been found effective. Using different procedures to test avoidance behavior, it was found that γ-MSH and ACTH-like neuropeptides had opposite effects. In this respect the activity of γ-MSH resembles that of opiate antagonists rather than that of β-endorphin. Accordingly, ACTH 1–24 -induced excessive grooming which is blocked by opiate antagonists, is attenuated by γ-MSH. In addition, γ-MSH injected into the periaqueductal gray matter of the brainstem of opiate naive rats elicited symptoms reminiscent of those seen after opiate withdrawal. γ-MSH attenuated more or less several effects of intracerebroventricularly administered β-endorphin (e.g. antinociception, hypothermia, α-MSH release) and decreased acquisition of heroin self-administration. Although γ-MSH at rather high doses displaced naloxone from its specific binding sites in brain homogenates, it did not interfere with β-endorphin-induced effects on in vitro muscle preparations (guinea pig ileum, rat rectum). Interestingly, γ-MSH induced relaxation of the rat rectum in vitro . It is postulated that γ-MSH may attenuate β-endorphin-induced effects by acting via γ-MSH receptor sites (functional antagonism), although a pharmacological antagonism cannot be excluded as yet.

Amygdaloid Lesions Block the Effect of Neuropeptides (Vasopressin, ACTH4-10) on Avoidance Behavior

Lesions in the amygdaloid complex result in an increased activity of rats in open field behavior in that generally more exploration and rearing is observed as compared with sham-operated animals. No effect of the lesion was observed on acquisition and extinction of an active avoidance response, but the amygdala lesions block the inhibitory effect of the neuropeptides vasopressin and ACTH4–10 on extinction of a conditioned avoidance response.

Microinjection of arginine8-vasopressin antiserum into the dorsal hippocampus attenuates passive avoidance behavior in rats

Antiserum to arginine8-vasopressin was microinjected bilaterally into the dentate gyrus of the dorsal hippocampus and the effect of passive avoidance behavior was studied. After the single learning trial of a passive avoidance response, immediate bilateral injection of 1 microliter antiserum (diluted to 1/50) attenuated passive avoidance responding 24 hr later. In immunocytochemical control studies with injection of undiluted antiserum into the dentate gyrus a spreading was observed towards the ventral hippocampus and the dorsal septum. Additionally, administration into the lateral ventricle of 2 microliters of 1/50 dilution of the antiserum did not affect the behavior. For an attenuation of passive avoidance behavior via intraventricular injection, 2 microliters of a 1/10 dilution of anti-AVP was required. These data suggest that endogenous vasopressin in the septo-hippocampal system might be involved in memory processes.

Differential effects of various stimuli on AVP levels in blood and cerebrospinal fluid

Water deprivation, drinking water containing 2% NaCl, or systemic injection with histamine or nicotine markedly increased plasma levels of vasopressin in rats. In contrast, none of the applied stimuli changed vasopressin levels in the CSF collected simultaneously from the same animal. These data suggest that the blood levels of vasopressin are controlled quite differently from CSF levels of this hormone.

Influence of peptides on reduced response of rats to electric footshock after acute administration of morphine.

Acute treatment of rats with morphine (10 mg/kg) resulted in a marked reduction of motor response to inescapable electric footshock (EFS). Nalorphine (2mg/kg) antagonized this action of morphine. Pretreatment with synthetic ACTH 1-24 (10 IU) 60 min prior to testing also inhibited this morphine-induced reduction, whereas other ACTH-like peptides, lacking corticotrophic activity, were ineffective. ACTH 1-24 had no effect on the response of adrenalectomized rats to EFS after morphine. In intact rats dexamethasone pretreatment 4 hr prior to testing also antagonized the action of morphine on EFS. Taken together these findings suggest that ACTH 1-24 interferes with the antinociceptive action of morphine and that the integrity of the adrenal is essential for demonstration of this antagonism.