Influence of progesterone on GAD65 and GAD67 mRNA expression in the dorsolateral striatum and prefrontal cortex of female rats repeatedly treated with cocaine

Female rats are intensely affected by cocaine, with estrogen probably playing an important role in this effect. Progesterone modulates the GABA system and attenuates the effects of cocaine; however, there is no information about its relevance in changing GABA synthesis pathways after cocaine administration to female rats. Our objective was to investigate the influence of progesterone on the effects of repeated cocaine administration on the isoenzymes of glutamic acid decarboxylase (GAD65 and GAD67) mRNA in brain areas involved in the addiction circuitry. Ovariectomized, intact and progesterone replacement-treated female rats received saline or cocaine (30 mg/kg, ip) acutely or repeatedly. GAD isoenzyme mRNA levels were determined in the dorsolateral striatum (dSTR) and prefrontal cortex (PFC) by RT-PCR, showing that repeated, but not acute, cocaine decreased GADs/β-actin mRNA ratio in the dSTR irrespective of the hormonal condition (GAD65: P < 0.001; and GAD67: P = 0.004). In the PFC, repeated cocaine decreased GAD65 and increased GAD67 mRNA ratio (P < 0.05). Progesterone replacement decreased both GAD isoenzymes mRNA ratio after acute cocaine in the PFC (P < 0.001) and repeated cocaine treatment reversed this decrease (P < 0.001). These results suggest that cocaine does not immediately affect GAD mRNA expression, while repeated cocaine decreases both GAD65 and GAD67 mRNA in the dSTR of female rats, independently of their hormonal conditions. In the PFC, repeated cocaine increases the expression of GAD isoenzymes, which were decreased due to progesterone replacement.

Influence of progesterone on GAD65 and GAD67 mRNA expression in the dorsolateral striatum and prefrontal cortex of female rats repeatedly treated with cocaine.

Female rats are intensely affected by cocaine, with estrogen probably playing an important role in this effect. Progesterone modulates the GABA system and attenuates the effects of cocaine; however, there is no information about its relevance in changing GABA synthesis pathways after cocaine administration to female rats. Our objective was to investigate the influence of progesterone on the effects of repeated cocaine administration on the isoenzymes of glutamic acid decarboxylase (GAD(65) and GAD(67)) mRNA in brain areas involved in the addiction circuitry. Ovariectomized, intact and progesterone replacement-treated female rats received saline or cocaine (30 mg/kg, ip) acutely or repeatedly. GAD isoenzyme mRNA levels were determined in the dorsolateral striatum (dSTR) and prefrontal cortex (PFC) by RT-PCR, showing that repeated, but not acute, cocaine decreased GADs/beta-actin mRNA ratio in the dSTR irrespective of the hormonal condition (GAD(65): P < 0.001; and GAD(67): P = 0.004). In the PFC, repeated cocaine decreased GAD(65) and increased GAD(67) mRNA ratio (P < 0.05). Progesterone replacement decreased both GAD isoenzymes mRNA ratio after acute cocaine in the PFC (P < 0.001) and repeated cocaine treatment reversed this decrease (P < 0.001). These results suggest that cocaine does not immediately affect GAD mRNA expression, while repeated cocaine decreases both GAD(65) and GAD(67) mRNA in the dSTR of female rats, independently of their hormonal conditions. In the PFC, repeated cocaine increases the expression of GAD isoenzymes, which were decreased due to progesterone replacement.

Gabaergic mechanisms of hypothalamic nuclei in the expression of conditioned fear.

The amygdala, the dorsal periaqueductal gray (dPAG), and the medial hypothalamus have long been recognized to be a neural system responsible for the generation and elaboration of unconditioned fear in the brain. It is also well known that this neural substrate is under a tonic inhibitory control exerted by GABA mechanisms. However, whereas there is a growing body of evidence to suggest that the amygdala and dPAG are also able to integrate conditioned fear, it is still unclear, however, how the distinct hypothalamic nuclei participate in fear conditioning. In this work we aimed to examine the extent to which the gabaergic mechanisms of this brain region are involved in conditioned fear using the fear-potentiated startle (FPS). Muscimol, a GABA-A receptor agonist, and semicarbazide, an inhibitor of the GABA synthesizing enzyme glutamic acid decarboxylase (GAD), were used as an enhancer and inhibitor of the GABA mechanisms, respectively. Muscimol and semicarbazide were injected into the anterior hypothalamus (AHN), the dorsomedial part of the ventromedial nucleus (VMHDM), the dorsomedial (DMH) or the dorsal premammillary (PMD) nuclei of male Wistar rats before test sessions of the fear conditioning paradigm. The injections into the DMH and PMD did not produce any significant effects on FPS. On the other hand, muscimol injections into the AHN and VMHDM caused significant reduction in FPS. These results indicate that injections of muscimol and semicarbazide into the DMH and PMD fail to change the FPS, whereas the enhancement of the GABA transmission in the AHN and VMHDM produces a reduction of the conditioned fear responses. On the other hand, the inhibition of this transmission led to an increase of this conditioned response in the AHN. Thus, whereas DMH and PMD are known to be part of the caudal-most region of the medial hypothalamic defensive system, which integrates unconditioned fear, systems mediating conditioned fear select the AHN and VMHDM nuclei that belong to the rostral-most portion of the hypothalamic defense area. Thus, distinct subsets of neurons in the hypothalamus could mediate different aspects of the defensive responses.

Acute ethanol induces Fos in GABAergic and non-GABAergic forebrain neurons: a double-labeling study in the medial prefrontal cortex and extended amygdala.

