Prolactin induces grooming in the rat: possible involvement of nigrostriatal dopaminergic system

Variation in prolactin is related to variation in sexual behavior and contact affiliation

Prolactin is associated with both maternal and paternal care and appears important in developing a bond between parent and infant. In contrast with oxytocin, another hormone important in infant care, there is scant information on the role of prolactin in maintaining adult heterosexual relationships. We present here the first results demonstrating a relationship between prolactin levels and sexual and contact affiliation behavior in a pair-bonded species. We studied cotton-top tamarins, a socially-monogamous, cooperatively-breeding primate. We measured chronic urinary prolactin levels over a four week period to include the entire female ovulatory cycle and correlated prolactin levels in males and females with simultaneous measures of contact affiliation and sexual behavior. Current mothers who were no longer nursing displayed lower amounts of sexual behavior and proximity than non-breeding females and also had marginally lower levels of prolactin. The prolactin levels of males and females were similar within pairs, and variation in prolactin levels for both sexes was explained both by the amount of sexual behavior and contact affiliation. The results parallel a previous study that compared oxytocin levels with sociosexual behavior in the same species, and supports the hypothesis that both prolactin and oxytocin are involved in pair-bonding as well as in infant care.

Low stress reactivity and neuroendocrine factors in the BTBR T+tf/J mouse model of autism

Autism is a neurodevelopmental disorder characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. BTBR T+tf/J (BTBR) is an inbred mouse strain that displays robust behavioral phenotypes with analogies to all three of the diagnostic symptoms of autism, including low social interactions, reduced vocalizations in social settings, and high levels of repetitive self-grooming. Autism-relevant phenotypes in BTBR offer translational tools to discover neurochemical mechanisms underlying unusual mouse behaviors relevant to symptoms of autism. Because repetitive self-grooming in mice may be a displacement behavior elevated by stressors, we investigated neuroendocrine markers of stress and behavioral reactivity to stressors in BTBR mice, as compared to C57BL/6J (B6), a standard inbred strain with high sociability. Radioimmunoassays replicated previous findings that circulating corticosterone is higher in BTBR than in B6. Higher basal glucocorticoid receptor mRNA and higher oxytocin peptide levels were detected in the brains of BTBR as compared to B6. No significant differences were detected in corticotrophin releasing factor (CRF) peptide or CRF mRNA. In response to behavioral stressors, BTBR and B6 were generally similar on behavioral tasks including stress-induced hyperthermia, elevated plus-maze, light ↔ dark exploration, tail flick, acoustic startle and prepulse inhibition. BTBR displayed less reactivity than B6 to a noxious thermal stimulus in the hot plate, and less immobility than B6 in both the forced swim and tail suspension depression-related tasks. BTBR, therefore, exhibited lower depression-like scores than B6 on two standard tests sensitive to antidepressants, did not differ from B6 on two well-validated anxiety-like behaviors, and did not exhibit unusual stress reactivity to sensory stimuli. Our findings support the interpretation that autism-relevant social deficits, vocalizations, and repetitive behaviors are not the result of abnormal stress reactivity in the BTBR mouse model of autism.

Synergistic effect of bismuth subgallate and borneol, the major components of Sulbogin, on the healing of skin wound

Most skin lesions heal delay and even heal efficiently within 1-2 weeks, the healed tissue is neither aesthetically nor functionally perfect. Therefore, facilitating skin healing rate and controlling healed skin quality are major aims of drug treatment for a wound event. Bismuth subgallate (BS) and Borneol (BO) are the two components of Sulbogin, a new Vaseline-based wound healing ointment, one for treating skin wounds. Although BO has antibiotic function, while BS is widely used clinically, neither has been used specifically for wound healing. The experiment described here aimed to study the effect of BS and BO on the healing of skin wounds. This study also compared the effects of BS and BO with Flamazine cream, which is currently the most popular drug for wound healing in hospitals. Full-thickness wounds (3 cm x 3 cm x 0.2 cm) were created on the back of adult male Sprague-Dawley rats. BS, BO, BS+BO, and Flamazine were then evenly applied to cheesecloth and placed over the lesion areas. The drug patches were replaced every 2-3 days until the wound areas were completely covered by epidermis in any kinds of drug treatment. The combined BS and BO treatment had the best effect on healing by decreasing lesion area, while increasing granulation tissue formation, re-epithelialization, eating behavior and reconstitution of skin appendages. This investigation showed that BS and BO have a synergistic effect on the skin wound restoration.

Detection of prolactin receptor mRNA in the corpus striatum and substantia nigra of the rat

The observation of prolactin modulation of the nigrostriatal dopaminergic system suggests the expression of prolactin receptor in the corpus striatum or substantia nigra. The present study investigated expression of prolactin receptor mRNA in tissues microdissected from the corpus striatum and substantia nigra of the rat. By using reverse transcription PCR combined with Southern hybridization, the long form of prolactin receptor mRNA was detected in the substantia nigra, caudate putamen, globus pallidus, and ventral pallidum in ovariectomized rats, whereas the short form was not detectable in any of these areas. Estrogen had no effect on expression of the long-form mRNA in the substantia nigra and corpus striatum. By using the RNase protection assay, the expression of both short and long forms of prolactin receptor mRNA was observed in the corpus striatum in ovariectomized rats. Again, levels of expression were not significantly altered by estrogen treatment. Both forms of prolactin receptor mRNA were clearly expressed in the choroid plexus and were up-regulated by estrogen treatment. The expression of both forms of prolactin receptor mRNA in nigrostriatal areas may help to support the hypothesis that prolactin has direct actions on these brain regions.

