Biomedical subjects

J T Pan

Publications and source records attributed to J T Pan.

At least 19 recordsLinked to original sources

PubMed2001

Potent inhibitory effect of selective D2 and D3 agonists on dopamine-responsive dorsomedial arcuate neurons in brain slices of estrogen-primed rats.

The possible involvement of dopamine D2 and D3 receptors in the action of dopamine (DA) on inhibiting dorsomedial arcuate nucleus (dmARN) neurons in brain slices was determined in this study. Fresh brain slices were prepared from ovariectomized, estrogen-primed Sprague-Dawley rats and used for extracellular single-unit recording. The dmARN neurons were first identified by their inhibitory responses to DA and then tested with PHNO and/or PD128907, selective D2 and D3 agonists, respectively. PD128907 in 5-50 nmole doses significantly inhibited the majority of DA-responsive dmARN neurons (86.3% of 44 units). Moreover, PHNO in 5-25 nmole doses inhibited all DA-responsive neurons tested (100% of 34 units). The inhibitory effects of PHNO and PD128907 were not only prominent; but also persisted in low Ca2+, high Mg2+ medium, indicating that they were acting directly on the recorded neuron. Pretreatment of either raclopride or U99194A, D2 and D3 receptor antagonists respectively, reversed the effects of DA in a few trials. In contrast, SKF81297, a D1 receptor agonist, induced variable responses in dmARN neurons. These results clearly indicate that DA may act through D2 and/or D3 receptors to exhibit an inhibitory effect on presumed TIDA neurons in dmARN.

Animals↗

PubMed2001

Prostaglandins may participate in opioidergic and cholinergic control of the diurnal changes of tuberoinfundibular dopaminergic neuronal activity and serum prolactin level in ovariectomized, estrogen-treated rats.

The roles of prostaglandins (PGs) involved in opioidergic, cholinergic, and serotonergic regulation of the diurnal changes of tuberoinfundibular dopaminergic (TIDA) neuronal activities were investigated in ovariectomized, estrogen-treated rats. Treatment with naloxone [10 mg/kg, intraperitoneal (i.p.)], atropine (5 mg/kg, i.p.), or ketanserin (10 mg/kg, i.p.) at either 1200 or 1400 h prevented the afternoon decrease of TIDA neuronal activity and the prolactin (PRL) surge. Intracerebroventricular (i.c.v.) injection of PGE(1) (5 microg/3 microl/rat) at 1500 h significantly reversed the effects of naloxone and atropine, but not that of ketanserin. In ovariectomized, estrogen-primed rats pretreated with indomethacin, i.c.v. injection of either nicotine (10 ng/rat) or fentanyl (10 ng/rat) failed to suppress the TIDA neuronal activity and to stimulate the PRL secretion. These data suggest that PG may be involved in opioidergic and cholinergic control of the diurnal changes of TIDA neuronal activity and the PRL secretion in ovariectomized (OVX) + E(2) rats.

Acetylcholine↗

PubMed2001

Prostaglandins play an important role in diurnal changes of tuberoinfundibular dopaminergic neuronal activity and prolactin secretion in ovariectomized, estrogen-treated rats.

Intracerebroventricular injection of prostaglandins (PGs) has long been shown to stimulate the secretion of prolactin (PRL). The action of specific PG and the underlying mechanism, however, remain inconclusive. In this study, we evaluated the involvement of PGs in the diurnal changes of the tuberoinfundibular dopaminergic (TIDA) neurons and PRL secretion in ovariectomized (OVX) rats treated with estrogen (E2). Prior treatment of indomethacin (50 mg/kg, subcutaneous) for 24 h significantly prevented the afternoon decrease of TIDA neuronal activity and blocked the PRL surge. Intracerebroventricular injection of PGE(1) (5 microg/3 microl/rat) at 1000 h significantly lowered the activity of TIDA neurons, while similar treatment of PGE2 was without effect. In OVX + E(2) rats pretreated with indomethacin, PGE(1) given at 15, but not 30 or 180 min before decapitation at 1500 h significantly reversed the effects of indomethacin on TIDA neuronal activity, while the blocked PRL surge was not reversed. The PGs also exhibited a stimulatory effect on nigrostriatal dopamine (DA) neurons with PGE2 being the most effective agent. These results indicate that endogenous PGs play a significant role in the control of central DA neurons, especially the diurnal changes of TIDA neuronal activity and PRL secretion in OVX + E2 rats.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2001

Involvement of central GABAergic neurons in basal and diurnal changes of tuberoinfundibular dopaminergic neuronal activity and prolactin secretion.

