Alex M. Babcock

Locomotor activity in the ischemic gerbil

Previous studies have shown that within 24 h after ischemic insult, gerbils exhibit an increase in locomotor activity. Because activity gradually diminishes to normal levels with repeated testing, it has been argued that this behavior represents a reversible or transient effect of ischemia. The present study challenged this notion by testing ischemic gerbils at a time when increased activity is not observed with repeated testing. Ischemic (5-min bilateral carotid occlusion) and sham gerbils were tested for 14 consecutive days after reperfusion in an open-field apparatus (n = 6/condition). As previously reported, ischemic gerbils exhibited a significant increase in activity (days 1 and 2) which returned to control levels with repeated testing (days 13 and 14). A second group of ischemic and sham gerbils (n = 6/condition) were tested only on days 13 and 14 after reperfusion. In contrast to those tested repeatedly, these ischemic gerbils displayed increased locomotor activity as compared with sham controls. In addition, gerbils in the repeated testing conditions were evaluated in a semi-novel testing environment on days 15 and 16 after surgery. The locomotor activity of ischemic gerbils significantly increased in response to the semi-novel environment. These results suggest that the effects of ischemia on locomotor activity are not limited to a brief period after occlusion and may represent a permanent deficit. In addition, as previously suggested, this behavior may represent a deficit in habituation or spatial mapping rather than motor hyperactivity.

Cholecystokinin stimulates and inhibits lordosis behavior in female rats

Recently, IP CCK-8 has been shown to inhibit lordosis in sexually experienced, estradiol benzoate (EB) and progesterone (P) primed rats. However, receptivity is influenced by prior sexual experience and/or exposure to sex steroids, as well as the steroid dosage administered before testing. Thus, we examined the effect of CCK-8 (3 micrograms/kg; IP) on lordosis in rats with different degrees of receptivity. Three weeks after ovariectomy, females were treated with EB followed 48 hr later with P, or with EB alone. CCK-8 significantly facilitated lordosis in rats given 5 micrograms EB. Following a 5 week nonexperimental period, animals were more receptive and CCK-8 significantly inhibited lordosis in the 5 or 10 micrograms EB groups. In a separate experiment, rats were ovariectomized, adrenalectomized, and treated with EB alone. As in the first experiment, CCK-8 facilitated and inhibited lordosis. CCK-8s effects were highly dependent on the females receptivity, facilitating lordosis when receptivity was low and inhibiting lordosis when receptivity was high (but not maximal). In conclusion, IP CCK-8 modulates lordosis behavior independent of P, but its effects depend on the females degree of receptivity.

Injections of cholecystokinin into the ventromedial hypothalamic nucleus inhibit lordosis behavior in the rat

In the central nervous system, the ventromedial nucleus of the hypothalamus (VMH) is a primary locus for the induction of lordosis behavior by estrogen. Tissue levels of cholecystokinin and its binding sites in the VMH are modulated by estrogen, suggesting a role for cholecystokinin in the regulation of lordosis behavior. The effects of exogenous cholecystokinin octapeptide (CCK-8) were examined by injecting CCK-8 into the VMH and measuring the frequency of lordotic responses. CCK-8 inhibited the frequency of lordotic responses in a dose-related fashion when the control rats had lordosis quotients of 60 and above. This inhibition is in agreement with previously reported results after peripheral injection of CCK-8, and is consistent with the hypothesis that CCK-8 in the VMH in involved in the regulation of lordosis behavior in the estrogen-primed rat.