Effect of suckling on prolactin receptor immunoreactivity in the hypothalamus of the rat

Previous studies showed that expression of prolactin (PRL) receptor is increased in numerous hypothalamic nuclei in mid-lactating rats. The increase in PRL receptor expression could be initated by neurohormonal changes during proestrus or pregnancy, or by the suckling stimulus during lactation. The present study investigated whether the PRL receptor expression in numerous hypothalamic nuclei is altered by the suckling stimulus. Three groups (n = 4) of rats on lactation day 10 were used: a continuously suckled group, a nonsuckled group (pups removed for 12 h) and a resuckled group (pups removed for 12 and then resuckled for 9 h). Animals were perfused with 2% paraformaldehyde and brains were sectioned (20 microm) for the immunofluorescence study. Immunoreactivity was semiquantitatively analyzed by counting the immunoreactive cells and measuring the immunostaining intensity in a specific area. Neurons expressing PRL receptors were observed in numerous hypothalamic areas with the highest number being in the arcuate, paraventricular and supraoptic nuclei. The PRL receptor immunofluorescence in several nuclei was significantly decreased in the nonsuckled group, and recovered in the resuckled group. These areas included the ventromedial preoptic, ventrolateral preoptic, lateroanterior hypothalamic, ventrolateral hypothalamic and ventromedial hypothalamic nuclei. PRL receptor immunoreactivity in other areas was not significantly altered by the suckling stimulus. These results demonstrate that expression of PRL receptor in hypothalamic nuclei was differentially affected by the suckling stimulus. PRL receptors in those nuclei which were significantly altered by suckling stimulus may play more critical roles during lactation than those areas which were less sensitive to the suckling stimulus.

Dual modulation of male sexual behavior in rats by central prolactin: relationship with in vivo striatal dopaminergic activity

Prolactin (PRL) appears to be localized in several brain structures. Central, behaviorally meaningful, neural actions of this protein have been demonstrated in a large number of studies. The present report describes sexual behavioral and in vivo neurochemical data obtained from adult male rats injected intracerebroventricularly acutely (10 micrograms) or chronically (5 days; 10 micrograms/day) with ovine prolactin (oPRL). The extracellular striatal concentrations of dopamine and serotonin metabolites were estimated by HPLC measurements in microdialysis perfusates. A single (10 micrograms) administration of oPRL facilitated sexual activity and increased extracellular striatal DOPAC, HVA and 5HIAA levels, whereas five daily intracerebroventricular injections of oPRL, decreased the sexual behavior and reduced DOPAC and HVA striatal extracellular concentrations in response to a central oPRL injection. These results show that acute and chronic central oPRL treatments have stimulatory and inhibitory effects on male sexual behavior, respectively. In addition, the results suggest that striatal dopaminergic activity is increased and decreased by acute and 5-day central oPRL treatments. These data suggest that behavioral effects of PRL occur simultaneously with changes in striatal dopaminergic activity.

The expression of neuropeptide-induced excessive grooming behavior in dopamine D1 and D2 receptor-deficient mice

Grooming behavior in rodents has long been related to dopamine receptors in the brain. However, the relative contribution of dopamine D1-like receptors (D1 and D5) and D2-like receptors (D2, D3 and D4) in this behavior has not been established yet. Spontaneous novelty-induced grooming (as assessed with a 30-min sampling test) was reduced in knockout mice lacking the dopamine D1, receptor. Furthermore, the intracerebroventricular (i.c.v.) injection of small quantities of oxytocin, prolactin or the adrenocorticotrophic hormone 1-24 fragment, ACTH-(1-24) was followed by a diminished level of novelty-induced excessive grooming. These neuropeptides caused a sustained increase in grooming level of control animals (wild type). Interestingly, the i.c.v. injection of beta-endorphin enhanced novelty-induced grooming to a level similar in control and knockout mice. The systemic administration of the dopamine D2 receptor antagonist, sulpiride did not suppress the residual grooming activity shown by animals injected with oxytocin, prolactin or ACTH-(1-24), and did not change the behavioral expression of those injected with beta-endorphin. In contrast, the systemic administration of the opioid receptor antagonist, naloxone, totally suppressed the residual grooming activity of oxytocin-, prolactin- or ACTH-(1-24)-injected mice and of those treated with beta-endorphin. In contrast with the behavioral deficit observed in dopamine D1 receptor-deficient mice, dopamine D2 receptor-null animals showed a normal expression of spontaneous novelty-induced grooming and a high level of grooming activity induced by i.c.v. injection of oxytocin, prolactin, ACTH-(1-24) or beta-endorphin. Again, the peripheral injection of naloxone was followed by a suppression of neuropeptide-induced excessive grooming in these animals. These data suggest that dopamine D1 receptors are involved in the expression of novelty-induced grooming in mice. In contrast, dopamine D2 receptors seem not to be important for the expression of this behavior. Furthermore, neuropeptide-enhanced grooming involves dopamine D1, but not dopamine D2 receptors. However, neurotransmitters other than dopamine (e.g., endorphins) may play a supplementary role in neuropeptide-enhanced grooming in mice.

Long-term behavioural and neuroendocrine changes in Roman high-(RHA/Verh) and low-(RLA-Verh) avoidance rats following neonatal handling

Roman high-(RHA/Verh) and low-(RLA/Verh) avoidance rats, originally selected and bred for rapid vs poor acquisition of a two-way active avoidance response, differ in emotional reactivity and coping style. These differences are associated with particular neuroendocrine and neurochemical characteristics. New data are presented here to show that the behavioural changes specifically induced by neonatal handling, i.e. decreased emotional reactivity, are associated with marked changes in the neuroendocrine responses of (hyperemotional) RLA/Verh rats to a novel environment. Eight months after neonatal handling, self-grooming behaviour, a reliable marker of emotional reactivity in this line of rats, was significantly decreased in RLA/Verh rats. Defecation scores were also significantly reduced in both lines. Moreover, there was a significant reduction in prolactin and corticosterone release following exposure to a novel environment in neonatally-handled RLA/Verh rats as compared to control, non-handled rats. No effects on prolactin and corticosterone release were observed in RHA/Verh rats. There was also no apparent effect of neonatal handling on coping style i.e. RLA/Verh rats did not increase their spontaneous exploration of novel environments. Thus, the phenotypic expression of basic traits of (high) neuroendocrine/emotional reactivity was specifically modulated by neonatal handling in RLA/Verh rats, whereas both the (hypoemotional) RHA/Verh rats as well as coping style in both lines remained unaffected. Changes in emotional reactivity were still apparent at 12 months of age when rats from the same groups were tested for hyponeophagia. These results suggest that psychogenetically selected lines such as RHA/RLA rats are suitable animal models to investigate interactions between genes and the environment in determining individual sensitivity to stress and coping styles, as well as potential vulnerability (or resistance) to the development of maladaptive syndromes similar to anxiety and mood disorders in humans.

