Mating elicited by spreading depression of electrical or electrical stimulation of the hippocampus and neocortex: a common cause

Rats do not experience cortical or hippocampal spreading depression as aversive

Cortical spreading depression (SD) may produce some symptoms of the aura of classical migraine but it is less probable that it can account for the headache. The aversiveness of SD was examined in unanesthetized rats. In Exp. 1, rats with implanted cortical cannulae were confined in the dark compartment of the step-through apparatus and repeated waves of SD were elicited in one hemisphere. After two such training sessions the rats did not evince passive avoidance of the compartment associated with cortical SD. In Exp. 2, thirsty rats with implanted hippocampal electrodes were trained to drink from two different spouts A and B. Hippocampal SD was elicited when the animal was drinking from spout A but not from spout B. Drinking was interrupted shortly after appearance of the SD wave and gradually recovered over the subsequent 10 min, but up to ten spout A-SD pairings did not change the animal's preference for spout A. It is concluded that cortical or hippocampal SD has no immediate or delayed aversive consequences.

Role of the hippocampus in the sex-dependent regulation of eating behavior: studies with kainic acid

Marked hyperphagia with an increase in the rate of body weight gain was noted in adult female rats 4 days after injections of 2 nmoles of kainic acid into the dorsal and ventral parts of hippocampus. The effect was still present 70 days later. At this time the increase in daily food intake and body weight gain amounted, respectively, to 39% and 93% over the control value. There was no change in water intake. The injection of kainic acid into only one part of the hippocampus--either dorsal or ventral--did not induce hyperphagia. Male rats with kainic acid lesion did not show changes in food intake or body weight gain as compared to vehicle-treated controls. In both sexes the degeneration of hippocampal perikarya induced by kainic acid was associated with a 50-60% decrease in glutamic acid decarboxylase activity and [3H]glutamate uptake, as well as with a small decrease in [3H]glutamate uptake in the hypothalamus, an area that receives glutamatergic fibers from the hippocampus. The results show that the hippocampus appears to play an important role in appetite motivation control by a mechanism which is sex-related.

Electroencephalographic spreading depression and concomitant behavioral changes induced by intrahippocampal injections of ACTH1-24 and D-Ala2-Met-enkephalinamide in the rat

ACTH1-24 (0.5 or 10 micrograms = 0.17 or 3.45 nmol) and D-Ala2-Met-enkephalinamide (DAME; 10 micrograms = 17.05 nmol) were injected unilaterally into the hippocampus of freely moving rats to examine their effects on EEG activity, DC potentials and behavior. In 85% of the rats DAME elicited spreading depression (SD) with epileptiform discharges preceding and following the wave of SD. The following behavioral changes were recorded. DAME- and KCl-induced SD were accompanied by an increase in locomotor activity and wet-dog shaking behavior, which occurred only during the period of SD. After a wave of SD induced by DAME a biphasic pattern of activity, consisting of an initial depression in locomotion followed by hyperactivity, appeared in 59% of the rats. ACTH1-24 elicited SD in 13% of the rats tested. Neither the dosage of ACTH1-24 nor the strain of rats influenced the occurrence of SD and the incidence of ACTH-induced grooming behavior. SD induced by KCl also resulted in excessive grooming comparable to that induced by ACTH1-24. In the case of KCl-induced SD, grooming began directly after the injection of KCl and was frequently interrupted by short periods of locomotion. ACTH-induced grooming had a later onset and episodes of stretching and yawning were observed. It can be concluded that the behavioral effects of the injection of DAME are unspecific responses to SD and seizure activity. However, ACTH-induced grooming is not solely a byproduct of SD, since it occurred also in the absence of SD.

Opiate induced feeding is not dependent on the hippocampus

It has been shown that spreading depression of the hippocampus can elicit feeding, and that several opioid peptides elicit spreading depression when injected into the hippocampus. To determine whether such depression is the primary mechanism by which opiates induce feeding, we tested the feeding effects of naloxone, an opiate antagonist, and butorphanol tartrate, a kappa-sigma agonist, on feeding in rats with and without hippocampal lesions. Naloxone tended to reduce intake approximately equally in the two groups. Similarly, the doses of butorphanol that increased intake in sham rats were equally effective in lesioned rats. It was concluded that the hippocampus is not the major structure mediating opiate-induced feeding.

