L.C. Saland

The mammalian pituitary intermediate lobe: an update on innervation and regulation.

The pituitary intermediate lobe (IL) in mammals is an area of uniform endocrine cells which synthesize and release specific peptide products of the proopiomelanocortin gene. The lobe receives direct synaptic connections onto the endocrine cells from hypothalamic dopaminergic neurons. This review updates information on the dopaminergic as well as the gamma-aminobutyric acid inhibitory neuroregulation for the IL. It also provides a discussion of stimulatory molecules which are likely to affect peptide release, particularly the neurotransmitter serotonin, which may be present via uptake into the dopaminergic nerve terminals. Other stimulatory molecules discussed which are likely to significantly affect peptide secretion are norepinephrine, corticotropin-releasing factor, and several opiate peptides. A new direction of study involves the potential interaction of neurotrophic factors, which are present in all areas of the pituitary, and may be suggested to have a supportive role for the neural elements of the IL. The endocrine cells of the IL and their direct hypothalamic innervation are considered to be an easily accessed peripheral model for study of both neural-endocrine and neurotrophic-target cell interactions.

Growth-associated protein 43 (GAP-43) and synaptophysin alterations in the dentate gyrus of patients with schizophrenia.

Growth-associated protein 43 (GAP-43) expression is critical for the proper establishment of neural circuitry, a process thought to be disrupted in schizophrenia. Previous work from our laboratory demonstrated decreased GAP-43 levels in post-mortem tissue from the entire hippocampal formation of affected individuals. In the present study, we used immunocytochemical techniques to localize alterations in GAP-43 protein to specific synapses. GAP-43 distribution was compared to that of synaptophysin, another synaptic protein known to be altered in schizophrenia. The levels and distribution of GAP-43 and synaptophysin proteins were measured in the dentate gyrus of subjects with schizophrenia and sex-, age-, and postmortem interval-matched normal controls and subjects with bipolar disorder. Tissue from subjects was provided by the Harvard Brain Tissue Resource Center. In control subjects, GAP-43 immunostaining was prominent in synaptic terminals in the inner molecular layer and hilar region. Subjects with schizophrenia had significant decreases in GAP-43 immunoreactivity in the hilus (p<0.05, paired t-test) and inner molecular layer (p<0.05, paired t-test) but not in the outer molecular layer. In the same tissues, synaptophysin immunoreactivity was significantly reduced in both the inner and outer molecular layers of the dentate gyrus (both p<0.01 by paired t-test), but not in the hilus. In contrast to patients with schizophrenia, GAP-43 and synaptophysin levels in subjects with bipolar disorder did not differ from controls. Given the relationship of GAP-43 and synaptophysin with the development and plasticity of synaptic connections, the observed alterations in the hippocampus of patients with schizophrenia may be related to cognitive deficits associated with this illness.

In Vitro and In Vivo Effects of β-Endorphin and Met-Enkephalin on Leukocyte Locomotion

Publisher Summary Several peptides have been described with chemotactic activity for neutrophils and monocytes. The one most widely studied has been formyl methionyl leucyl phenylalanine (f-MLP). This peptide is a potent chemotactic factor for both monocytes and neutrophils, and recent studies have demonstrated the presence of specific receptors for these peptides on human neutrophils, and monocytes. Although these peptides are potent chemotactic factors, there is no evidence that they are naturally produced by the host, although the production of similar agents by bacteria has been described. Recently the hypotensive, vasodilator and smooth muscle contracting peptide, substance P has been shown to stimulate rabbit neutrophil chemotaxis and lysosomal enzyme release. This neuropeptide also blocks the binding of f-MLP to its receptor, and, therefore, may act through this receptor. Substance P has also been associated with pain transmission. Other nervous system-produced peptides, such as amino and carboxyterminal substituent tetrapeptides of angiotension, have been shown to be chemotactic for human monocytes, with lesser activity for neutrophils. Other studies have shown that human mononuclear phagocytes specifically bind [1125]8-L-arginine-vasopressin, and that vasoactive intestinal polypeptides can be found in polymorphonuclear leukocytes. All of these studies indicate that cells of the immune system may be directly affected by products of the central nervous system. As immigration of leukocytes to a site of inflammation is a primary step in host defense, it is the purpose of this study to determine if P-endorphin or the 5 amino acid constituent of P-endorphin, Met-enkephalin, have any effect on monocyte, lymphocyte or neutrophil locomotor responses.