Distribution of prolactin receptor immunoreactivity in the brain of estrogen-treated, ovariectomized rats

Although there is extensive evidence for effects of prolactin (PRL) on the brain, knowledge about the PRL receptor (PRL-R) in the brain is limited. By using monoclonal antibodies raised against purified rat liver PRL-R, the distribution of PRL-R was investigated by immunohistochemistry in brains of the estrogen-treated ovariectomized (OVX+E) rat and the adult male rat. Immunohistochemistry was performed by using the avidin biotinylated horse radish peroxidase macromolecular complex method. In both male and OVX+E rats, strong immunostaining was detected in the choroid plexus of all cerebral ventricles. This immunostaining was localized predominately on epithelial cell membranes. In the OVX+E female rat, scattered immunoreactive perikarya were observed in the arcuate nucleus, periventricular hypothalamic nucleus, preoptic area, suprachiasmatic nucleus, and supraoptic nucleus of the hypothalamus. Immunostaining in hypothalamic nuclei was localized on neuronal cell bodies as well as on neuronal processes. In addition, there was extensive PRL-R immunoreactivity throughout the globus pallidus and ventral pallidum. Immunostaining in these striatal regions was not associated with neuronal cell bodies but appeared to be localized on processes or glial cells. In the male rat, less immunostaining was observed in the hypothalamus, and there was no immunostaining in the corpus striatum. No significant staining was observed in the cerebral cortex, thalamus, or hindbrain of either male or OVX+E rats. The implication of PRL-R existence in these brain regions remains to be investigated.

Effects of acute and long-term domperidone treatment on prolactin and gonadal hormone levels and sexual behavior of male and female rats

Domperidone (DOMP), a dopamine D2 blocker that is unable to cross the blood-brain barrier, is an experimental tool used to induce hyperprolactinemia. Acute and long-term DOMP administration was tested in male and female rats for its effects on sexual behavior and plasma gonadal hormone levels. DOMP (4.0 mg/kg) was injected I.P. either acutely or daily for 30 days. Acute treatment failed to modify any behavioral parameter observed. The 5-day treatment stimulated and the 30-day treatment failed to inhibit sexual behavior of male rats. Serum testosterone levels were significantly reduced after 30 days of treatment in male rats. The 30-day treatment also inhibited sexual behavior and enhanced plasma progesterone levels in ovariectomized and intact female rats, respectively. The present results may be due to DOMP-induced long-term hyperprolactinemia. Alternatively, blockade of dopamine peripheral receptors induced by this treatment may also be responsible for the behavioral changes reported here. Moreover, these data suggest that female rats are more susceptible than males to the behavioral effects of long-term hyperprolactinemia.

Spontaneous gestures following right hemisphere infarct

Neurobehavioral studies of gesturing have been largely limited to left hemisphere damaged (LHD) patients. We compared spontaneous gesturing in seven right hemisphere damaged (RHD) patients, seven LHD patients, and seven normal controls (NHD) during videotaped interviews. Two judges coded symbolic, expressive, grooming, and fidgeting gestures in 120 10-sec intervals of videotape per patient. We found that RHD patients made significantly more total gestures and grooming gestures with the hand ipsilateral to their lesion than did LHD patients. Furthermore, RHD patients made more total and grooming gestures with their right hand than NHD subjects did with either hand. There were no differences in gesture production between the right and left hands of NHD patients. These results suggest that RHD produces enhanced gesturing, particularly involving grooming behavior.

Cellular and molecular mechanisms of impaired dopaminergic function during aging

One important cause of impaired motor function during aging is deterioration of the dopamine system. Such motor deficits in experimental animals can be closely related to loss of striatal dopamine receptors, and similar observations have now been made in humans. Two mechanisms account for the age-related decrease in striatal dopamine receptor levels: loss of receptor-containing neurons and reduced rates of receptor synthesis. The striatal neurons affected by aging appear to reside in a kainic-acid-sensitive population. Attempts to mimic those death mechanisms which occur in vivo using cultured neurons suggest that large D2-dopamine-receptor-containing cells may be the most vulnerable. Whether dopamine itself, the endogenous neurotransmitter for the cells, may ultimately be toxic to these neurons remains to be determined. The levels of D2-receptor mRNA in the surviving neurons is reduced during aging. This decrement is apparently due to a decreased rate of mRNA biosynthesis. Future experiments must therefore focus on the regulatory elements of this gene in order to determine why its transcription is selectively affected by aging. Finally, various interventions have been shown to delay or reverse the age changes characteristic of the dopaminergic system. Both dopamine receptors and motor function have been manipulated by diet and exercise as well as 6-OH-dopamine lesions and estrogen and prolactin administration. The possibility that such treatments might eventually be utilized therapeutically has become increasingly real as our knowledge of the affected cellular and molecular processes continues to expand.

Prolactin receptor mRNA localization in the hypothalamus by in situ hybridization

Prolactin receptors may mediate the action of prolactin in the brain to influence behavior and neuroendocrine secretions. We recently demonstrated prolactin receptor gene expression in the anterior and medial basal hypothalamus and not in the cortex by the reverse transcription-polymerase chain reaction. In this paper, we localize the prolactin receptor gene expression to individual cells with in situ hybridization. Several steps in the in situ hybridization method were modified to increase sensitivity by using (i) probes complementary to the coding sequence of the extracellular binding domain common to both long and short prolactin receptor, (ii) more stringent hybridization and wash conditions to reduce background and (iii) higher specific activity, more complex and saturating amounts of probe. We detected prolactin receptor gene expression in cells of the periventricular area of the preoptic nucleus, medial preoptic nucleus, supraoptic nucleus, rostral arcuate nucleus and choroid plexus. Cortical brain tissue, which has been demonstrated previously by reverse-transcription polymerase chain reaction to be lacking in prolactin receptor mRNA, did not have any detectable signal for the receptor mRNA and was used as an indication of background levels of signal. The mean area of silver grains over labeled cells in periventricular area of the preoptic nucleus, medial preoptic nucleus, supraoptic nucleus, arcuate nucleus, lateral ventromedial nucleus was at least 10 times greater than the background in the cortex of the same brain section.

