Typology of employers offering line manager training for mental health

BACKGROUND

Mental ill health has a high economic impact on society and employers. National and international policy advocates line manager (LM) training in mental health as a key intervention, but little is known about employer training provisions.

AIMS

To explore the prevalence and characteristics of organizations that offer LM training in mental health.

METHODS

Secondary analysis of existing longitudinal anonymised organizational-level survey data derived from computer-assisted telephone interview surveys collected in four waves (2020:1900 firms, 2021:1551, 2022:1904, 2023:1902) in England, before, during and after a global pandemic.

RESULTS

The proportion of organizations offering LM training in mental health increased pre- to post-pandemic (2020:50%, 2023:59%) but 41% do not currently provide it. Logistic regression confirmed that LM training is more likely to be offered by large-sized enterprises, organizations with a larger proportion of employees who are younger (aged 25-49), female, disabled and from ethnic minority communities. Sector patterns were inconsistent, but in 2023, organizations from the 'Hospitality' and 'Business Services' sectors were more likely to provide LM training than other sectors.

CONCLUSIONS

Continued efforts are needed to increase the proportion of employers offering LM training in mental health, particularly small- to medium-sized enterprises, and organizations with predominantly male, White and/or older workforces.

The Principles of the ‘New Competition’: An Empirical Assessment of Ireland's Position

An assessment is provided of the extent to which industrial development policy and manufacturing firms in Ireland have embraced the four principles of the ‘New Competition’ outlined by Professor Michael Best. Comparisons with Germany arc made throughout the paper. A functional analysis of industrial development spending in Northern Ireland and the Republic of Ireland suggests that less than a tenth of all expenditure is targeted at improving sectoral competitiveness. Less than 2% is aimed directly at developing collaboration and cooperation between firms, The remainder is counterstrategic, grant aiding the development of individual firms. Although plants in Ireland are found to have more extensive network linkages than those in Germany, these were predominantly between companies which were part of the same group rather than collaborative relationships between independent plants. The limited information available suggests that the production operations of manufacturing plants in Ireland are less flexible than those of German plants. In terms of product development, plants in Ireland had more multifunctional involvement and less functional demarcation than plants in Germany. Plants in Ireland also had similar product-quality aspirations to their German counterparts. Political and operational difficulties are likely to arise in the adoption of a more strategic industrial policy. Firms in Ireland may also be constrained by available human and financial resources in their attempts to embrace the principles of the New Competition.

Snapshots reflecting the lives of siblings of children with autism spectrum disorders

BACKGROUND

Past research focused on the effects of raising a child with autism spectrum disorder on families. However, most research examined parents' perspectives rather than siblings' perspectives. Therefore, the purpose of this qualitative descriptive design was to use photo elicitation to capture perspectives of siblings living with a child with autism spectrum disorder.

METHODS

Fourteen siblings (nine male) of 13 children with autism spectrum disorder received disposable cameras with 24-27 colour exposures, and were asked to photograph what was important to them within 2 weeks. After developing snapshots, investigators interviewed siblings about their photographs, and used open, axial and selective coding to determine photograph categories and subcategories.

RESULTS

Two major categories were found: people (family members, non-family members) and non-people (personal items/objects, animals, buildings, scenery). Interviews about photographs reflected experiences siblings had with people/non-people in the snapshots and their normal everyday activities. Most photographs revealed family life and activities any sibling would experience whether or not they lived in a family raising a child with autism spectrum disorder.

CONCLUSIONS

Photo elicitation facilitates communication between children and health-care professionals, and provides information about living with a child with autism spectrum disorder from the sibling's perspective. This information contributes to our knowledge base and allows development of specific intervention plans for siblings of these children.

[Multicystic kidney disease in a segment of horseshoe kidney: an uncommon combination of malformations]

Multicystic dysplasia is the most common type of renal cystic disease, and it is one of the most common causes of an abdominal mass in infants. The contralateral system is also frequently abnormal. The most commonly associated anomalies are contralateral ureteropelvic junction obstruction and contralateral vesicoureteral reflux. In a few cases, multicystic dysplasia involves a horseshoe kidney or one pole of a duplex kidney. We present a female patient diagnosed with this condition at 9 years old, when she was being studied due to recurrent abdominal pain. The renal function was normal.

