Effect of short- and long-term administration of lithium on the release of endogenous 5-HT in the hippocampus of the rat in vivo and in vitro.

The present study determined the effect of short- (3 days) and long- (21 days) term treatment with lithium on the release of 5-hydroxytryptamine (5-HT) form the hippocampus of the rat, measured both in vivo using microdialysis and in vitro using incubated slices. In the in vivo experiments (on the chloral hydrate-anaesthetized rat) electrical stimulation of the dorsal raphe nucleus for 20 min evoked an increase of 5-HT in dialysates of hippocampus, which both lasted for the duration of the stimulus and was frequency-dependent (2-10 Hz). Electrical stimulation of the dorsal raphe nucleus, at low stimulation pulse frequencies (2 and 3 Hz), released 3-4 fold more 5-HT in rats treated for 3 days with lithium chloride (3 mmol/kg s.c. twice daily), compared to controls. However, the effect of stimulation of the dorsal raphe nucleus was not altered in rats receiving lithium in the diet for 21 days. Basal levels of 5-HT in hippocampal dialysates for rats receiving long- but not short-term treatment with lithium, were significantly lower than controls. In agreement with the in vivo experiments, the in vitro experiments showed that depolarization (high potassium)-evoked release of endogenous 5-HT from slices of hippocampus of rats treated with short- but not long-term administration of lithium was enhanced compared to controls. These experiments provide direct biochemical evidence that short-term treatment with lithium increases depolarization-evoked release of endogenous 5-HT in the hippocampus, an effect which may be related to the rapid antidepressant actions of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of endogenous 5-hydroxytryptamine in rat ventral hippocampus evoked by electrical stimulation of the dorsal raphe nucleus as detected by microdialysis: sensitivity to tetrodotoxin, calcium and calcium antagonists.

We have utilized the brain microdialysis technique in an attempt to measure excitation-secretion coupled release of endogenous 5-hydroxytryptamine in rat brain in vivo and investigated the pharmacology of the voltage-sensitive calcium channel involved in this process. All experiments were carried out using chloral hydrate anaesthetized rats. Ascending serotoninergic neurons were electrically stimulated using an electrode implanted into the dorsal raphe nucleus. A dialysis probe was implanted into the ventral hippocampus and continuously perfused with artificial cerebrospinal fluid containing the selective 5-hydroxytryptamine uptake inhibitor citalopram (1 microM). Twenty-minute perfusates were analysed for endogenous 5-hydroxytryptamine using high performance liquid chromatography with electrochemical detection. Electrical stimulation (cathodal monophasic 1 ms pulses, 300 microA, 2-10 Hz) of the dorsal raphe nucleus for 20 min induced an immediate release of 5-hydroxytryptamine which lasted for the duration of the stimulus and was frequency-dependent. The calculated amount of 5-hydroxytryptamine release per electrical impulse was constant over the frequency range used. Addition of tetrodotoxin (10 microM) to, or omission of calcium from, the perfusion medium reduced the spontaneous output of 5-hydroxytryptamine by 60-70% and caused a near complete inhibition of the effect of low frequency (3 Hz) electrical stimulation of the dorsal raphe nucleus. Local perfusion with cadmium (30 and 300 microM), which is reported to antagonize both N- and L-type voltage-sensitive calcium channels, also caused a pronounced decrease of basal output of 5-hydroxytryptamine and a marked, but not complete inhibition of the effect of nerve stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

5-HT1 agonists reduce 5-hydroxytryptamine release in rat hippocampus in vivo as determined by brain microdialysis.

1. An intracerebral perfusion method, brain microdialysis, was used to assess changes of 5-hydroxytryptamine (5-HT) release in the ventral hippocampus of the chloral hydrate-anaesthetized rat in response to systemic administration of a variety of 5-HT1 receptor agonists. 2. A stable output of reliably detectable endogenous 5-HT was measured in dialysates collected from ventral hippocampus with the 5-HT reuptake inhibitor, citalopram, present in the perfusion medium. 3. Under these conditions the putative 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) caused a dose-dependent (5-250 micrograms kg-1, s.c.) reduction of 5-HT in hippocampal dialysates. 4. Similarly, the putative 5-HT1A agonists gepirone (5 mg kg-1, s.c.), ipsapirone (5 mg kg-1, s.c.) and buspirone (5 mg kg-1, s.c.) markedly reduced levels of 5-HT in hippocampal perfusates whereas their common metabolite 1-(2-pyrimidinyl) piperazine (5 mg kg-1, s.c.), which does not bind to central 5-HT1A recognition sites, had no effect. 5. 5-Methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969), a drug with reported high affinity for brain 5-HT1B binding sites, also produced a dose-dependent (0.25-5 mg kg-1, s.c.) decrease of hippocampal 5-HT output. 6. These data are direct biochemical evidence that systemically administered putative 5-HT1A and 5-HT1B agonists markedly inhibit 5-HT release in rat ventral hippocampus in vivo.