Domperidone induces a probenecid-sensitive rise in immunoreactive prolactin in cerebroventricular perfusates in female rats

The present study examined immunoreactive prolactin (ir-PRL) access into the cerebrospinal fluid (CSF) by monitoring ir-PRL levels in the blood and cerebroventricular perfusates of ovariectomized (ovx) rats treated with the dopamine antagonist, domperidone (DOMP). In Expt. 1 PRL plasma levels were measured in rats treated with DOMP i.p. (2.5, 5.0 and 10.0 mg/kg). All doses of DOMP significantly increased PRL plasma levels. In Expt. 2 animals were treated i.p. with DOMP (10 mg/kg) or DOMP plus the active transport blocking agent, probenecid (PROB; 250 mg/kg). Plasma PRL and ir-PRL in cerebroventricular perfusates were measured in separate sets of animals using catheters and a push-pull perfusion system, respectively. DOMP induced an increase in plasma PRL that was followed 30-40 min later by a rise in ventricular perfusates ir-PRL levels. PROB treatment induced a greater increase in plasma PRL levels in DOMP-treated animals, but delayed the DOMP-induced increase in ir-PRL ventricular perfusate ir-PRL levels. The delay in the rise of ir-PRL in ventricular perfusates observed in rats treated with DOMP plus PROB may be due to a PROB's interference with the transport of PRL from the blood into CSF. These results suggest that under some conditions ir-PRL in CSF originates from the pituitary.

Prolactin stimulation of protein kinase C activity in the rat hypothalamus

Stimulation of cultured hypothalamic slices with PRL causes a rapid translocation of a Ca2+/phospholipid dependent protein kinase from the cytosol to the membrane fraction. The translocation of PKC from the cytosol to the membrane occurred at physiological concentrations of PRL with a maximal response occurring at 10(-10) M. At concentrations above this, there was less PKC activity translocated from the cytosol to the membrane. When injected into the medial preoptic area of the hypothalamus, PRL resulted in a similar translocation of PKC activity. These data clearly indicate that PRL can activate PKC in the rat hypothalamus, and suggest that PKC may be one of the transmembrane signaling mechanisms involved in the regulation of brain function by prolactin.

Changes in feeding activity, plasma luteinizing hormone, and testes weight in ring doves following hypothalamic injections of prolactin

Abstract Microinjections of ovine prolactin were administered unilaterally to the ventromedial hypothalamic nucleus and the preoptic-suprachiasmatic region in adult male ring doves in an attempt to determine the site(s) at which intracranial injections of prolactin act to alter feeding behaviour and gonadotropin secretion in this species. Food intake and body weight were measured daily during a 6-day pretreatment period and the 5-day treatment period that immediately followed. During the treatment period, birds received twice daily injections (0.5 mul) of either 2.5 ng ovine prolactin or saline vehicle. An additional group of birds with cannulae in the ventromedial nucleus were given twice daily injections of 25 ng ovine prolactin. Although food consumption was unaffected by low dose prolactin treatment, birds given 25 ng prolactin injections into the ventromedial nucleus showed a significant augmentation in food intake. Injections of 25 ng prolactin into the preoptic area also increased feeding; however, the magnitude of this hyperphagic response, as expressed relative to pretreatment levels, was less than that observed following prolactin injection into the ventromedial nucleus. No differences were observed between prolactin-treated and vehicle-treated birds in either cannulation group when testes weights and plasma luteinizing hormone concentrations were compared at the end of the treatment period. However, the possibility that prolactin influenced changes in luteinizing hormone and testes weight relative to baseline values could not be assessed due to constraints imposed by the experimental paradigm used. These results suggest that prolactin-sensitive neurons in the ventromedial hypothalamic region and the preoptic area are potential sites of prolactin action in promoting hyperphagia in ring doves. However, the role of these sites in mediating prolactin-induced suppression of gonadotropin secretion in this species remains to be clarified.

Effect of age at the time of pituitary grafting on behavioral recovery in dwarf mice

The effects of ectopic pituitary isograft implanted in 13- or 21-day-old Snell dwarf mice on their freely expressed behavior were examined over a 14- or 31-day period. This mutant strain has severe anterohypophyseal deficiency which causes high levels of inactivity and abnormally low exploratory activity. The graft totally normalized these behaviors. Results showed that the time necessary for inducing behavioral changes is independent of age of the animals at the time of grafting, but the age at which implantation occurs influences the speed of full behavioral normalization. The possible involvement of prolactin and growth hormone in such behavioral improvement is discussed.

Reduction of motor behavioural deficits in senescence via chronic prolactin or estrogen administration: time course and putative mechanisms of action

The effects of chronic estrogen (E2), rat prolactin (rPRL), modified ovine prolactin (mPRL) administration on motor behavior (inclined screen performance) and striatal dopamine (DA) (D2subtype) receptor concentrations were examined in senescent (greater than 24 months of age) female rats, mPRL possesses no lactotrophic activity. Administration of either E2 or rPRL was effective in improving both inclined screen performance (increased time that the animal could remain on the screen by 95 and 413 s, respectively, compared to highest pre-injection performance) and striatal D2 receptor concentrations (14 and 20% respectively). These were indications, however, from separate analyses that improvements in inclined screen performance were seen prior to any increases in striatal D2 receptor concentrations. These early performance increases seemed instead to be the result of improved muscarinic receptor control over striatal DA autoreceptor function. Later improvements in inclined screen performance (at 6-7 days after the E2 injections were begun) were more dependent on increased striatal DA receptor concentrations. A second set of experiments which involved the injection of E2 into senescent male as well as female rats indicated that there were no sex differences in improvements in inclined screen performance, and that once the E2 injections were discontinued, performance returned to preadministration levels. The results are discussed in terms of two important processes that may be involved in mediating enhanced inclined screen performance following E2 administration: (1) enhancement of muscarinic receptor regulation of DA autoreceptor function; and (2) increases in striatal DA receptor density.

