Multiregional cerebral blood flow changes induced by a cholinomimetic drug

Autoradiographic distribution of cerebral blood flow increases elicited by stimulation of the nucleus basalis magnocellularis in the unanesthetized rat

The nucleus basalis magnocellularis (NBM) of the rat, equivalent of Meynert's nucleus in the primate, is the origin of the main cholinergic innervation of the cerebral cortex. Stimulation of this area has been previously shown to induced marked, cholinergically mediated, blood flow increases in the frontal and parietal cortices. However, the complete distribution of the cerebrovascular effects of NBM stimulation within the whole brain has not been determined. In the present study, we used the [14C]iodoantipyrine autoradiographic method to measure local cerebral blood flow (CBF) in the unanesthetized rat, chronically implanted with a stimulation electrode. We performed unilateral electrical stimulation of the NBM in order to compare both the interhemispheric differences in blood flow and the differences with a group of sham-stimulated rats. Considerable blood flow increases were found in most neocortical areas, exceeding 400% in the frontal area, compared to the control group. Marked responses also appeared in discrete subcortical regions such as the zona incerta, some thalamic nuclei and structures of the extrapyramidal system. These responses were mostly ipsilateral to the stimulation. The significance and the distribution of these blood flow increases are related first, to anatomical and functional data on mainly the cholinergic projections from the NBM, but also non-cholinergic pathways connected with the NBM, second, to biochemical data on the basalocortical system, and third, to the limited ultrastructural data on the innervation of microvascular elements. This cerebrovascular study represents a step in the elucidation of the function of the basalocortical system and provides data which may be related to certain deficits of degenerative disorders such as Alzheimer's disease in which this system is consistently affected.

Cholinergic and vasoactive intestinal polypeptidergic innervation of the cerebral arteries

Acetylcholine and vasoactive intestinal polypeptide are not only two vasoactive agonists that predominantly induce a vasodilatation of the cerebral arteries, but also correspond to neurotransmitters that innervate the various anatomical segments of the cerebral vasculature. The distinct patterns of the cerebrovascular cholinergic and vasoactive intestinal polypeptidergic innervation, their neurochemistry, in vitro and in vivo pharmacology, as well as the putative pathophysiological implications of these neurotransmission systems are critically summarized on the basis of the most recently published literature.

Incongruence of regional cerebral blood flow increase and blood-brain barrier opening in rabbits at the onset of seizures induced by bicuculline, methoxypyridoxine, and kainic acid

Cerebral blood flow (CBF) was estimated using [3H]nicotine as tracer in 18 discrete rabbit brain regions at the onset of generalized seizures induced by bicuculline (BC), methoxypyridoxine (MP), and kainic acid (KA) and compared with the previously described regional pattern of blood-brain barrier (BBB) opening. Regional CBF increased 3- to 5-fold in BC-seizures, 2- to 3-fold (except in inferior colliculus) in MP-seizures, and twofold (no change in inferior colliculus) and periaqueductal gray) in KA-seizures. In general, CBF elevation was greater in areas with a high original CBF, and below average in regions with a low control value. However, under each condition a few areas did not follow this rule, viz. the occipital cortex and the basal part of the cerebellar vermis with low flow values in BC-seizures, the inferior colliculus with no change and the pallidum with a relatively high flow during MP-seizures, and limbic system areas with an exceptionally high flow during KA-seizures. The usual rise in arterial blood pressure (BP) at the onset of the seizure, necessary for the development of a BBB lesion, was absent in a few animals with BC- and MP-seizures, yet, their CBF was elevated in most regions although to a lesser extent. No relationship appeared to exist between the rise in CBF and the regional pattern of BBB opening. It is concluded that a loss of cerebral autoregulation is a prerequisite for BBB leakage, but the location of the opening is determined by neuronally derived factors which differ from convulsant to convulsant and from brain region to brain region.

Regional changes in cerebral blood flow and blood-brain barrier permeability during epileptiform seizures and in acute hypertension in rabbits

Interrelationship between the breakdown of the blood-brain barrier (BBB) to Evans blue and elevations in the regional cerebral blood flow (rCBF) was studied in rabbits subjected to adrenaline- or metaraminol-induced systemic hypertension and also in bicuculline-induced seizures. The rCBF was assessed in small samples from various regions of the brain with the use of [3H]nicotine, and the permeability of the BBB was evaluated with an Evans blue tracer. In acute hypertension, Evans blue extravasations were observed in the occipital cortex and sometimes in the superior colliculus, i.e., the regions which also showed the highest elevations in rCBF. The breakdown of the BBB in acute hypertension was clearly related to the rate of mean arterial blood pressure rise, being much less pronounced in the metaraminol group, which showed a much slower blood pressure elevation rate. In bicuculline-induced seizures, there was no evident correlation between the amplitude of rCBF elevations and Evans blue extravasations. Preservation of BBB integrity was observed in areas showing high elevations in the rCBF.