SUMMARY1. Membrane hyperpolarization and decreased excitability produced by galanin were investigated in vitro on parasympathetic postganglionic neurones in the cardiac ganglion of the mudpuppy, Necturus maculosus.2. Galanin produced a slowly developing hyperpolarization which, in 2-5 mM-KCl, reversed at -105-4 + 2-7 mV. The reversal potential was shifted by 38-7 + 4-9 mV following a fourfold elevation of the extracellular potassium concentration.3. Galanin inhibited action potential firing in spontaneously active neurones and decreased the number of spikes in a train produced by long (500-680 ms) depolarizing current pulses. Both effects were independent of the galanin-induced hyperpolarization.4. Galanin increased the threshold for spike generation, prolonged the spike hyperpolarizing after-potential and decreased the maximum rate of rise, amplitude and maximum rate of fall of the sodium spike. These effects occurred independently of the galanin-induced hyperpolarization.5. Galanin decreased the amplitude and duration of TTX-insensitive spikes initiated in cells maintained in a solution containing 9 mM-calcium, 20 mM-TEA and 1-5 uM-TTX.6. These results suggest that a galanin-like peptide may act as an inhibitory transmitter in the mudpuppy cardiac ganglion.

A correlated biochemical and histochemical study was undertaken to identify and quantify the presence of different biogenic amines and a substance P-like peptide within the parasympathetic cardiac ganglion of the mudpuppy (Necturus maculosus). Tissue extracts of the cardiac septum containing the parasympathetic cardiac ganglia from control animals were found, by high-pressure liquid chromatography, to contain significant amounts of norepinephrine (NE), epinephrine (E), dopamine (DA), and 5-HT. To allow neural elements of extraganglionic origin to degenerate, ganglia were explanted and maintained in organ culture for 8 d. Extracts from these explanted preparations had no detectable level of E, and NE was reduced, whereas DA and 5-HT levels were similar to those of control preparations. The results indicated that some of the neurons intrinsic to the cardiac septum contain DA and 5-HT and that most (greater than 70%) of the E and NE found in this tissue is of extrinsic origin. Histochemistry of control and explanted preparations showed 5-HT-immunoreactive and catecholamine-containing intrinsic neurons. A substance P-like peptide was identified by radioimmune assay in septal extracts. The peptide content diminished by one-third to one-fifth in preparations maintained in organ culture for 8-14 d, suggesting that a significant amount of the substance P-like peptide is derived from extraganglionic sources. Immunocytochemical studies demonstrated the presence of numerous long substance P-immunoreactive fibers coursing across the septum, branching over cardiac muscle fibers, and forming pericellular networks around individual parasympathetic ganglion cells and clusters of ganglion cells. In addition, numerous small intrinsic neurons exhibited immunoreactivity for substance P. Comparison of the substance P-staining patterns in control and explanted ganglia suggests that the majority of the long substance P-immunoreactive fibers innervating the mudpuppy cardiac ganglion cells are not parasympathetic preganglionic fibers. Rather, it is hypothesized that these fibers are processes of primary sensory fibers. The present observations indicate that the mudpuppy cardiac ganglion exhibits a complex organization similar to that of mammalian sympathetic and enteric ganglia.

The dystonic rat (dt) is an autosomal recessive mutant displaying a complex motor syndrome that includes sustained axial twisting movements. The syndrome is correlated with increased glutamic acid decarboxylase activity in the deep cerebellar nuclei and increased cerebellar norepinephrine levels in comparison with phenotypically normal littermates. Biochemical, behavioral, and anatomical techniques were used to investigate the possibility that the abnormalities noted in the cerebellum of the dt rat were indicative of altered function of the major projection neurons of the cerebellar cortex, the Purkinje cells. Phenotypically normal rats showed tremor in response to harmaline, a drug that acts on the inferior olive to produce bursting in the climbing fiber pathway. Dystonic rats were insensitive to the effects of harmaline but did respond to oxotremorine. Levels of the cyclic nucleotide 3',5'-cyclic guanosine monophosphate, a biochemical marker for Purkinje cells, increased in response to harmaline in normal rats but were significantly lower in dystonic rats under both basal and harmaline-stimulated conditions. Purkinje cell soma size was reduced in the dystonic rats but no other morphological correlates of the behavioral or biochemical deficits were noted. Taken together with other observations on this mutant, the results suggest an impairment in the cerebellum or in its connections with lower brainstem and spinal cord sites.