Effects of prolactin on tyrosine hydroxylase activity of central dopaminergic neurons of male rats

Previous work from our laboratory has indicated that ovine prolactin can produce a rapid stimulation (within 1 h) of dopamine release from nigrostriatal and mesolimbic dopaminergic neurons of male rats. In the present experiment we attempted to determine whether this effect of prolactin was a function of an increase in the activation of dopamine synthesis. To examine this possibility we used the drug NSD 1015. This drug is a decarboxylase inhibitor that leads to dopa accumulation and is used as an index of in vivo tyrosine hydroxylase activity. Our results demonstrated that ovine prolactin increased turnover of dopamine but had no effect upon tyrosine hydroxylase activation (up to 4 h) in both dorsal and ventral striatal dopaminergic neurons. In contrast, ovine prolacting had a clear effect (within 4 h) on tyrosine hydroxylase activity in mediobasal hypothalamic dopaminergic neurons. These results suggest that ovine prolactin can differentially alter synthesis/release processes of dopamine from these sites.

Time course and response specificity of prolactin-induced hyperphagia in ring doves

Intracranial injections of prolactin (PRL) have been previously shown to elevate food and water intake in ring doves. In an attempt to further characterize these PRL-induced behavioral responses and the time course of PRL action, food and/or water intake were measured as frequent intervals in male doves given a single intracerebroventricular (ICV) injection of ovine PRL (44 pmoles) or vehicle under food deprivation, water deprivation, or nondeprivation conditions. PRL increased food consumption by 35-50% over baseline levels in water deprived and nondeprived doves, although response latencies (10 hr) and durations (greater than 24 hr) were considerably longer than those reported for other orexigenic peptides. Behavioral observations of nondeprived doves further revealed that PRL significantly increased total time spent feeding and average feeding bout duration. In contrast to this pattern, water intake remained unchanged in food deprived doves and was only marginally increased in nondeprived doves following PRL treatment. Collectively, these results suggest that PRL promotes a selective and long-lasting hyperphagia which may in turn augment drinking activity.

Hyperprolactinemia-induced modifications in vasoactive intestinal peptide binding site densities in the rat central nervous system and pituitary gland: evidence for an interaction between estradiol-17 beta and prolactin effects

Hyperprolactinemia was induced in ovariectomized rats by implanting estradiol-17 beta pellets, grafting extrapituitaries, or by a combination of both treatments. Subsequently, the effect of increasing plasma prolactin levels on both central and pituitary receptors for vasoactive intestinal peptide (VIP), a neuropeptide known to stimulate prolactin release was investigated. The results obtained by quantitative autoradiography show that the density of VIP binding sites is modified in restricted areas of the central nervous system (striatum, several cortical, thalamic and limbic structures) and in the pituitary in hyperprolactinemic animals. The present results suggest that changes in plasma prolactin levels may control VIP receptor site density in both brain and pituitary. Moreover, direct effects of estradiol-17 beta and possible interactions between estradiol-17 beta and prolactin are observed on both brain and pituitary VIP binding sites.

Prolactin as a protective factor in stress-induced biological changes

The adenohypophyseal hormone prolactin (PRL) is released during stress of physical and psychological nature. In animals, this hormone facilitates adaptive behavior, induces analgesia, and enhances grooming behavior. It also reduces corticosterone secretion and the incidence of gastric ulcers induced by physical stress. It is possible that PRL plays a protective role against stress-induced biological modifications in animals.

Regional distribution and species variation of prolactin binding sites in the brain

The binding of 125I-labeled ovine prolactin (125I-oPRL) to membranes from different brain regions of pigeon, rabbit, rat, pig, calf, horse, and ewe was studied. The hypothalamus from rabbit, pig, horse, and pigeon showed a low but specific binding for 125I-oPRL clearly different from the other brain regions examined (cortex and cerebellum), whereas in the brain from rat, calf, and ewe the binding was very small and quite uniform in the various regions. Also the membranes from choroid plexus of rabbit, pig, calf, and horse showed an evident specific binding for prolactin. The binding of 125I-oPRL to hypothalamus and choroid plexus membranes from rabbit and horse was inhibited in a dose-dependent manner by unlabeled oPRL and hGH but not by many other polypeptide hormones. Scatchard analysis of the binding revealed the presence of binding sites with low capacity and high affinity for ovine ligand.

Molecular transduction mechanisms in ACTH-induced grooming

Intraventricular administration of ACTH1-24 induces excessive grooming in the rat. Ethogram analysis shows that the peptide does not alter grooming behavior seen in a novel box, but that it prolongs the duration of the grooming bout. Extensive structure-activity studies have been performed which suggest that the active site lies in a region (5-13) of the ACTH molecule. Interestingly, the (1-24) sequence is fully active, whereas (1-10) and (11-24) alone or in combination are inactive, pointing to a specific stereoconformation necessary to induce grooming. However, despite the fact that there are ACTH-and/or alpha-MSH-containing peptidergic neurons, no conclusive evidence is available demonstrating stereospecific, saturable binding sites for these peptides in brain. The analysis of the neural substrate underlying ACTH-induced excessive grooming has been performed by means of electrolytic lesions of specific brain regions and by neuropharmacological manipulations. The data suggest that the periaqueductal gray is the primary target for ACTH and that the activity of neostriatum and accumbens, via a nigro-colliculus-periaqueductal gray pathway, modulates the display of excessive grooming. An important feature of the neural substrate is that it displays single-dose tolerance to the peptide during the first hours after the first peptide injection. It is suggested that the tolerance is a feature of an opioid receptor-containing component of the neural substrate. The molecular mechanism of action of ACTH is complex and may involve different transmembrane signal transduction systems. The peptide decreases the degree of phosphorylation of a neuron-specific, synaptic phosphoprotein B-50 by inhibition of protein kinase C. It is concluded that changes in the degree of phosphorylation of B-50 regulate the activity of the lipid kinase phosphatidylinositol 4-phosphate kinase. Therefore, the B-50 protein seems to be part of a negative feedback loop in the receptor-activated hydrolysis of phosphatidylinositol 4,5-bis-phosphate (PIP2). There is increasing evidence that the molecular mechanism by which ACTH brings about the grooming response involves a change in phosphorylation of B-50. Firstly, the structure-activity relationship of ACTH-induced excessive grooming is nearly identical to that obtained for ACTH-induced inhibition of protein kinase C.(ABSTRACT TRUNCATED AT 400 WORDS)

The influence of neurotensin, naloxone, and haloperidol on elements of excessive grooming behavior induced by ACTH

Naloxone, haloperidol, and neurotensin suppress ACTH-induced grooming. The suppressive effects of naloxone and of haloperidol on ACTH-induced grooming are observed following subcutaneous as well as intracerebroventricular administration. The suppression of ACTH-induced grooming by these drugs is not accompanied by a change in the relative distribution of grooming elements. From previous data and from the results of the present study it is suggested that the underlying substrate involved in ACTH-induced excessive grooming may differ from that of bombesin-induced grooming.

