Immunohistochemical localization of gastrin-cholecystokinin-like material in the central nervous system of the migratory locust

Brain, corpora cardiaca (CC)-corpora allata (CA) complex, suboesophageal ganglion, thoracic and abdominal ganglia of adults, larvae and embryos of Locusta migratoria have been immunohistochemically screened for gastrin cholecystokinin (CCK-8(s]-like material. In adult, numerous immunoreactive neurons and nerve fibres are located, with a marked symmetry, in various parts of the brain and throughout the ventral nerve cord. In the median part of the brain, cell bodies belonging neither to cellular type A1 nor A2 (following Victoria blue-paraldehyde fuchsin staining) are immunopositive; their processes terminate in the upper protocerebral neuropile. In lateral parts of the brain, external cell bodies send axons into CC and some up to CA, other internal have processes which terminate in the neuropile of the brain. Two of these latter cells react also with methionine-enkephalin antiserum. In the ventral nerve cord, in addition to numerous perikarya, immunoreactive arborizations terminate in the neuropile or in close association with the sheath, at the dorsal part of all ganglia. This CCK-8(s) distribution pattern is observed only at the two last larval instars, but is precociously detected in the abdominal nerve cord of embryos, one day before hatching.     

Intracisternal neurotoxins and monoamine neurons innervating the spinal cord: Acute and chronic effects on cell and axon counts and nerve terminal densities

Summary The total number of catecholamine (CA) and 5-hydroxy-trydroxy-tryptamine (5-HT) containing nerve cell bodies in groups A1-7 and B1-3 were counted using Falck-Hillarp fluorescence histochemistry and found to be about 5000 and about 6300 respectively. The total number of CA axons in the white matter of the spinal cord was found to be about 4300 at the cervical level and about 3300 at the lumbar level as revealed in cryostat sections. Together with previous studies our quantitative results suggest that individual cell bodies in locus coeruleus send axon collaterals to the spinal cord, cortex cerebri, cortex cerebelli and probably also other areas of the brain.The decrease in number of CA axons in spinal cord occurred approximately at the level where the CA nerve terminal innervation of the sympathetic lateral column ends. Single CA axons were observed to give off multiple branches at right angles, suggesting that single CA axons innervate several different levels of the grey matter.A transient loss of visible CA cell bodies in groups A1-7 was observed after intracisternal injection of 25–50 g 6-hydroxydopamine (6-OH-DA). A permanent loss of visible 5-HT cell bodies in groups B1-3 was observed after 25 g 5,6-dihydroxy-tryptamine (5,6-HT) given intracisternally, a transient decrease was obtained when the same dose of 5,6-HT was given intraventricularly.CA nerve terminals regenerated in a cranio-caudal direction along the motoneuron columns after lesioning with 6-OH-DA given intracisternally. The reappearing CA nerve terminals seemed to outline the longitudinally oriented dendritic bundles of the motoneurons and was exclusively found in these areas of the ventral horn. Thus, no substantial CA nerve terminal reinnervation of zona intermedia or the dorsal horn was observed. About 10% of the CA axons running in white matter were left after intracisternal 6-OH-DA and found at all levels of the cord. The number of remaining CA axons did not increase with time.After 10–50 g 5,6-HT given intracisternally a return of 5-HT nerve terminals was only observed in cervical segments. There was a 60–90% decrease in number of axons that accumulated 5-HT after an acute transverse lesion and no recovery of the number of such accumulations was observed during the following six months.It was concluded that regeneration of CA nerve terminals in the spinal cord can occur after lesioning with 6-OH-DA given intracisternally. Regeneration of 5-HT nerve terminals following intracisternal 5,6-HT is very restricted probably because of the permanent loss of 5-HT cell bodies obtained by the intracisternal route of administration as opposed to the intraventricular route. It was suggested that the reappearing CA nerve terminals were derived from locus coeruleus and that they were specifically guided by the motoneuron columns.     