Effects of cholecystokinin on male copulatory behavior and lordosis behavior in male rats

Because the distribution of cholecystokinin octapeptide (CCK-8) within the hypothalamus and limbic system overlaps with steroid concentrating regions, and because these areas are involved in the regulation of reproductive behaviors, we examined the effects of exogenous CCK-8 on male copulatory behavior and lordosis behavior in the male rat. Peripheral administration of a dose of CCK-8 that altered lordosis behavior in females (3 micrograms/kg, intraperitoneal) was ineffective in altering male copulatory behavior in males, either before or after gonadectomy, and was also ineffective in altering lordosis behavior after estrogen priming. In a separate experiment, CCK-8 injected into the lateral ventricle also did not affect male copulatory behavior, but lordosis behavior was increased dramatically after gonadectomy and estrogen priming. Although these results do not answer the question whether CCK-8 is acting to inhibit a neural system that normally suppresses lordosis behavior or is acting to stimulate a facilitatory circuit, these results do indicate the existence of an estrogen sensitive neural substrate in males on which CCK can act to facilitate lordosis behavior.

Neuropeptide Y attenuates satiety: evidence from a detailed analysis of patterns ingestion

Centrally injected neuropeptide Y (NPY) is a potent stimulant of ingestive behavior capable of augmenting both food and fluid intake in fully satiated animals. To gain further insight into NPYs mechanism of action, we recorded patterns of licking behavior in rats drinking sweetened condensed milk solutions immediately after lateral ventricular injection of NPY (10 micrograms) or vehicle. In a separate study, we examined licking patterns after 23 h food deprivation (FD) that produced approximately the same total intake as NPY. Consistent with previous reports, we found NPY stimulated intake by increasing total ingestion time and total volume consumed during a 1-h test. Although NPY increased the number of bouts of licking and shortened pauses between bouts, it also decreased mean bout size, bout duration and within-bout lick rate (local rate). It had no significant effect on start latency or lick efficiency (licks/ml). Further analyses revealed that NPY attenuated satiety (reduced slope of lick-rate functions with session time) but had no significant effect on the beginning lick rate, a measure related to orosensory excitation. In contrast to NPY, FD increased both the beginning lick rate and individual bout size without changing either the mean number of bouts or the pause between bouts. In general, NPY stimulated an intermittent pattern of licking and delayed satiation whereas FD increased the initial rate of licking and the size of individual bouts without changing the basic licking pattern. The increase in initial lick rate suggests that FD, unlike NPY, enhances orosensory stimulation. These data compliment previous results showing that NPY increases the motivation to eat.(ABSTRACT TRUNCATED AT 250 WORDS)

Baclofen is neuroprotective and prevents loss of calcium/calmodulin-dependent protein kinase II immunoreactivity in the ischemic gerbil hippocampus

Excessive release of glutamate during transient cerebral ischemia initiates a cascade of events that leads to the delayed and selective death of neurons located in the hippocampus. Activity of calcium calmodulin kinase II (CaM kinase), a protein kinase critical to neuronal functioning, disappears following ischemia. The in vivo link between glutamate excitoxicity and alterations in CaM kinase activity has not been extensively studied. Baclofen, a selective γ‐aminobutyric acid (GABA)B receptor agonist, has been shown to inhibit glutamate release. The present study evaluated the neuroprotective efficacy of this compound and assessed early changes in hippocampal‐dependent behaviors and CaM kinase immunoreactivity following transient cerebral ischemia. Baclofen (50 mg/kg) prevented both the loss of hippocampal CA1 pyramidal cells and the reduction in hippocampal CaM kinase immunoreactivity observed in control animals following ischemic insult. Cerebral ischemia produced a significant increase in working memory errors; however, baclofen failed to attenuate this memory deficit. Results confirm that baclofen is neuroprotective and support a link between glutamate excitotoxicity and reductions in CaM kinase immunoreactivity.

Cholecystokinin and bombesin suppress operant responding for food reward

The effects of intraperitoneal injections of cholecystokinin (CCK) and bombesin (BBS) on food-rewarded operant responding were investigated. Response rates were significantly suppressed following administrations of CCK (0.7, 1.4, and 2.9 micrograms/kg). The effects appeared to be dose dependent. Responding was also suppressed following injections of BBS (6 and 16 micrograms/kg). These results confirm and extend previous findings concerning the possible function of these peptides.

