C.H. Vanderwolf

Near-total loss of ‘learning’ and ‘memory’ as a result of combined cholinergic and serotonergic blockade in the rat

Previous work has indicated that activation of the cerebral cortex (i.e. elicitation of low-voltage fast activity in the neocortex and rhythmical slow activity in the hippocampus) is dependent on corticipetal cholinergic and serotonergic projections. Treatment with a combination of p-chlorophenylalanine (an inhibitor of the synthesis of serotonin) plus atropine or scopolamine (muscarinic cholinergic antagonists) can suppress all cerebral activation. In this paper, the behavioral effects of single or combined blockade of cholinergic and serotonergic neurotransmission were studied using a shock avoidance test, an open field test, a swim-to-platform test, a hypothalamic self-stimulation test and a test of grooming behavior. The results show that blockade of cerebral activation produces a condition analogous to global dementia but does not produce sleep or coma. The hypothesis that cholinergic and serotonergic neurotransmission provides a basis for learning and memory is discussed critically.

Components of weasel and fox odors elicit fast wave bursts in the dentate gyrus of rats

Previous work has shown that olfactory stimulation with toluene, xylene and other organic solvents elicits a burst of 15-30 Hz fast waves in the dentate gyrus of male rats. Other odorous substances including food, rat vaginal secretions and rat excrement were much less effective. In the present study we confirm that water, ammonia, rat food, rat cage litter and the presence of a conspecific did not reliably elicit dentate fast wave responses but that toluene and methyl methacrylate were very effective. We further show that both 2-propylthietane, which is a component of weasel gland secretions, and trimethyl thiazoline, an ingredient of fox droppings, elicited dentate fast waves as effectively as toluene and methyl methacrylate and that putrescine, cadaverine, butyric acid, caproic acid and indole were ineffective by comparison. Similarly, orally administered solutions of acetic acid, quinine, sodium chloride and sucrose were ineffective. These findings raise the possibility that the dentate fast waves elicited in the rat may be part of a cerebral response to the odor of a potential predator, such as the weasel or fox.

Role of the neocortex in the water maze task in the rat: a detailed behavioral and Golgi-Cox analysis

The role of the neocortex in acquisition of the water maze task was investigated with both detailed behavioral and anatomical analyses. The neocortical areas examined were: (1). primary visual and posterior parietal areas Oc1 and Oc2M, (2). parietal area Par1, and (3). prefrontal areas Cg1, Cg3, IL, and part of Fr2 of Zilles, 1985. In Experiment 1, the effects of lesions in these areas were examined separately in different groups of naive male hooded rats. Additional rats were given water maze strategy pretraining before receiving a lesion. Strategy pretraining was used to separate water maze strategy learning from spatial learning to evaluate the contribution of the neocortical areas to these two components of task acquisition. All groups of naive lesioned rats were impaired in the task. In contrast, corresponding groups of pretrained lesioned rats performed as well as controls on all behavioral measures. In Experiment 2, the same neocortical areas lesioned in Experiment 1 were examined with the Golgi-Cox method to determine whether water maze training was associated with changes in the dendritic arborization of neocortical pyramidal cells. Contrary to expectations, no anatomical changes that could be ascribed to the behavioral training were seen in the areas and cortical layers examined. The data suggest that (1). these areas contribute to water maze strategy learning in naive rats, (2). none of the areas are crucially required for spatial learning provided rats are familiar with the general behavioral strategies required in the task before the lesion is made, and (3). any changes in neuronal morphology that occur as a consequence of the training may be subtle and widely distributed.

Transcallosal evoked potentials in relation to behavior in the rat: Effects of atropine, p-chlorophenylalanine, reserpine, scopolamine and trifluoperazine

Single pulse electrical stimulation of the sensorimotor cortex in waking rats produced an evoked response in the contralateral sensorimotor cortex. The slow wave response consisted of: (1) an early component that was negative at the pial surface and in layer V, and was associated with multiunit discharge; and (2) a late component that was mainly negative at the surface, positive in layer V, and was associated with multiunit suppression. Previous research suggests that the early component represents summed excitatory postsynaptic potentials; the late component summed inhibitory postsynaptic potentials. Both components could be elicited by direct stimulation of the corpus callosum and both were abolished by midline callosal section. The amplitude and duration of the late component varied with concurrent motor activity in a striking manner. It was large during waking immobility and also during face-washing, licking the paws, chewing food and drinking water, but was much reduced or absent during head movements, walking and changes in posture. Only minor changes were associated with the transition from waking immobility to slow wave sleep. A series of pharmacological experiments indicated that the behavior-related variation in the late component of the transcallosal evoked response was dependent on both cholinergic and serotonergic transmission.

