Majid B. Shaikh

Regulation of feline aggression by the bed nucleus of stria terminalis

The purpose of this experiment was to study the possible modulatory role of the bed nucleus of stria terminalis (BNST) in the regulation of affective defense and quiet biting attack reactions in the cat. The experimental paradigm employed concurrent electrical stimulation of the hypothalamic attack sites and of the BNST. The results of the present study demonstrate that concurrent electrical stimulation of the BNST can differentially modulate the two different forms of aggressive behavior by facilitating affective defense and by suppressing quiet biting attack.

An analysis of the mechanisms underlying septal area control of hypothalamically elicited aggression in the cat

An experiment was performed to determine the role of the hippocampal formation in the regulation of quiet biting attach behavior elicited from electrical stimulation of the hypothalamus. The results showed clearly that stimulation of the dorsal hippocampus resulted in an increased latency to quiet biting attack and that ventral hippocampal stimulation resulted in a decreased latency to quiet biting attack. In addition, the results indicate that those sites in the ventral hippocampal formation from which facilitation of attack can be produced are linked to sensory mechanisms associated with trigeminal reflexes established during hypothalamic stimulation inasmuch as stimulation of these sites increase the lateral extent of the effective sensory field of the lipline. No effect was observed upon a motor component of the jaw-opening response--the latency to jaw-opening-during ventral hippocampal stimulation. In contrast, no effects were observed upon either sensory or motor components of the hypothalamically-elicited jaw-opening response as a result of stimulation of dorsal hippocampal sites. Deoxyglucose autoradiography revealed that the major effect of stimulation of modulatory sites in both the dorsal and ventral hippocampal formation was exerted upon the lateral septal nucleus. Thus, it is proposed that hippocampal modulation of hypothalamically-elicited quiet biting attack is mediated primarily through the lateral septal nucleus.

Topographically organized midbrain modulation of predatory and defensive aggression in the cat

Hypothalamic sites from which quiet biting attack and affective defense were elicited, were concurrently stimulated with others in the midbrain from which modulation of these behaviors was attempted. Stimulation of medial and lateral aspects of the tegmentum differentially modulated quiet biting attack and affective defense behavior. Facilitation of quiet attack and suppression of affective defense resulted from stimulation of the lateral tegmentum, while suppression of quiet attack and facilitation of affective defense followed stimulation of its medial aspect.

Medial amygdaloid suppression of predatory attack behavior in the cat: I. Role of a substance P pathway from the medial amygdala to the medial hypothalamus

The medial amygdala is known to powerfully suppress predatory attack behavior in the cat, but the mechanisms underlying such modulation remain unknown. The present study tested the hypothesis that medial amygdaloid suppression of predatory attack is mediated, in part, by a pathway from the medial amygdala to the medial hypothalamus which utilizes substance P as a neurotransmitter. Stimulating electrodes were implanted into the medial amygdala and cannula electrodes were implanted into both the medial and lateral hypothalamus. Predatory attack behavior was elicited by electrical stimulation of the lateral hypothalamus. In the first phase of the study, paired trials compared attack latencies of single stimulation of the lateral hypothalamus with those following dual stimulation of the lateral hypothalamus and medial amygdala. Attack latencies were significantly elevated following dual stimulation of the medial amygdala and lateral hypothalamus. In the second phase of the study, dose and time dependent decreases in response suppression were noted following the infusion of the substance P (NK1) receptor antagonist, CP96.345 (in doses of 0.05, 0.5 and 2.5 nmol) into the medial hypothalamus. In third phase of the study, the effects of microinjections of the substance P receptor agonist, [Sar9.Met(O2)11]-substance P (in doses of 0.5, 1.0 and 2.0 nmol), directly into the medial hypothalamus upon lateral hypothalamically elicited predatory attack behavior were determined. Microinfusion of this drug elevated attack response latencies in a dose- and time-dependent manner. In addition, pretreatment with CP96,345 into the medial hypothalamus blocked the suppressive effects of subsequent delivery of [Sar9,Met(O2)11]-substance P into the same medial hypothalamic site. Other parts of the study demonstrated the presence of: (1) high densities of substance P receptors in the ventromedial hypothalamus, and (2) neurons that are positively labeled for substance P that project from the medial amygdala to the ventromedial hypothalamus as demonstrated by retrograde labeling with Fluoro-Gold. These findings provide support for the hypothesis that medial amygdaloid suppression of lateral hypothalamically elicited predatory attack behavior includes a substance P pathway from the medial amygdala to the medial hypothalamus. The findings further suggest that stimulation of the medial amygdala activates substance P receptors in the medial hypothalamus, thus triggering an inhibitory mechanism from the medial to the lateral hypothalamus, resulting in suppression of predatory attack behavior.

