Glutamate, substance P (SP) and neurokinin A (NKA) are all found in fine primary afferent fibres and can be released upon noxious stimulation of the corresponding cutaneous receptive field. The possibility of a role in nociception for the metabotropic class of glutamate receptors (mGluRs) as well as those at which SP and NKA preferentially act (NK<SUB>1</SUB> and NK<SUB>2</SUB>), was investigated in the present study. Since protein kinase C (PKC) has been shown to be important in the mediation of noxious, but not non-nociceptive inputs, the potential role of this and several other signal transduction pathways in sensory inputs was assessed here, especially in the context of actions via mGluRs. (a) Extracellular recordings were made from single dorsal horn neurons (laminae III-V) in the spinal cords of chloralose/urethane anaesthetised rats. Activity evoked by innocuous brushing of the cutaneous receptive field was not reduced by ionophoresis of mGluR antagonists L-1-amino-3-phosphopropionic acid (AP3), (R,S)- or (S)-4-carboxy-3-hydroxyphenylglycine (CHPG). This investigation demonstrates a role for spinal cord mGluRs in the transmission of sustained nociception, possibly mediated by PKC, CamKII and PLA<SUB>2</SUB>. NK<SUB>2</SUB> receptors appear to have a selective role in thermal inputs to the spinal cord, whereas this study provided no evidence for an overt role of NK<SUB>1</SUB> receptors in the nociceptive models assessed. It is possible that NK<SUB>1</SUB> receptors play a greater role in more prolonged or severe nociceptive inputs. The present data suggest however that not only NK<SUB>2</SUB>, but also NK<SUB>1</SUB> receptors exhibit a functional interaction with the influence of mGluRs on nociceptive thresholds.

No description available.

No description available.

Several techniques were used to study the morphology of the salivary apparatus of the cockroach, Nauphoeta cinerea. A general survey of the ultrastructure was made. The acinar cells were of two distinct types: peripheral and central cells. The ducts that these cells give rise to could be classified into three morphologically distinct areas. The fine structure of the reservoir ducts was also studied. Intracellular injections of Procion yellow dye and the use of lanthanum, as an electron dense marker, showed that there were many intercalated gap-junctions between the septate desmosomes of the acinar cells. The innervation of the apparatus was studied in detail and it was observed, using techniques of fluorescence histochemistry and electron microscopy, that the salivary nerves, which arise from the suboesophageal ganglion, branch over the surface of the acini. The axons associated with the acini were found to be of two morphologically distinct types, designated type A and type B. Several histochemical tests indicated that type A axons contained a catecholamine. It was attempted to stimulate the salivary nerves. This resulted in structural changes within peripheral cells and type A axons. When the salivary nerves were cut several degenerating axon profiles could be identified in association with the gland cells. This was not observed when the stomatogastric nerve was cut. Finally, enzyme-inhibiting drugs were used to interrupt the synthetic pathways of catecholamines. These experiments led to a number of unexpected results including the observation that some of the actions of these drugs appeared to be post-synaptic.

No description available.

The main body of this work contributes to an understanding of the development and growth of skeletal muscle in a range of Vertebrates from fish to pigs. Particular emphasis is paid to the contribution of numbers and types of muscle fibres to overall muscle growth and ultimate mass, and also to the mechanisms whereby factors such as nutrition in mammals and temperature in fish may affect these parameters. The work is divided into three main sections. The first section covers aspects of prenatal mammalian development including myogenesis and placentation. Muscle develops as two populations of muscle fibres. Primary myofibres form first and this is followed by the formation of a larger populations of secondary fibres. Restricting maternal nutrition may compromise the formation of secondary fibres but not primaries. Studies on the placenta and on levels of specific factors, e.g. insulin-like growth factors, has given some insight into the mechanism of nutritional effects on muscle fibre development. Nutritional experiments have highlighted energy levels in the earlier stages of gestation as most critical in the development of muscle fibre number. This finding has been developed in pig experiments which have shown that extra feed in early gestation can produce piglets with more secondary fibres at birth and which grow faster and more efficiently to slaughter. The second section incorporates work on postnatal mammalian muscle. Studies, on pigs in particular, have shown that primary fibre number relates more to genotype that does secondary fibre number. Total muscle fibre number correlates with some parameters of carcass leanness and with postnatal growth rate and feed conversion efficiency. The influence of factors such as nutrition, dwarfism, obesity and sex on aspects of muscle growth and muscle fibre types has been studied as well as the functional adaptation of muscle metabolism in different species. The third section includes work on fish muscle development and growth in a range of species.

