Modulation of electrically evoked acetylcholine release in cultured rat septal neurones

The electrically evoked release of acetylcholine and its modulation via auto- and heteroreceptors were studied in primary cell cultures prepared from embryonic rat septum (ED 17). Cultures were grown for 1, 2 or 3 weeks on circular, poly D-lysine-coated glass coverslips. They developed a dense network of non-neuronal and neuronal cells, only some of which were immunopositive for choline acetyltransferase. To measure acetylcholine release, the cells on the coverslips were pre-incubated with [3H]choline (0.1 micromol/L), superfused with modified Krebs-Henseleit buffer at 25 degrees C and electrically stimulated twice for 2 min (S1, S2; 3 Hz, 0.5 ms, 90-100 mA). The electrically evoked overflow of [3H] from the cells consisted of approximately 80% of authentic [3H]Ach, was largely Ca2+-dependent and tetrodotoxin sensitive, and hence represents an action potential-evoked, exocytotic release of acetylcholine. Using pairs of selective agonists and antagonist added before S2, muscarinic autoreceptors, as well as inhibitory adenosine A1- and opioid mu-receptors, could be detected, whereas delta-opioid receptors were not found. Evoked [3H] overflow from cultures grown for 1 week, although Ca2+ dependent and tetrodotoxin sensitive, was insensitive to the muscarinic agonist oxotremorine, whereas the effect of oxotremorine on cells grown for 3 weeks was even more pronounced than that in 2-week-old cultures. In conclusion, similar to observations on rat septal tissue in vivo, acetylcholine release from septal cholinergic neurones grown in vitro is inhibited via muscarinic, adenosine A1 and mu-opioid receptors. This in vitro model may prove useful in the exploration of regulatory mechanisms underlying the expression of release modulating receptors on septal cholinergic neurones.

Postnatal development of opioid receptors modulating acetylcholine release in hippocampus and septum of the rat

The postnatal development of presynaptic opioid receptors inhibiting the release of acetylcholine (ACh) was studied in rat brain hippocampus, medial septum (MS) and diagonal band of Broca (DB). To this end, the corresponding brain slices (350 microm thick) of rats of various postnatal ages (postnatal day 4 [P4] to P16, and adult) were preincubated with [(3)H]choline and stimulated twice for 2 min (S(1), S(2): at 3 Hz, 2 ms, 60 mA) during superfusion with physiological buffer containing hemicholinium-3. In parallel, the activity of choline acetyltransferase (ChAT) was determined in crude homogenates of the tissues as a marker for the development of cholinergic neurons. At any postnatal age, the electrically evoked overflow of tritium from slices preincubated with [(3)H]choline was highest in the DB, followed by the MS and the hippocampus. The evoked [(3)H]overflow increased with postnatal age, reached about 50% (MS, DB) or 30% (hippocampus) of the corresponding adult levels at P16 and correlated significantly with the corresponding ChAT activities. Presence of the preferential mu-opioid receptor agonist DAMGO during S(2) significantly inhibited the evoked overflow of tritium already at P4 in DB and MS, whereas in the hippocampus significant inhibitory effects were first observed at P8 only. Moreover, adult levels of inhibition due to DAMGO were reached at P16 in the DB and MS but not in the hippocampus. In septal areas, also the effect of the preferential delta-opioid receptor agonist DPDPE on the evoked [(3)H]overflow was studied: in contrast to DAMGO, however, significant inhibitory effects of DPDPE were first observed at P12 only. In conclusion, the postnatal development of presynaptic mu-opioid receptors on cholinergic neurons in the DB and MS starts earlier than in the hippocampus and precedes that of presynaptic delta-opioid receptors.

Characterization of opioid receptor types modulating acetylcholine release in septal regions of the rat brain