The role of the frontal lobes in memory: evidence from unilateral frontal resections for relief of intractable epilepsy

The current investigation explored processes associated with memory deficits in patients with frontal lobe dysfunction. Specifically, we examined deficits associated with the encoding, consolidation, and retrieval of information in memory in 53 patients who underwent either a unilateral frontal (N=13) or temporal (N=40) lobe resection for relief of intractable epilepsy. Post-surgical memory scores indicated that the frontal group and the temporal group did not differ in consolidation of information, as defined by the information forgotten between immediate and delayed recall. Instead, the temporal group evidenced significantly poorer recall of verbal information at both immediate and delayed recall. This effect was especially strong in the left temporal group for the recall of verbal information. Although no group differences were observed in the degree to which patients semantically organized information or made recency discriminations, the frontal group exhibited significantly weaker release from proactive interference than the temporal group, suggesting some impairment in encoding and retrieval processes associated with frontal lobe dysfunction.

Conduction aphasia and the arcuate fasciculus: A reexamination of the Wernicke-Geschwind model

Wernicke, and later Geschwind, posited that the critical lesion in conduction aphasia is in the dominant hemisphere's arcuate fasciculus. This white matter pathway was thought to connect the anterior language production areas with the posterior language areas that contain auditory memories of words (a phonological lexicon). Alternatively, conduction aphasia might be induced by cortical dysfunction, which impairs the phonological output lexicon. We observed an epileptic patient who, during cortical stimulation of her posterior superior temporal gyrus, demonstrated frequent phonemic paraphasias, decreased repetition of words, and yet had intact semantic knowledge, a pattern consistent with conduction aphasia. These findings suggest that cortical dysfunction alone may induce conduction aphasia.

Intractable temporal lobe epilepsy: comparison of positron emission tomography with qualitative and quantitative MR

PURPOSE

To compare the ability of qualitative fludeoxyglucose F 18 positron emission tomography (QPET), qualitative MR imaging (QMR), and quantitative MR imaging with hippocampal formation volumetric assessment (HV MR) to lateralize the seizure focus in patients with temporal lobe epilepsy.

METHODS

Sixteen consecutive patients undergoing presurgical examination for temporal lobe seizures had QPET, QMR, and HV MR. The presence of temporal lobe epilepsy was confirmed by Engel class I or II outcomes at 1-year postoperative follow-up examinations. A QPET, QMR, or HV MR study was considered to be lateralizing if it matched the side of the seizure focus, nonlateralizing if it did not lateralize the seizure focus to either temporal lobe, or incorrectly lateralizing if it lateralized the seizure focus to the incorrect side.

RESULTS

Of 16 patients with proved temporal lobe seizures, QPET was correctly lateralizing in nine (56%), nonlateralizing in six (37.5%), and incorrectly lateralizing in one (6%). QMR was correctly lateralizing in six (37.5%), nonlateralizing in six (37.5%), and incorrectly lateralizing in four (25%). HV MR was correctly lateralizing in all 16 patients (100%). Age at onset, seizure duration, and total number of seizures did not correlate with QPET, QMR, and HV MR lateralization.

CONCLUSIONS

Our results show that each imaging technique yields useful information for seizure lateralization in temporal lobe epilepsy and that HV MR yields considerably more information that QPET or QMR.

The taste of monosodium glutamate: membrane receptors in taste buds

Receptor proteins for photoreception have been studied for several decades. More recently, putative receptors for olfaction have been isolated and characterized. In contrast, no receptors for taste have been identified yet by molecular cloning. This report describes experiments aimed at identifying a receptor responsible for the taste of monosodium glutamate (MSG). Using reverse transcriptase (RT)-PCR, we found that several ionotropic glutamate receptors are present in rat lingual tissues. However, these receptors also could be detected in lingual tissue devoid of taste buds. On the other hand, RT-PCR and RNase protection assays indicated that a G-protein-coupled metabotropic glutamate receptor, mGluR4, also is expressed in lingual tissues and is limited only to taste buds. In situ hybridization demonstrated that mGluR4 is detectable in 40-70% of vallate and foliate taste buds but not in surrounding nonsensory epithelium, confirming the localization of this metabotropic receptor to gustatory cells. Expression of mGluR4 in taste buds is higher in preweaning rats compared with adult rats. This may correspond to the known higher sensitivity to the taste of MSG in juvenile rodents. Finally, behavioral studies have indicated that MSG and L-2-amino-4-phosphonobutyrate (L-AP4), a ligand for mGluR4, elicit similar tastes in rats. We conclude that mGluR4 may be a chemosensory receptor responsible, in part, for the taste of MSG.