Corticotropin-releasing factor (CRF) and neurotransmitters modulate melanotropic peptide release from rat neurointermediate pituitary in vitro

Isolated pituitary neurointermediate lobes from adult male Sprague-Dawley rats were incubated for up to 90 minutes in media containing stimulatory or inhibitory agents, to study the potential effects on secretion of alpha-melanocyte stimulating hormone (alpha-MSH) from the pars intermedia. Dopamine (DA), as expected, inhibited the release of alpha-MSH, as measured by radioimmunoassay (RIA), while corticotropin-releasing factor (CRF) and serotonin (5-HT) stimulated peptide release to varying degrees over the incubation period. A combination of DA with CRF produced an inhibition of peptide release, suggesting that DA suppresses the stimulatory effects of the hypothalamic peptide. Immune staining of pituitary tissue for beta endorphin or alpha-MSH, and quantified for staining intensity, supported the specific effects of stimulation or inhibition of the respective treatments. In addition, electron microscopy of incubated tissues demonstrated alterations in secretory vesicles and membranous organelles which were consistent with peptide secretion patterns. Our in vitro findings suggest that neurotransmitters and hypothalamic peptide, which are present together in vivo in the pituitary intermediate lobe, interact at the level of the endocrine cells to modulate pro-opiomelanocortin peptide secretion.

Chronic ethanol modulates delta and mu-opioid receptor expression in rat CNS: immunohistochemical analysis with quantitiative confocal microscopy

Ethanol consumption affects levels of endogenous opioids as well as opioid receptors in both animals and humans. We studied the expression of delta (delta) and mu (mu) opioid receptors (ORs) in brain sections of adult male Sprague-Dawley rats after 2 weeks of consuming ethanol in a liquid diet, with comparisons to sections from pair-fed control animals. Immunohistochemical staining for the ORs, using selective antibodies, and quantitation of confocal images, revealed increased expression of delta-ORs in hippocampal CA1 of the chronic ethanol-treated rats. In contrast, mu-ORs decreased in their expression after ethanol treatment in multiple brain areas, including cortex, hippocampus, midbrain colliculi, striatum and nucleus accumbens. The alterations in immunoreactive OR expression may be related to reduced functional coupling of the ORs to G-proteins, as found in prior studies in several brain regions, using the same chronic ethanol diet protocol. Changes in OR expression and functional coupling in the CNS may be factors in ongoing ethanol consumption and tolerance.

The lateral recess of the third ventricle in teleosts: An electron microscopic and golgi study

SummaryThe ependyma lining the lateral recess of the third ventricle of the teleost inferior lobe has been studied by light and electron microscopy, including Golgi impregnation methods. As many as five different cell types appear to line the ventricle, but some of these may be similar cells in different stages of activity. One cell type contains small dense-cored vesicles and appears to have processes extending into deeper portions of the lobe. Golgi preparations reveal subependymal cells with apical processes extending to the ventricle and basal extensions which may reach the pial surface. The present observations are discussed in relation to similar studies in other fishes, amphibians and mammals. Possible functions for the various cells observed are suggested.

In vivo Effects of Serotonergic Agents on AIpha-MeIanocyte-StimuIating Hormone Secretion

