F.C. Barone

Afferent connections to the lateral hypothalamus: A horseradish peroxidase study in the rat ☆

Horseradish peroxidase, 13% Sigma Type VI, was administered iontophoretically to the mid lateral hypothalamus (LH) of male hooded rats. Animals were perfused intracardially on the following day and brains were removed and sliced in the coronal or sagittal planes into 30-50 micrometer sections. Sections were processed with DAB and BDH for the brown and blue reaction products and later examined by bright and dark field microscopy for the presence and location of retrogradely labeled neurons. Results indicate that a significant number of afferent connections to the LH originate in the olfactory and accumbens nuclei, pyriform cortex, olfactory tracts, magnocellular and medial preoptic and anterior hypothalamic regions, stria terminalis, stria hypothalamic tract, diagonal tract of Broca, caudate-putamen and globus pallidus, internal capsule, lateral septal nuclei, lateral preoptic area and anterior medial forebrain bundle, the various amygdaloid nuclei, zona incerta, perifornical region, dorsal and ventral medial hypothalamic areas, supraoptic, paraventricular and periventricular nuclei, posterior hypothalamus and medial forebrain bundle, ventral thalamic nuclei, the fields of Forel, arcuate and mammillary nuclei, adjacent to the fasciculus retroflexus, in the ventral tegmental area of Tsai, interpeduncular nucleus, substantia nigra, mesencephalic reticular formation, periaqueductal gray, locus coeruleus and parabrachial region. Results are discussed in terms of previous anatomical and neurophysiological data, probable pathways, and the function of LH neurons.

Vagal and gastric connections to the central nervous system determined by the transport of horseradish peroxidase

Horseradish peroxidase (HRP, Sigma Type VI) crystals were encased in a parafilm envelope and applied to the transected central ends of the left and right cervical vagus nerves and the anterior and posterior esophageal vagus nerves of adult male hooded rats. Injections of 30% HRP were made into the muscle wall of the fundus and antrum regions of the stomach. After 48 hr survival time, animals were perfused intracardially with a phosphate buffer plus sucrose wash followed by glutaraldehyde and paraformaldehyde fixative. The brain stem, spinal cord and corresponding dorsal root ganglia, superior cervical sympathetic ganglion, and the nodose ganglion were removed and cut into 50 micron sections. All tissue was processed with tetramethylbenzidine (TMB) for the blue reaction according to Mesulum and counterstained with neutral red. Sequential sections were examined under a microscope. Labeled neurons and nerve terminals were identified using bright and dark field condensers and polarized light. In tissue from animals that had HRP applied to the cervical vagus nerves, retrogradely labeled neurons were identified ipsilaterally in the medulla located in the dorsal motor nucleus of the vagus (DMN) and the nucleus ambiguus (NA). Labeled cells extended from the DMN into the spinal cord in ventral-medial and laminae X regions C1 and C2 of cervical segments. Many neurons were labeled in the nodose ganglion. Anterogradely labeled terminals were observed throughout and adjacent to the solitary nucleus (NTS) dorsal to the DMN and intermixed among labeled neurons located in the DMN. In tissue from animals that had HRP applied to the esophageal vagus nerves, similar labeling was observed. However, fewer neurons were identified in the NA, the nodose ganglion, and only in laminae X of the cervical spinal cord segments C1 and C2. Also, very little terminal labeling was observed in and adjacent to the NTS. Labeled neurons in tissue from animals that had HRP injected into the stomach wall were observed bilaterally in the DMN, nodose ganglion, and only in laminae X at the C1 and C2 levels of the spinal cord. Labeled neurons also were observed in the dorsal root ganglia of the thoracic cord. These data indicate that cervical cord and NA neurons are important in the supradiaphragmatic motor innervation by the vagus. Also, many afferents to the NTS originate above the diaphragm. In addition, some afferents from the stomach enter the central nervous system via the thoracic spinal cord.

Effects of acute and chronic administration of caffeine on schedule dependent and schedule induced behavior

The effects of caffeine (3.125, 6.25, 12.5, 25, 50, and 100 mg/kg) on lever pressing, schedule induced licking and water consumption induced by a fixed interval 1 min schedule were studied. Changes in these dependent variables were assessed when animals were reduced to 80% of their initial body weight by partial food deprivation and when body weights recovered after the animals were returned to conditions of ad lib feeding. Results indicate differential effects of the drug between animals at 80% body weight and when they are permitted to recover. Tolerance was examined for a single large dose only for the same dependent variables in animals at 80% body weight.