Immunohistochemical localization of gastrin-cholecystokinin-like material in the central nervous system of the migratory locust

Summary Brain, corpora cardiaca (CC)-corpora allata (CA) complex, suboesophageal ganglion, thoracic and abdominal ganglia of adults, larvae and embryos of Locusta migratoria have been immunohistochemically screened for gastrin cholecystokinin (CCK-8(s))-like material. In adult, numerous immunoreactive neurons and nerve fibres are located, with a marked symmetry, in various parts of the brain and throughout the ventral nerve cord. In the median part of the brain, cell bodies belonging neither to cellular type A1 nor A2 (following Victoria blue-paraldehyde fuchsin staining) are immunopositive; their processes terminate in the upper protocerebral neuropile. In lateral parts of the brain, external cell bodies send axons into CC and some up to CA, other internal have processes which terminate in the neuropile of the brain. Two of these latter cells react also with methionine-enkephalin antiserum. In the ventral nerve cord, in addition to numerous perikarya, immunore-active arborizations terminate in the neuropile or in close association with the sheath, at the dorsal part of all ganglia.This CCK-8(s) distribution pattern is observed only at the two last larval instars, but is precociously detected in the abdominal nerve cord of embryos, one day before hatching.     

Chilling affects allatal cell proliferation via antennae and protocerebral neurons in the cockroach Diploptera punctata

The corpora allata (CA) cells in a mated female of the cockroach Diploptera punctata undergo numerous mitotic divisions before an increase in juvenile hormone synthesis. A previous study demonstrated that this mitotic wave could be suppressed by exposure of the mated female to melting ice. Herein, we report that chilling suppresses CA mitosis via antennal perception. Cell proliferation-suppressing stimuli from chilling were acquired in proportion to the length of time of exposure to the low temperature and the physical length of the antennae exposed to chilling. Sixty basal antennal annuli should remain exposed to chilling for at least 1.5 h in order to suppress mitotic divisions in CA. Mitotic divisions in corpus allatum are suppressed by stimuli from contralateral antenna, predominantly via pars intercerebralis neurons. Selective disconnection of pars intercerebralis neurons from CA, prior to chilling, restored the mitotic wave in CA. Cellular divisions did not occur in CA of chilled females if either pars lateralis neurons were severed or left intact.     

The relationship between the ventral nerve cord, body size and phylogeny in ground beetles (Goleoptera: Garabidae)

The ventral nerve cord in the family Carabidae (considered in the widest sense! exhibits variations in the degree of fusion of thoracic and abdominal ganglia. There are usually three discrete thoracic ganglia and between one and seven discrete abdominal ganglia, the number differing between tribes. Of the 44 tribes and 177 species examined, 38 tribes contained species showing no differences in the degree of ventral nerve cord consolidation. However, the remaining six tribes showed variations in the degree of ventral nerve cord consolidation between genera (Lebiini, Cychrini, Nebriini, Scaritini, Licinini and Brachinini), whilst one genus showed variations between species (Leistus , Nebriini). No variation in ventral nerve cord consolidation was observed in conspecifics. The degree of ventral nerve cord consolidation is inversely proportional to overall body length. With respect to phylogeny, the degree of consolidation of the nerve cord docs not consistently support the traditional Carabinae-Harpalinae subfamily division. However, the Harpalinae always have four or less discrete abdominal ganglia (with the sole exception of the Broscinij, whilst the Carabinae exhibit almost the whole range of variations. Thus the Harpalinae (or the major pari of it) may be a monophyletic group, but this is not true of the Carabinae. Trends in the degree of ventral nerve cord consolidation for the various tribes were noted, and phylogenetic implications were evaluated wherever possible.     

