Biomedical subjects
Publications and source records attributed to C R Gardner.
Preparations of longitudinal muscle respond to catecholamines if the ventral nerve cords are present, and also to 5-hydroxytryptamine. The response to 5HT is complex if the central nervous system is present, but muscle alone is probably inhibited.
The effects of the bile salts, sodium taurocholate and sodium glycocholate on the structural integrity of liposomes of different lipid compositions were studied. The bile salt concentrations were in the range encountered in the human intestine and the incubations were conducted at 37 degrees C. Two measures of liposome integrity were used: (a) changes in their light-scattering properties; and (b) release of entrapped potassium chromate. The results show that "fluid" liposomes, i.e., those prepared from phospholipids whose phase transition temperatures are below 37 degrees C, were totally disrupted in the presence of 10 mM bile salts at pH 7.4, and their entire contents were released. In the case of liposomes prepared from phospholipids with phase transition temperatures above 37 degrees C, the effect of the bile salts became less pronounced as the phase transition temperature increased. Nevertheless, a considerable proportion of the entrapped marker compound was released from liposomes with phase transition temperatures as high as 60 degrees C. The relevance of these results to the reported liposome-mediated gastrointestinal uptake of insulin is discussed.
Extracellular action potentials of spontaneously active units were studied in the basal septum and medial preoptic area (SPOA). Units responded in a similar way during stimulation of the amygdala, the reticular formation, the medial geniculate nucleus or the ventral hippocampus. The initial response was either short latency (6--35 msec) excitation or inhibition, the latter being predominant. A percentage of neurones (14.5%) did not respond. Only one response did not have an inhibitory component and responses have been further classified on the basis of the presence or absence of a postinhibitory excitation, and its rhythmicity. Single neurones tended to respond in a similar way to stimulation of different sites. Long inhibition (100--400 msec) is often preceded by excitation and may be a recurrent mechanism whilst short inhibition (18--55 msec) may be a 'direct' mechamism. Long inhibition may be mediated by GABA as it is weakened by intravenous bicuculline whilst short inhibition was not affected. A small amplitude barrage of action potentials at the onset of inhibition was suggested to be generated by inhibitory interneurones within the SPOA. Rhythmic postinhibitory excitatory responses suggest transmission of activity from stimulation sites to the SPOA via the thalamus. A hypothesis for local neuronal circuitry of spontaneously active neurones in the SPOA was proposed.
Extracellular microelectrode recordings were made from single neurones in the medial preoptic area and basal septum of normal female rats anaesthetised with urethane and the effects of stimulation of the ipsilateral amygdala (AMY) was tested. 1. Quiescent cells were excited with latencies between 4 and greater than 40 msec with the majority being between 10 and 27 msec. Variable latency, changing latency and recruitment were observed and suggest that many pathways are oligo- or polysynaptic. 2. A minority of spontaneously active units (20.6%) were excited with latencies between 5 and 36 msec. The predominant initial response was inhibition (67.1%). The remaining 12.3% of neurones did not respond. 3. A predominantly positive complex field potential was associated with excitation, particularly of quiescent neurones. 4. Inhibitory responses were classified according to duration (short: 20-60 msec; long: 100-400 msec). All responses contained an inhibitory component. Responses were further described on the basis of presence and rhythmicity of post-inhibitory excitation. 5. The majority of action potentials evoked from quiescent neurones were of small amplitude (80-150 mu/V) and occurred in small groups. These characteristics and their occurrence at the onset of inhibition are consistent with the view that all or a proportion of them may be generated by inhibitory interneurones. 6. Only minor differences were observed between response characteristics evoked by stimulation of the corticomedial or basolateral AMY indicating that differential effects of these regions on adenohypophysial hormone secretion are determined at the septopreoptic level.
The effects of leptazol and bicuculline on the efflux of endogenous acetylcholine (ACh) from the surface of the cerebral cortex have been related to EEG activity in urethane-anaesthetised rats. During seizure activity there was a calcium dependent increase in ACh efflux which was related to increase EEG activity and clonic muscle movements. ACh release and EEG activity were reduced during convulsive activity by trimethadione but not phenytoin. Phenobarbitone reduced convulsive EEG activity but left ACh release relatively unaffected. Blood pressure changes induced by convulsant and anticonvulsant drugs were not consistently related to EEG activity or ACh release. It is suggested that ACh efflux from the cerebral cortex is closely related to the activity of neurones within the cortex where it is released from nerve endings. Comparison of EEG changes induced by anticonvulsants and urethane during control and convulsant activity showed that only trimethadione produces anticonvulsant activity unaccompanied by general CNS depression.
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