Quantified volumes of temporal lobe structures in patients with epilepsy

The T1-weighted volumetric magnetic resonance images of 31 patients with intractable temporal lobe epilepsy, and 13 control subjects matched for age and sex, were subjected to semiautomated threshold analysis. The method used proved to be relatively fast and reliable. An index of temporal lobe interhemispheric asymmetry was extracted by thresholding high-signal (white matter) pixels. Patients had significantly more asymmetrical indices for white matter and hippocampal volumes that did control subjects, and the two indices were significantly correlated, providing evidence for the validity of the white matter index. Differences in both indices were consistent with decreased tissue on the side of the focus. In classification analyses a combination of these two indices correctly predicted the side of focus at a greater rate than did either used alone. Findings provide support for the hypothesis that seizure activity is associated with atrophy in both mesial and lateral temporal lobe structures.

Hippocampal volumetrics differentiate patients with temporal lobe epilepsy and extratemporal lobe epilepsy

OBJECTIVE

To determine whether the occurrence of hippocampal formation (HF) volumetric asymmetry can reliably discriminate between complex partial seizures (CPSs) of a temporal lobe origin and CPSs of an extra-temporal lobe origin in a prospective study of patients with intractable CPSs (approximately 70% of patients have electrographic foci in the temporal lobe [HF volumetric asymmetry on magnetic resonance imaging scans has been shown to lateralize such foci reliably)].

DESIGN

We examined HF volumetrics on magnetic resonance imaging scans that were acquired with a 1-T magnetic resonance imaging scanner (Siemens Magnetom, Siemens Medical Systems, Iselin, NJ) by using magnetization-prepared rapid gradient echo three-dimensional sequences (producing a gapless series of high-contrast 1.25-mm images). These data were compared with ictal, interictal, invasive, and noninvasive videoelectroencephalographic monitoring data, functional imaging data, and outcome data to define each patient's type of epilepsy.

SETTING AND PATIENTS

Forty-one patients were recruited from a tertiary university comprehensive epilepsy program, and 22 control subjects were recruited from the neurologically normal university community.

RESULTS

Among the control subjects, the difference in HF volumetrics (right-left HF volumetrics) was + 0.085 +/- 0.253 cm3. Of the 41 patients, 25 had temporal lobe epilepsy. When we set the upper limit of normal at the mean +/- 3 SDs, all patients beyond the upper limit had CPSs of a temporal lobe origin. Of the patients with temporal lobe epilepsy, only three fell within normal limits. No patient with CPSs of an extratemporal lobe origin fell beyond the upper limit.

CONCLUSION

The presence of significant HF volumetric asymmetry makes it highly unlikely that a patient's CPSs are of an extratemporal lobe origin.

Ca(2+)-dependent Cl- conductance in taste cells from Necturus

1. Taste responses adapt to a constant chemical stimulus. The present study describes a new ionic conductance in taste cells--a Ca(2+)-dependent anion conductance that may explain taste adaptation. 2. Patch-clamp recordings were made on isolated Necturus taste cells or on taste cells in lingual slices. When Na+ and K+ currents were eliminated with tetrodotoxin (TTX) and tetraethyl-ammonium (TEA) in the bath and replacing K+ with N-methyl-D-glucamine (NMDG+) in the pipette, Ca2+ currents were followed by prolonged outward currents. Outward current was abolished when Ca2+ was substituted with Ba2+ or when Cl- was replaced with large organic anions (methanesulfonate, isethionate, or ascorbate). 3. The outward, Ca-dependent current was reduced by certain agents that block Cl- conductances in other tissues, namely 4-acet-amido-4-isothiocyanostilbene-2,2-disulfonic acid (SITS) and 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS). However, other Cl- channel blockers--9-AC, furosemide and an antibody to Cl channels-had little or no specific effect on the Ca-dependent outward current in Necturus taste cells. 4. We postulate that the biological action of this Ca-dependent anion conductance in situ is to terminate depolarizing receptor potentials, even during maintained chemostimulation, thereby playing an important role in chemosensory adaptation and modulation of impulse discharge patterns in taste buds.