Pharmacological characterization of 8-OH-DPAT-induced inhibition of rat hippocampal 5-HT release in vivo as measured by microdialysis.

1. We have previously found that the putative 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) decreases hippocampal 5-hydroxytryptamine (5-HT) release in the anaesthetized rat, as measured by brain microdialysis. The present study attempted to characterize the receptor involved in this response using a range of monoamine receptor antagonists. 2. The classical 5-HT receptor antagonists, metergoline (5 mg kg-1 s.c.), methysergide (10 mg kg-1 s.c.) and methiothepin (10 mg kg-1 s.c.) each reduced dialysate levels of 5-HT which complicated their use as antagonists in these experiments. Nevertheless, pretreatment with metergoline but not methiothepin and methysergide partially reduced the 5-HT response to a maximally effective dose of 8-OH-DPAT (0.25 mg kg-1 s.c.). 3. The mixed 5-HT 1/beta-adrenoceptor antagonist pindolol (8 mg kg-1 s.c.) was without effect on spontaneous 5-HT output but attenuated the effect of both maximally (0.25 mg kg-1 s.c.) and submaximally (0.05 mg kg-1 s.c.) effective dose of 8-OH-DPAT. In comparison, propranolol (10 mg kg-1 s.c.) did not affect 5-HT output when injected alone and did not alter the response to 8-OH-DPAT (0.25 mg kg-1 s.c.). 4. The 5-HT2 receptor antagonist ritanserin (0.2 mg kg-1 s.c.) and the 5-HT3 receptor antagonist BRL 43694 (0.5 mg kg-1 s.c.) neither altered 5-HT output alone nor significantly changed the response to 8-OH-DPAT (0.25 mg kg-1 s.c.). 5. The 8-OH-DPAT (0.25 mg kg-' s.c.) response was not affected by pretreatment with either the dopamine D2-receptor antagonist sulpiride (10mgkg-1 s.c.) or the alpha/alpha 2-adrenoceptor antagonist phentolamine (10mg kg-1 s.c.). 6. We conclude from these data that the decrease of hippocampal 5-HT output induced by 8-OHDPAT does not involve 5-HT2, 5-HT3, adrenoceptors or dopamine D2-receptors and that activation of a 5-HT1 class of receptor seems probable. Full classification of the 8-OH-DPAT response awaits development of a suitably selective 5-HT1 receptor antagonist with low intrinsic activity at the somatodendritic 5-HT autoreceptor.

Further investigation of the in vivo pharmacological properties of the putative 5-HT1A antagonist, BMY 7378.

The present study examined the actions of the putative 5-HT1A antagonist BMY 7378 on central pre- and postsynaptic 5-HT1A function in the rat in vivo. Unlike the direct acting 5-HT1A agonist 8-hydroxy-2-(di-n-pro-pylamino)tetralin (8-OH-DPAT), BMY 7378 (0.25-5 mg/kg s.c.) did not induce the full postsynaptically mediated 5-HT behavioural syndrome (forepaw treading, head weaving, flat body posture hindlimb abduction). Indeed, the maximal 5-HT behavioural syndrome scores of BMY 7378 were about 10% of those for 8-OH-DPAT. Following pretreatment, however, BMY 7378 dose dependently (0.25-5 mg/kg s.c.) reduced to undetectable levels forepaw treading and head weaving induced by 8-OH-DPAT (0.75 mg/kg s.c.). BMY 7378 also inhibited stereotypy and locomotor activity induced by 0.5 mg/kg apomorphine although this effect was only statistically significant at the highest dose tested (5 mg/kg). In contrast to its apparent 5-HT1A antagonist properties in the behavioural experiments, BMY 7378 caused a marked and dose-dependent (0.01-1.0 mg/kg s.c.) decrease of 5-HT release in ventral hippocampus of the anaesthetized rat as detected by brain microdialysis. This effect of BMY 7378 had a similar onset and duration of action but with slightly reduced efficacy compared to that previously described for 8-OH-DPAT. As with 8-OH-DPAT, the inhibitory effect of BMY 7378 on 5-HT release was attenuated by pretreatment with the 5-HT1 receptor/beta-adrenoceptor antagonist pindolol (8 mg/kg s.c.) but not its counterpart propranolol (20 mg/kg s.c.). Pretreatment with a combination of the beta 1- and beta 2-adrenoceptor antagonists metoprolol (4 mg/kg s.c.) and ICI 118 551 (4 mg/kg s.c.), respectively, did not alter the 5-HT response to BMY 7378. From these data we conclude that BMY 7378 is a mixed agonist/antagonist at central 5-HT1A receptors.