Are emotion and motivation localized in the limbic system and nucleus accumbens

Groups of control rats without surgery or groups of rats prepared with surgical lesions of the septal nuclei, amygdala, cingulate cortex, accumbens nucleus, section of the fornix, or sham surgical operations, were tested in a simple autonomic conditioning situation (conditioned defecation). Control rats and rats with lesions of the accumbens nucleus were also tested in a straight alley maze under varying conditions of water deprivation. In general, the lesions had little effect except that amygdaloid damage impaired acquisition of conditioned defecation. The theory that emotion and motivation can be localized in the limbic system and nucleus accumbens is discussed critically.

A critique of Rushton on race, brain size and intelligence

Abstract A critique is presented of that portion of Rushtons theory on the role of race in heritable behavior that deals with race, brain size, and intelligence. The critique is based on an examination of all of the evidence that Rushton cited, as well as additional evidence. We find that the methods employed and data obtained by the cited studies are seriously flawed. Additional studies not cited by Rushton suggest a different ordering of brain size than that concluded by him. Strained logic, a failure to take into account alternative explanations, and contrary data seriously limit Rushtons effort. We conclude that there is no credible evidence to support Rushtons claimed relation between race, brain size, and intelligence.

Anti-muscarinic drug effects in a swim-to-platform test: dose-response relations

Rats were given subcutaneous or intraperitoneal injections of scopolamine, intraperitoneal injections of atropine, or control injections, and trained on a simple swim-to-platform task. Errors were proportional to dose for both drugs over a wide range. No difference was found in the effects of intraperitoneal or subcutaneous scopolamine but scopolamine was 25 times more potent than atropine. The potency of both drugs in impairing swim-to-platform behavior was similar to their potency in abolishing the cholinergic component of neocortical low voltage fast activity. The electrocortical effect of anticholinergic drugs may be a major factor in the behavioral impairment they produce.

Animal models of human amnesia and dementia : hippocampal and amygdala ablation compared with serotonergic and cholinergic blockade in the rat

The behavioral effects of combined bilateral hippocampal and amygdala ablation (previously proposed as a model of human global amnesia) were compared to those seen with central blockade of the ascending cholinergic and serotonergic projections (a possible model of human global dementia) in male hooded rats. Rats were prepared with: (a) bilateral surgical lesions of the hippocampus and amygdala; (b) pharmacological blockade of central cholinergic and serotonergic function by systemic injections of scopolamine and p-chlorophenylalanine; and (c) neurotoxic lesions of the rostrally projecting serotonergic nuclei in the brainstem using intracerebral injections of 5,7-dihydroxytryptamine, later combined with scopolamine. The behavioral tests used were: an open field test, a swim-to-platform test, and a Lashley III maze. In all 3 tests, rats with either the neurotoxin lesions plus scopolamine or p-chlorophenylalanine plus scopolamine treatment showed greater impairments in comparison with controls than did the combined lesion group. These results indicate that simultaneous blockade of central serotonergic and cholinergic transmission has a greater effect on some aspects of the organization of behavior than large surgical lesions of the hippocampus and amygdala.

Effects of water temperature and core temperature on rat's performance in a swim-to-platform test

Hypothermic rats are grossly deficient in acquisition in a simple swim-to-platform task if the core temperature is 28-30 degrees C or lower. However, the ability to swim is relatively well preserved. Normothermic rats perform slightly better in cold water than in warm water.

Combined video and computer analysis of the relation between the hemispheric response and behavior

Abstract A method is described which allows a double-blind analysis of neural activity and concurrent behavior in an objective and rigorous way. Applying the method to the study of the interhemispheric evoked potential in the rat revealed a clear correlation between the neural response and behavior.