Intracerebroventricular injection of anti-prolactin serum suppresses excessive grooming of pituitary homografted rats

Rats with endogenous hyperprolactinaemia, as induced by pituitary homografts under the kidney capsule, displayed increased grooming behavior as compared to that of sham-operated animals. Twelve days after surgery, intracerebroventricular injection of anti-prolactin serum (dilution 1:100, 1 microliter) suppressed the excessive grooming of homografted rats. These observations suggest that prolactin from a peripheral source may reach the central nervous system to affect brain mechanisms involved in grooming behavior.

Dopamine neurotransmission in the nucleus accumbens may be involved in oxytocin-enhanced grooming behavior of the rat

Intracerebroventricular (ICV) infusion of a low dose of oxytocin enhanced novelty-induced grooming in male rats. The present experiments were undertaken to investigate whether dopamine neurotransmission in the nucleus accumbens is involved in this effect. Bilateral lesions of the nucleus accumbens by microinjections of 6-hydroxydopamine (6-OHDA) totally prevented the enhancement of grooming behavior after subsequent ICV infusion of oxytocin. Furthermore, bilateral injections of the dopamine receptor antagonist, haloperidol, into the nucleus accumbens completely suppressed grooming behavior of rats infused ICV with oxytocin. These results suggest that dopamine neurotransmission in the nucleus accumbens is involved in the behavioral response enhanced by the peptide.

Effects of sustained hyperprolactinemia induced by chronic treatment with domperidone on central dopaminergic systems in the rat

Chronic treatment with Domperidone (DOM) had no effect on basal prolactin (PRL) secretion or basal levels of Dopamine (DA) metabolites in basal hypothalamus and striatum as compared with the vehicle treated rats. Animals chronically treated with DOM did not present tolerance to a challenge dose of Haloperidol (HAL) and DOM either measuring PRL secretion or striatal DA metabolite levels. The PRL-induced increase in hypothalamic 3,4-dihydroxyphenylacetic acid (DOPAC) was reduced. These results were accompanied by no change at striatal DA receptors, a slight reduction in density-affinity at hypothalamic DA receptors but clear-cut modification in pituitary DA receptors with the appearance of a high affinity-low capacity binding sites. It can be surmised that sustained hyperprolactinemia may induce tolerance in hypothalamic Tuberoinfundibular (TIDA) neurons involved in the inhibitory control of PRL secretion and a change in the kinetic properties of pituitary DA receptors, but it does not consistently affect the activity of the nigro-striatal DA system.

Oxytocin potently enhances novelty-induced grooming behavior in the rat

Intracerebroventricular (i.c.v.) injection of oxytocin was followed by an enhancement of novelty-induced grooming in male and female rats. This effect was dose-dependent, in a dose range of 0.1-10 micrograms. Grooming activity of rats injected i.c.v. with 10 micrograms of oxytocin was 9-fold higher than that of saline-injected controls. The analysis of behavioral element composition revealed an increased occurrence of genital grooming in oxytocin-injected rats. A time-course study revealed a sustained increase in grooming activity of oxytocin-treated rats during 45 min of behavioral testing. Intraperitoneal (i.p.) injection of the dopamine antagonist, haloperidol, totally suppressed oxytocin-enhanced grooming. Furthermore, i.p. injection of the opiate receptor antagonist, naloxone, was followed by an attenuation but not a suppression of grooming enhanced by i.c.v. administration of oxytocin. In addition, a small but significant increase in grooming activity was observed after subcutaneous injection of oxytocin. These results suggest that oxytocin-enhanced grooming behavior involves central mechanisms, e.g. dopamine and opioid transmission in the brain.

Dopaminergic modulation of ACTH-induced grooming

ACTH-(1-24)-induced grooming was studied after administration of the peptide into the substantia nigra or intracerebroventricularly (i.c.v.). The modulation of dopamine receptors in neostriatum (with haloperidol and apomorphine) and nucleus accumbens (with 3,4-dihydroxyphenylamino-2-imidazoline hydrochloride; DPI and ergometrine) was investigated. In the nucleus accumbens, the modulatory effects of ergometrine and DPI on ACTH-(1-24)-induced grooming were based on their affinity for dopamine receptors and not on their affinity for adrenoceptors. Intrastriatal application of dopaminergic agents inhibited i.c.v. ACTH-(1-24)-induced excessive grooming, whereas the grooming score was enhanced if ACTH-(1-24) was administered into the substantia nigra. The finding of differential effects of dopaminergic agents on ACTH-induced excessive grooming depending on the route of administration indicate that i.c.v. ACTH-induced excessive grooming is not mediated solely through the substantia nigra. The increase in grooming behavior seen after the intrastriatal administration of dopaminergic agents - when ACTH was injected into the substantia nigra - suggests the involvement of the striato-nigral GABAergic pathway. Local injections of ACTH-(1-24) into the periaqueductal gray also induced excessive grooming. Since a second injection of ACTH-(1-24) into the periaqueductal gray did not lead to a grooming response, irrespective of where the first injection of ACTH-(1-24) was given (i.c.v. into the nigra or via the periaqueductal gray) it is suggested that this structure seems to play a primary role in the induction of excessive grooming. Therefore the modulatory effects of the dopaminergic influence on ACTH-(1-24)-induced grooming may be exerted via the striato-nigro-collicular pathway.

Reduction of motor behavioral deficits in senescent animals via chronic prolactin administration. II. Non-stereotypic behaviors

The effects of chronic prolactin administration on three non-stereotypic psychomotor behaviors (inclined screen performance, rod walking and wire hanging) were examined in senescent (24 month) Fisher 344 rats. Prolactin (150 ng/hr) was administered for 7 days via Alzet minipumps to rats which had been pretested on the three tasks. The animals were tested on days 4 and 7 following the implants and the pumps were removed after testing on day 7. In order to assess the persistence of any prolactin effects on psychomotor performance the animals were tested again on days 7 and 14 after pump removal. Control animals were implanted with Alzet pumps containing only saline and tested in a similar manner. Results demonstrated that the prolactin treated animals showed improvements on both the inclined screen and rod walking tasks but not the wire hanging test. Moreover, the improved performance seen on the inclined screen test persisted for as long as 7 days after pump removal. Results are discussed in terms of the importance of techniques which increase striatal dopaminergic responsivity on enhancing psychomotor performance in senescence.