Retrograde effects of target atrophy on submandibular ganglion neurons

1. To study the retrograde effects of changes in target tissue upon the innervating nerve supply, we have examined the parasympathetic submandibular ganglion of the adult rat. Neurons of this ganglion innervate the submandibular and sublingual salivary glands. 2. Ligating the salivary ducts leads to rapid and prolonged salivary gland cell atrophy. 3. Duct ligations, without direct injury to the glandular nerve supply, initially produced few alterations in the ganglion. After 8 wk, however, neuron number was reduced by 50%. The numbers of presynaptic inputs/neuron and synapses/neuron perimeter were not affected by the cell loss. 4. After 1 wk of duct ligation in which the glandular nerve supply was intentionally damaged, some ganglionic neurons have lost all presynaptic inputs, suggesting synaptic disjunction. This is followed at 3 wk by a 40% decrease in neuron number and an increase in the number of inputs per (remaining) ganglion cell. However, the number of synapses/neuronal profile was unchanged. 5. Thus axotomy plus target atrophy causes synaptic disjunction, neuron cell death, and input rearrangement, presumably due to a combination of direct injury effects and an abrupt loss of peripheral trophic supplies. 6. In contrast, target atrophy alone produced more gradual changes in submandibular ganglion neurons. Only prolonged target atrophy leads to a decrease in the number of ganglionic neurons, perhaps due to the gradual loss of peripheral trophic supplies. However, other features, such as the number of inputs/cell and the number of synapses/neuron perimeter, remain unaltered. Evidently, the gradual loss of trophic support does not result in synaptic disjunction to the degree needed to produce presynaptic input rearrangement.

Neonatal synapse elimination in the rat submandibular ganglion: effect of retarded target growth

1. We have studied synapse elimination in the submandibular ganglion of neonatal rats to determine the effects of retarded target growth on synaptic development. Neurons of this ganglion provide parasympathetic innervation to the submandibular and sublingual salivary glands. 2. Ligating the main salivary ducts 2-4 days after birth at a point where nerve fibers were not damaged reduces gland weight by 55% during the 2nd wk after birth and 80% by adulthood. 3. In control animals, the average number of preganglionic inputs/neuron normally declines steadily during the first few weeks after birth, before stabilizing during the 5th wk at the control adult level. Between birth and adulthood, the number of ganglionic neurons increases by 150%. 4. Ganglia from duct-ligated animals showed an acceleration in the process of synapse elimination. Input number in experimental ganglia reached the control adult level during the 3rd wk after birth. This acceleration is confined solely to ganglia that innervate the underdeveloped glands. 5. The loss of inputs was not further enhanced by prolonged target atrophy. Thus average input numbers to neurons of 5th wk or adult experimental ganglia were not different from age-matched control values. 6. No differences from control values were seen in most cases for resting potentials, input resistances, or cell size. However, the increase in neuron number was retarded in experimental animals, and the number of synapses/neuronal profile was reduced in the adult animals. 7. Thus subnormal target growth leads to an acceleration in the process of synaptic elimination in neonatal rats. This acceleration may be mediated by alterations in the level of trophic factors emanating from the target.

On the two subdivisions and intrinsic synaptic connexions in the submandibular ganglion of the rat

Parasympathetic neurones in the submandibular ganglion of the rat innervate the submandibular and sublingual salivary glands. Neurones which innervate the submandibular gland (s.m. neurones) are usually located along the salivary ducts which drain both glands. Neurones which innervate the sublingual gland (s.l. neurones) are located in the thin sheet of tissue which lies between the salivary ducts and the lingual nerve. The existence and characteristics of intrinsic synaptic connexions were studied electrophysiologically in these two divisions of the submandibular ganglion. Three days or more after denervating the ganglion two types of excitatory intrinsic synaptic potentials--chemical and electrical--were recorded in ganglion cells. Chemical synaptic responses were reversibly blocked by nicotinic antagonists such as hexamethonium (10 microM) and D-tubocurarine (100 microM). Intrinsic chemical synapses were common among s.m. neurones (present in 72% of neurones) but only 12% of s.l. neurones were coupled with chemical synapses. Electrical coupling was found among 31% of s.m. neurones but was not observed between s.l. neurones. Electrotonic coupling in s.m. neurones in denervated and intact ganglia was directly demonstrated by impaling adjacent neurones with separate micro-electrodes. The average coupling ratio for current pulses injected into one cell and recorded in the adjacent cell was 0.06. During the first 30 days after birth, the number of synaptic inputs from preganglionic (chorda tympani) axons was markedly reduced in both s.m. and s.l. neurones, whereas the incidence of electrical synaptic connexions remained unchanged. The effect of long-term denervation (up to 4 months) on intrinsic synapses was examined. The membrane properties of the parasympathetic neurones and the intrinsic synaptic connexions were maintained without marked changes. It is concluded that the submandibular ganglion in the rat consists of two distinct populations of parasympathetic neurones. The two classes of neurones differ in (1) their location within the ganglion, (2) their target organs and (3) the incidence of intrinsic synapses. Possible mechanisms for the development, maintenance and function of these intrinsic synapses are discussed.