The relationship between the ventral nerve cord,body size and phylogeny in ground beetles (Coleoptera: Carabidae)

The ventral nerve cord in the family Carabidae (considered in the widest sense! exhibits variations in the degree of fusion of thoracic and abdominal ganglia. There are usually three discrete thoracic ganglia and between one and seven discrete abdominal ganglia, the number differing between tribes. Of the 44 tribes and 177 species examined, 38 tribes contained species showing no differences in the degree of ventral nerve cord consolidation. However, the remaining six tribes showed variations in the degree of ventral nerve cord consolidation between genera (Lebiini, Cychrini, Nebriini, Scaritini, Licinini and Brachinini), whilst one genus showed variations between species (Leistus, Nebriini). No variation in ventral nerve cord consolidation was observed in conspecifics. The degree of ventral nerve cord consolidation is inversely proportional to overall body length. With respect to phylogeny, the degree of consolidation of the nerve cord docs not consistently support the traditional Carabinae-Harpalinae subfamily division. However, the Harpalinae always have four or less discrete abdominal ganglia (with the sole exception of the Broscinij, whilst the Carabinae exhibit almost the whole range of variations. Thus the Harpalinae (or the major pari of it) may be a monophyletic group, but this is not true of the Carabinae. Trends in the degree of ventral nerve cord consolidation for the various tribes were noted, and phylogenetic implications were evaluated wherever possible.     

Regulation of pheromone inhibition in mated females of Choristoneura fumiferana and C. rosaceana

In the spruce budworm, Choristoneura fumiferana, and the obliquebanded leafroller, C. rosaceana, mating significantly depressed pheromone production after 24 h. On subsequent days, the pheromone titre increased slightly in C. fumiferana, but not in C. rosaceana. No pheromonostatic activity was associated with male accessory sex gland (ASG) extracts, 20-hydroxy-ecdysone or hemolymph taken from mated females. However, pheromone production in mated females was not suppressed when the ventral nerve cord (VNC) was transected prior to mating, indicating that an intact VNC is required to permanently switch off pheromone production after mating. As suggested for other moth species, the presence of sperm in the spermatheca probably triggers the release of a signal, via the VNC, to inhibit pheromone production. The fact that in both species the brain-suboesophageal ganglion (Br-SEG) of mated females contains pheromonotropic activity and that their pheromone glands may be stimulated by the synthetic pheromone-biosynthesis-activating-neuropeptide (PBAN) or a brain extract supports the hypothesis that the neural signal prevents the release of PBAN into the hemolymph rather than inhibiting its biosynthesis. Therefore, we speculate that following the depletion of sperm in the spermatheca, the neural signal declines and is less effective in preventing the release of PBAN, thereby stimulating the resumption of pheromone production, as seen in mated C. fumiferana females. In a previous study, mating was shown to induce a significant rise in the juvenile hormone (JH) titre of both Choristoneura female moths, suggesting that post-mating pheromone inhibition may be under hormonal regulation. However, following topical applications or injections of the juvenile hormone analogue (JHA) and JH II into virgins, the pheromone only declined significantly 48 h after treatment in C. rosaceana. This suggests that the significant rise in the hemolymph JH titre after mating in C. rosaceana females plays a role in keeping the pheromone titre consistently low throughout their reproductive life. These findings will be discussed in relation to the different life histories of the two Choristoneura species.     

The catecholaminergic system of an annelid (Ophryotrocha puerilis,Polychaeta)

Summary The complex catecholaminergic (CA) nervous system of the polychaete Ophryotrocha puerilis is documented using glyoxylic acid induced fluorescence (GIF) and immunohistochemistry. CA-neurons are found both in the central and peripheral nervous system. In the brain, about 50 CA-neurons are present in the perikaryal layer together with numerous CA fibres. Two pairs of CA perikarya are characteristic for each ganglion of the ventral nerve cord. CA-neurites in the ventral nerve cord are mainly arranged in 4 strands paralleling the longitudinal axis of the worm. Fluorescent neurons with receptive ciliary structures are present in body appendages (antennae, palps, urites, parapodial cirri), in the body-wall, and within the oesophageal wall. Furthermore, a subepidermal nerve net of free CA nerve endings has been found. After incubation of specimens with dopamine prior to the development of GIF more fluorescent perikarya could be observed; the fluorescence was also intensified. Pre-incubation with reserpine reduced the intensity of GIF. Results of high pressure liquid chromatography and immunostaining with a polyclonal antibody against a dopamine-glutaraldehyde-complex suggest that dopamine is the major CA transmitter. It is thought that dopaminergic neurons together with ciliary receptive structures act as mechano- and/or chemoreceptors.     