Central administration of gamma-aminobutyric acid (GABA) has been shown to stimulate the secretion of prolactin (PRL). Whether GABA acts via dopamine, the major PRL-inhibiting hormone, and which GABA receptor type(s) is involved have not been ascertained. Both GABA(A) and GABA(B) receptor agonists and/or antagonists were administered centrally in this study and their effects on both basal and diurnal changes of tuberoinfundibular dopaminergic (TIDA) neuronal activity were determined by measuring the concentration of 3,4-dihydroxyphenylacetic acid (DOPAC) in the median eminence (ME). Serum PRL level was determined by RIA. Ovariectomized, estrogen-primed Sprague-Dawley rats implanted with intracerebroventricular (icv) cannulae were used. Muscimol (1 ng/3 microl/rat, icv), a GABA(A) receptor agonist, but not baclofen (1-100 ng/3 microl/rat, icv), a GABA(B) receptor agonist, injected in the morning significantly lowered and elevated ME DOPAC and serum PRL levels, respectively at 15 and 30 min. Lower and higher doses of muscimol were not effective. The effects of muscimol could also be prevented by co-administration of bicuculline (0.1-10 ng/3 microl, icv), a GABA(A) receptor antagonist. When bicuculline (10-500 ng/3 microl, icv) was given in the afternoon (at 1500 h), it significantly reversed the lowered ME DOPAC level in the afternoon and prevented the concurrent PRL surge. We conclude that endogenous GABA acting through GABA(A) receptors may play a significant role in the control of basal and diurnal changes of TIDA neuronal activity, and in turn, PRL secretion.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2000

Dopamine and 7-OH-DPAT may act on D(3) receptors to inhibit tuberoinfundibular dopaminergic neurons.

Whether the tuberoinfundibular dopaminergic (TIDA) neurons resided in the dorsomedial arcuate nucleus (dmARN) can respond to dopamine and a dopamine D(3) receptor agonist, 7-hydroxydipropylaminotetralin (7-OH-DPAT), was the focus of this study. In studies using extracellular single-unit recording of dmARN neurons in brain slices obtained from ovariectomized rats, dopamine and 7-OH-DPAT inhibited 60.1% (n = 141) and 80.9% (n = 47) of recorded dmARN neurons, respectively. Other dopamine D(1) or D(2) receptor agonists were not as effective. Intracerebroventricular injection of 7-OH-DPAT (10(-9) mol/3 microl) in ovariectomized, estrogen-primed rats significantly lowered the TIDA neuronal activity as determined by 3, 4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence. Co-administration of a putative D(3) receptor antagonist, U-99194A, could prevent the effect of 7-OH-DPAT. Unilateral microinjection of 7-OH-DPAT or dopamine itself (10(-11)-10(-9) mol/0.2 microl) into the right dmARN exhibited the same inhibitory effect on TIDA neurons. In all, dopamine may act on D(3) receptors to exhibit an inhibitory effect on its own release from the TIDA neurons.

Animals↗

PubMed2000

Stimulatory and entraining effect of melatonin on tuberoinfundibular dopaminergic neuron activity and inhibition on prolactin secretion.