Further evidence for the presence of specific binding sites for prolactin in the rabbit brain. Preferential distribution in the hypothalamus and substantia nigra

In the present research we have extended our work on the presence of binding sites for prolactin in the rabbit brain focusing our attention on the brain areas with high dopamine cell bodies density. Among these areas the hypothalamus showed the highest specific binding of labeled ovine prolactin (oPRL). Clearly detectible specific binding was observed also in substantia nigra, whereas in other brain regions the specific binding was very small, except for the striatum where a low but not negligible binding was found in female rabbits. The binding of 125I-oPRL showed a hormonal specificity and Scatchard analysis of the binding showed no clear difference in dissociation constant (Kd) between hypothalamus, nigra and striatum.

Catecholamine utilization in specific rat brain nuclei after short-term hyperprolactinaemia

Endogenous hyperprolactinaemia was induced in intact male rats by transplantation of pituitaries under the kidney capsule. Five days later the utilization of noradrenaline (NA) and dopamine (DA) in individual brain nuclei and changes of plasma prolaction (PRL) were measured. Inhibition of catecholamine synthesis by alpha-methyl-p-tyrosine (alpha-MPT) was used to measure utilization. Hyperprolactinaemia increased the utilization of NA in the locus coeruleus, the cell-body region of the dorsal noradrenergic bundle (DNB), but decreased it in some terminal projections of the same pathway (e.g. the cingulate gyrus). DA utilization was increased by hyperprolactinaemia in the eminentia mediana. In the nigrostriatal DA-ergic projection, hyperprolactinaemia decreased the utilization of DA in the cell-body region (substantia nigra) and increased it in the terminal projection (nucleus caudatus). In the ventral tegmental area (mesolimbic DA-ergic projection), hyperprolactinaemia decreased the utilization of DA. It is concluded that hyperprolactinaemia affects neurotransmission in the hypothalamus and also in specific extrahypothalamic pathways (e.g. DNB, nigrostriatal and mesolimbic DA-ergic projections) and that these changes may correlate with some behavioural effects of the pituitary hormone.

Prolactin and sexual behavior: a review

Despite the large body of evidence showing that prolactin (PRL) can suppress sexual behavior in humans and rodents, it is still unclear how this hormone affects sexual capacity of male subjects. Few studies have been performed on the effects of PRL on female sexual behavior. Short-term hyperprolactinaemia seems to facilitate some elements of sexual behavior in male rats. Furthermore, contrasting finding exist on the effects of drug-induced hyperprolactinaemia on sexual capacity of male animals. The possible mechanisms of action (on peripheral organs, endocrine, central) or PRL on male behavior are discussed in details.

Effects of mastectomy and vagotomy on grooming behavior of the rat: possible involvement of prolactin

Surgical interventions such as unilateral mastectomy or vagotomy affect plasma prolactin (PRL) levels. Right-side mastectomized rats exhibiting high levels of plasma PRL showed increased grooming behavior. Left-side mastectomized rats with low levels of plasma PRL performed poor grooming activity. Bilateral mastectomy that caused a slight increase in plasma PRL levels was followed by enhanced grooming behavior. Both left and right vagotomy resulted in a significant increase in plasma PRL levels. However, only left-side vagotomized rats exhibited increased levels of grooming behavior, while no difference between right-side vagotomized rats and controls occurred. It is possible that changes in plasma PRL levels induced by surgical interventions affect grooming activity of the rat. However, the hypothesis that the integrity of peripheral organs is important for the display of grooming behavior cannot be ruled out.

Enhancement of hypophysectomy-induced dopamine receptor hypersensitivity in male rats by chronic haloperidol administration

It has been reported that hypophysectomy (HYPOX) would antagonize the development of a neuroleptic-induced dopamine receptor hypersensitivity, and suggested that the neuroleptic-induced dopamine receptor hypersensitivity may be mediated by the neuroleptic-induced hyperprolactinemia. Conversely, we and others have reported on the ability of HYPOX animals to develop a neuroleptic-induced dopamine receptor hypersensitivity. The present study was undertaken to define the possible role(s) of prolactin in the modulation of striatal dopamine receptor sensitivity. The data from these studies indicate: that HYPOX alone will result in the development of a striatal dopamine receptor hypersensitivity; that the HYPOX-induced dopamine receptor hypersensitivity could be increased by the chronic administration and withdrawal of haloperidol; that administration of prolactin to HYPOX rats would partially antagonize the development of the neuroleptic-induced dopamine receptor hypersensitivity; and that the administration of prolactin alone had minimal effects on the apomorphine-induced behavior or neurochemistry of the HYPOX animals. These results suggest that the neuroleptics do not require the presence of a pituitary secretion (specifically, prolactin) to induce a striatal dopamine receptor hypersensitivity; however, they do indicate that a pituitary secretion, perhaps prolactin, may have the ability to modulate striatal dopamine sensitivity.

Role of prolactin-opiate interactions in the central regulation of pain threshold

Endogenous hyperprolactinaemia induced by anterior pituitary transplantation under the kidney capsule has been found to reduce the behavioural responsiveness to electrical footshock and to increase morphine-induced analgesia. The apparent analgesic effect of prolactin has been related to the stimulation of nigro-striatal dopaminergic transmission, as suggested by the increase in striatal dopamine turnover observed in hyperprolactinaemic rats. It seems likely that central opiate system is involved in the behavioural effects of prolactin. Thus, naloxone prevents the effects of hyperprolactinaemia on footshock responsiveness and heroin self-administration is decreased in hyperprolactinaemic rats.