Medial amygdaloid suppression of predatory attack behavior in the cat: II. Role of a GABAergic pathway from the medial to the lateral hypothalamus

The medial amygdala is known to powerfully suppress predatory attack behavior elicited by electrical stimulation of the lateral hypothalamus of the cat. In the preceding paper, it was shown that the initial limb of a pathway subserving suppression of predatory attack from the medial amygdala to the lateral hypothalamus projects to the ventromedial hypothalamus and its functions are mediated by substance P. The present study tested the hypothesis that the second limb of the pathway subserving medial amygdaloid suppression of predatory attack behavior projects from the medial to lateral hypothalamus and its functions are mediated by GABA. Cannula electrodes were implanted into the lateral hypothalamus for elicitation of predatory attack behavior as well as for the microinfusion of GABA compounds. Monopolar stimulating electrodes were implanted into sites within the medial amygdala from which subseizure levels of stimulation could suppress predatory attack behavior. Initially, the effects of dual stimulation of the medial amygdala and lateral hypothalamus upon response latencies for predatory attack were compared with single stimulation of the lateral hypothalamus alone. Dual stimulation was shown to significantly suppress predatory attack elicited from the lateral hypothalamus. Then, the GABAA receptor antagonist, bicuculline, was microinjected into sites within the lateral hypothalamus from which predatory attack was elicited in doses of 0.015, 0.075 and 0.15 nmol and paired trials of single and dual stimulation were again repeated in a manner identical to that applied prior to drug administration. Drug infusion produced a blockade of medial amygdaloid suppression of predatory attack in a time- and dose-dependent manner. Conversely, microinfusions of the GABAA receptor agonist, muscimol (10, 25 and 50 pmol), into the same lateral hypothalamic attack site in the absence of medial amygdaloid stimulation suppressed predatory attack, thus simulating the effects of medial amygdaloid stimulation. Furthermore, pretreatment with bicuculline microinjected into the lateral hypothalamus blocked the suppressive effects of substance P, that was infused into the ventromedial hypothalamus, upon predatory attack. Receptor autoradiography demonstrated the presence of high affinity binding for GABAA receptors in the lateral hypothalamus. A combination of immunocytochemical and retrograde axonal tract tracing procedures, in which Fluoro-Gold was microinjected into the lateral hypothalamic attack sites, revealed the presence of populations of neurons labeled for both Fluoro-Gold and GABA in the ventromedial hypothalamus. These findings provide new evidence for the existence of a pathway from the medial to lateral hypothalamus whose functions are mediated by GABA. Thus, the overall findings provide support for the view that the pathway from the medial amygdala to the lateral hypothalamus underlying suppression of predatory attack behavior involves a two-neuronal arc: the first neuron projects from the medial amygdala to the medial hypothalamus and its functions are mediated by substance P: the second neuron involves a GABAergic pathway originating in the ventromedial hypothalamus and which projects to the lateral hypothalamus.

The effects of intrahypothalamic injections of norepinephrine upon affective defense behavior in the cat.

The effects of norepinephrine microinjected into the anterior hypothalamus were examined in feline affective defense behavior elicited by electrical stimulation of the region of the ventromedial nucleus. Anterior hypothalamic sites from which affective defense behavior could also be elicited by electrical stimulation and which are known to receive inputs from both the ventromedial nucleus and brainstem noradrenergic neurons were selected for pharmacological analysis. Intracerebral injections of 250 ng (1 nM) and 500 ng (2 nM) quantities of norepinephrine placed into the anterior hypothalamus resulted in a significant lowering of the attack thresholds. These reductions in response thresholds which were reversed by either pre- or post-treatment with yohimbine, indicate that the noradrenergic system may play an important role in the regulation of affective defense behavior.

A [14C]2-deoxyglucose analysis of the functional neural pathways of the limbic forebrain in the rat. IV. A pathway from the prefrontal cortical-medial thalamic system to the hypothalamus

The present study utilized the [14C]2-deoxyglucose (2-DG) cell labeling procedure to characterize a functional pathway from the prefrontal cortex (Pfc) and mediodorsal thalamic nucleus (MD) to the hypothalamus. Rats were injected with 2-DG prior to a 45 min experimental paradigm consisting of alternating 30 s on-off periods of electrical brain stimulation. Standard procedures were utilized for the removal and processing of brain tissue for X-ray autoradiography. In the first phase of this study, stimulation applied to the prefrontal cortex generally yielded a pattern of 2-DG distribution consistent with the findings of classical anatomical studies. Stimulation of the dorsomedial and ventromedial prefrontal cortex or the infralimbic cortex produced the most effective activation of the diencephalon. This activation was primarily limited to MD, with no involvement of any region of the hypothalamus. In the second phase of this study, brain regions activated following stimulation of sites along the rostro-caudal axis of MD were examined. Stimulation of MD resulted in the activation of the nucleus reuniens and other midline and non-specific thalamic nuclei. Stimulation of this nucleus also activated the ventromedial thalamic nucleus, medial aspects of the nucleus accumbens and the medial and sulcal prefrontal cortices. Again, in each of these cases, labeling within any region of the hypothalamus could not be detected. Since MD stimulation activated the midline thalamus, and the nucleus reuniens in particular, the last phase of this experiment involved stimulation of the nucleus reuniens in order to determine the source of medial thalamic inputs to the hypothalamus. Stimulation of the nucleus reuniens activated fibers which were distributed to both the medial and lateral hypothalamus. In addition, stimulation also activated the descending periventricular system, which could be followed to the level of the midbrain central gray and such limbic structures as the hippocampal formation, septal area, amygdala and prefrontal cortex. These findings indicate that Pfc-MD activation of the hypothalamus is achieved indirectly via interneurons within the nucleus reuniens.