The aims of the present study were to determine if melatonin exerts an effect on prolactin (PRL) secretion via the tuberoinfundibular dopaminergic (TIDA) neurons and if endogenous or exogenous melatonin has an entraining effect on the rhythmic changes of TIDA neuronal activity and PRL secretion. Melatonin given in the morning (10:00 h), dose- (0.01-1 mg/kg, ip) and time- (at 15 and 60 min, but not at 30 min) dependently stimulated TIDA neuronal activity in ovariectomized (OVX), estrogen-treated rats as determined by 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence (ME). Serum PRL was concurrently inhibited by the injection. Melatonin administered in the afternoon (15:00 h) was even more effective in stimulating the lowered TIDA neuronal activity and inhibiting the increased PRL level than that given in the morning (10:00 h). S-20098, a melatonin agonist was also effective in stimulating the TIDA neurons. In contrast, S-20928, a putative melatonin antagonist, while it had no effect by itself, blocked the effect of S-20098. Although S-20928 failed to prevent melatonin's effect on ME DOPAC levels, six interspaced injections of S-20928, from 18:00 to 01:30 h, significantly blocked the increase of ME DOPAC levels at 03:00 h, indicating that the endogenous melatonin may play a role. We further used rats that received daily injection of melatonin (1 mg/kg, ip) at 18:00 h for 10 days and found that the injection augmented basal TIDA neuronal activity at 11:00 h and blunted the afternoon PRL surge. In all, melatonin can have an inhibitory effect on PRL secretion by stimulating the TIDA neurons, and it may help to entrain the circadian rhythms of both TIDA neuronal activity and PRL secretion.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2000

An endogenous serotonergic rhythm acting on 5-HT(2A) receptors may be involved in the diurnal changes in tuberoinfundibular dopaminergic neuronal activity and prolactin secretion in female rats.

The central serotonergic system has long been known to have a stimulatory role on the secretion of prolactin (PRL). The integrity of serotonergic neurotransmission is essential for the expression of the estrogen-induced afternoon PRL surge. Whether its effect on PRL involves change in the activity of tuberoinfundibular dopaminergic (TIDA) neurons has not been ascertained. In adult ovariectomized rats treated with estrogen, depletion of central serotonin (5-HT) by 5,7-dihydroxytryptamine (5,7-DHT, 200 microg/rat, i.c.v.) effectively prevented the afternoon fall in TIDA neuronal activity (using the levels of 3,4-dihydroxyphenylalanine and 3, 4-dihydroxyphenylacetic acid (DOPAC), and the ratio of DOPAC/dopamine in the median eminence as indices), and blunted the afternoon PRL surge. A single injection of a 5-HT(2A) receptor antagonist, ketanserin (5 mg/kg, i.p. at 12.00 h), also had the same effects on the diurnal changes in TIDA neuronal activity and PRL secretion as the treatment with 5,7-DHT did. Intracerebroventricular injection of a 5-HT(2) receptor agonist 2, 5-dimethoxy-4-iodoamphetamine (DOI) in the morning inhibited the TIDA neuronal activity and stimulated PRL secretion in a dose-dependent manner; while injection of a 5-HT(1) agonist, 8-hydroxy-dipropylaminotetralin, was without effect. Injection of DOI in 5,7-DHT-pretreated rats at 14.30 h also lowered the TIDA neuronal activity and reinstated the PRL surge. In all, endogenous 5-HT, acting through the 5-HT(2A) receptor, appears to exhibit an inhibitory effect on TIDA neuronal activity during the afternoon, which is essential for the PRL surge.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1999

Transient elevation in plasma prolactin level in rats with temporal lobe status epilepticus.

Microinjection of kainic acid into the CA3 subfield of hippocampus in anesthetized rats elicited seizure-like hippocampal EEG activity that persisted for more than 180 minutes. There was a concomitant rise in plasma prolactin level that peaked at 15 to 20 minutes but endured less than 60 minutes. We conclude that plasma prolactin exhibited only transient elevations during experimental temporal lobe status epilepticus in rats.

Animals↗

PubMed1999

Single-unit activity of dorsomedial arcuate neurons and diurnal changes of tuberoinfundibular dopaminergic neuron activity in female rats with neonatal monosodium glutamate treatment.

