Neurotensin and tyrosine hydroxylase in the tuberoinfundibular system of the guinea pig hypothalamus with special emphasis to lactation status

Mapping of neurotensin in the alpaca (Lama pacos) brainstem

We studied the distribution of cell bodies and fibres containing neurotensin (NT) in the brainstem of the alpaca using an indirect immunoperoxidase technique. Immunoreactive fibres were widely distributed throughout the brainstem, whereas the distribution of cell bodies was less widespread. Immunoreactive perikarya were only found in the mesencephalic and bulbar reticular formation, periaqueductal grey, nucleus of the solitary tract, laminar spinal trigeminal nucleus and in the inferior colliculus. A high density of fibres containing NT was found in the dorsal nucleus of the raphe, marginal nucleus of the brachium conjunctivum, locus coeruleus, inferior colliculus, inter-peduncular nucleus, substantia nigra, periaqueductal grey, reticular formation of the mesencephalon, pons and medulla oblongata, nucleus of the solitary tract, laminar spinal trigeminal nucleus, hypoglossal nucleus, inferior central nucleus and in the tegmental reticular nucleus. The widespread distribution indicates that NT might be involved in multiple physiological actions in the alpaca brainstem; this must be investigated in the future as alpacas lives from 0 m above sea level to altitudes of up 5000 m and hence the involvement of this neuropeptide in special and unique regulatory physiological mechanisms could be suggested.

Maternal undernutrition in early gestation alters molecular regulation of the hypothalamic-pituitary-adrenal axis in the ovine fetus

We have demonstrated previously that plasma adrenocorticotropin hormone and cortisol responses to exogenous and endogenous stimuli are reduced in fetuses of mildly undernourished ewes. In the present study, we examined the molecular regulation of fetal hypothalamic-pituitary-adrenal (HPA) axis function at 127-130 days gestation (dGA) following 15% reduction in maternal nutrition between 0 and 70 dGA. Using in situ hybridization, we found that corticotropin releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus (PVN) was lower in fetuses from nutrient restricted ewes than in controls. Restricted fetuses also had greater levels of mRNA encoding preproenkephalin (PENK) and magnocellular arginine vasopressin (AVP) in the PVN. Expression of oxytocin mRNA and parvocellular AVP mRNA in the PVN and pro-opiomelanocortin mRNA in the pituitary were unchanged. Glucocorticoid receptor mRNA expression was unaltered at the PVN, but was reduced (> 40%) in the anterior pituitary of restricted fetuses. Northern blot analysis demonstrated that levels of adrenal P450scc mRNA and P450(C17) mRNA were not different between the groups. We conclude that the reduction in HPA function reported previously is mediated, at least in part, by a decrease in expression of CRH mRNA and increase in PENK mRNA in the PVN.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides from 1994 through 1998

Effects of peptides on the central nervous system are presented in two ways so as to provide a cross-listing. In the first table, the peptides are listed alphabetically. In the second table, the central nervous system effects are arranged alphabetically. No longer can there be any doubt that peptides affect the central nervous system, sometimes in several ways.

Double immunocytochemistry in pre-embedding electron microscopy for the detection of neurotensin and tyrosine hydroxylase in the guinea pig, using two primary antisera raised in the same species

In this study we identified for electron microscopy two different antigens (neurotensin and tyrosine hydroxylase) in the same pre-embedding section of nervous tissue, using two antibodies obtained in the same species. Optimal ultrastructural results were obtained without adding to the fixative either glutaraldehyde or acrolein (normally used for electron microscopy techniques). The different developing methods used in this study (DAB in combination with either 1 nm silver-enhanced colloidal gold or benzidine dihydrochloride) are perfectly distinguishable at the ultrastructural level, and show some advantages over other previously described developing procedures. For instance, the use of small gold particles (1 nm) reduces the severity of membrane damage caused by tissue penetration of the bigger gold particles (5 nm). In addition, the reaction products are stable, so there is no need to stabilize them before osmication, as is necessary in other developing methods such as the TMB procedure. The immunolabeling results obtained in this study were similar in both developing methods, although synaptic profiles were more readily visible when the DAB/colloidal gold procedure was used. Using electron microscopy, we have detected TH immunoreactivity in dendrites and perikarya receiving synaptic contacts from NT-positive terminals, as well as TH-immunoreactive inputs on NT-positive neurons, at both the somatic and dendritic levels.

Reciprocal synaptic connections between neurotensin- and tyrosine hydroxylase-immunoreactive neurons in the mediobasal hypothalamus of the guinea pig

Neurotensin (NT) and dopamine are two neurotransmitters which are present in the hypothalamus of mammals and are often distributed in identical areas. In particular, in the periventricular anterior hypothalamus and in the arcuate nucleus, images of apposition between perikarya and fibers containing dopamine or neurotensin have frequently been observed at the light microscope level. The aim of this study was to answer, at the ultrastructural level in the A12 and A14 catecholaminergic cell groups, the question as to the existence of the possible synaptic nature of such contacts. To this end, NT and tyrosine hydroxylase (TH) were simultaneously visualized using double pre-embedding immunocytochemical methods. In the A12 arcuate area, synaptic contacts were demonstrated between TH-immunoreactive terminals and NT-labeled perikarya and dendrites. The opposite pattern, i.e., NT-stained terminals synapsing onto TH-positive neurons, was also observed. In contrast, only NT synaptic inputs onto TH-stained cell bodies could be demonstrated in the hypothalamic periventricular nucleus. In addition, immunoreactive terminals stained for NT or TH were observed to make synaptic contacts with perikaryal profiles stained for the same antigen. These results demonstrate a strong synaptic NT input onto the dopaminergic neurons of the mediobasal hypothalamus and suggest a reciprocal influence, at least in part, of catecholaminergic terminals on arcuate NT-containing neurons.