Effect of acute administration of L-tryptophan on the release of 5-HT in rat hippocampus in relation to serotoninergic neuronal activity: an in vivo microdialysis study.

Here we have used the brain microdialysis method to test the effect of the 5-HT precursor L-tryptophan on 5-HT release. The release of endogenous 5-HT was measured in ventral hippocampus of the anesthetized rat both under basal conditions and when serotoninergic neuronal activity was raised by electrical stimulation of the dorsal raphe nucleus (DRN). Low frequency electrical stimulation of the DRN evoked a frequency-dependent (2-10 Hz) release of hippocampal 5-HT. The electrically evoked release of 5-HT was markedly enhanced by pretreatment with L-tryptophan (50 and 100 mg/kg i.p.). The effect of L-tryptophan on evoked release of 5-HT was dose-related, detectable at low (2 Hz) stimulation frequencies, and became stronger as the stimulation frequency increased. L-Tryptophan (10, 50 and 100 mg/kg i.p.) had no effect on basal output of 5-HT. We conclude from these findings that elevation of 5-HT precursor availability increases 5-HT release in hippocampus in vivo under conditions of increased serotoninergic neuronal activity.

Doppler-free two-photon absorption spectroscopy with a frequency-modulated dye laser.

A new method of Doppler-free two-photon spectroscopy has been developed in which a frequency-modulated (FM) dye laser is used to perform high-resolution spectroscopy. This provides an ideal method of locking a broadband FM laser to a narrow atomic or molecular reference line, a necessary step in using the FM laser for optical-frequency metrology. The method may also be used to test how closely the FM dye laser approaches a pure FM oscillation.

In vivo measurement of extracellular 5-hydroxytryptamine in hippocampus of the anaesthetized rat using microdialysis: changes in relation to 5-hydroxytryptaminergic neuronal activity.

The effect of manipulating the activity of central 5-hydroxytryptamine (5-HT) neurones on extracellular 5-HT in ventral hippocampus of the chloral hydrate-anaesthetized rat was studied using the brain perfusion method, microdialysis. Basal levels of 5-HT in the dialysates were close to the detection limits of our assay using HPLC with electrochemical detection. However, addition of the selective 5-HT reuptake inhibitor citalopram (10(-6) M) to the perfusion medium produced readily measurable amounts of dialysate 5-HT. Citalopram, therefore, was used throughout our experiments. Hippocampal dialysate levels of 5-HT sharply declined over the first hour after dialysis probe implantation, but then became constant. This stable output of 5-HT was reduced by 57% in rats treated 14 days previously with intracerebroventricular injections of the 5-HT neurotoxin 5,7-dihydroxytryptamine. Electrical stimulation (1-ms pulse width, 300 microA, 2-20 Hz) of the dorsal raphe nucleus for 20 min caused a rapid rise in hippocampal 5-HT output, which immediately declined on cessation of the stimulus and was frequency-dependent. Addition of tetrodotoxin (10(-6) M) to the perfusion medium reduced 5-HT levels to 75% of predrug values. Injection of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (0.5 and 2.5 micrograms) into the dorsal raphe nucleus caused a dose-related fall in hippocampal output of 5-HT compared to saline-injected controls. We conclude from these data that the spontaneous output of endogenous 5-HT into hippocampal dialysates, measured under our experimental conditions, predominantly originates from central 5-HT neurones and changes in accordance with their electrical activity.

Development of parthenogenetic and fertilized mouse embryos in the uterus and in extra-uterine sites.

Mouse eggs were activated with hyaluronidase in vitro and subsequently transferred to the oviduct. In the female reproductive tract they formed morulae and blastocysts which died soon after implantation. Haploid blastocysts were transferred beneath the kidney capsule and here some formed disorganized egg-cylinder structures in a week. Morulae and blastocysts from haploid and diploid parthenogenones were also transferred beneath the testis capsule. Two to four months later the growths which had formed were sectioned. They contained neural tissue, pigment, keratinized epithelium, glandular epithelium, ciliated epithelium, cartilage, bone, muscle, adipose tissue, and haemopoietic tissue. The range of cell types was similar to that produced by fertilized control blastocysts except that the parthenogenones did not form identifiable yolk-sac carcinoma or embryonal carcinoma cells. The growths from haploid and diploid parthenogenones in the testis were stained with Feulgen and their DNA content measured. Growths from diploid embryos contained the normal diploid amount of DNA while growths from haploid embryos contained less than this amount. Cell cultures were prepared from the growths. The cells which were investigated contained no Y chromosome, suggesting that they were derived from the embryonic cells rather than the cells of the male host. These cells contained a near diploid chromosome number, although some of them were originally derived from haploid embryos.