We used an in vivo pharmacological approach to investigate the potential influence of serotonin (5-HT) on peptide release from the intermediate lobe (IL) of the rat pituitary. Plasma levels of alpha-melanocyte-stimulating hormone (alpha-MSH) as well as the ultrastructural appearance of IL cells were used as indicators of IL secretory activity. Plasma beta-endorphin levels were also measured to assess the effectiveness of 5-HT-acting drugs. Intraperitoneal administration of 5-hydroxy-L-tryptophan, the synthetic precursor of 5-HT, dramatically elevated the content of 5-HT in the neurointermediate lobe but did not alter plasma titers of alpha-MSH. Treatment with the 5-HT reuptake blocker fluoxetine elevated plasma levels of beta-endorphin but not alpha-MSH. Administration of the 5-HT1/5-HT2 agonist MK-212 produced an elevation in both plasma alpha-MSH and beta-endorphin levels. Quantitative morphometry of IL cells at the ultrastructural level revealed that MK-212 treatment selectively causes depletion of electron-lucent but not electron-dense secretory granules from the cytoplasm of IL cells. Pretreatment with the selective D2 dopamine agonist apomorphine blocked MK-212-induced release of alpha-MSH but not beta-endorphin. Our results show that manipulation of 5-HT synthesis/reuptake does not affect release of alpha-MSH, but that direct activation of 5-HT receptors with the nonselective agonist MK-212 stimulates alpha-MSH release. The ability of apomorphine to block MK-212-induced release of alpha-MSH suggests a direct antagonism between dopaminergic and serotonergic regulation of alpha-MSH release.

Serotonin-immunoreactive nerve fibers of the rat pituitary: effects of anticatecholamine and antiserotonin drugs on staining patterns

Serotonin-immunoreactive (5-HT-IR) nerve fibers observed in the pars intermedia and pars nervosa of the rat pituitary gland were examined after treatment of animals with antiserotonergic or anti-catecholaminergic drugs. p-Chlorophenylalanine, (PCPA), an inhibitor of 5-HT synthesis, eliminated staining in both areas of pituitary gland. p-Chloroamphetamine (PCA), a serotonin neurotoxin, did not produce a significant change in 5-HT-IR from control tissue. Unexpectedly, 6-hydroxydopamine (6-OHDA), a catecholamine neurotoxin, eliminated 5-HT staining in the pars intermedia, but not in the pars nervosa. These observations suggest that 5-HT present in fibers innervating the intermediate and neural lobes is synthesized in axons locally, or is taken up into fibers from extrinsic sources. In addition, catecholamines and 5-HT may co-exist in nerve terminals of both lobes of the pituitary gland.

Benzodiazepine suppression of corticotropin-releasing factor (CRF)-induced beta-endorphin release from rat neurointermediate pituitary

Dopamine and gamma-aminobutyric acid (GABA) inhibit POMC peptide release from the pituitary intermediate lobe, via interaction with D2 or GABA-A/benzodiazepine receptors. Here, we examined the effects of an antianxiety triazolobenzodiazepine, adinazolam, on corticotropin-releasing factor (CRF)-stimulated POMC peptide secretion from the rat neurointermediate pituitary. Neurointermediate lobes (NILS) were incubated with CRF (10(-7) M), then adinazolam (10(-8) or (10(-9) M) was added, with CRF remaining in the medium. Aliquots were removed at 15-min intervals and frozen for radioimmunoassay of beta-endorphin. Adinazolam alone did not significantly affect secretion as compared to controls or CRF alone. Adinazolam incubated with CRF led to significant inhibition of beta-endorphin secretion, as compared to CRF alone. In addition, adinazolam was as effective as dopamine or the CRF antagonist, alpha-helical CRF, in preventing CRF-induced beta-endorphin release. Adinazolam appears to act directly on the pituitary to suppress hormone release induced by a stress-related hypothalamic peptide.

Naloxone Prevents Dark-Background Adaptation in Amphibians

Pituitary intermediate lobe melanocyte-stimulating hormone (MSH) is responsible for normal skin darkening in amphibians. Light-background adapted frogs (Rana pipiens) injected with naloxone and placed on black backgrounds maintain melanophore indices and pituitary cytology characteristic of light-background adaptation. In vitro and in vivo experiments showed that naloxone hydrochloride did not have a direct effect on skin melanophores or on the neurointermediate lobe. These data suggest that naloxone acts at the level of the central nervous system to inhibit the mechanism(s) responsible for release of MSH when light-background adapted frogs are placed on a dark background. Release of MSH, known to be tonically inhibited by the hypothalamus, may be modulated by opiate receptor-dependent mechanisms.