Effects of LH kainic acid infusions on ingestion and autonomic activity

Abstract The effects of lateral hypothalamic (LH) infusions of kainic acid (KA) were determined on ingestive behavior, body weight, and motor and autonomic activity. In Experiment 1 male hooded rats received bilateral LH infusions of isotonic saline in volumes of 0.5 or 1.0 μl, 3.0 μg KA in volumes of 0.5 or 1.0 μl, or 6.0 μg of KA in a volume of 1.0 μl. All animals receiving 6.0 μg/1.0 μl of KA died. The 3.0 μg/0.5 μl dose resulted in transient decreases in food and water consumption and body weight. Animals receiving this dose no longer drank in response to 2 cc/kg 15% NaCl injections, exhibited attenuated drinking in response to 24 hr water and food deprivation, exhibited a transient decrease in eating following food deprivation and decreased eating following 750 mg/kg injections of 2-deoxy-D-glucose. Minimal effects on these measures were observed following the 3.0 μg/1.0 μl dose. In Experiment 2 rats received unilateral infusions of KA and the effects on motor and autonomic activity and ingestive behavior and body weight were compared to unilateral saline infused animals and animals with radiofrequency lesions. Only transient decreases in food consumption lasting 1–2 days were observed for both unilateral KA LH infused and lesioned animals. In KA infused rats contralateral exophthalamus, rapid shallow breathing, bilateral mydriasis, no contralateral pupillary constriction response, excessive salivation, body tremors, seizures, convulsions, teeth chattering, contralateral tail suspension induced spinning and turning, and elevated body temperature were observed for up to 6 hr following the infusion. Results are discussed in terms of lateral ventral diencephalic neurons involved in the more permanent deficits associated with bilateral LH damage.

Effects of continuous intramesenteric infusion of glucose and amino acids on food intake in rats.

Abstract Prolonged infusions of various fluids at a rate of 21 ml/23.5 hr through the mesenteric vein and the vena were performed on rats and effects on ad lib food intake were determined. Results indicate that continuous intramesenteric infusion of 5–10% glucose solutions or a 5% Aminofusin L solution suppresses food intake. No effects were observed when solutions were infused via the caval vein. A 10% solution of 3-O-methyl-d-glucose did not affect food intake when introduced by either route. These data support directly the presence of glucose and amino acid receptive mechanisms in the portohepatic system involved in the control of food intake.

Effects of microiontophoretically applied chemicals on hypothalamic neural activity

Seven barrel electrodes were utilized to record simultaneously from and apply chemicals to single neurons in the hypothalamus of anesthesized male hooded rats. When a stable baseline discharge frequency was established for lateral preoptic area (LPA) or lateral hypothalamic (LH) neurons, glutamate, norepinephrine, acetylcholine, glucose and sodium were administered microiontophoretically. In addition, the effects of microiontophoretically administered chemicals and LPA or LH electrical stimulation on hypothalamic neural activity were in some cases determined for the same neuron. Recordings from 53 hypothalamic neurons indicate that the direct application of these chemicals affect LPA and LH neural activity at relatively low ejection currents in a dose related manner. In the LPA, glutamate which has a nonspecific effect and increased the discharge frequency in 96% of the cells tested, was used to establish the reliability of the techniques and baseline. Norepinephrine decreased (73%), acetylcholine increased (28%) and decreased (12%), glucose increased (12%), and sodium increased (4%) discharge frequency. In the LH, glutamate increased (91%), norepinephrine decreased (33%), acetylcholine increased (50%) and decreased (14%), glucose increased (12%) and decreased (6%), and sodium increased (20%) discharge frequency. Also, significant relations between chemical and electrical stimulation suggest that norepinephrine and possibly acetylcholine might be involved in the interactions between the LPA and LH neurons. Results are discussed in terms of the neurochemical modulation of ingestive behavior.