大鼠脊髓挤压伤后NT-3、NT-4在腹角运动神经元表达的变化

我们前面的研究已证实,神经生长因子和脑源性神经营养因子与成年大鼠挤压性脊髓损伤修复有关。在本研究中,通过免疫组织化学ABC法,我们探讨了挤压伤后不同时间脊髓腹角神经元NT-3和NT-4的表达。结果显示,在对照组,NT-3和NT-4的阳性反应主要分布在脊髓腹角神经元,挤压性脊髓损伤后7天和21天,NT-3阳性神经元的数量较对照组和24小时组明显增加,比较之,损伤后24小时和7天,NT-4阳性神经元的数量已较正常者增多,且NT-T的反应强度21天者较24小时和7天者有增多。结果表明NT-3和NT-4的表达在挤压性损伤后的脊髓腹角神经元被不同程度地上调,提示NT-3和NT-4可能与挤压性脊髓损伤修复有关。     

Competence of blastomeres for the expression of molecular tissue markers is acquired by diverse mechanisms in the embryo of Platynereis (Annelida)

This paper is devoted to the role of cell divisions for the establishment of histospecificity in the embryo of the spiralian, Platynereis dumerilii (Annelida). We have incubated successive cleavage stages in cytochalasin B (CCB) and observed whether the cells thereafter were able to acquire the competence for expressing histospecific antigens of larval gland cells (labelled by the monoclonal antibody OI64) and of neural components of the ventral nerve cord (labelled by mAb OI7 or by testing acety1cholinesterase activity), respectively. Incubation in CCB results in permanent cleavage arrest, but does not necessarily interfere with biochemical differentiation of such markers. Synthesis of the differentiation marker specific for larval gland cells does not require any cleavages but this capacity becomes restricted to the 1a and 1b cell lines if cleavages are allowed to occur. In contrast, the progenitors of neural cells need at least 6.5 h of normal development before they acquire the competence to synthesize two neural differentiation markers, which can be demonstrated after at least two more days of development. Thus, prespecifying and diversifying cleavages are a prerequisite for neurogenesis and production of the investigated neural markers. Competence for the expression of histospecific antigens may also depend on cell-cell interactions. If 20–24 h old embryos are treated with puromycin, pioneering fibres fail to grow out from a pair of posterior nerve cell progenitors as they would have done normally 24–48 h after fertilization. Concomitantly, a number of potential nerve cells which now do not come into contact with pioneering fibres do not express the neural antigen. This suggests that a local inductive stimulus from the pioneering fibres normally imprints cell fate onto ventral plate cells and turns them into neuroblasts. Correspondence to: A.W.C. Dorresteijn     

Post-embryonic development in the ventral cord of Caenorhabditis elegans.

56 nerve cells are added to the ventral cord and associated ganglia of Caenorhabditis elegans at about the time of the first larval moult. These cells are produced by the uniform division of 13 neuroblasts followed by a defined pattern of cell deaths. Comparison with the data in the previous paper suggests that there is a relationship between the ancestry of a cell and its function. The significance of programmed cell death is discussed.     

Behavioral plasticity and central regeneration of locomotor reflexes in the freshwater oligochaete, Lumbriculus variegatus. I: Transection studies

Abstract. Access to the ventral nerve cord in living specimens of Lumbriculus variegatus , an aquatic oligochaete, is normally impossible because surgical invasion induces segmental autotomy (self-fragmentation). We show here that nicotine is a powerful paralytic agent that reversibly immobilizes worms, blocks segmental autotomy, and allows experimental access to the nerve cord. Using nicotine-treated worms, we transected the ventral nerve cord and used non-invasive electrophysiological recordings and behavioral analyses to characterize the functional recovery of giant nerve fibers and other reflex pathways. Initially, after transection, medial giant fiber (MGF) and lateral giant fiber (LGF) spikes conducted up to, but not across, the transection site. Reestablishment of MGF and LGF through-conduction across the transection site occurred as early as 10 h (usually by 20 h) after transection. Analyses of non-giant-mediated behavioral responses (i.e., helical swimming and body reversal) were also made following nerve cord transection. Immediately after transection, functional reorganization of touch-evoked locomotor reflexes occurred, so that the two portions of the worm anterior and posterior to the transection site were independently capable of helical swimming and body reversal responses. Similar reorganization of responses occurred in amputated body fragments. Reversion back to the original whole-body pattern of swimming and reversal occurred as early as 8 h after transection. Thus, functional restoration of the non-giant central pathways appeared slightly faster than giant fiber pathways. The results demonstrate the remarkable plasticity of locomotor reflex behaviors immediately after nerve cord transection or segment amputation. They also demonstrate the exceptional speed and specificity of regeneration of the central pathways that mediate locomotor reflexes.     