Regenerative impulses in taste cells

Taste cells and nongustatory epithelial cells in the isolated lingual mucosa from the mud puppy Necturus maculosus were impaled with microelectrodes. The taste cells, but not surrounding epithelial cells, were electrically excitable when directly stimulated with current passed through the recording electrode. Action potentials produced by taste cells had both a sodium and a calcium component.

Impairment of neutrophil chemotaxis by serum from patients with chronic lymphoproliferative disease

The sera of 74 individuals with chronic lymphoproliferative disease were screened for the presence of inhibitory activity against neutrophil chemotaxis. This was present in more than half the patients with IgA myeloma and Hodgkin's disease but was less common in chronic lymphocytic leukaemia, lymphocytic lymphoma and non-IgA paraproteinaemia. Heating the sera prior to testing frequently enhanced inhibitory activity particularly in myeloma and lymphoma.

Granulocyte chemotaxis: multiple assay screening using a raft technique

The assessment of granulocyte chemotaxis is complicated by the difficulty of precisely reproducing results in serial estimations and deciding on the best end point which would reflect most accurately the degree of travel taken by the cells under observation. The methods in use are generally based on the Boyden chamber, following this, we have further developed the principle of the "raft" technique of chamber based migration. In order to overcome the problems associated with reproducibility of results when performing multiple assays of chemotaxis, especially when sera of widely differing activity are encountered in the screening procedure, we have used a "batching" system and a simple method of presenting the results so that they are comparable.

Somatic motor axons can innervate autonomic neurones in the frog heart

1. The effects of sympathetic and parasympathetic stimulation on the heart rate in frogs were tested after hearts were reinnervated with a somatic motor nerve. When frogs were vagotomized and hypoglossal axons were redirected to the heart for 8 or more weeks, stimulating the redirected hypoglossus nerve produced a parasympathetic-like inhibition of the heart. Stimulating sympathetic rami of the anastomosed hypoglossus nerve produced cardiac acceleration.2. Individual parasympathetic neurones received synaptic input from hypoglossal terminals. The excitatory post-synaptic potentials evoked by hypoglossal stimulation were much smaller than those evoked by vagal stimulation in control or vagal-reinnervated ganglia. However, hypoglossal axons innervated most (71%) of the ganglion cells and this level of innervation persisted for at least 60 weeks.3. Hypoglossal axons formed networks of varicose terminals within cardiac ganglia and established axo-axonic synapses with parasympathetic neurones. Hypoglossal terminals did not reinnervate the neuronal perikarya, in contrast to vagal axons in control or vagal-reinnervated ganglia.4. Axo-axonic synapses from redirected hypoglossal axons were identified in cardiac ganglia by bathing isolated hearts in horseradish peroxidase (HRP) and stimulating the redirected nerve. Electron micrographs showed that axo-axonic synapses contained HRP-labelled presynaptic vesicles.5. The source of foreign innervation in experimental cardiac ganglia was confirmed to be hypoglossal motoneurones (a), by comparing the conduction velocity of the redirected presynaptic axons (1.32 m/sec) with regenerating vagal preganglionic fibres (< 0.3 m/sec), and (b), by retrograde HRP-labelling of large motoneurones in the hypoglossal nucleus after applying peroxidase to the axons which had grown into the heart.

Reinnervation of denervated parasympathetic neurones in cardiac ganglia from Rana pipiens

1. The sequence of events during reinnervation of the cardiac ganglion in the frog following interruption of the vagosympathetic nerve supply was studied with both electrophysiological and morphological techniques. 2. When cardiac ganglia were denervated by crushing the vagosympathetic nerve supply to the heart all synaptic endings on parasympathetic ganglion cells degenerated. Vacated post-synaptic densities were detected on denervated neurones for periods of at least 7 weeks. 3. The earliest signs of reinnervation were subthreshold responses evoked by stimulating the regenerating vagosympathetic trunks 2 1/2-3 weeks after crushing the cardiac branches of the vagus nerves. Analysis of the reversal potentials of these responses indicated that these synapses were distant from the cell body. 4. At slightly longer times (4-5 weeks), regenerating synapses could be recognized on post-ganglionic axons; no synapses were detected on the neuronal perikarya at these times. 5. By 6-7 weeks following denervation, vagal synapses reinnervated neuronal perikarya as well as post-ganglionic axons. At the same time, vacated post-synaptic densities declined in number. Furthermore, vagal stimulation at this stage evoked large, suprathreshold post-synaptic potentials. 6. These studies indicate that post-ganglionic axons are the initial sites for reinnervation of parasympathetic neurones in the heart. Only some time later are neuronal perikarya reinnervated and ganglionic transmission completely restored.