Effects of ventral tegmental area stimulation and microiontophoretic application of dopamine and norepinephrine on hypothalamic neurons

The effects of ventral tegmental area of Tsai (VTA) stimulation on lateral hypothalamic (LH), lateral preoptic area (LPA). and medial hypothalamic neuronal activity were determined in anesthetized rats. Recordings from 81 hypothalamic neurons indicate that stimulation produces predominantly decreases in hypothalamic neuron activity. Increase in activity due to VTA stimulation occurred less frequently. Following single rectangular pulse stimulation, 0.5 msec. 0-500 microA, short latency decreases in activity occurred. Longer latency increases in discharge frequency were also observed. Dose response relations were established for 56% of the LH neurons, 78% of the LPA neurons, and for 82% of the medial hypothalamic neurons following VTA stimulation. Decreases and in a few cases increases in activity seemed to involve only one or two synapses. Antidromic responses verified interconnections between the VTA and the hypothalamus and revealed relatively slow conduction velocities of 0.45 and 0.81 m/sec. The changes in discharge frequency which occurred following VTA stimulation were similar in direction to the effects of the direct microiontophoretic application of dopamine (DA) or norepinephrine (NE). Since DA increased or decreased while NE decreased discharge frequency, these microiontophoretic tests indicated that the shorter latency VTA stimulation induced increases in decreases in neural activity were associated with VTA dopaminergic neuron stimulation and that in some cases short and long latency decreases in neuronal activity were due to activation of VTA ventral bundle NE fibers of passage or to indirect polysynaptic mechanisms. Results demonstrate the interconnections between various regions of the hypothalamus and the VTA along the extent of the medial forebrain bundle (MFB). The cross-validation of neuroanatomical and various electrophysiological methods in establishing the nature of hypothalamic connections was discussed.

Effects of periaqueductal gray stimulation on diencephalic neural activity

The effects of ipsilateral mesencephalic periaqueductal gray (PAG) stimulation on lateral hypothalamic (LH), lateral preoptic area (LPA), and ventral and subthalamic activity were determined in anesthetized rats. Recordings from 119 diencephalic neurons indicate that the PAG provides a predominantly inhibitory input to diencephalic neurons. Excitatory input occurred infrequently in the hypothalamus and was not observed in the thalamus. Following single rectangular pulse stimulation, 0.5 msec, 0-500 micro A, short latency decreases in activity occurred. Longer latency increases in discharge frequency were also observed. Dose response relations were established for 74% of the LH neurons, 68% of the LPA neurons, and for 72% of the ventral and subthalamic neurons following VTA stimulation. Decreases and, in a few hypothalamic neurons, increases in activity seemed to involve only one or two synapses. The effects of contralateral PAG stimulation on LPA-LH neuronal activity were alos determined. Dose response relations were established for 66% of the LPA-LH neurons following contralateral stimulation. However, results were different in that many more cells were increased with a shorter latency and at a lower threshold following contralateral stimulation. Antidromic responses verified PAG and diencephalic interconnections and revealed relatively slow conduction velocities, less than 1.0 m/sec. Results were discussed in terms of the anatomy of known PAG pathways, PAG neuronal activation vs. PAG fibers of passage, and the functions of midbrain-hypothalamic interconnections in the integration of somatic, visceral and nociceptive sensory inputs.

Schedule induced eating in water deprived rats

Abstract Significant schedule induced eating occurred in water deprived rats at 80% body weight when water was delivered in a 0.1 ml dipper on FT-1 and FI-1 min schedules. The animals tested during the FT-1 min schedule demonstrated the greatest schedule induced eating. Both FT-1 min and FI-1 min schedules resulted in significantly more eating than that which occurred when animals received the same amount of water which was followed by free access to food pellets for a similar 1 hr test period. The critical factor in producing schedule induced eating seems to be the physical arrangement of the food relative to the water delivery mechanism.

Neurophysiological determination of lateral hypothalamic and lateral preoptic interconnections

Abstract The effects of lateral hypothalamic (LH) stimulation on ipsilateral lateral preoptic area (LPA) neuronal activity were determined in anesthetized rats. The effects of LPA stimulation on LH neuronal activity were also determined. Recordings from 99 hypothalamic neurons indicate that reciprocal inhibitory relations exists between the LPA and LH. Following single rectangular pulse, 0.5 msec, 0–500 μA, stimulation short latency decreases in activity occurred. Longer latency increases in activity were also observed. Dose response relations were established for 90% of the LPA neurons following LH stimulation and for 80% of the LH neurons following LPA stimulation. Decreases and in a few cases increases in activity seemed to involve only one or two synapses. Antidromic responses revealed relatively slow conduction velocities of 0.4–0.9 m/sec. Results demonstrate a considerable degree of interconnectivity between the LPA and LH along the extent of the medial forebrain bundle. In addition to establishing the nature of these interconnections, the cross validation between the horseradish peroxidase neuroanatomical technique and electrophysiological methods was discussed as a means of determining hypothalamic organization and function.