Neonatal monosodium glutamate (MSG)-treated rats were used in this study to answer two questions: (1) whether or not the dopamine-responsive dorsomedial arcuate (dm-ARN) neurons are tuberoinfundibular dopaminergic (TIDA) neurons, and (2) whether or not the remaining TIDA neurons in MSG-treated rats are functioning normally. MSG (4 mg/g b. wt., subcutaneously [s.c.]) or saline was given to neonatal Sprague-Dawley rats on days 1, 3, 5, 7, and 9 after birth. The female rats were ovariectomized at 50 days of age and treated with estrogen for 1 week before they were used between 65-90 days of age. The tyrosine hydroxylase-immunoreactive (TH-ir) neurons located in the dm and ventrolateral (vl) parts of the ARN were significantly reduced in MSG-treated rats, as determined by immunohistochemical method. Some TH-ir cells, however, were visible along the border of the third ventricle. Using single-unit recording in brain slices, we found that dopamine inhibited significantly fewer percentage of dm-ARN neurons in MSG-treated (28.2%, n = 39) than in saline-treated rats (73.3%, n = 15). In contrast, bombesin exhibited similar effects (over 70% excitation) in both groups. Using neurochemical means, neonatal MSG treatment produced significant decreases of both 3,4-dihydroxyphenylacetic acid and dopamine levels, but not their ratios, in the median eminence. Moreover, the diurnal change of TIDA neuronal activity persisted in the MSG-treated rats; so did the estrogen-induced afternoon prolactin surge. All these results indicate that neonatal MSG-treatment reduced the number and altered the location of TIDA and dopamine-responsive dm-ARN neurons. The remaining TIDA neurons seemed to be able to maintain their basal activities and diurnal rhythm.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1999

A variant of Saccharomyces cerevisiae pep4 strain with improved oligotrophic proliferation, cell survival and heterologous secretion of alpha-amylase.

A variant of Saccharomyces cerevisiae pep4 strain 20B12, with improved oligotrophic proliferation, cell survival and secretion of heterologous mouse alpha-amylase, is described. Previously we reported a procedure to enrich NI transformants that are not inhibited by cytotoxic expression of hepatitis B virus surface antigen in the secretion pathway of the protease-A-deficient (pep4) strain. To use the NI cells as a host for heterologous expression, we tried to amend the introduced pYAS/12S vector and obtain a host strain, NI-C, with stable NI phenotype and trp1 marker restored. Southern analysis of genomic DNA of NI-C suggested that the original pYAS/12S was abnormally rearranged and not completely corrected. Further assay showed that the viability and mitotic ability of the NI-C strain were increased. While using the NI-C strain as host for plasmid transformation and heterologous expression of mouse alpha-amylase, we observed that transformed colonies grew more quickly and secreted more alpha-amylase than general yeast strains. A further test showed that the NI-C strain was able to use mouse alpha-amylase as a positive selection marker to form transformed colonies on nitrogen-starved plates that contain starch as the sole carbon source. The results imply that the NI-C variant is an improved pep4 strain that can be used for heterologous expression and for the development of new selective markers in the yeast transformation system.

Animals↗

PubMed1999

Stimulatory role of prolactin on the development of tuberoinfundibular dopaminergic neurones in prepubertal female rats: studies with cysteamine and somatostatin.

Cysteamine, a potent depletor of prolactin and somatostatin, was used to determine the role of prolactin and somatostatin in the control of central dopamine neurones in prepubertal rats. Cysteamine (100 mg/kg, i.p., twice daily) was injected for 7, 14 or 21 days in 28-day-old Sprague-Dawley female rats in one study and for 3 days in 35-day-old rats in another. In control rats, the 3, 4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence increased threefold from day 35 to day 49, and serum prolactin concentration increased about 50%. Cysteamine lowered serum prolactin concentrations to 20%, and median eminence DOPAC and dopamine levels to 32-50% of control levels in both studies. The DOPAC levels in the nucleus accumbens and striatum were also lowered, while both DOPAC and dopamine in the paraventricular nucleus and periventricular nucleus (A14) were increased by cysteamine. A single injection of rat prolactin (0.01, 0.1 or 1 mg/kg) significantly increased DOPAC or DOPA levels in the median eminence, nucleus accumbens and striatum, but not in the paraventricular nucleus or A14 at 14 h later in 28-day old female rats or in 40-day-old rats pretreated with cysteamine. In contrast, central injection of somatostatin dose (0.001-1 microg/rat) and time (30-90 min) dependently decreased the DOPAC levels in the median eminence, paraventricular nucleus and A14 and increased those in the nucleus accumbens and striatum of adult female rats. These results indicate that serum prolactin is important for the maturation and maintenance of dopamine systems in the median eminence, nucleus accumbens and striatum, while somatostatin exhibits inhibitory and stimulatory effects on hypothalamic and midbrain dopamine systems, respectively.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1999

Nitric oxide plays an important role in the diurnal change of tuberoinfundibular dopaminergic neuronal activity and prolactin secretion in ovariectomized, estrogen/progesterone-treated rats.