Lateralized hunger: ipsilateral attenuation of cortical spreading depression-induced feeding after unilateral 6-OHDA injection into the substantia nigra

Unilateral injections of 6-hydroxydopamine into the substantia nigra in the rat significantly attenuated cortical spreading depression (CSD)-induced eating from the hemisphere ipsilateral but not contralateral to the lesion. The lateralized decrease in elicited feeding was correlated with postlesion body weight loss, striatal catecholamine depletion (dopamine, 94%; norepinephrine, 52%) and amphetamine-induced ipsilateral turning, and can be characterized as an inability of the lesioned nigrostriatal system to maintain the CSD-elicited response rather than a failure to induce it. The interhemispheric control procedure allows us to exclude various general sensory and motor deficits to account for the decrement of feeding, and to attribute the feeding deficit to a reduced nigrostriatal transmission. It is suggested that CSD-induced feeding is due to an activation of integrative sensorimotor systems (especially the nigrostriatal dopamine system), rather than to homeostatic imbalances.

Unilateral cortical spreading depression in the rat: effects on feeding, drinking and other behaviors

The effects of unilateral cortical spreading depression (CSD) on feeding, drinking and other behaviors were studied in rats. CSD waves were elicited by a microinjection of KC1 solution through an implanted cannula. The animal's behavior and slow potential changes (SPC) accompanying CSD were then simultaneously monitored for 20 min. Intensive face grooming was observed while the CSD wave-front propagated across the sensorimotor cortex. Animals commenced their first feeding or drinking shortly after the invasion of the negative SPC into the frontal cortex of Krieg's area 6 and 10 [14] had reached its maximum height. A two-way switching effect between the first feeding or drinking and quiescence (freezing) and a close relationship between their onsets were observed. The results are discussed specifically in relation to cortico-hypothalamic pathways.

Circling and consumatory behavior induced by striatal and neocortical spreading depression

Single waves of spreading depression (SD) were induced in freely moving Sprague Dawley rats by microinjection of KCl solution into either neocortex or caudate nucleus. DC recordings of slow potential changes (SPC) revealed that a wave of SD propagates from the neocortex to the caudate nucleus in only a very few cases (12.5% of trials, involving 4.3% of the SPC waves). This result contrasts with earlier reported higher incidences of neocortical-striatal transmission of SD, and suggests that such transmission may vary across rat strains. Invasion of the caudate nucleus by a wave of neocortical SD was accompanied by contralateral circling in 50% of the cases. Similarly, SD induced by injection of KCl into the striatum was accompanied by circling in 43% of trials. It was also found that neocortical SD-induced feeding generally occurred only upon recovery of neocortex from the slow potential negativity, and that invasion of the caudate nucleus by SD is not involved in the elicited feeding phenomenon.

Electrophysiological concomitants of eating induced from neocortex and hippocampus by electrical stimulation and injection of KC1 or norepinephrine

EEG and DC activity were recorded from the hippocampus and neocortex in freely moving rats during consummatory behavior elicited by electrical stimulation and application of KC1 or norepinephrine to these structures. Eating induced by KC1 application or electrical stimulation of the neocortex or hippocampus was accompanied by single or multiple waves of spreading depression (SD), i.e., by traveling slow potential change. An analysis of single vs. multiple cortical SD waves indicated that when multiple waves occurred, feeding was elicited by the first wave. Injection of norepinephrine into the hippocampus resulted in a significantly larger and qualitatively different feeding response compared to KC1 injections. No apparent changes in the EEG or DC activity occurred upon norepinephrine injections.

Pavlovian conditioning of eating induced by spreading depression in cortex, striatum and hippocampus of rats

A single wave of unilateral spreading depression in the cortex, hippocampus or caudate nucleus of rats elicits eating after 2-6 min. The present experiments provide evidence that such spreading depression-induced eating can be classically conditioned to a complex conditioned stimulus. A wave of spreading depression was triggered by injection of 0.5-2.0 mul of 25 percent KCl solution. In a first experiment successful conditioning was demonstrated in 20 rats, involving 7 cortical, 5 caudate and 8 hippocampal spreading depression sites. Four animals failed to show any conditioned eating. A control group of 8 animals, in which cortical spreading depression did not induce eating, showed no increase in eating in the presence of the CS after conditioning trials. A second experiment, which included pseudoconditioning and NaCl control groups, confirmed the results obtained in Experiment 1. Classical conditioning was successful in 11 animals, involving 6 cortical and 5 caudate spreading depression sites. Neither the pseudoconditioning (14 animals, involving 8 cortical and 6 caudate spreading depression sites) not the NaCl control group (8 animals, all with cortical sites), showed eating in the presence of the CS. In both experiments the conditioned eating underwent gradual extinction.