V.M. Wiegant

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.

Differential release of amino acids, neuropeptides, and catecholamines from isolated nerve terminals

We have investigated transmitter release from small and large dense-core vesicles in nerve terminals isolated from guinea pig hippocampus. Small vesicles are found in clusters near the active zone, and large dense-core vesicles are located at ectopic sites. The abilities of Ca2+ channel activation and uniform elevation of Ca2+ concentration (with ionophores) to evoke secretion of representative amino acids, catecholamines, and neuropeptides were compared. For a given increase in Ca2+ concentration, ionophore was less effective than Ca2+ channel activation in releasing amino acids, but not in releasing cholecystokinin-8. Titration of the average Ca2+ concentration showed that the Ca2+ affinity for cholecystokinin-8 secretion was higher than that for amino acids. Catecholamine release showed intermediate behavior. It is concluded that neuropeptide release is triggered by small elevations in the Ca2+ concentration in the bulk cytoplasm, whereas secretion of amino acids requires higher elevations, as produced in the vicinity of Ca2+ channels.

Salivary cortisol and cardiovascular activity during stress in oppositional-defiant disorder boys and normal controls

BACKGROUND Arousal-regulating mechanisms are important in explaining individual differences in antisocial behavior. METHODS Alterations in salivary cortisol concentration and cardiovascular activity were studied in 21 boys with oppositional defiant disorder (ODD) and 31 normal controls (NC) during a 2-hour stressful procedure involving frustration and provocation. RESULTS Baseline levels of heart rate (HR) were significantly lower in the ODD group, but their HR levels were higher during provocation and frustration. Cortisol levels in the ODD group were overall lower than those of the NC group, and the effect of stress seemed to be minimal and similar for both groups; however, individual differences were large. Since anxiety plays an important mediating role in cortisol response, subjects were divided into one of four groups based on the intensity of their externalizing behavior and anxiousness. Cortisol increase due to stress exposure was strongest in highly externalizing and highly anxious subjects; cortisol decrease was strongest in those subjects who were high in externalizing behavior and low in anxiousness. CONCLUSIONS The results of the study support an important role for hypothalamic-pituitary-adrenal axis sympathetic autonomic functioning in persistent antisocial behavior in young boys.

Evidence for a direct neuronal pathway from the suprachiasmatic nucleus to the gonadotropin-releasing hormone system: combined tracing and light and electron microscopic immunocytochemical studies

The timing and occurrence of the preovulatory luteinizing hormone (LH) surge in the female rodent are critically dependent on the integrity of the suprachiasmatic nucleus (SCN). Destruction of the SCN leads to a cessation of the ovarian cycle, whereas implantation of estrogen in ovariectomized rats results in daily LH surges. The anatomical substrate for these effects is not known. Previous studies involving lesions of the SCN have suggested the presence of a direct vasoactive intestinal polypeptide (VIP)‐containing pathway to gonadotropin‐releasing hormone (GnRH) neurons. To further investigate the direct connection between the SCN and the GnRH system, we have used tract‐tracing with the anterograde tracer Phaseolus vulgaris‐leucoagglutinin (PhaL) in combination with an immunocytochemical staining for GnRH in light and electron microscopic studies. Small, unilateral PhaL deposits, especially when they were placed in the rostral ventrolateral portion of the SCN, revealed a bilateral projection to the preoptic area, where PhaL‐immunoreactive fibers were regularly found in close apposition to GnRH neurons. Ultrastructural studies showed synaptic interaction of PhaL‐containing fibers with GnRH‐immunoreactive (IR) cell bodies, thus demonstrating a direct SCN‐GnRH connection. Taken together, these data provide evidence for the existence of a monosynaptic pathway from the SCN to the GnRH system in the hypothalamus of the female rat. We suggest that this pathway may contain at least VIP as a putative transmitter and may play a role in the circadian regulation of the estrous cycle in the female rat. J. Comp. Neurol. 384:569–579, 1997.

Stress, Depression and Hippocampal Apoptosis.

In this review, we summarize and discuss recent studies on structural plasticity changes, particularly apoptosis, in the mammalian hippocampus in relation to stress and depression. Apoptosis continues to occur, yet with very low numbers, in the adult hippocampal dentate gyrus (DG) of various species. Stress and steroid exposure modulate the rate of apoptosis in the DG. Contrary to earlier studies, the impact of chronic stress on structural parameters of the hippocampus like cell number and volume, is rather modest, and requires prolonged and severe stress exposure before only small reductions (< 10 %) become detectable. This does not exclude other structural parameters, like synaptic terminal structure, or dendritic arborization from being significantly altered in critical hippocampal subregions like the DG and/or CA3. Neither does it imply that the functional implications of the changes after stress are also modest. Of interest, most of the structural plasticity changes appear transient and are generally reversible after appropiate recovery periods, or following cessation or blockade of the stress or corticosteroid exposure. The temporary slowing down of both apoptosis and adult proliferation, i.e. the DG turnover, after chronic stress will affect the overall composition, average age and identity of DG cells, and will have considerable consequences for the connectivity, input and properties of the hippocampal circuit and thus for memory function. Modulation of apoptosis and neurogenesis, by drugs interfering with stress components like MR and/or GR, and/or mediators of the cell death cascade, may therefore provide important drug targets for the modulation of mood and memory.