A significant diurnal change of tuberoinfundibular dopaminergic (TIDA) neuronal activity coincident with the estrogen (E2)-induced afternoon PRL surge has been reported in ovariectomized, E2-primed (OVX+E2) rats. Systemic injection of a nitric oxide (NO) synthase (NOS) inhibitor, N(G)-nitro-L-arginine (L-NA, 50 mg/kg, i.p. at 1000 and 1200 h), significantly blocked the diurnal changes of TIDA neuronal activity and PRL secretion at 1500 and 1700 h in OVX+E2 rats. Coadministration of L-arginine (300 mg/kg, i.p.) with L-NA completely prevented the effects of L-NA. Total nitrite/nitrate levels in the serum of L-NA- and L-NA+L-arginine-treated rats substantiated the effects of L-NA and L-arginine on NO production. Pretreatment of antisense oligodeoxynucleotide (ODN; 1 microg/3 microl; intracerebroventricularly at 48, 24, and 7 h before sacrifice) against the messenger RNA (mRNA) of constitutive NOS, i.e. neuronal NOS or endothelial NOS, was also effective in preventing the diurnal changes of TIDA neuronal activity and PRL surge at 1500 h. The same treatment of antisense ODN against the mRNA of inducible NOS, i.e. macrophage NOS, had no effect. Progesterone (P4) has been reported to advance and augment the diurnal changes of TIDA neuronal activity and the afternoon PRL surge, by 1 h, in both proestrous and OVX+E2 rats. We further showed that L-NA dose dependently (50 but not 5 mg/kg, i.p. at 1000 and 1200 h) blocked the effect of P4 on TIDA neurons and serum PRL at 1300 h, which effect could be negated by simultaneous administration of L-arginine (300 mg/kg, i.p.). Pretreatment with antisense ODNs against the mRNA of neuronal NOS or endothelial NOS, but not macrophage NOS, was also effective in preventing the P4's effect on TIDA neuronal activity and PRL secretion at 1300 h. In summary, NO may play a physiological role in the E2- and P4-regulated diurnal changes of TIDA neuronal activity and PRL secretion.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1998

Progesterone advances the diurnal rhythm of tuberoinfundibular dopaminergic neuronal activity and the prolactin surge in ovariectomized, estrogen-primed rats and in intact proestrous rats.

A diurnal change of tuberoinfundibular dopaminergic (TIDA) neuronal activity exists in female rats, which is prerequisite for the estrogen-induced afternoon PRL surge. Because progesterone (P4) administered in the morning can advance and amplify the PRL surge, it is of interest to learn whether its action involves the TIDA neuron. In adult ovariectomized and estrogen-primed Sprague-Dawley rats, P4 (2 mg/kg, s.c.), given at 0800 h, exhibited a significant effect in advancing and amplifying the afternoon PRL surge, as determined by both chronic catheterization and decapitation methods of blood sampling. The afternoon decrease of TIDA neuronal activity, as determined by 3,4-dihydroxyphenylacetic acid concentration in the median eminence, was also advanced from 1400 to 1300 h. These effects of P4 on PRL surge and TIDA neuronal activity were shown to be dose- (from 0.5-4 mg/kg) and estrogen-dependent. To determine whether the effect of P4 was indeed acting via specific P4 receptor (PR), we used a PR antagonist, RU486, an antisense oligodeoxynucleotide (ODN) for PR messenger RNA (mRNA), and an antibody against PR in this study, to answer this question. Treatments of RU486 (5 mg x 3, s.c.) for 1-2 days before, and on the sampling day, were effective in antagonizing the effects of P4 on TIDA neuronal activity and on PRL secretion. Intracerebroventricular injection of an antisense ODN (4 nM) for PR mRNA or of an antibody (1:1 and 1:5) against PR for 2 days (24 and 48 h before decapitation) also were effective. Treatments of RU486 on the sampling day only, of sense ODN for PR mRNA, or of diluted PR antibody (1:10) were without significant effect. The involvement of P4 or PR on modulating the TIDA neuronal rhythm and the PRL surge also was shown in proestrous rats. In conclusion, P4 may play a significant modulatory role on rhythmic changes of the TIDA neuronal activity and the PRL surge in the female rats.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1997

Circadian change of dopaminergic neuron activity: effects of constant light and melatonin.

