Interaction between negative inotropic effects of halothane and nifedipine in the isolated rat heart

Isobolographic analysis was used to assess quantitatively the combined direct negative inotropic effect of halothane and nifedipine as well as to define the type of interaction between these two agents. Experiments were performed on an isolated rat heart preparation. Developed left ventricular pressure and dP/dtmax were used as indices of inotropic action. It was found that the combination of halothane and nifedipine gives mostly additive direct negative inotropic effect. However, with a small level of myocardial depression (ED25), there was some deviation from the additive interaction toward an infra-additive effect (p less than 0.01), and with a high level of depression (ED75), some deviation toward a supra-additive effect (p less than 0.05).     

Immunochemical properties of junctional and extrajunctional acetylcholine receptor

Immunological assays were performed to compare two distinct forms of the nicotinic acetylcholine receptor (AChR): junctional (JR) and extrajunctional receptor (EJR). Antibodies from myasthenia gravis patients' sera inhibited the binding of [¹²⁵I]α-bungarotoxin (BGT), to EJR more effectively than binding to JR. Immunological differences between JR and EJR were confirmed by other assay methods. In all cases, EJR appeared to have antigenic determinants not found on JR. It was established that enzymatic removal of carbohydrates from EJR caused it to more closely resemble JR. Thus differences between JR and EJR may be due, in part, to carbohydrate residues found on EJR that are absent on JR. The extent of antibody binding to EJR was examined by gel filtration methods. Immunochemical studies of bands from SDS gels showed that antibodies are present in myasthenic serum which react with the 3 subunits (42, 53, 64 kdaltons) of AChR to varying degrees.     

Afferents to the trigeminal and facial motor nuclei in pigeon (Columba livia L.): Central connections of jaw motoneurons

Trigeminal and facial motor nuclei innervating the pigeon's jaw muscles were identified using a combination of microstimulation and EMG recording and HRP injections were made iontophoretically. The trigeminal motor nucleus receives an ipsilateral projection from sensory neurons in the trigeminal mesencephalic nucleus which forms the afferent limb of the monosynaptic stretch reflex of the jaw-closers. Both the trigeminal and facial motor nuclei receive bilateral projections from interneurons in the intertrigeminal area and the lateral (parvocellular) reticular formation of the pons and medulla. These neurons serve as premotor elements in the control of jaw movements, mediating ascending, descending and internuclear connections. The similarity of inputs to the trigeminal and facial nuclei may reflect their common function as jaw motoneurons in this species.     

Changes in the structure of synapses associated with learning

Two experiments were conducted to investigate the effects of training on a region of the chick brain known to be critically involved in imprinting, the intermediate and medial extent of the hyperstriatum ventrale (IMHV). In the first experiment, three groups of chicks were used: (i) dark-reared (n = 9), (ii) trained for 20 min (n = 17), and (iii) trained for 140 min (n = 7). Chicks were trained by exposing them when they were approximately 21 hr old to a flashing red light. Chicks were killed when they were approximately 30 hr old and blocks of tissue were removed from the right and left IMHV. Stereological techniques were used to measure from electron micrographs the numerical density of dendritic spine and shaft synapses and the length of the postsynaptic density of these synaptic junctions. There was a significant effect of training only in the left IMHV and on only one measure, the overall mean length of the postsynaptic density of spine synapses, SPL. This measure was significantly greater by 17.2% in chicks trained for 140 min than in dark-reared controls. There was no significant effect of training for 20 min. In the second experiment one group of chicks (n = 15) was exposed to a rotating red box for a total of 3 hr. Another group of chicks was dark-reared (n = 15). The chicks were killed when they were approximately 46 hr old. Samples from the hyperstriatum accessorium and IMHV of the right and left sides were analyzed. Training was associated with a significant change, an increase, only of SPL in the left IMHV.(ABSTRACT TRUNCATED AT 250 WORDS)