Reinnervation of the amphibian cardiac ganglion after complete or partial denervation

The interactions between regenerating and sprouted nerve terminals during reinnervation of neurones were tested in the parasympathetic cardiac ganglion in frogs. 1. After partial (unilateral) vagotomy, remaining intact preganglionic vagal axons rapidly sprouted and innervated the entire ganglion. At later intervals after nerve damage, regenerating vagal axons were able to reinnervate ganglion cells despite the presence of synapses from sprouted nerve terminals. 2. When vagal reinnervation took place after unilateral vagotomy, synaptic input from the sprouted vagus nerve declined. 3. The presence of synapses from intact and sprouted nerve terminals in the ganglion after partial denervation measurably delayed the rate of vagal reinnervation. 4. After complete denervation (bilateral vagotomy), ganglionic reinnervation was rapid and complete. However, cells initially received an excessive number of preganglionic inputs and an abnormal distribution of left/right vagal innervation in the ganglion. 5. At long intervals (up to 85 weeks) after ganglionic reinnervation, some reduction of excess vagal inputs took place, indicating there was a slow re-organization of ganglionic synapses. 6. The number of boutons per cell body as revealed by zinc iodide-osmium staining remained constant after vagal reinnervation, despite an initial excessive synaptic reinnervation and subsequent synaptic remodelling.

Competitive elimination of foreign motor innervation on autonomic neurones in the frog heart

1. Somatic motoneurones are capable of forming functional synapses when redirected to vagotomized autonomic neurones in the frog heart. We tested if regenerating vagus nerves could reinnervate ganglion cells in the presence of foreign hypoglossal innervation and, furthermore, whether hypoglossal innervation persisted when vagal axons regenerated to the heart. 2. Simulating the redirected hypoglossus nerve produced a parasympathetic-like cardiac inhibition in the absence of vagal regeneration. However, when the vagus nerve was allowed to regenerate to the heart, vagal cardio-inhibition was restored and hypoglossal inhibition disappeared. 3. Intracellular recordings showed that 71% of the cardiac ganglion cells were innervated by hypoglossal axons before vagal regeneration, but that this value fell to less than 9% over a period of 40 weeks during vagal regeneration. 4. If the vagus nerve was prevented from regenerating to the heart, hypoglossal innervation did not decline, indicating that elimination of the foreign motor innervation was dependent upon vagal reinnervation. 5. Although hypoglossal terminals formed synapses only on the axons of parasympathetic ganglion cells, regenerating vagal fibres re-established synaptic contact both on axons as well as on neuronal perikarya. 6. The data indicate that in the frog parasympathetic cardiac ganglion, extensive synaptic remodelling can take place during reinnervation and that previously established, inappropriate inputs can be functionally eliminated by regeneration of the native nerve supply.

"Hybrid" synapses formed by foreign innervation of parasympathetic neurons: a model for selectivity during competitive reinnervation

Selectivity of synapse formation after nerve regeneration was tested in the parasympathetic cardiac ganglion of frogs (Rana pipiens). First, we tested the ability of somatic motor axons to establish synaptic connections with denervated ganglion cells by implanting the hypoglossus nerve into the vagotomized heart. After several weeks, stimulation of the implanted hypoglossus mediated a parasympathetic-like inhibition of the heart rate, and synaptic responses produced by hypoglossal stimulation were recorded intracellularly in ganglion cells. Light and electron microscopy indicated that implanted hypoglossal nerve terminals contacted parasympathetic ganglion cells only on their axons and not on the cell body (where most vagal synapses are found in control animals). Second, we tested whether regenerating vagal preganglionic axons would complete with foreign (hypoglossal) terminals for innervation of cardiac ganglion cells. We allowed the vagus nerve to regenerate in animals in which the implanted hypoglossus had established functional contacts with the cardiac ganglion. Vagal axons were able to reinnervate the heart and reestablish synaptic connections on the cell bodies of ganglion cells. Furthermore, functional transmission at the foriegn (hypoglossal) terminals disappeared concomitant with vagal reinnervation.