Importance of Preoperative Training and Maze Difficulty in Task Performance Following Hippocampal Damage in the Gerbil

A series of experiments was conducted to evaluate the effects of preoperative training on three variations of a spatial working memory task following ischemic damage to the hippocampus. A discrete trial, pair-run procedure in a standard T-maze apparatus was used. Ischemic and sham gerbils were tested on a Win/Shift, Win/Shift Delay (10 s), or Win/Stay task with or without preoperative training. Gerbils tested on the Win/Shift or Win/Shift Delay tasks did not exhibit improved performance as a result of pretraining. Ischemic gerbils in Win/Shift tasks exhibited working memory impairment with or without preoperative training. In contrast, pretraining was found to significantly improve the performance of gerbils tested in the Win/Stay task. Choice accuracy of pretrained ischemic gerbils was not significantly different from controls. These data suggest that preoperative training can influence performance, however the difficulty of the task and/or the amount of pretraining are important variables. The tendency for rodents to alternate makes the Win/Shift task ideal when extensive training or testing is not possible.

Neurotensin-induced hypothermia prevents hippocampal neuronal damage and increased locomotor activity in ischemic gerbils

Hypothermia induced by surface cooling has shown to protect vulnerable regions of the brain during an ischemic insult. This study evaluated the neuroprotective efficacy of neurotensin, a potent hypothermic agent, using a 5-min carotid occlusion procedure in the gerbil. In Experiment 1, the dose-response and time course of neurotensin-induced hypothermia were evaluated (n = 5/dose). Central infusion of 10, 20, and 30 micrograms neurotensin were found to significantly decrease core body temperature of conscious gerbils within 30 min of administration. In Experiment 2, gerbils pretreated with 30 micrograms neurotensin were permitted to become hypothermic or were maintained at 37 degrees-38 degrees C (rectal) during ischemic insult. Other gerbils were pretreated with peptide vehicle prior to ischemic insult (at 37 degrees -38 degrees C) or underwent a sham procedure (n = 6/condition). At 24 h after surgery, gerbils were tested for increased locomotor activity in an open-field apparatus. Gerbils pretreated with peptide vehicle or neurotensin and maintained at 37 degrees-38 degrees C during ischemia had significantly higher activity levels compared to the other treated groups. In contrast, gerbils made hypothermic with neurotensin exhibited activity levels similar to sham gerbils. Histological assessment revealed that neurotensin-induced hypothermia protected the CA1 region from ischemic damage.

Transient cerebral ischemia decreases calcium/ calmodulin-dependent protein kinase II immunoreactivity, but not mRNA levels in the gerbil hippocampus

During transient cerebral ischemia, intracellular calcium increases initiating a cascade of events which leads to the delayed death of neurons located in the hippocampus. Coupled to this calcium disturbance is the rapid decrease of calcium/calmodulin kinase II (CaM kinase) activity, a protein kinase critical to neuronal functioning. The present study correlated the increased locomotor activity following ischemic insult with alterations in CaM kinase mRNA levels and immunocytochemical labeling of alpha and beta CaM kinase subunits in the hippocampus. The protective effect of hypothermia was also compared with CaM kinase mRNA levels and immunoreactivity. Levels of CaM kinase message for either alpha or beta subunits was not altered in ischemic gerbils compared to sham or hypothermic ischemic conditions. Immunoreactivity for both the alpha and beta subunits was markedly reduced in the vulnerable CA1 region of ischemic animals compared to sham controls. Gerbils that underwent the ischemic insult while hypothermic showed no decrement in staining. CaM kinase-like immunoreactivity in the ischemia-resistant CA3 sector was not altered following ischemia. These data suggest that the loss of hippocampal CaM kinase immunoreactivity observed at 24 h following ischemia is not associated with a reduction in CaM kinase mRNA levels and support the notion that the rapid decline in CaM kinase activity following ischemic insult is a result of a posttranslational modification and/or translocation of the enzyme.