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.

Lesions of the Suprachiasmatic Nucleus Indicate the Presence of a Direct Vasoactive Intestinal Polypeptide‐Containing Projection to Gonadotrophin‐Releasing Hormone Neurons in the Female Rat

In non‐seasonal breeders like the rat, the influence of the suprachiasmatic nucleus (SCN) on reproduction is most clearly expressed in the female. Complete lesions of the SCN induce persistent oestrus (anovulation) in intact female rats, whereas oestrogen implantation in ovariectomized rats results in daily luteinizing hormone surges. Vasoactive intestinal polypeptide (VIP), a peptide synthesized in cell bodies of the SCN, inhibits the increase in pulsatile luteinizing hormone release observed in ovariectomized female rats. In search of the anatomical basis for these observations, the present study employs an immunocytochemical double staining for VIP and gonadotrophin‐releasing hormone (GnRH) at the light microscopical level. It was demonstrated that approximately 45% of the GnRH positive neurons in the diagonal band of Broca, the preoptic and anterior hypothalamic area of female rats are innervated by VIP‐containing processes. To investigate whether these VIP‐containing fibres represent a direct projection of the SCN to the GnRH system, unilateral thermic SCN lesions were made.

VASOPRESSIN INDUCES A LUTEINIZING HORMONE SURGE IN OVARIECTOMIZED, ESTRADIOL-TREATED RATS WITH LESIONS OF THE SUPRACHIASMATIC NUCLEUS

The luteinizing hormone surge in the female rat is the result of the integration of multiple signals within the medial preoptic area. The medial preoptic area contains gonadotropin-releasing hormone neurons that are responsible for the release of luteinizing hormone, neurons containing estrogen receptors and terminals originating from the suprachiasmatic nucleus with, for example, vasopressin as neurotransmitter. Both the medial preoptic area and suprachiasmatic nucleus are crucial for the occurrence of luteinizing hormone surges, since lesioning of either nucleus prevents pre-ovulatory and steroid-induced luteinizing hormone surges. In this study, we investigated whether vasopressin in the medial preoptic area could be the daily neuronal signal from the suprachiasmatic nucleus responsible for the timing of the luteinizing hormone surge. Vasopressin (50 ng/microl) or Ringer solution was administered by reverse microdialysis from Zeitgeber times 7.5 to 12.5 into the medial preoptic area of ovariectomized, estradiol-treated rats. The suprachiasmatic nucleus was lesioned to remove all cyclic luteinizing hormone secretion. This was evaluated by monitoring behavioral activity; animals that were arrhythmic were included in the experiments. Hourly blood samples were taken to measure plasma luteinizing hormone levels. Preoptic vasopressin administration induced a surge-like luteinizing hormone pattern in suprachiasmatic nucleus-lesioned animals, whereas constant, basal luteinizing hormone levels were found in the control animals. These data show that vasopressin, by itself, is able to trigger the luteinizing hormone surge in suprachiasmatic nucleus-lesioned rats. We propose that vasopressin is a timing signal from the suprachiasmatic nucleus responsible for the activation of the hypothalamo-pituitary-gonadal axis in the female rat.

Psychoendocrinological Assessment of the Menstrual Cycle: The Relationship Between Hormones, Sexuality, and Mood

The role of sex hormones in sexuality and mood across the menstrual cycle was investigated. Twenty-one normal healthy women were followed for one menstrual cycle. Blood samples were taken frequently, and analyzed for estradiol, progesterone, testosterone, androstenedione, dehydroepiandrosterone sulfate, cortisol, and sex hormone-binding globulin. A diary concerning sexual interest and behavior, and different moods, was completed daily. Although the sample was not large, a clear effect of menstrual cycle phase on levels of testosterone and the free testosterone index was demonstrated. In a preliminary screening interview, 11 of the 21 women had reported that they suffered from premenstrual complaints (PC), the other 10 had reported no complaints in the premenstrual phase (NPC). Significant differences between the two groups were established in estradiol and the estradiol–progesterone ratio, with the NPC group having higher levels of both endocrine parameters across different menstrual samples. Psychologically, a cycle effect on tension and sexual interest was demonstrated. The NPC group reported a peak in sexual interest in the premenstrual phase, whereas the PC group reported a peak in the ovulatory phase. There was a difference between the two groups in feelings of fatigue but not in other moods across the menstrual cycle. The study provides further evidence of the importance of androgen levels in womens sexuality and shows again that the relationship between menstrual cycle phase and sexuality is much clearer than between phase and mood.

ACTH-induced inhibition of endogenous rat brain protein phosphorylation in vitro: Structure activity

ACTH1–24 inhibits the endogenous phosphorylation in vitro of distinct SPM protein bands. Using N-terminal fragments of ACTH, the structure-activity requirements for this effect were studied. A rather complex interaction of the ACTH fragments with endogenous SPM phosphorylation was observed. The effects were not only dependent on the primary structure of the peptide used, but also on the protein band studied and the ATP/SPM ratio used in the incubation system. ACTH1–24 did not interfere with the ATP-hydrolyzing activity of the SPM preparation, nor did it influence the endogenous phosphatase activity. Therefore, a direct interaction of ACTH with SPM protein kinase(s) is likely to be responsible for its effect on phosphorylation.