Prolactin-enhanced grooming behavior: interaction with ACTH

The interaction between prolactin (PRL) and ACTH in enhancing grooming behavior after intracerebroventricular (i.c.v.) administration was investigated in intact and endogenously hyperprolactinaemic rats. In intact rats, 4 h after the i.c.v. injection of rat PRL or ACTH, a subsequent administration of ACTH or rat PRL did induce similar excessive grooming as observed after the first injections. In hyperprolactinaemic rats, which displayed excessive grooming 12 days after homografting adenopituitaries under the kidney capsule, i.c.v. injection of rat PRL failed to enhance further the grooming activity while this behavior was substantially enhanced by i.c.v. injection of ACTH1-24. Twenty-six days after surgery, when the grooming activity of hyperprolactinaemic rats was at the same level as control animals, the i.c.v. injection of rat PRL was effective in inducing excessive grooming in control but not in hyperprolactinaemic animals. In contrast, at this time the i.c.v. injection of ACTH1-24 induced again excessive grooming in both hyperprolactinaemic and control rats. Accordingly, there was no cross-tolerance between PRL and ACTH in inducing excessive grooming, but hyperprolactinaemic rats became hyposensitive to exogenous PRL. It is suggested that although PRL and ACTH may affect common neurotransmitter systems in the brain, the two hormones probably act on independent neural mechanisms in inducing excessive grooming in the rat.

Dopamine involvement in ACTH-induced grooming behavior

Low doses of dopamine agonists and antagonists were tested for their effects on the excessive grooming behavior induced by intracerebroventricular (ICV) injections of ACTH1-24. Grooming scores were significantly depressed at doses of haloperidol, metoclopramide, pimozide, and butaclamol that did not decrease locomotor activity. In fact at two doses of haloperidol (0.067 and 0.10 mg/kg), grooming scores were decreased while locomotor activity was increased significantly. Metoclopramide increased grooming scores at a dose reported to block presynaptic dopamine receptors. Apomorphine potentiated the grooming induced by low doses of ACTH. These data support the hypothesis that dopaminergic neurotransmission is necessary for the display of ACTH-induced grooming behavior.

Behavioral responses of long-term hyperprolactinaemic rats

Rats with long-term endogenous hyperprolactinaemia induced by pituitary homografts under the kidney capsule displayed an enhancement of amphetamine- and apomorphine-induced stereotypy, a facilitated acquisition of active avoidance behavior and a decreased responsiveness to electrical footshock. However, no difference between homografted and sham-operated rats was observed with respect to grooming behavior. It is concluded that at least two processes occur during prolonged hyperprolactinaemia, i.e. development of tolerance to prolactin with respect to enhanced grooming activity and of supersensitivity of postsynaptic dopaminergic receptor systems. These two processes may be dependent or independent from each other.

Prolactin increases the density of striatal dopamine receptors in normal and hypophysectomized male rats

Administration of prolactin to adult male rats, by S.C. injection, significantly increases the density of the striatal dopamine (DA) receptors, without altering the apparent affinity of the receptors for [3H]spiroperidol. Larger doses of prolactin are required to increase the density of the striatal DA receptors in hypophysectomized rats compared to normal rats. These results suggest that prolactin might be the common mediator of the increase in striatal DA receptor density produced by either estrogen or haloperidol administration. Monitoring and/or altering prolactin levels might be informative in neurologic or psychiatric disorders involving striatal DA neurotransmission.

Endogenous hyperprolactinaemia and avoidance behaviors of the rat

The influence of endogenous hyperprolactinaemia induced by pituitary homografts under the kidney capsule on conditioned avoidance behaviors of the rat has been investigated. Acquisition of active avoidance behavior, as studied in shuttle-box and pole jumping test situations, appeared to be facilitated in homografted rats in comparison with sham-operated animals. Extinction behavior was not affected in the same tests. Retention of one-trial learning passive avoidance behavior in homografted rats was similar to that of sham-operated animals. Hyperprolactinaemia resulted in a diminished behavioral responsiveness to electrical footshock. It is concluded that endogenous hyperprolactinaemia selectively affects acquisition, but not retention performance of avoidance behaviors.

Prolactin and estradiol increase striatal dopamine receptor density in intact, castrated and hypophysectomized rats

1. Ovariectomized female or intact male rats were implanted with three adenohypophyses under the kidney capsule or treated with 17 beta-estradiol (10 micrograms twice daily) for 2 weeks. 2. In animals of both sexes, the pituitary-implanted and estradiol-treated rats had elevated plasma prolactin levels and had increased levels of striatal dopamine receptors. 3. We next investigated the possibility of an indirect action of estradiol via prolactin using hypophysectomized female rats (hypox) treated with 17 beta-estradiol or ovine prolactin (500 micrograms, twice daily) for 5 days. 4. Striatal dopamine receptor concentration was lower in hypox animals as compared to ovariectomized (85%, p less than 0.05) or intact female rats at random stage of the estrous cycle (76%, p less than 0.05) while the affinity (KD) of [3H]spiperone for these dopaminergic sites remained unchanged. 5. Treatment with estradiol or prolactin increased the level of striatal dopamine receptors (HYPOX + estradiol: 144% vs HYPOX, p less than 0.05; HYPOX + prolactin: 147% vs HYPOX, p less than 0.05). 6. These results indicate that high prolactin levels induced by pituitary implants or by injections of ovine prolactin lead, as observed with chronic estradiol treatment, to an increased density of striatal dopamine receptors. However, the effect of estradiol may not be explained exclusively by increased prolactin levels since the supersensitivity is also observed in hypophysectomized animals.

Behavioral effects of phosphatidylserine in aged rats

The behavioral effects of 5 days of administration of phosphatidylserine (PS) was studied in aged rats. The intraperitoneal (5, 10, and 20 mg/kg) or intracerebroventricular (5, 10, and 20 micrograms/2 microliters) injection of PS liposomes caused a facilitated acquisition of active avoidance behavior as studied in shuttle-box and pole jumping test situations. The retention of active and passive avoidance responses was also improved. No substantial difference between PS-treated and control animals was apparent either in the responsiveness to electrical footshock or in the motor activity tested in an open field. Grooming behavior appeared to be enhanced in rats treated with the highest dose of the substance. Since PS affects both central catecholaminergic and cholinergic transmission, which is known to be impaired in old animals, the possibility that the behavioral effects of PS involve brain dopamine and/or acetylcholine systems is discussed.