Chromosome aberrations induced by aflatoxin B1 in rat bone marrow cells in vivo and their suppression by green tea

Aflatoxin B1 (AFB1)-induced chromosome aberrations (CA) in rat bone marrow cells consisted mainly of gaps and breaks. Cells with exchanges and multiple CA were observed infrequently. The incidence of aberrant cells and the number of aberrations per cell were at their maximum levels 18 h after the AFB1 injection. They were dependent on the administered dose of AFB1. Rats given the hot water extract from green tea (GTE) 24 h before they were injected with AFB1 displayed considerably suppressed AFB1-induced CA in their bone marrow cells. Rats administered GTE 2 h before or after the AFB1 injection showed no suppressive effect. The suppressive effect of GTE on AFB1-induced CA paralleled the dose of GTE when given in the range between 0.1 and 2 g/kg body weight; higher doses produced no additional suppression. On the other hand, rats given the hot water extract from black tea or coffee 24 or 2 h before the AFB1 injection showed no suppressive effect. The administration of caffeine 24 h before the AFB1 injection suppressed AFB1-induced CA as well as the administration of caffeine 2 h before the AFB1 injection. However, the suppression rate with 2 h was larger than with 24 h. The suppression by ellagic acid was found only when it was given 2 h before the AFB1 injection. The administration of ascorbic acid or tannic acid did not significantly suppress AFB1-induced CA. The tannin mixture extracted from green tea (GTTM) showed a similar tendency to GTE, that is, the administration of GTTM 24 h before the AFB1 injection potently suppressed AFB1-induced CA, while the administration of GTTM 2 h before the AFB1 injection did not suppress them significantly. The suppressive effect of GTTM on AFB1-induced CA paralleled the dose of GTTM when given in the range of 75-450 mg/kg body weight.     

Factors involved in the post-copulatory neural inhibition of pheromone production in Choristoneura fumiferana and C. rosaceana females

Normal mating lasts approximately 3 h in Choristoneura fumiferana and C. rosaceana. Data generated from interrupted matings showed that the act of mating did not suppress pheromone production (pheromonostasis) in either species although, in C. rosaceana, pheromone titre declined slightly the night following mating. In both species the migration of sperm to the spermatheca (SP) occurred several hours after mating, and coincided with a significant and permanent depression in pheromone titre, as well as egg fertilisation and oviposition. However, disrupting matings within 2 h of the onset resulted in oviposition patterns similar to virgins in both species, with mostly infertile eggs being laid by C. fumiferana females while oviposition was totally inhibited in C. rosaceana. The transection of the ventral nerve cord (VNC) 1 h post-mating did not result in the depression of pheromone titres the following night in either species but if the VNC was transected 3 h post-mating, pheromonostasis was observed. While 25% of C. fumiferana females had sperm in their SP 2 h after mating, it took at least 4 h in C. rosaceana. This suggests that while the physical presence of sperm in the SP may play some role in the termination of pheromone production in C. fumiferana, other factors must trigger the neural signal that elicits pheromonostasis in both species. A better understanding of the temporal dynamics of both apyrene and eupyrene sperm within the different parts of the female reproductive system might clarify these interspecific differences.     