Twenty-four hour profiles of tuberoinfundibular (TI), nigrostriatal and mesolimbic dopaminergic (DA) neuronal activities were assessed in estrogen-primed ovariectomized rats using DOPAC and DOPA levels in terminal regions of DA neurons. Significant decreases in DOPAC and DOPA levels in the median eminence were observed at 17.00 and 21.00 h, which corresponded with higher serum prolactin levels. DOPAC or DOPA levels in the striatum and nucleus accumbens were, however, significantly higher during the dark (21.00-05.00 h) phase. In rats kept under conditions of continuous light, no late afternoon decline in median eminence DOPA was observed; this decline could be reinstated by repeated injections of melatonin between 18.00 and 01.30 h for 3 days. In summary, circadian rhythms of central DA neurons were shown and melatonin may play an entraining role.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1997

Nicotinic control of tuberoinfundibular dopaminergic neuron activity and prolactin secretion: diurnal rhythm and involvement of endogenous opioidergic system.

The possible involvement of cholinergic and opioidergic neurons in the control of diurnal changes of tuberoinfundibular dopaminergic (TIDA) neuronal activity was reported. Adult Sprague-Dawley rats ovariectomized and treated with estrogen were used. All drugs were administered centrally through preimplanted intracerebroventricular cannula, and both TIDA neuronal activity and serum prolactin level were determined. Nicotine (10 ng/3 microl/rat) given at 10:00 h significantly inhibited TIDA neuronal activity from 5 to 30 min and stimulated serum PRL levels at 5 and 15 min. Co-administration of either mecamylamine (1 microg) or naloxone (2.5 microg) prevented both nicotine's effects. A dose-related (0.1-100 ng) effect of nicotine on TIDA neuronal activity and serum PRL level was also observed in the morning when TIDA neuronal activity is high and serum PRL level is low, but not in the afternoon when the former activity is low and the latter is high. When atropine (20 microg), naloxone (25 microg) or Nor-BNI (20 microg) was given at 14:00 h all increased the lowered TIDA neuronal activity in the afternoon. When atropine was co-administered with either naloxone or Nor-BNI, however, no additive effect was observed. Submaximal doses of atropine (0.2 microg), mecamylamine (0.1 microg) or naloxone (0.25 microg) was also effective in stimulating the afternoon levels of TIDA neuronal activity and inhibiting serum PRL, and no additive effect was observed either. Moreover, simultaneous injection of morphine (15 microg) prevented atropine's effect in the afternoon. These results indicate that cholinergic neurons may act through activating the endogenous opioidergic neurons to exhibit an inhibitory effect on TIDA neuronal activity and a stimulatory one on prolactin secretion. A diurnal difference in its endogenous activity between morning and afternoon was also implicated.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1997

Inhibitory effect of dopamine on dorsomedial arcuate neurons in rat brain slices: potentiation by coadministration of cocaine.

Whether dopamine (DA) can have a direct effect on the tuberoinfundibular dopaminergic neurons has been a controversial issue. The present report used single-unit recording of neurons in dorsomedial region of the arcuate nucleus, where most tuberoinfundibular dopaminergic neurons are located, to study this question. By focusing our recording in this region, we found that DA in 25-250 nmol ranges inhibited a significant number of arcuate neurons tested (74.2% of 182 units). The inhibitory effect of DA was not only prominent in most cases, it also persisted in low Ca2+, high Mg2+ solution in several trials. Cocaine, a drug of abuse whose main effect is due to its inhibition of DA transporters and increasing the DA concentration in synaptic clefts, also inhibited a significant number of arcuate neurons by itself (51.5% of 97 units), although its effects were lesser than those of DA. Nevertheless, when coadministered with DA, cocaine significantly potentiated the inhibitory effect of DA in 82% of DA-responsive units (n = 39). These results clearly demonstrate that DA exhibits a predominantly inhibitory effect on presumed DA neurons in dorsomedial arcuate nucleus. The effects of cocaine further support this notion.

