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The origin of substance P-containing fibres in the inferior mesenteric ganglion of the guinea-pig was studied by combining retrograde tracing and indirect immunofluorescence techniques. 'True Blue' or propidium iodide was injected into the inferior mesenteric ganglion. Four days later the animals were perfused with formalin and the dorsal root ganglia L2 and L3 were dissected out. Sections of the spinal ganglia were cut on a cryostat and analysed in a fluorescence microscope with appropriate filter combinations and subsequently processed for indirect immunofluorescence using antiserum to substance P. Several ganglion cells containing both dye (True Blue or propidium iodide) and substance P-like immunoreactivity were observed, strongly supporting the view that at least some of the substance P fibres in the inferior mesenteric ganglion are of sensory nature. Taken together with physiological results from other workers, the present findings suggest that substance P can be released from peripheral, sensory nerve endings, inducing changes in the membrane potential of sympathetic neurons.

The effects of increased extracellular calcium levels on the responses of the motor nerve terminal to agents that increased intracellular levels of cyclic AMP was studied on the in vivo cat soleus muscle preparation. The neural and muscle responses to intra-arterially administered NaF, an activator of adenylate cyclase, and dbcAMP progressively increased as blood calcium levels rose. These results provide additional support for the hypothesis of an interaction between calcium and cyclic AMP in motor nerve endings.

The distribution of low-affinity sodium-sensitive binding sites of [3H]mazindol were studied in rat hypothalamic nuclei. Using microdissection methods, it was demonstrated that the highest level of [3H]mazindol binding is localized to the paraventricular nucleus (PVN) and the lowest binding is observed in the lateral hypothalamus. Following food deprivation, a significant decrease in [3H]mazindol binding in the PVN and ventromedial hypothalamus (VHM) were observed. Refeeding food-deprived rats resulted in restoration of the level of binding in the PVN, and this was correlated with changes in blood glucose levels. Thus, changes in the binding of [3H]mazindol in the PVN may reflect local changes in glucose levels. In related studies, the involvement of the PVN in the regulation of food deprivation or 2-deoxyglucose (2-DG)-induced food intake was studied. Application of amphetamine (20 micrograms) into the PVN had no effect on food deprivation induced feeding, but significantly inhibited 2-DG induced (glucoprivic) feeding. The PVN may play an important role in the glucostatic regulation of feeding and in mediating the anorectic action of amphetamine and related anorectic drugs on glucoprivic feeding.

Interactions between neuronal responses mediated by dynorphin A1-8 and GABA were investigated in the substantia nigra zona reticulata. Extracellular recordings and microiontophoresis were performed using five-barrel microelectrodes in chloral hydrate-anesthetized male rats. When iontophoresed alone, dynorphin A1-Q significantly inhibited the firing of 22% of the neurons tested. The inhibition was rapid in onset and recovery and was dose-dependent. In another 22% of the cells, iontophoretic dynorphin produced an increase in the baseline firing rate which was slow in both onset and offset; the remaining 56% were unaffected by dynorphin. When GABA and dynorphin A1-8 were applied in conjunction, the inhibitory action of GABA was attenuated in 61% of the cells; whereas, when dynorphin and GABA were ejected simultaneously onto the cells that were inhibited by dynorphin A1-8, the respective inhibitory effects of dynorphin and GABA appeared to be additive. The kappa antagonist, MR-2266, failed to block the ability of dynorphin A1-8 to attenuate the action of GABA. In addition, the non-opiate peptide des-tyr-dynorphin A2-17, produced effects similar to that of dynorphin A1-8. The role of dynorphin in the basal ganglia and its interaction with the other major transmitter in the substantia nigra zona reticulata, GABA, is discussed.