Hirudo medicinalis: A Platform for Investigating Genes in Neural Repair

We have used the nervous system of themedicinal leech as a preparation to study the molecular basis of neural repair. The leech central nervous system, unlikemammalian CNS, can regenerate to restore function, and contains identified nerve cells of known function and connectivity.We have constructed subtractive cDNAprobes from whole and regenerating ganglia of the ventral nerve cord and have used these to screen a serotonergic Retzius neuron library. This identifies genes that are regulated as a result of axotomy, and are expressed by the Retzius cell.This approach identifies many genes, both novel and known. Many of the known genes identified have homologues in vertebrates, including man. For example, genes encoding thioredoxin (TRX), Rough Endoplasmic Reticulum Protein 1 (RER-1) and ATP tsynthase are upregulated at 24 h postinjury in leech nerve cord.To investigate the functional role of regulated genes in neuron regrowthwe are using microinjection of antisense oligonucleotides in combination with horseradish peroxidase to knock down expression of a chosen gene and to assess regeneration in single neurons in 3-D ganglion culture. As an example of this approach we describe experiments to microinject antisense oligonucleotide to a leech isoform of the structural protein, Protein 4.1.Our approach thus identifies genes regulated at different times after injury thatmay underpin the intrinsic ability of leech neurons to survive damage, to initiate regrowth programs and to remake functional connections. It enables us to determine the time course of gene expression in the regenerating nerve cord, and to study the effects of gene knockdown in identified neurons regenerating in defined conditions in culture.     

Response to chilling of tomato mesophyll protoplasts

Freshly isolated protoplasts from tomato leaves show two completely different responses to a chilling treatment of 12 h at 7° C prior to culture at 29° C, depending on the presence or absence of glucose in the medium. In the culture medium with glucose as osmoticum, where the rate of cell divisions under optimal culture conditions is relatively high (about 20% plating efficiency), protoplasts were drastically injured by the chilling procedure and died. In the medium with mannitol as the osmoticum instead of glucose, where the plating efficiency even under optimal conditions is rather low (about 8%), protoplasts withstand the chilling procedure. More-over, after the chilling treatment when the protoplasts were transferred to the optimal culture temperature of 29° C, the plating efficiency was raised to about 20%, which is the same level as in the glucose-containing medium without chilling. This effect was not observed when the medium in which the protoplasts were suspended during the chilling period was replaced with fresh medium. This suggests that under these conditions tomato protoplasts produce and excrete a factor in the cold that improves the vitality of the cells or stimulates cell division. The possible relationship between chilling sensitivity of tomato protoplasts and their ability to divide will be discussed.     

Regional Distribution of Immunoreactive-Thyrotrophin-Releasing Hormone and Substance P, and Indoleamines in Human Spinal Cord

The regional distributions of thyrotrophin-releasing hormone (TRH) and substance P in postmortem human spinal cord were determined by radioimmunoassay in fresh tissue taken from 22 patients who died without known neurological disease. Dorsal, ventral, and intermediolateral spinal cord regions were obtained from different segmental levels (lumbar L1, 2, 3, and 4; thoracic groups T1-3, T4-6, T7-9, and T10-12) together with selective regions of grey matter of lumbar spinal cord. The effects on peptide levels of the age of the patient, the postmortem time interval, and freezing the tissue samples prior to assay were assessed. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in regional lumbar and thoracic tissue using HPLC with electrochemical detection. Substance P was found in the highest concentration in the dorsal spinal cord, with no significant segmental differences. In contrast, TRH was present in higher levels in the ventral rather than the dorsal spinal cord, with segmental differences. There was a significant difference in the 5-HT/5-HIAA ratio between dorsal and ventral spinal cord, with the highest ratio in the ventral spinal cord. There were no significant differences in substance P, TRH, or 5-HT levels in spinal cords between 5 and 20 h postmortem or from patients aged between 65 and 90 years. Freezing the tissue (-80 degrees C for 24 h) prior to assay significantly reduced TRH and substance P levels compared to samples assayed immediately without prior freezing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunohistochemical demonstration of a CCK-like peptide in the nervous system of a marine annelid worm,Nereis diversicolor O.F. Müller