Presynaptic opioid receptors of the delta- and mu-types have been shown to inhibit the release of acetylcholine (ACh) in the rat striatum and hippocampus, respectively, but it is unknown whether opioid receptors modulate the release of ACh also in the region of origin of the hippocampal cholinergic innervation, the septum. To answer this question, slices (350 microm) of the medial septal area and of the diagonal band of Broca, as well as (for comparison) of the hippocampus, were prepared from adult male Wistar rats. The slices were incubated with [3H]choline, superfused in the presence of hemicholinium-3 (10 microM) and stimulated twice (S1, S2) by electrical fields (360 pulses, 3 Hz, 2 ms, 60 mA); opioid receptor agonists were present during S2. The preferential mu-agonist [D-Ala2,N-Me-Phe4,Gly-ol5]enkephalin (DAMGO) inhibited the evoked ACh release by maximally about 40% in hippocampal slices and acted even more strongly in the medial septal area, or the diagonal band of Broca (about 60% or 75% maximal inhibition, respectively). These effects were reduced or abolished by the preferential mu-antagonist naloxone, which showed no effects when given alone. Using naloxone in the presence of a cocktail of peptidase inhibitors, no evidence for an endogenous tone of opioid peptides was found in the medial septal area, diagonal band of Broca or the hippocampus. Using the preferential delta-agonist [D-Pen2, D-Pen5]enkephalin (DPDPE) and the delta-antagonist naltrindole, a delta-opioid receptor inhibiting evoked ACh release was clearly detectable both in the medial septal area and the diagonal band of Broca, but not in the hippocampus, whereas the preferential kappa-agonist trans-3,4-dichloro-N-methyl-N-[2(1-pyrrolidinyl)cyclo-hexyl] benzeneacetamide (U50,488H) had only weak or no effects. In addition to the functional experiments, double in-situ hybridization studies were performed, in which cells containing mRNA for choline acetyltransferase (ChAT) were labeled by an antibody-linked enzymatic staining procedure, whereas mRNAs for mu- or delta-opioid receptors were detected with radioactive probes. These experiments revealed that in the septal region mainly mu-opioid receptors were expressed by neurons positive for ChAT mRNA, whereas in the rat striatum the expression of delta-opioid receptors prevailed in those neurons. We conclude that in the septal area of the rat brain, in contrast to the rat striatum and hippocampus, both presynaptic mu- and delta-opioid receptors modulate the evoked release of ACh. Whether presynaptic mu- and delta-opioid receptors occur on the same or on different septal cells or axon terminals remains to be clarified.

Modulation of acetylcholine and 5-hydroxytryptamine release in hippocampal slices of rats with fimbria-fornix lesions and intrahippocampal grafts containing cholinergic and/or serotonergic neurons

Three-month-old Long-Evans female rats sustained aspirative lesions of the dorsal septohippocampal pathways and, 2 weeks later, received intrahippocampal suspension grafts containing fetal cells from the mesencephalic raphe (rich in serotonergic neurons; RAPHE), the medial septum and the diagonal band of Broca (rich in cholinergic neurons; SEPT), or a mixture of both (COTR). Lesion-only (LES) and sham-operated rats (SHAM) were used as controls. Hippocampal slices of these rats (5-9 month after surgery) were preincubated with [3H]choline or [3H]5-HT, superfused continuously (in the presence of hemicholinium-3 or fluvoxamine) and stimulated electrically (360 pulses, 2 ms, 3 Hz, 26-28 mA) in order to study the presynaptic modulation of acetylcholine (ACh) and serotonin (5-HT) release. The accumulation of [3H]choline and the evoked overflow of [3H]ACh were significantly reduced in slices from LES and RAPHE rats, but reached a close-to-normal level in SEPT and COTR rats. As to accumulation and overflow of [3H]5-HT, the lesion-induced reduction was compensated for only in RAPHE and COTR rats. The relative amount of evoked [3H]5-HT release (in % of tissue-3H) was significantly increased in LES and SEPT rats. Only slight differences (group LES) were found in the sensitivity of muscarinic and serotonergic autoreceptors towards oxotremorine and CP 93,129, respectively. Moreover, CP 93,129 induced a significantly weaker inhibition of ACh release in slices of COTR rats than in all other groups. Using the 5-HT1A receptor agonist 8-OH-DPAT and antagonist Way 100,635, no evidence for a modulatory influence of 5-HT1A receptors was found in RAPHE and COTR rats. It is concluded that despite substantial lesion- and graft-induced changes in the amount of ACh and 5-HT released by hippocampal slices of lesion-only or grafted rats, the presynaptic modulation of these transmitters is only slightly affected by changes in the neuronal environment.

The potentiation of amphetamine-induced hyperlocomotion by fimbria-fornix lesions in rats is abolished by intrahippocampal grafts rich in serotonergic neurons