Enkephalinergic involvement in periaqueductal gray control of hypothalamically elicited predatory attack in the cat.

The effects of central infusion of naloxone into the midbrain periaqueductal gray (PAG) upon predatory attack behavior in the cat were studied in 12 cats. Initially, quiet biting attack was elicited by electrical stimulation of sites within the lateral hypothalamus using monopolar electrodes. Then cannula-electrodes were implanted into sites within the PAG from which electrical stimulation facilitated or suppressed the attack response. Following identification of modulatory sites within the PAG, naloxone (1.0 micrograms/0.5 microliter) was microinjected into those sites and the effects upon hypothalamically elicited attack were assessed. At nine of twelve sites in the PAG where suppression was obtained, administration of naloxone served to block those effects. Similarly, at six of eight facilitatory sites within the PAG, naloxone also blocked the modulatory effects of PAG stimulation. However, vehicle (isotonic saline) alone did not alter the modulatory effects of PAG stimulation. Administration of DAME (250 ng/0.3 microliter) into PAG modulatory sites in four cats, two which facilitated and two that suppressed the attack response, reversed the effects of naloxone at these sites. These results demonstrate that opioid peptides within the PAG play a complex role in the expression of predatory attack behavior in the cat.

Neurochemical mechanisms underlying amygdaloid modulation of aggressive behavior in the cat

Studies designed to determine the respective roles of substance P, excitatory amino acids, and enkephalins in amygdaloid modulation of defensive rage behavior in the cat are presented. The basic design of these studies involved three stages. In stage I, cannula electrodes for stimulation and drug infusion were implanted into medial hypothalamic of midbrain periaqueductal gray (PAG) sites from which defensive rage behavior could be elicited. Then, a stimulating electrode was implanted into a site within the medial, basal, or central nuclear complex from which modulation of the defensive rage response could be obtained. Amygdaloid modulation of defensive rage was determined in the following manner: it employed the paradigm of dual stimulation in which comparisons were made of response latencies between alternate trials of dual (i.e., amygdala+medial hypothalamus [or PAG]) and single stimulation of the hypothalamus or PAG alone. Thus, stage I established the baseline level of modulation (i.e., facilitation or suppression of defensive rage) in the predrug stimulation period. In stage II, a selective or non-selective receptor antagonist for a given transmitter system was administered either peripherally or intracerebrally at the defensive rage site, after which time the same dual stimulation paradigm was then repeated over the ensuing 180 min postinjection period in order to determine the effects of drug delivery upon amydaloid modulation of defensive rage. Stage III of the study took place at the completion of the pharmacological testing phase. The retrograde axonal tracer, Fluoro-Gold, was microinjected into the defensive rage site within the medial hypothalamus or PAG, and following a 6-14 day survival period, animals were sacrificed and brains were processed for histological and immunocytochemical analyses for the neurotransmitters noted above. This procedure thus permitted identification of cells within the amygdala which were labeled retrogradely and which were also immunostained positively for substance P, excitatory amino acids, or enkephalin. For studies involving substance P, defensive rage was elicited from the medial hypothalamus and for studies examining the roles of excitatory amino acids and enkaphalin, defensive rage was elicited from the PAG. In the first study, facilitation of hypothalamically elicited defensive rage was obtained with dual stimulation of the medial nucleus of the amygdala. In separate experiments, the selective NK 1 non-peptide antagonist, CP 96,345, was administered both peripherally as well as intracerabrally into the hypothalamic defensive rage sites in doses of 0.5-4.0 mg/kg (i.p.) and 0.5-2.5 nmol (i.c.). Following drug delivery, the facilitatory effects of medial amygdaloid stimulation were blocked ina dose- and time-dependent manner in which the effects were noted as early as 5 min postinjection. The maximum drug dose (4.0 mg/kg) employed for peripheral administration resulted in a 42% reduction in the facilitatory effects of the medial amygdala (P<0.002). This drug, when microinjected directly into medial hypothalamic defensive rage sites at the maximum dose level of 2.5 nmol, resulted in an 84% reduction of the suppressive effects of amygdaloid stimulation (P<0.5) at 5 min postinjection. In the next study, an N-methyl-D-aspartate (NMDA) antagonist, DL-α-amino-7-phosphonoheptanoic acid (AP-7), was administered either peripherally (0.1-1.0 mg/kg) or intracerebrally (0.2 and 2.0 nmol) into PAG defensive rage sites