Stimulation of the subcallosal fornix excites neurones in the cat preoptic region which project to the medial basal hypothalamus and in the medial forebrain bundle

Influences from different areas of the cerebral cortex on preoptic neurons: morphological and electrophysiological data

Spatial organization of neurons in the prefrontal and cingulate cortex, cortex of the piriform lobe and the hippocampus which project axons to the preoptic region, has been studied in cats using horseradish peroxidase tracing. Cortical areas were selected taking into consideration their phylogenetical distinctions. The prefrontal cortex was found to send a major portion of fibres to the preoptic region, while the density of units forming such connections was maximal in the cingulate cortex. Field potentials and neuronal reactions of the medial and lateral divisions of the preoptic region and the adjacent hypothalamic zones were studied in ketamine-anaesthetized cats. The most pronounced field potentials were recorded in the preoptic region upon stimulation of the cortex of the piriform lobe and cingulate cortex. There was a close correlation between the responses of single neurons and components of the field potentials. The majority of neurons responding to cortical stimuli were located mainly in the lateral preoptic region, where the larger amount of primary excitatory reactions were recorded. The medial preoptic region contained a smaller number of responsive neurons prevailingly generating the primary inhibitory reactions. For the lateral preoptic region the inhibition/excitation ratio was 0.6:1 at all cortical stimulations, but for the medial region it was 5.8:1. In the preoptic division adjoining the bed nucleus of the stria terminalis, the primary inhibitory reactions considerably prevailed over the primary excitatory; on the other hand, in the supraoptic nucleus the primary excitatory reactions prevailed weakly (ratios of 4.9:1 and 0.7:1, respectively). The preoptic region was found to be a zone of wide convergence of cortical inputs to single cells, where three-quarters of neurons responded to the stimulation of two, three or even four cortical areas.

Responses in the diagonal band of Broca, adjacent septal nuclei and the islands of Calleja of cats to stimulation of the subcallosal fornix, medial basal hypothalamus and medial forebrain bundle

The projection of neurons in the septal nuclei and the insula magna of the islands of Callaja (IC) was explored together with their response to stimulation of the fornix. The septal nuclei all contained neurons projecting in the medial forebrain bundle (MFB). Only the diagonal band of Broca (DBB) and the lateral septal nucleus (LS) contained many neurons projecting toward the medial basal hypothalamus (MBH). The spatial distribution of neurons excited by stimulation of the fornix in the DBB was almost identical with the distribution of neurons projecting toward the MBH and there was considerable overlap (10/28 cells). In the medial septal nucleus the spatial distribution of neurons excited by stimulation of the fornix and neurons projecting in the MFB was similar and there was considerable overlap (6/21 cells). The connectivity of the IC resembled that of the MS but there was little overlap between the neurons excited by fornix stimulation and those projecting in the MFB (1/27 cells). In the LS there were almost equal numbers of neurons projecting in the MFB and toward the MBH but there was very little input from the fornix. Neurons were significantly more often excited by stimulation of the lateral fornix, carrying axons from the subiculum, than they were by medial stimulation exciting axons from Ammon's horn. Axons projecting toward the MBH or in the MFB had conduction velocities less than 1 m/s.