The distribution of the granule chymase Sheep Mast Cell Proteinase (SMCP) was determined in trachea, bronchus, bronchial lymph node, thymus, spleen, liver, flank skin, abomasum, duodenum, jejunum, ileum, colon and mesenteric lymph node by immunohistochemistry and by ELISA using a polyclonal, affinity purified anti-SMCP antibody. The toluidine blue and SMCP-positive cell counts were closely correlated for all tissues examined (r<SUP>2</SUP> = 0.96, P<0.001), with the exception of skin and liver. On the basis of reactivity to the anti-SMCP antibody, two populations of ovine mast cells were identified. SMCP-positive cells (analogous to the gastronintenstinal or mucosal mast cell [MMC] subset) were present in all tissues examined whereas SMCP-negative cells were present in skin (the putative ovine connective tissue mast cell [CTMC] subset) and comprised-98% of the ovine dermal mast cell population. The functional heterogeneity of the ovine dermal mast cell population was investigated in cutaneous challenge studies using the secretagogues calcium ionophore A23187 (A23187), substance P (sP) and compound 48/80 (48/80), which are known to activate CTMC subsets in other species. Although only A23187 and sP evoked an immediate weal response (P<0.05; Mann-Whitney U test [MW]), all three agents evoked dermal neutrophil influx (P<0.05; MW) with extensive mast cell degranulation (P<0.05; MW), thus identifying these agents as putative ovine dermal mast cell secretagogues. As SMCP may be released into the dermis following degranulation, its effect in ovine skin <I>in vivo</I> was investigated. SMCP (36μg - 36ng/50μl) evoked a dose-dependent immediate cutaneous response characterised by weal formation (maximal by three hours after injection (P<0.05; MW)) accompanied by dermal neutrophil influx (P<0.05; MW) and concomitant mast cell degranulation (P<0.05; MW). There was no subsequent delayed component to this response (24 to 72 hours).

The role of the Merkel cell-neurite complex in the transduction process in slowly adapting type 1 (SA1) cutaneous mechanoreceptors is unresolved. One hypothesis, based largely on the ultrastructure of Merkel cell-neurite complexes, suggests that chemosynaptic transmission occurs between the Merkel cell and its subjacent nerve terminal. This idea was investigated by mechanically stimulating SA1 mechanoreceptors exposed to pharmacologically active agents in several experimental preparations; an <i>in vivo</i> rat model, an <i>in vivo</i> feline isolated hind limb perfusion model and a novel isolated rat skin-nerve preparation. After exposure to the calcium channel blockers Mg2+ , Cd2+ and verapamil hydrochloride there was a dose dependent decline in the response of the SA1 mechanoreceptors to mechanical stimulation. Given that an influx of Ca2+ ions is required for stimulus-secretion coupling, these results support the hypothesis of chemosynaptic transmission. Immunohistochemical studies have shown that a met-enkephalin-like substance is associated with the dense cored vesicles in rodent Merkel cells. The idea that met-enkephalin was the transmitter substance in rat Merkel cell-neurite complexes was tested using the opiate antagonist naloxone and the agonist met-enkephalin in the isolated rat skin-nerve preparation. Met-enkephalin caused a dose dependent decline in the response of the SA1 mechanoreceptors to mechanical stimulation. This effect was antagonised by naloxone, indicating the presence of functional opioid receptors in the SA1 sensory receptor. However, this result indicates that met-enkephalin is not the excitatory transmitter substance in rat Merkel cell-neurite complexes, though it does have a modulatory role. The results presented in this thesis support the hypothesis that chemosynaptic transmission is involved in the transduction process in the Merkel cell-neurite complex.

No description available.

No description available.