Effects of the serotonin-uptake inhibitor, fluoxetine, on immunoreactive serotonin innervation in the rat pituitary gland

Saland, L.C.; Wallace, James A.; Reyes, Edward; Samora, A.; Maez, D.; Comunas, F.

doi:10.1016/0361-9230(87)90091-8

Cited by 11 publications

(2 citation statements)

References 39 publications

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“…There is evi dence that 5-HT neurons may mediate release of POMC-de rived peptides from the IL as well. Anatomic studies indicate that the IL is innervated by 5-HT-immunoreactive neurons [8][9][10][11][12][13]. Serotonin (5-HTj) receptors have been demonstrated on IL cells, suggesting a physiological role for 5-HT in regulating IL secretory activity' [14].…”

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confidence: 99%

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

Carr¹,

Saland²,

Samora³

et al. 1991

Neuroendocrinology

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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 α-melanocyte-stimulating hormone (α-MSH) as well as the ultrastructural appearance of IL cells were used as indicators of IL secretory activity. Plasma β-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 α-MSH. Treatment with the 5-HT reuptake blocker fluoxetine elevated plasma levels of β-endorphin but not α-MSH. Administration of the 5-HT₁/5-HT₂ agonist MK-212 produced an elevation in both plasma α-MSH and β-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 apomoφhine blocked MK-212-induced release of α-MSH but not β-endorphin. Our results show that manipulation of 5-HT synthesis/reuptake does not affect release of α-MSH, but that direct activation of 5-HT receptors with the nonselective agonist MK-212 stimulates α-MSH release. The ability of apomoφhine to block MK-212-induced release of α-MSH suggests a direct antagonism between dopaminergic and serotonergic regulation of α-MSH release.

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confidence: 99%

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

Carr¹,

Saland²,

Samora³

et al. 1991

Neuroendocrinology

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“…Additionally, serotonin has been detected in TH-positive axons (Saland et al, 1988b). Saland et al (1988b) demonstrated that the presence of serotonin in the lobe results from axonal uptake, as evidenced by the abolition of serotonin immunostaining following peripheral administration of the serotonin-uptake inhibitor fluoxetine (Saland et al, 1987). Furthermore, in vitro experiments suggest serotonin uptake via a dopamine transporter (Vanhatalo and Soinila, 1994).…”

Section: Discussionmentioning

confidence: 97%

Differential innervation of individual melanotropes suggests a role for nonsynaptic inhibitory regulation of the developing and adult rat pituitary intermediate lobe

Chronwall

Sands

Cummings

et al. 1998

Synapse

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Dopamine and GABA were detected in intermediate lobe axons around birth, and early axons were closely apposed to glial cells and processes, possibly using them for guidance. In the adult, axons containing colocalized dopamine and GABA were distributed in a distinct pattern within the lobe, with plexuses located dorsally and ventrally. Axons preferentially followed glial processes in interlobular septa, yet were also interspersed between melanotropes. Individual melanotropes were contacted by varying numbers of axon terminals, with some devoid of contacts. Boutons contained both small clear vesicles and large dense-cored vesicles; membrane specializations were not well-developed. From these findings we concluded that in addition to direct synaptic inhibition, dopamine and GABA could stimulate their receptors by mechanisms similar to "parasynaptic" [Schmitt (1984) Neuroscience, 13:991-1001] or "volume" [Agnati et al. (1995) Neuroscience, 69:711-726] transmission as proposed for the CNS. Humoral agents passing into the intermediate lobe from portal vessels, thus acting as classical hormones, further regulate the melanotropes. Moreover, approximately 50% of the axonal elements were closely apposed to glia, suggesting that glia could have regulatory roles. Previous studies from our laboratory [Chronwall et al. (1987) Endocrinology, 120:1201-1211; Chronwall et al. (1988) Endocrinology, 123:1992:1202] demonstrated heterogeneity in proopiomelanocortin (POMC) biosynthesis among individual melanotropes, prompting the hypothesis that the degree of innervation could govern the expression of certain molecules. We combined immunohistochemistry and in situ hybridization histochemistry to evaluate whether melanotrope molecular heterogenity is spatially correlated with axons and terminals. Tentatively, melanotropes expressing low levels of POMC and alpha1A subunit P/Q type Ca2+ channel mRNAs often were apposed to axons, whereas those with low levels of D2L receptor mRNA rarely were contacted by axons, suggesting that innervation could be one of the factors inducing and maintaining heterogeneity.

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Colocalization of dopamine and serotonin in the rat pituitary gland and in the nuclei innervating it

et al. 1995

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Effects of the serotonin-uptake inhibitor, fluoxetine, on immunoreactive serotonin innervation in the rat pituitary gland

Cited by 11 publications

References 39 publications

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

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

Differential innervation of individual melanotropes suggests a role for nonsynaptic inhibitory regulation of the developing and adult rat pituitary intermediate lobe

Colocalization of dopamine and serotonin in the rat pituitary gland and in the nuclei innervating it

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