Cholinergic Projections to the Cortex of the Rat Brain

497 Cholinergic Projections to the Cortex of the Rat Brain H. WENK, V . BIGL and U. MEYER Institute of Anatomy, Humboldt University, Berlin and Paul Flechsig Brain Research Institute, Karl-Marx-University, Leipzig (G.D.R.) Some cortical brain areas of rats were investigated after stereotaxic lesions of several structures of the basal forebrain. Choline acetyltransferase (ChAT) activity was estimated biochemically, and acetylcholinesterase (AChE) by both quantitative histochemical and biochemical methods. After subtotal lesions of the medial septal nuclei, of the lateral preoptic area and of the substantia innominata the activities of AChE and ChAT in several cortical areas descreased t o moderate or low residual values indicating direct cholinergic projections t o paleo-, archiand neocortical parts of the brain. The cholinergic fibres t o paleocortical fields originate in the magnocellular nucleus of the lateral preoptic region. The archicortical hippocampal formation is supplied with cholinergic fibres arising in the medial septal nuclei. The medial limbic cortex receives its cholinergic innervation from the nucleus of the diagonal band of Broca while the neocortical fields are supplied with cholinergic fibres from scattered cell groups situated in the substantia innominata of the basal forebrain. These cells are possibly homologous t o the nucleus basalis of Meynert described principally in primates. The cells of origin occupy surprisingly small areas but because of the enormous preterminal ramifications they give rise t o a widespread monosynaptic and ipsilateral projection. This is remarkably similar to the arrangement of monoamine-containing neurones of the brain stem which provide the monoaminergic innervation of the forebrain. It seems, therefore, that the cortical neurones are subject t o two antagonistic influences, the cholinergic system and the monoaminergic system, which modulate and control the specific pattern of excitation in the cortex in a manner resembling the control function exerted by the sympathetic and parasympathetic system in the periphery.

Differences in Transmitter Release at Different Synapses of the Frog Sartorius Muscle L.N. ZEFIROV and A.L. ZEFIROV

Kazan State V.I. Ulyanov -Lenin University, Kazan (U.S.S.R.) Microelectrode recording from Mg2+-blocked end-plates was used t o analyse changes in quantum content ( m ) , probability of release ( p ) and available transmitter store ( n ) in frog sartorius muscle fibres during repetitive nerve stimulation at 10 Hz. Measurements were made o n the large fibres from the inner surface of the muscle, and on t h e small fibres o n the outer surface (Zefirov, A.L., et al., Bull. exp. Biol. Med., 1978, in press). In large fibres repetitive nerve stimulation caused first an increase, and then a sharp fall in m . In small fibres, the initial increase was smaller and the subsequent decrease was very gradual. In small fibres the maximum rate of transmitter release was about half that of large fibres. Evaluation of binomial release parameters (Bennett, M.R. and Florin, T., J . Physiol. (Lond.), 238, 93-107, 1974) showed that n was smaller in small fibres (range 5-60) than in large fibres (range 30- 160). During repetitive stimulation p increased steadily in large fibres, whereas it showed little change in small fibres. I t is suggested that these differences are related t o the different length of synaptic contact in large and small fibres(Kun0, M., et al., J. Physiol. (Lond.), 213,545-556, 1971).