Impulse blockade in frog cardiac ganglion does not resemble partial denervation in changing synaptic organization

Partial denervation of parasympathetic neurons in the frog heart by surgical section of one vagus nerve results in a marked reorganization of functional synaptic connections made by the remaining vagus nerve. These changes are not simply due to a lack of impulse activity per se in the sectioned nerve because blockage of impulses in one vagus with tetrodotoxin-impregnated cuffs did not cause similar changes in the innervation pattern of the ganglion. Furthermore, tetrodotoxin-blocked vagal fibers retain their ability to sprout and can form new synapses on denervated neurons.

The acetylcholine sensitivity of the surface membrane of multiply-innervated parasympathetic ganglion cells in the mudpuppy before and after partial denervation

1. The surface chemosensitivity to iontophoretically applied acetylcholine (ACh) of single nerve cells in the cardiac ganglion of the mudpuppy was examined. 2. Some synapses on the neurones can be recognized in the living preparation with differential interference contrast optics. Identified synaptic regions of the ganglion cells were more sensitive to ACh than were other areas. The mean sensitivity of synaptic areas was 509 mV/nC, but that of random spots on the cell surface (which were mainly non-synaptic) was only 190 mV/nC. The mean rise time of ACh responses at synapses was 23 msec and at random spots was 36 msec. These data suggest that the density of ACh receptors is highest under the synapses on the post-synaptic membrane. 3. When some, but not all, of the presynaptic terminals on the ganglion cells are destroyed by cutting the vagus nerve, the sensitivity of the entire surface membrane to applied ACh increases. This increase in sensitivity reaches a maximum about 4-6 weeks after the operation. 4. Synaptic transmission at excitatory collateral synapses which remain after vagal degeneration is not altered by this hypersensitivity. 5. Neurones from ganglia which have been isolated and maintained in organ culture also become hypersensitive to applied ACh. this heightened chemosensitivity deveoops much faster in vitro; hypersensitivity in cultured ganglia becomes manifest within 4-5 days, in contrast with 4-6 weeks after vagus degeneration in vivo.

An electrophysiological study of chemical and electrical synapses on neurones in the parasympathetic cardiac ganglion of the mudpuppy, Necturus maculosus: evidence for intrinsic ganglionic innervation

1. The cardiac ganglion of the mudpuppy is situated on a thin sheet of tissue. Two nerve cell types can be distinguished readily in the living preparation - principal cells and smaller interneurones which synapse with the principal cells. The purpose of this study was to investigate synaptic transmission and the functional organization of neuronal connections of ganglion cells with intracellular micro-electrodes. 2. Stimulation of the preganglionic, vagus, nerves evoked a large excitatory response in principal cells. About three quarters of these neurones were innervated by a single vagal axon. The remaining cells received two or more preganglionic nerve fibres. 3. The quantum content of vagal excitatory post-synaptic potentials (e.p.s.p.s) was measured. Normally, the e.p.s.p. was suprathreshold and consisted of about twenty-two quanta, whereas only about nine quanta were required to reach threshold and initiate an action potential. 4. Intracellular stimulation of principal cells evoked e.p.s.p.s in neighbouring principal cells. The responses were blocked by cholinergic antagonists. These potentials were caused by excitation of principal cell axon collateral synapses. 5. Principal cells also formed electrical junctions with each other. These electrical junctions were very weak. Although they transmitted slow potential changes, only a small response was recorded in one cell when an electrically coupled neighbouring cell fired an impulse. The resistance of the electrical junction between principal cells was calculated to be about 5-8 X 10(8) omega. 6. Stable penetrations of interneurones were only rarely achieved, making it difficult to study their functional relationship to principal cells. Action potentials were recorded from interneurones in a few instances. 7. These data demonstrate that parasympathetic ganglion cells in the heart of the mudpuppy receive innervation from more than one source involving both chemical and electrical synapses, and that some of the synapses are intrinsic to the ganglion.

