Involvement of dopamine D2 receptor in the diurnal changes of tuberoinfundibular dopaminergic neuron activity and prolactin secretion in female rats.

Background: An endogenous dopaminergic (DA) tone acting on D3 receptors has been shown to inhibit tuberoinfundibular (TI) DA neuron activity and stimulate prolactin (PRL) surge in the afternoon of estrogen-primed ovariectomized (OVX+E2) rats. Whether D2 receptor (D2R) is also involved in the regulation of TIDA and PRL rhythms was determined in this study.

Results: Intracerebroventricular (icv) injection of PHNO, a D2R agonist, in the morning inhibited TIDA and midbrain DA neurons' activities, and stimulated PRL secretion.

An endogenous dopaminergic tone acting on dopamine D3 receptors may be involved in diurnal changes of tuberoinfundibular dopaminergic neuron activity and prolactin secretion in estrogen-primed ovariectomized rats.

The diurnal rhythm of tuberoinfundibular dopaminergic (TIDA) neuron activity, i.e., high in the morning and low in the afternoon, is prerequisite for the afternoon prolactin (PRL) surge in proestrous and estrogen-primed ovariectomized (OVX) female rats.

The spontaneous firing rates of dopamine-inhibited dorsomedial arcuate neurons exhibit a diurnal rhythm in brain slices obtained from ovariectomized plus estrogen-treated rats.

The activity of tuberoinfundibular dopaminergic (TIDA) neurons exhibits a diurnal rhythm in female rats, as determined by neurochemical investigation. Whether the spontaneous firing rates of presumed TIDA neurons in the dorsomedial arcuate nucleus (dmARN) also exhibit a diurnal pattern has yet to be ascertained. Single-unit activities of 131 dmARN neurons were recorded in brain slices prepared from 83 ovariectomized plus estrogen-primed rats, and grouped according to their responses to dopamine and the time at which they were observed.

CART peptide increases the mesolimbic dopaminergic neuronal activity: a microdialysis study.

The effects of cocaine-and amphetamine-regulated transcript (CART) peptide on extracellular concentrations of dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the shell region of the nucleus accumbens (AcbSh) were determined by microdialysis in conscious rats. Intracerebroventricular injections of various doses (0.1-5 microg/5 microl/rat) of CART(55-102) elicited dose-dependent increases of extracellular DOPAC and HVA concentration in the AcbSh, suggesting that CART(55-102) peptide has a psychostimulant-like effect via activation of the mesolimbic dopaminergic system.

Differential effects of colchicine on central dopaminergic neuronal activity and prolactin secretion in estrogen-primed ovariectomized rats.

Colchicine is a potent chemical that disrupts the assembly of microtubulin and affects the integrity of cytoskeleton. It is commonly used to block the axonal transport in neurons. Central administration of colchicine (48 microg/3 microl/rat) two days earlier significantly lowered 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the striatum and nucleus accumbens, both in the morning and in the afternoon.

Involvement of angiotensin II, TRH and prolactin-releasing peptide in the estrogen-induced afternoon prolactin surge in female rats: studies using antisense technology.

The roles of endogenous angiotensin II (AII), thyrotropin-releasing hormone (TRH) and prolactin-releasing peptide (PrRP) on the estrogen-induced prolactin (PRL) surge and the diurnal change of tuberoinfundibular dopaminergic (TIDA) neuronal activity were assessed in this study. Ovariectomized, estrogen-primed rats implanted with intracerebroventricular cannula received daily injection of antisense oligodeoxynucleotide (ODN, 10 microg/3 microl) against the mRNA of AII, TRH or PrRP for two days. Artificial cerebrospinal fluid or the sense ODN were used as the control.

Effects of prolactin-releasing peptide on tuberoinfundibular dopaminergic neuronal activity and prolactin secretion in estrogen-treated female rats.

Both systemic and central effects of a newly discovered prolactin (PRL)-releasing factor (PRF), prolactin-releasing peptide (PrRP), were determined in this study. Systemic injection of PrRP (1 and 10 microg/rat, i.v.

Pretreatment with antisense oligodeoxynucleotide against D(2) or D(3) receptor mRNA diminished dopamine's inhibitory effect on dorsomedial arcuate neurons in brain slices of estrogen-treated ovariectomized rats.

A high percentage of dopamine (DA)-responsive neurons has been repeatedly shown in hypothalamic dorsomedial arcuate nucleus (dmARN) using single-unit recording in brain slices. Both D(2) and D(3) receptors may be involved in the inhibitory action of DA as indicated by results obtained from using specific DA agonists and antagonists. To further delineate the DA receptor types involved, ovariectomized, estrogen-primed Sprague-Dawley rats pretreated with antisense oligodeoxynucleotide (ODN, 10 microg/3 microl, i.