The purpose of this study was to further address the hypothesis that ethanol activates GABAergic neurons in specific brain neurocircuits that mediate motivated behavior and control of action, such as the central extended amygdala and medial prefrontal cortex. Male Sprague-Dawley rats received habituation to 7 days of daily intragastric administration of water (5 ml/kg) followed by a single acute intragastric dose of ethanol (2.5 g/kg) or water then, 2 h later, by paraformaldehyde perfusion. Rats left undisturbed in the animal room throughout the experiment were also perfused (naive group). Brain sections were processed for single Fos immunohistochemistry or dual Fos immunohistochemistry/glutamic acid decarboxylase (GAD) mRNA in situ hybridization. Intragastric water administration increased the number of Fos-immunoreactive cells in the infralimbic cortex and lateral part of the central nucleus of the amygdala compared with the naive group. Ethanol administration increased the number of Fos-immunoreactive cells in the infralimbic (+57.5%) and prelimbic (+105.3%) cortices, nucleus accumbens shell region (+88.2%), medial part of the central nucleus of the amygdala (+160%), and lateral part of the bed nucleus of the stria terminalis (+198.8%) compared with the water-treated group. In the nucleus accumbens shell region, central nucleus of the amygdala, and bed nucleus of the stria terminalis, more than 80% of Fos-immunoreactive neurons were GABAergic after ethanol administration. In contrast, in the prelimbic cortex, 75% of Fos-immunoreactive neurons were not GABAergic. These results constitute new evidence for region-specific functional interactions between ethanol and GABAergic neurons.

Fos-like immunoreactivity in the brain associated with freezing or escape induced by inhibition of either glutamic acid decarboxylase or GABAA receptors in the dorsal periaqueductal gray.

GABAergic neurons exert tonic control over the neural substrates of aversion in the dorsal periaqueductal gray (dPAG). It has been shown that electrical stimulation of this region at freezing or escape thresholds activates different neural circuits in the brain. Since electrical stimulation activates cell bodies and fibers of passage, it is necessary to use chemical stimulation that activates only post-synaptic receptors. To investigate this issue further, reduction of GABA transmission was performed with local injections of either the GABA-A receptor antagonist bicuculline or the glutamic acid decarboxylase (GAD) inhibitor semicarbazide into the dorsolateral periaqueductal gray (dlPAG). Local infusions of semicarbazide (5.0 microg/0.2 microl) or bicuculline (40 ng/0.2 microl) into this region caused freezing and escape, respectively. The results obtained showed that freezing behavior induced by semicarbazide was associated with an increase in Fos expression in the laterodorsal nucleus of the thalamus (LD) and ventrolateral periaqueductal gray (vlPAG), while bicuculline-induced escape was related to widespread increase in Fos labeling, notably in the columns of the periaqueductal gray, hypothalamus nuclei, the central amygdaloid nucleus (Ce), the LD, the cuneiform nucleus (CnF) and the locus coeruleus (LC). Thus, the present data support the notion that freezing and escape behaviors induced by GABA blockade in the dlPAG are neurally segregated: freezing activates only structures that are mainly involved in sensory processing, and bicuculline-induced escape activates structures involved in both sensory processing and motor output of defensive behavior. Therefore, the freezing elicited by activation of dlPAG appears to be related to the acquisition of aversive information, whereas most brain structures involved in the defense reaction are recruited during escape.

Glutamic acid decarboxylase in rat olfactory bulb: effect of ovarian steroids or male pheromones.

The effect of ovarian steroids and pheromones on the activity of glutamic acid decarboxylase, the enzyme that synthesizes gamma-aminobutyric acid (GABA), was studied in the rat olfactory bulbs. The enzyme activity was measured in the main and accessory olfactory bulbs at 11:00 h and 17:00 h in ovariectomized rats, and in rats treated with ovarian steroids or exposed to male pheromones. The enzyme activity in both bulbs showed a diurnal fluctuation that was not affected in the accessory bulbs by the exposure to pheromones while the rhythm disappeared in the main bulbs. Estrogen and estrogen-progesterone treatments decreased the enzyme activity in both bulbs either in the morning or in the afternoon. The exposure of ovariectomized estrogen-primed rats to male pheromones reversed the effect of estrogen on the enzyme activity in the morning but not in the afternoon. Ovarian hormones plus pheromones prevented the steroid effect only in the morning. These results support the view that in olfactory bulbs, the GABAergic system can be modulated by endocrine and pheromonal factors.

Glutamic acid decarboxylase activity of the olfactory bulb in male rats is influenced by olfactory stimuli and hormonal status.

Changes is glutamate decarboxylase activity (GAD) in the main (MOB) and accessory (AOB) olfactory bulbs were determined at 11:00 hr and 17:00 hr in intact odor deprived (IOD) male rats exposed to female olfactory stimuli, and in castrated odor deprived males (COD) either injected with testosterone (T), exposed to female pheromone or injected with T and exposed to pheromone. Grouping IOD males by female olfactory stimulus and time of the day. MOB and AOB-GAD activity changed in the morning and not in the afternoon. In COD males, T injection induced an increased response in MOB-GAD activity 24 hr later either in the morning or in the afternoon, while no changes were seen at 11:00 or 17:00 hr exposure to female odor. In the AOB of COD males, both T administration or exposure to female pheromone, only induced an increase of enzyme activity in the morning. The association of T and female pheromone, decreased morning GAD activity both in the MOB and in the AOB compared with the values of COD males treated with T. In the afternoon this association had no effect compared with MOB, AOB-GAD activity of COD males injected with testosterone. These results indicate that hormonal and olfactory inputs in IOD and COD males are effective in changing olfactory bulb-GAD activity mainly in the morning.