Summary Perikarya and nerve fibers containing a substance immunologically related to CCK-8 were detected in the nervous system of Nereis, a marine annelid worm. The most noteworthy immunostaining was seen in cell bodies, localized at the periphery of the brain, within nuclei 5, 6, 7, 9, 10, 13, 14, 15, 17, 20, 23–24. Immunoreactive fibers were also found in the neuropile without any particular grouping. Numerous other positive perikarya occur in the medio-ventral portion of the ventral nerve cord, and in the ventral and dorsal parts of the suboesophageal ganglion. In addition to the cell bodies in the cerebral external layer, immunoreactive axons were abundantly observed in the connectives between the ganglia. Moreover, our results demonstrate CCK-like staining in neurons showing variations in size and shape, and in affinity for paraldehyde fuchsin. The present results support the hypothesis that this peptide may exert a role as neurotransmitter or neuromodulator in annelids.     

Learning-dependent plasticity of hippocampal CA1 pyramidal neuron postburst afterhyperpolarizations and increased excitability after inhibitory avoidance learning depend upon basolateral amygdala inputs

Hippocampal pyramidal neurons in vitro exhibit transient learning-dependent reductions in the amplitude and duration of calcium-dependent postburst afterhyperpolarizations (AHPs), accompanied by other increases in excitability (i.e., increased firing rate, or reduced spike-frequency accommodation) after trace eyeblink conditioning or spatial learning, with a time-course appropriate to support consolidation of the learned tasks. Both these tasks require multiple days of training for acquisition. The hippocampus also plays a role in acquisition of single trial inhibitory avoidance learning. The current study assessed AHP plasticity in this single-trial learning task using in vitro tissue slices prepared at varying intervals posttrial using intracellular current-clamp recordings. Reduced AHPs and reduced accommodation were seen in ventral CA1 pyramidal neurons within 1 h posttraining, plasticity which persisted 24 h but was extinguished >72 h posttrial. There was also a reduction in ventral CA1 AHPs and accommodation 1 h following simple exposure to the IA apparatus (a novel context) but this change was extinguished by 24 h postexposure. Reductions in AHPs and accommodation were also seen in dorsal CA1 pyramidal neurons, but were delayed until 24 h posttrial and extinguished at >72 h posttrial. Finally, transient inactivation of the basolateral complex of the amygdala (with the local anesthetics lidocaine or bupivacaine) either immediately before or immediately posttrial blocked both learning and learning-dependent changes in excitability in the hippocampus assessed 24 h posttrial. CA3 pyramidal neurons showed no reductions in AHP peak amplitude or accommodation following IA training or context exposure.     

Gas Exchange and Co-regulation of Photochemical and Nonphotochemical Quenching in Bean during Chilling at Ambient and Elevated Carbon Dioxide

The effects of elevated (700 micromol mol(-1)) and ambient (350 micromol mol(-1)) CO(2) on gas exchange parameters and chlorophyll fluorescence were measured on bean (Phaseolus vulgaris) during 24 h chilling treatments at 6.5 degrees C. Consistent with previous research on this cultivar, photosynthetic decline during chilling was not significantly affected by CO(2) while post-chilling recovery was more rapid at elevated compared to ambient CO(2). Our primary focus was whether there were also CO(2)-mediated differences in demand on nonphotochemical quenching (NPQ) processes during the chilling treatments. We found that photosystem II quantum yield and total NPQ were similar between the CO(2) treatments during chilling. In both CO(2) treatments, chilling caused a shift from total NPQ largely composed of q(E), the protective, rapidly responding component of NPQ, to total NPQ dominated by the more slowly relaxing q(I), related to both protective and damage processes. The switch from q(E) to q(I) during chilling was more pronounced in the elevated CO(2) plants. Using complementary plots of the quantum yields of photochemistry and NPQ we demonstrate that, despite CO(2) effects on the partitioning of NPQ into q(E) and q(I) during chilling, total NPQ was regulated at both CO(2) levels to maximize photochemical utilization of absorbed light energy and dissipate only that fraction of light energy that was in excess of the capacity of photosynthesis. Photodamage did occur during chilling but was repaired within 3 h recovery from chilling in both CO(2) treatments.