Animals↗

PubMed1997

Atrial natriuretic peptide negatively modulates the stimulatory effects of angiotensin II on tuberoinfundibular dopaminergic neuronal activity. Neurochemical and electrophysiological studies.

The effects of angiotensin II (AII) and natriuretic peptide (ANP), alone or in combination, on tuberoinfundibular dopaminergic (TIDA) neuronal activity and on serum PRL levels were examined in this study. The TIDA neuronal activity was determined by measuring 3,4-dihydroxyphenylacetic acid (DOPAC) concentration in the median eminence using high-performance liquid chromatography plus electrochemical detection, and serum PRL levels were determined by radioimmunoassay. Intracerebroventricular injection of AII induced both time (5-60 min)- and dose (0.01-1 microg)-dependent effects by stimulating TIDA neuronal activity and inhibiting serum PRL levels in ovariectomized, estrogen-treated rats. ANP in 0.01-10 microg doses, on the other hand, had no significant effect on TIDA neurons, nor on serum PRL at 30 min. When ANP (in 0.1-10 microg doses) was co-administered with AII (1 microg dose), it dose-dependently attenuated the effects of AII on TIDA neuronal activity and on serum PRL levels. In a separate study using single-unit recording of neurons of the dorsomedial arcuate nucleus (dmARC) in brain slices, where most TIDA neurons reside, AII stimulated 68.0% of 72 units recorded. Few (5.6%) units were inhibited and the remaining ones were not responsive. ANP alone was mostly ineffective on dmARC neurons (63.0% of 54 units), and it stimulated and inhibited 22.2 and 14.8% of them, respectively. When ANP was co-administered with AII to AII-responsive units, however, it significantly attenuated the effects of AII in 81.5% of 27 units. Other neurons were unaffected. Thus, results from the in vivo study indicate that ANP can negatively modulate the stimulatory effect of AII on hypothalamic TIDA neurons and the inhibitory effect on serum PRL levels; and the in vitro electrophysiological data substantiates this observation by showing that ANP exerts a similar modulation on dmARC neurons.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1997

The genome of Moloney murine leukemia virus can be integrated by the integrase of human immunodeficiency virus type 1 expressed alone in vivo.

An in vivo integration assay using the expressed human immunodeficiency virus type 1 (HIV-1) integrase (IN) protein and plasmids carrying a copy of the infectious Moloney murine leukemia virus (MuLV) provirus genome as substrates is presented. The HIV-1 IN gene was taken from vector pINSD and cloned into vector pXT1 to give pXT1-IN. Two and three nucleotides from the circle junction on one pair of U3 and U5 attachment (att) sequences on an infectious MuLV provirus vector pMLV-K were changed by means of site-directed mutagenesis to that of the corresponding HIV-1 att sequences to generate vector pMLV*(U3U5). The MuLV IN sequence was partially deleted for vectors pMLV-K and pMLV*(U3U5) to generate vectors pMLV delta IN and pMLV*(U3U5) delta IN. Integration of these wild type and MuLV IN partially deleted or att mutated MuLV provirus vectors in the transfected cells by the expressed HIV-1 IN was monitored by means of a non-radioactive reverse transcriptase (RT) assay for released and collected virions. No RT activity was detected for the NIH/3T3 cell singly transfected with vector pMLV delta IN. However some RT activities were observed for the HIV-1 IN expressing cell transfected either with vectors pMLV delta IN or pMLV*(U3U5) delta IN. This indicated that in the absence of other HIV-1 proteins expressed the MuLV provirus genome was integrated by the expressed HIV-1 IN protein. The integration of these MuLV provirus genomes was further confirmed by polymerase chain reaction analysis on the genomic DNA extracted from the transfected cells using the MuLV IN sequence remained from partial deletion as a target.

Cell Line↗