Synaptic organization and acetylcholine sensitivity of multiply innervated autonomic ganglion cells

The principal cells of the mudpuppy cardiac ganglion receive synapses from three sources: vagal axons, interneurons and axon collaterals from other principal cells. The simplicity of the structural organization and the visual clarity in the living preparation provide favorable conditions for examining the function of these synapses and how different classes of synapses on the same cell influence its function. We have studied the sensitivity of the principal cells to iontophoretically applied acetylcholine--the transmitter at synapses made by the vagal axons and by postganglionic axon collaterals from other principal cells. In normal ganglia, the ACh sensitivity on the cell surface is highest at the region of synapses. Partial denervation, produced by severing the vagus nerves, results in an increased ACh sensitivity in nonsynaptic areas but does not appear to affect synaptic transmission at the remaining synapses.

The membrane effects, and sensitivity to strychnine, of neural inhibition of the Mauthner cell, and its inhibition by glycine and GABA

1. Anionic conductance changes in Mauthner neurones of goldfish were measured during synaptically evoked inhibition and inhibition caused by iontophoretic application of the putative inhibitory transmitters glycine and gamma-aminobutyric acid (GABA).2. The effects of either amino acid were indistinguishable from those of the neural inhibitory transmitter(s). The membrane permeability during the neural or drug response was increased to Br(-), Cl(-), I(-), SCN(-), NO(3) (-), ClO(3) (-), and formate (HCOO(-)), but not to HCO(3) (-), BrO(3) (-), IO(3) (-), SO(4) (-), HPO(4) (-), H(2)PO(4) (-), acetate and citrate.3. Strychnine was injected intramuscularly, iontophoretically, or applied topically to the exposed brain in order to compare quantitatively its ability to prevent inhibition evoked by synaptic activation and by pharmacological means. Inhibitions were measured by the increase in membrane conductance.4. Strychnine, at concentrations just adequate to block completely the late collateral inhibition (LCI) and crossed VIII nerve inhibition, had little effect on the pharmacological inhibition caused by glycine, and sometimes there was no detectable effect at all. In one experiment even a local iontophoretic application of strychnine in a sufficient dose to diffuse over the cell and block the LCI almost completely, merely halved the effect of a small dose of glycine applied to the same localized region of the membrane.5. Higher concentrations of strychnine than those necessary to block synaptically evoked inhibition would reduce the effect of glycine but not that of GABA. The evidence indicated that any apparent effect of strychnine upon GABA could be explained by displacement of the GABA-containing iontophoretic pipette.6. The glycine-blocking action of iontophoretic pulses of strychnine was of relatively very slow onset and long duration compared to the effects of pulses of glycine and GABA.7. These findings can be interpreted as either (1) strychnine has a presynaptic action, preventing the release of inhibitory neurotransmitter, in addition to its less potent post-synaptic one in blocking pharmacological inhibition, or (2) strychnine acts entirely post-synaptically, but the physiological transmitter action differs from that of glycine and GABA in being considerably more sensitive to strychnine antagonism. In either case, the use of strychnine as evidence for the claim that glycine is an inhibitory neurotransmitter at the Mauthner cell is questionable.

Analysis of Mauthner cell responses to iontophoretically delivered pulses of GABA, glycine and L-glutamate

1. The intracellularly recorded responses of goldfish Mauthner neurones to iontophoretically applied pulses of amino acids have been analysed: their time courses have been compared with each other, and with those predicted from diffusion theory.2. The rise time of the response to GABA is slower than that to glycine or L-glutamate. The response curves of the latter substances were very similar, and unlike that of GABA were markedly affected by increasing the distance of pipette-tip from the membrane. The results suggest that the time course of the responses to glycine and L-glutamate are determined mainly by free diffusion in the brain tissue (at least within about 200 mum of the cell), while that to GABA must be rate-limited by other factors, e.g. drug-receptor activation time.3. The possibility that the responses are influenced by some desensitizing process was investigated by applying a second (test) drug pulse during the response to a prior conditioning one. In the case of glycine and of L-glutamate there was no attenuation of the response to a second pulse at any time. With GABA, however, the second response was reduced during the period of the conditioning response; the reduction was progressively less marked the later the test pulse occurred. A similar effect with GABA was seen when glycine was used as the test pulse. The responses to long-maintained drug pulses also indicated that for GABA, but not for glycine or glutamate, there seems to be some desensitizing process present.4. Calculated time courses of responses to brief pulses of glycine and of L-glutamate (based upon diffusion theory) differed somewhat from the observed curves, largely during the falling phase. However, when the calculations were based upon second-order reactions (two molecules of drug per receptor) the diffusion model gave results very like the observed ones.5. Possible implications of these results for the role these three amino acids may have as neuro-transmitters are mentioned.