The effects of verapamil on the force of contraction of soleus and gastrocnemius muscles of the cat were examined in vivo. The rapid intra-arterial administration of verapamil (100-800 micrograms/kg) produced a dose-dependent increase in the contractile force of soleus and gastrocnemius muscles stimulated supramaximally via their nerves. Verapamil also potentiated twitch tension in d-tubocurarine-treated, directly stimulated soleus preparations. This agent had no effect, however, on the contractile force of 14- to 16-day chronically denervated, directly stimulated soleus muscle. Verapamil (400 microgram/kg, i.a.) also produced a significant increase in muscle action potential duration while having no effect on amplitudes, rise times or resting membrane potential. It is concluded that verapamil acts directly on innervated skeletal muscle to increase muscle force and it is suggested that the probable site of action is at the muscle membrane.

The distribution of substance P and leucine enkephalin in mid- and fore-brain areas of the rat was studied using a radioimmunocytochemical method. The secondary antibody was labeled with 125I and the sections apposed to LKB Ultrofilm or emulsion-dipped. In alternate sections an extensive distribution of substance P and enkephalin immunoreactive material was seen in frontal, cingulate, retrosplenial, and entorhinal cortices. Substance P and enkephalin exhibited a remarkable overlap in many of these cortical areas as well as in the nucleus accumbens, caudate, portions of the hypothalamus, amygdala, thalamus and central gray. Differences in distribution were seen in the retrosplenial cortex, septum, ventromedial hypothalamus, hippocampus, the substantia nigra and the superior colliculus. The results provide a detailed immunohistochemical demonstration of the laminar patterns of substance P and enkephalin in the cortex of the rat. The results are discussed in terms of the interaction of substance P and enkephalin. The matches and mismatches of immunoreactive substance P and enkephalin and the locations of their receptors are also examined.

The indirect immunofluorescence technique was used to demonstrate the coexistence of somatostatin together with avian pancreatic polypeptide-like immunoreactivity within certain neurons of the rat forebrain. Numerous neurons containing these peptides were observed in the neocortex, hippocampus, olfactory tubercle, striatum, nucleus accumbens and lateral septum. In studies of serial sections stained alternately for these two peptides, and in restaining experiments, It could be determined that in many neurons in these areas these two peptides coexisted. In other brain areas such as the anterior periventricular hypothalamus, somatostatin cells were never found to contain avian pancreatic polypeptide-like immunoreactivity. Also, within the pancreas these two peptides were never found to coexist in the same cells. The findings represent a further example of the coexistence of more than one neuropeptide within a single neuron.

Dopaminergic neurons of the substantia nigra pars compacta are excited by nicotine and acetylcholine, and possess both high-affinity nicotine binding sites and intense acetylcholinesterase activity, consistent with a cholinoceptive role. A probable source of cholinergic afferents is the pedunculopontine nucleus, which forms part of a prominent group of cholinergic perikarya located caudal to the substantia nigra in the tegmentum. Although pedunculopontine efferents, many of them cholinergic, project to the substantia nigra pars compacta, it has not been established whether they terminate in this structure. In the first experiment, which combined retrograde tracing with immunohistochemical visualization of cholinergic neurons, cholinergic cells in and around the pedunculopontine nucleus were found to send projections to the substantia nigra. This projection was almost completely ipsilateral. Subsequent experiments employed anaesthetized rats; kainate was microinfused into tegmental sites in order to stimulate local cholinergic perikarya, and concurrently, extracellular recordings were made of single dopaminergic neurons in the substantia nigra. Consistent with our anatomical findings, unilateral microinfusion of kainic acid in or near the pedunculopontine nucleus increased the firing rate of dopaminergic neurons situated remotely in the ipsilateral substantia nigra. The kainate-induced excitation of nigral dopaminergic neurons was dose-related and was prevented by intravenous administration of the centrally-acting nicotinic cholinergic antagonist mecamylamine. These results suggest that cholinergic perikarya in the vicinity of the pedunculopontine tegmental nucleus innervate dopaminergic neurons in the substantia nigra pars compacta via nicotinic receptors.