Three-month old Long-Evans female rats were submitted to aspirative lesions of the fimbria-fornix and intrahippocampal grafts of a cell suspension prepared from a region of the fetal brain including the septum and the diagonal band of Broca (rich in cholinergic neurons) or the raphe (rich in serotonergic neurons). A group of lesioned rats was grafted with both suspensions mixed. Lesion-only and sham-operated rats served as controls. Four months after the lesions, all rats were tested daily for locomotor activity in their home cage, 1 day without being injected, 2 days with an injection of NaCl and 5 days with an injection of 1 mg/kg (i.p.) d-amphetamine. The effects of the lesions and grafts were assessed by measuring the accumulation of [3H]-choline or [3H]-5-hydroxytryptamine (5-HT) by hippocampal slices, and the electrically-evoked release of tritium. Amphetamine injections produced hyperlocomotion which was potentiated by the lesion. This lesion-induced potentiation was also found in rats with septal grafts, but not in those with raphe or co-grafts. The uptake and electrically-evoked release of [3H]-acetylcholine or [3H]-5-HT were reduced in hippocampal slices from lesion-only rats. In rats which received grafts of septal cells or co-grafts, but not in those with raphe grafts, uptake and release of [3H]-acetylcholine were close to normal. Uptake and release of [3H]-5-HT were close to normal in rats with raphe grafts or with co-grafts, but not in those with septal grafts. Altogether, these data suggest that damage to the serotonergic afferents of the hippocampus might play some role in the potentiation of amphetamine-induced hyperlocomotion associated with fimbria-fornix lesions.

Postnatal development of muscarinic autoreceptors in the rat brain: lateral and medial septal nuclei and the diagonal band of Broca

The postnatal development of the release of acetylcholine (ACh) and of presynaptic, release-inhibiting muscarinic autoreceptors was studied in the lateral septum (LS), the medial septum (MS) and the diagonal band of Broca (DB) of the rat brain. To this end, slices (350 micrometer thick) containing these brain regions from rats of various postnatal ages (postnatal day 3 [P3] to P16, and adult) were pre-incubated with [3H]choline and stimulated twice (S1, S2: 360 pulses, 3 Hz) during superfusion with physiological buffer containing hemicholinium-3 (10 microM). In addition, the activity of choline acetyltransferase (ChAT, in crude homogenates) was determined as a marker for the development of cholinergic functions. At any postnatal age, the electrically-evoked overflow of tritium from slices pre-incubated with [3H]choline was highest in the DB, followed by the MS whereas in slices containing the LS, it was only small. In all septal regions, the evoked [3H]overflow was Ca2+-dependent and tetrodotoxin-sensitive at P3. It increased with postnatal age and reached about 60% of the corresponding adult levels at P16. Presence of the muscarinic agonist oxotremorine (1 microM) during S2 significantly inhibited the evoked overflow of tritium beginning from P5: no significant effect was detected at P3. The ACh esterase inhibitor physostigmine (1 microM) exhibited significant inhibitory effects from P13 onwards, whereas the muscarinic antagonist atropine (1 microM) did not change the evoked ACh release. The activity of ChAT, as measured for these septal regions at various postnatal ages, correlated well with the [3H]overflow induced by electrical stimulation. In conclusion, (1) electrically-evoked release of ACh was measured for the first time in three septal subregions; (2) the postnatal development of the presynaptic cholinergic functions: ChAT activity, ACh release and muscarinic autoreceptors occurs almost synchronously in these regions of the septal complex and parallels that in the hippocampal formation; (3) as in the hippocampus, the postnatal development of autoreceptors was delayed with respect to the exocytotic release of ACh.

Modulation of 5-hydroxytryptamine release in hippocampal slices of rats: effects of fimbria-fornix lesions on 5-HT1B-autoreceptor and alpha2-heteroreceptor function

Fimbria-fornix lesions disrupt important parts of serotonergic and noradrenergic hippocampal afferents and elicit sprouting of sympathetic fibers from the superior cervical ganglion. Since 5-hydroxytryptamine (5-HT) release in the hippocampus is modulated by 5-HT1B auto- and alpha2-heteroreceptors, we investigated whether such lesions may alter these presynaptic mechanisms. Hippocampal slices of sham-operated (SHAM) and fimbria-fornix-lesioned (LES) rats (14 months after surgery) were preincubated with [3H]5-HT, superfused continuously, and stimulated electrically using two stimulation conditions: either (a) 360 pulses 3 Hz, or (b) 20 pulses 100 Hz (2 ms, 28 mA, 4 V/chamber). The amount of [3H]5-HT taken up by slices from LES rats was significantly reduced, whereas the evoked 5-HT release (in percent of tissue-3H) was unchanged compared to that of SHAM rats. The 5-HT1B agonist CP 93,129 or the alpha2-agonist UK 14,304 reduced the evoked 5-HT release more potently in slices from LES rats, but only using stimulation condition (a), which permits inhibition by endogenously released transmitters. In LES rats, the facilitatory effect of the 5-HT antagonist metitepine was weaker, whereas that of the alpha2-antagonist idazoxane was more pronounced than in SHAM rats. In LES rats, hippocampal 5-HT content was reduced to about 45% of SHAM levels, whereas that of noradrenaline was increased by about 30% (high-performance liquid chromatography). We conclude: (1) despite LES-induced changes in tissue levels of endogenous ligands, there is no down- or upregulation of 5-HT1B-autoreceptors or alpha2-heteroreceptors on serotonergic neurons in the denervated rat hippocampus. (2) The reduced endogenous autoinhibition (by 5-HT) seems to be compensated for by an increased heteroinhibition (by noradrenaline).

Solution structure of the motile major sperm protein (MSP) of Ascaris suum - evidence for two manganese binding sites and the possible role of divalent cations in filament formation

The major sperm protein (MSP) of Ascaris suum mediates amoeboid motility by forming an extensive intermeshed system of cytoskeletal filaments analogous to that formed by actin in many other amoeboid cells. MSP is a dimeric molecule that polymerizes to form non-polar filaments constructed from two helical subfilaments that wind round one another. Moreover, MSP filaments can interact with one another to form higher-order assemblies without requiring the range of accessory proteins usually employed in actin-based systems. A knowledge of how MSP polymerizes and forms the hierarchical series of helical MSP macromolecular assemblies is fundamental to understanding locomotion in these cells. Here we describe the solution structure of MSP dimers determined by NMR spectroscopy under conditions where MSP does not polymerize to form filaments. The solution structure is indistinguishable from that observed in putative MSP subfilament helices by X-ray crystallography, indicating that MSP polymerization is not accompanied by a major conformational change. We also show that the rate of MSP polymerization associated with movement of vesicles in an in vitro motility assay is enhanced by the presence of magnesium and manganese ions and use NMR to show that the primary residues that bind these ions are 24-25 and 83-86. These residues are distant from the interface formed between MSP dimers in subfilament helices, and so are probably not involved in this level of polymerization. Instead the manganese and magnesium ion binding appears to be associated with the assembly of subfilaments into filaments and their subsequent aggregation into bundles.

Postnatal development of muscarinic autoreceptors modulating acetylcholine release in the septohippocampal cholinergic system. II. Cell body region: septum

We studied the postnatal development of the release of acetylcholine (ACh) and of presynaptic, release-inhibiting muscarinic autoreceptors in the cell body region of the septohippocampal cholinergic pathway. To this end, septal slices (350 microns thick) from rats of various postnatal ages (postnatal day 3 [P3] to P16) were preincubated with [3H]choline and stimulated twice (S1, S2: 360 pulses, 2 ms, 3 Hz, 60 mA) during superfusion with physiological buffer containing hemicholinium-3 (10 microM). In parallel, the activities of hemicholinium-sensitive high-affinity choline uptake (HACU, in synaptosomes) and of choline acetyltransferase (ChAT, in crude homogenates) were determined as markers for the development of cholinergic functions. In septal slices preincubated with [3H]choline, the electrically evoked overflow of 3H at S1 increased from 0.31% (P3) to 2.10% of tissue 3H (P16), the latter value being still lower than that of septal slices from adult rats (3.46% of tissue 3H). Already at P3, the evoked overflow of 3H was Ca(2+)-dependent and sensitive to tetrodotoxin, indicating an action potential-evoked exocytotic mechanism of ACh release early after birth. Presence of the muscarinic agonist oxotremorine (1 microM) significantly inhibited the evoked ACh release in septal slices beginning from P5: no significant effect was detectable at P3. The ACh esterase inhibitor physostigmine (1 microM) exhibited significant inhibitory effects from P13 onwards. The muscarinic antagonist atropine (1 microM) enhanced the evoked ACh release only in septal tissue from adult rats. The specific activities of HACU, or ChAT showed a 2- or 8-fold increase, respectively, from P3 to P16. In conclusion, presynaptic cholinergic functions seem to develop almost in parallel both in the cell body and the target area of the septohippocampal projection: also in the septal region nerve terminals on axon collaterals are endowed very early (at least at P3) with the apparatus for action potential-induced, exocytotic release of ACh. In contrast, the appearance of feedback inhibition via presynaptic muscarinic autoreceptors is delayed. Autoinhibition due to endogenously released ACh can be detected only later, most probably when endogenous ACh concentrations in the septal nuclei have reached a threshold value.

The motile major sperm protein (MSP) from Ascaris suum is a symmetric dimer in solution

The major sperm protein (MSP) of Ascaris suum mediates amoeboid motility by forming an extensive intermeshed system of cytoskeletal filaments analogous to that formed by actin in many amoeboid cells. We have used a combination of biochemical and NMR methods to show that, in contrast to actin, MSP exist in solution as a symmetrical dimer. This result has important implications for the mechanism of both MSP filament assembly and the recognition of different MSP isoforms in vivo.